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Purpose: To characterize a large, international cohort of children with nystagmus., Methods: Data were collected from a single-center, prospectively developed database on patients with nystagmus. Outcome variables for this study included: (1) demographic characteristics, (2) nystagmus type, (3) clinical characteristics, (4) associated ophthalmic conditions, (5) associated non-ophthalmic conditions, (6) special testing findings, and (7) treatments., Results: Six hundred patients from 38 states and 30 countries were included. Age ranged from birth to younger than 18 years (mean: 15.2 years), 58% were female, 55% were race other than White, 75% had infantile nystagmus syndrome, 17% had neurologically significant nystagmus, 7% had fusion maldevelopment nystagmus syndrome, 64% had strabismus, 56% had an anomalous head posture, 94% had a significant refractive error, 64% had an associated ophthalmic abnormality (excluding ametropia), and 45% had an associated systemic condition. Special testing showed abnormalities in 67% and 95% had treatment directed at their nystagmus., Conclusions: The most common diagnosis in this cohort is neurologically non-significant infantile nystagmus syndrome. Eye movement recordings provide a path toward accurate diagnosis and classification. There was a high prevalence of underlying ocular and/or systemic conditions requiring ophthalmic special testing as part of a diagnostic routine. Clinical treatments are available to most patients. [ J Pediatr Ophthalmol Strabismus . 2023;60(6):406-410.] .

Purpose: To survey paediatric eye care providers to identify current patterns of prescribing for hyperopia., Methods: Paediatric eye care providers were invited, via email, to participate in a survey to evaluate current age-based refractive error prescribing practices. Questions were designed to determine which factors may influence the survey participant's prescribing pattern (e.g., patient's age, magnitude of hyperopia, patient's symptoms, heterophoria and stereopsis) and if the providers were to prescribe, how much hyperopic correction would they prescribe (e.g., full or partial prescription). The response distributions by profession (optometry and ophthalmology) were compared using the Kolmogorov-Smirnov cumulative distribution function test., Results: Responses were submitted by 738 participants regarding how they prescribe for their hyperopic patients. Most providers within each profession considered similar clinical factors when prescribing. The percentages of optometrists and ophthalmologists who reported considering the factor often differed significantly. Factors considered similarly by both optometrists and ophthalmologists were the presence of symptoms (98.0%, p = 0.14), presence of astigmatism and/or anisometropia (97.5%, p = 0.06) and the possibility of teasing (8.3%, p = 0.49). A wide range of prescribing was observed within each profession, with some providers reporting that they would prescribe for low levels of hyperopia while others reported that they would never prescribe. When prescribing for bilateral hyperopia in children with age-normal visual acuity and no manifest deviation or symptoms, the threshold for prescribing decreased with age for both professions, with ophthalmologists typically prescribing 1.5-2 D less than optometrists. The threshold for prescribing also decreased for both optometrists and ophthalmologists when children had associated clinical factors (e.g., esophoria or reduced near visual function). Optometrists and ophthalmologists most commonly prescribed based on cycloplegic refraction, although optometrists most commonly prescribed based on both the manifest and cycloplegic refraction for children ≥7 years., Conclusion: Prescribing patterns for paediatric hyperopia vary significantly among eye care providers., (© 2023 The Authors. Ophthalmic and Physiological Optics published by John Wiley & Sons Ltd on behalf of College of Optometrists.)

The last 40 years of clinical experience and investigation of nystagmus in infancy and childhood have resulted in a clearer understanding and characterization of the disorder and provided guidelines for the beneficial effects of increased medical, optical, and surgical treatments. Our modern understanding is due to the results of contribution by scientists and clinicians representing vision, neurology, bioengineering, genetics, and pediatrics. From this group, a new classification system was developed. The routine use of eye-movement recordings (EMR) and its characteristics have made the largest contribution to this increased knowledge. The value of EMR is due to the observation of specific waveforms, which are the basis for classification, neuro-pathophysiology, effect on vision, and a measure of nystagmus response to treatment. Successful treatment of the visual system is now directed toward associated afferent system abnormalities (decreased acuity, amblyopia, ametropia, retinal and optic pathway disease, and photophobia), centrally at the neuronal level responsible for the oscillations (oral and topical medications) and peripherally to reduce the underlying oscillation (eye-muscle surgery and botulinum toxin). Evidence over the last 40 years has shown that these treatments result in increased spatial acuity, contrast sensitivity, visual recognition time, motion processing, gaze-dependent visual acuity, and anomalous head posturing. The hope of this review is that clinicians now provide hope for these patients and families and can be counseled that nystagmus treatment is available.

Purpose: To characterize the genotypic and phenotypic spectrum of foveal hypoplasia (FH)., Design: Multicenter, observational study., Participants: A total of 907 patients with a confirmed molecular diagnosis of albinism, PAX6, SLC38A8, FRMD7, AHR, or achromatopsia from 12 centers in 9 countries (n = 523) or extracted from publicly available datasets from previously reported literature (n = 384)., Methods: Individuals with a confirmed molecular diagnosis and availability of foveal OCT scans were identified from 12 centers or from the literature between January 2011 and March 2021. A genetic diagnosis was confirmed by sequence analysis. Grading of FH was derived from OCT scans., Main Outcome Measures: Grade of FH, presence or absence of photoreceptor specialization (PRS+ vs. PRS-), molecular diagnosis, and visual acuity (VA)., Results: The most common genetic etiology for typical FH in our cohort was albinism (67.5%), followed by PAX6 (21.8%), SLC38A8 (6.8%), and FRMD7 (3.5%) variants. AHR variants were rare (0.4%). Atypical FH was seen in 67.4% of achromatopsia cases. Atypical FH in achromatopsia had significantly worse VA than typical FH (P < 0.0001). There was a significant difference in the spectrum of FH grades based on the molecular diagnosis (chi-square = 60.4, P < 0.0001). All SLC38A8 cases were PRS- (P = 0.003), whereas all FRMD7 cases were PRS+ (P < 0.0001). Analysis of albinism subtypes revealed a significant difference in the grade of FH (chi-square = 31.4, P < 0.0001) and VA (P = 0.0003) between oculocutaneous albinism (OCA) compared with ocular albinism (OA) and Hermansky-Pudlak syndrome (HPS). Ocular albinism and HPS demonstrated higher grades of FH and worse VA than OCA. There was a significant difference (P < 0.0001) in VA between FRMD7 variants compared with other diagnoses associated with FH., Conclusions: We characterized the phenotypic and genotypic spectrum of FH. Atypical FH is associated with a worse prognosis than all other forms of FH. In typical FH, our data suggest that arrested retinal development occurs earlier in SLC38A8, OA, HPS, and AHR variants and later in FRMD7 variants. The defined time period of foveal developmental arrest for OCA and PAX6 variants seems to demonstrate more variability. Our findings provide mechanistic insight into disorders associated with FH and have significant prognostic and diagnostic value., (Copyright © 2022 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.)

Purpose: To investigate anomalous head posturing in patients with INS., Methods: This was a prospective, cohort analysis of clinical and anomalous head posture (AHP) data in 34 patients with INS and an AHP. Particular outcome measures included measurement of AHP in three dimensions of pitch (anterior posterior flexion/extension), yaw (lateral rotation), and roll (lateral flexion) during best-corrected binocular acuity testing and during their subjective sense of straight. Patients were also queried as to their subjective sense of head posture in forced straight position and in their preferred AHP. The paired t test was used to determine significance in differences between measures., Results: A total of 34 patients (19 males [56%]) 9-56 years of age (mean, 16.5 ± 6) were included. Associated systemic or ocular system deficits were present in 30 patients (88%). AHP during best-corrected visual acuity testing averaged 16.5° ± 8.20° (range, 10°-51°), which was significantly different from the mean voluntary "comfortable" position only in the pitch and roll directions (P < 0.001). There was a significant noncongruous response during subjective response to head posturing with most sensing their head as "crooked" (76.5%) when manually straightened (P = 0.001)., Conclusions: The clinical AHP of patients with INS exists in all three spatial dimensions of pitch, yaw, and roll. Although the visual system may be causally related to the onset, amount, and direction of a compensatory AHP in patients with INS, its persistence over time or after surgical intervention is likely due to a combination of visual system (eg, nystagmus, strabismus) and nonvisual system (egocentric and musculo-skeletal) factors., (Copyright © 2021 American Association for Pediatric Ophthalmology and Strabismus. Published by Elsevier Inc. All rights reserved.)

Medicine has a six-fold role to play in war, 1) selection of suitable military personnel, 2) to protect against disease, 3) to give medical attention and treatment to those who are ill and injured, 4) to assist in the rehabilitation of the disabled, 5) research to improve etiology and treatments of disease, and 6) the unit surgeon serves as a special staff officer to the military commander at all levels of a battalion and above, along with the attorney and chaplain, and supplies medical input into all plans whether it be training or combat operations. This article focuses on the realization by soldiers, since antiquity, the importance of the visual system in battle, how this was measured, and how modern military visual requirements have evolved along with the science of ophthalmology. Necessity and natural selection were the driving forces for recruitment and assignment in ancient and medieval armies. Since the advent of mechanized warfare, more soldiers can perform more tasks, more uniformly, radically changing the way soldiers are selected. Modern military duty eligibility requirements and assignments are now the result of special tests and documentation procedures resulting from a mixture of medical knowledge, science, and potential legal consequences. Nowhere is this more evident in the stringent visual system requirements for military service., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Purpose: To characterize the effects of eye muscle surgery on patients older than 18 years with infantile nystagmus syndrome (INS) who have had only optical treatment., Methods: This was a prospective, single-center, interventional case series analysis of clinical and electro-phyisological data before and after surgery. Outcome measures included: clinical characteristics, surgical procedure, and preoperative and postoperative binocular best corrected visual acuity (BCVA) in the null position, anomalous head posture (AHP), contrast sensitivity, strabismic deviation, and nystagmus acuity function (NAFX). Postoperative data used were collected for a minimum of 12 months after surgery. Parametric and non-parametric statistical analysis of the outcome measures was performed., Results: Ages ranged from 18 to 72 years (average: 36 years) and follow-up from 12 to 74 months (average: 26 months). A surgical algorithm of nine separate procedures involving at least two recti muscles on each eye was used for each patient. Most patients had associated systemic and/or ocular diagnoses, including albinism (35%), amblyopia (23%), optic nerve or retinal disorders (48%), refractive error (80%), AHP (44%), aperiodicity (27%), and strabismus (69%). There were no serious surgical complications, with a reoperation rate of 12%. There were significant group mean increases in BVCA, AHP, contrast sensitivity, strabismic deviation, and NAFX after surgery. Sixty percent of patients who were legally ineligible for driving prior to surgery became eligible after eye muscle surgery., Conclusions: Adult patients with INS showed sustained improvement in many afferent and efferent measures of visual function after eye muscle surgery. [ J Pediatr Ophthalmol Strabismus . 2021;58(2):93-104.] .

Purpose: To determine the ocular and systemic safety of using topical Lambda-Cyhalothrin (LCL) in a canine model of infantile nystagmus syndrome (INS). The rationale for this proposal is based on a case study of a patient whose INS improved after inadvertent ocular exposure to a pyrethroid pesticide containing LCL., Methods: After in-vitro safety testing and IUCAC approval, we studied increasing concentrations of topical LCL drops (0.002% to 0.07%) in canines with a purposely bred defect in the RPE65 gene resulting in both retinal degeneration and INS. We collected data on ocular and systemic effects and performed eye-movement recordings (EMR)., Results: At the 0.07% concentration dose of LCL, there was minimal, reversible, conjunctival hyperemia. There was no other ocular or systemic toxicity. At the 0.06% dose, there was a visible decrease in the INS and EMR showed a 153%-240% increase in the nystagmus acuity function and a 30%-70% decrease in amplitude across gaze. There was also a 40%-60% decrease in intraocular pressure while on the drop in both eyes., Conclusion: This animal study suggests this new pharmacological agent has potential for topical treatment of both INS and diseases with raised intraocular pressure. Further, this new treatment approach confirms the importance of extraocular muscle proprioception in ocular motor diseases and their treatment., Competing Interests: None

Purpose: To describe a patient with chronic periocular pain after bilateral photorefractive keratectomy (PRK) and ocular neuralgia that was controlled with regular orbital steroid and anesthetic injections., Methods: Case report., Results: A 21-year-old man presented 3 months following bilateral PRK surgery in severe bilateral orbital pain. Previous treatments included topical (artificial tears, corticosteroids, and nonsteroidal anti-inflammatory drugs [NSAIDs) and oral (NSAIDs, opioids, and pregabalin) therapies with minimal pain relief. A bilateral orbital triamcinolone acetonide 40 mg/cc and 0.25% bupivacaine injection was done after a successful, diagnostic unilateral 0.25% bupivacaine injection. Following bilateral bupivacaine and triamcinolone acetonide injections, pain intensity improved from 7 of 9 to 1 of 3 out of 10. Repeat injections have been regularly performed over the past 3 years, allowing the patient to experience improved symptoms lasting from 4 to 9 months., Conclusions: In this case, orbital nerve blocks provided relief and may be considered as a potential treatment for orbital neuralgia after refractive surgery. [J Refract Surg. 2019;35(8):534-537.]., (Copyright 2019, SLACK Incorporated.)

Precis: Glaucoma suspect was the most prevalent category in this study followed by glaucoma associated with acquired ocular anomaly and juvenile open-angle glaucoma. Primary congenital glaucoma was diagnosed in only 3% of the population studied., Purpose: To describe the prevalence and clinical characteristics of childhood glaucoma diagnosed over a 10-year period among patients aged 18 years or below who were seen at a tertiary care children's hospital using the new Childhood Glaucoma Research Network classification system., Methods: Medical records of all patients aged 18 years or below (n=108) who were diagnosed with glaucoma between January 1, 2008 through September 30, 2018 were reviewed. Data collected included demographics (age at diagnosis, sex, and family history of glaucoma), intraocular pressure, disc-to-cup ratio, retinal nerve fiber layer thickness, and refractive errors. Clinical characteristics of each patient were evaluated according to the criteria established by Childhood Glaucoma Research Network. Categorical distributional equivalence comparisons were performed using the Pearson χ test. A P-value <0.05 was defined as statistically significant., Results: A total of 108 patients with a diagnosis of childhood glaucoma or glaucoma suspect were included in this study. Sixty-four percent of these patients were males (P<0.0001). The mean age at the time of diagnosis was 7.07±5.4 years. "Glaucoma suspect" was the most prevalent category (46%, P=0.0002), followed by glaucoma associated with the acquired ocular anomaly (20%) and juvenile open-angle glaucoma (16%). Primary congenital glaucoma represented 3% and all these patients were males. Sixty-nine percent of the patients had bilateral involvement (P=0.0073). The highest intraocular pressure recorded in the study was 57 mm Hg, the largest cup-to-disc ratio was 0.96, and the lowest retinal nerve fiber layer measurement was 39 μm. Ninety-two percent of the patients had refractive errors and 85% of them had astigmatism., Conclusions: Establishing a pattern and the associated clinical characteristics of childhood glaucoma at tertiary care children's hospitals will help in developing collaborative research efforts and effective treatment/management strategies for children with these rare groups of disorders.

Purpose: To test the hypothesis that eye muscle surgery in treatment of patients with acquired downbeat nystagmus results in improvement measures of visual and ocular motor function., Methods: This is a prospective, interventional case series analysis of clinical and electrophyisological data before and after eye muscle surgery in 17 patients with acquired downbeat nystagmus who did not respond to medical treatments. Outcome measures included: 1) routine demography and clinical characteristics, 2) subjective oscillopsia (SO), 3) binocular best-corrected visual acuity in the null position (BVA), 3) primary position strabismic deviation (SD), 5) anomalous head posture (AHP), 6) contrast sensitivity function (CS), and 7) nystagmus slow phase velocity (SPV). All patients were followed at least 12 months. Parametric and non-parametric statistical analysis of outcome measure data above pre- and post-treatment were perfomed using standard software on grouped data using computerized software., Results: Patients' age ranged from 5 to 85 years (average 27 years). About 59% were male. Follow up ranged from 1-10 years (average 2.0 years). Around 70% had an associated central nervous systemic diagnosis, 100% had an AHP, oscillopsia and decreased CS, 53% had other eye disease, and 59% had strabismus. There were no complications from surgery. There were signficant post-treatment improvements in mean/median group BVA, SO, SD, AHP, CS, and SPV., Conclusion: This study supports the hypothesis that eye muscle surgery as treatments for patients with acquired downbeat nystagmus can result in improvements in multiple aspects of ocular motor and visual functions., Competing Interests: None

Purpose: To describe the effects of extraocular muscle extirpation performed after previous eye muscle surgery in a 20-year-old woman with infantile nystagmus syndrome (INS) for whom we have 19 years of follow-up data., Methods: Clinical examinations were performed. Eye movement data analysis was carried out using the eXpanded Nystagmus Acuity Function (NAFX) and longest foveation domain (LFD)., Results: The patient re-presented to the authors at age 20, 2 years after bilateral anterior myectomy of the horizontal rectus muscles, bilateral anterior nasal transposition of the inferior oblique muscle, and bilateral superior oblique recessions. Evaluation revealed deterioration in nystagmus at lateral gaze angles, new incomitant strabismus with severe loss of convergence, limited ductions, saccadic hypometria, slow saccades, and hypo-accommodation. Also, there was a pre- to post-extirpation minimal change of 21% in her peak NAFX, a 50% decrease in LFD, plus a predominant, asymmetric, multiplanar oscillation., Conclusions: It appears that in this patient, horizontal extirpation failed to abolish the nystagmus and caused significant, new, symptomatic deficits interfering with many of the patient's visual functions., (Copyright © 2018 American Association for Pediatric Ophthalmology and Strabismus. Published by Elsevier Inc. All rights reserved.)

Purpose: This study presents test-retest reliability of optotype visual acuity (OVA) across 60° of horizontal gaze position in patients with infantile nystagmus syndrome (INS). Also, the validity of the metric gaze-dependent functional vision space (GDFVS) is shown in patients with INS., Methods: In experiment 1, OVA was measured twice in seven horizontal gaze positions from 30° left to right in 10° steps in 20 subjects with INS and 14 without INS. Test-retest reliability was assessed using intraclass correlation coefficient (ICC) in each gaze. OVA area under the curve (AUC) was calculated with horizontal eye position on the x-axis, and logMAR visual acuity on the y-axis and then converted to GDFVS. In experiment 2, validity of GDFVS was determined over 40° horizontal gaze by applying the 95% limits of agreement from experiment 1 to pre- and post-treatment GDFVS values from 85 patients with INS., Results: In experiment 1, test-retest reliability for OVA was high (ICC ≥ 0.88) as the difference in test-retest was on average less than 0.1 logMAR in each gaze position. In experiment 2, as a group, INS subjects had a significant increase (P < 0.001) in the size of their GDFVS that exceeded the 95% limits of agreement found during test-retest., Conclusions: OVA is a reliable measure in INS patients across 60° of horizontal gaze position. GDFVS is a valid clinical method to be used to quantify OVA as a function of eye position in INS patients. This method captures the dynamic nature of OVA in INS patients and may be a valuable measure to quantify visual function patients with INS, particularly in quantifying change as part of clinical studies.

The authors report a new technique to treat complete cranial nerve III palsy. A 15-year-old girl underwent botulinum toxin injection into the lateral rectus muscle, nasal transposition of both the superior and inferior oblique muscles to the medial rectus insertion, and absorbable suture globe fixation to the nasal orbital periosteum. Six months postoperatively, her primary position eye deviation was within 12 prism diopters of orthotropia with limitation of ductions in all directions. [J Pediatr Ophthalmol Strabismus. 2017;54:e13-e17]., (Copyright 2017, SLACK Incorporated.)

We report the vitreous concentration of bevacizumab after injection for the treatment of retinopathy of prematurity (ROP). A premature neonate diagnosed with type 1 ROP was treated in both eyes with 0.625 mg intravitreal bevacizumab injection at 32 weeks' postconceptual age. Eleven weeks later there was complete regression clinically, but the patient died. Vitreous samples taken at autopsy revealed a bevacizumab vitreous concentration of 41.57 ng/ml. Histopathology of the retina showed residual preretinal neovascularization. Bevacizumab elimination from the infant vitreous is similar to that of adults, and, although complete regression was clinically apparent, it was not confirmed histopathologically., (Copyright © 2016 American Association for Pediatric Ophthalmology and Strabismus. Published by Elsevier Inc. All rights reserved.)

Background: Multiple procedures have been described to treat a large-angle esodeviation with an associated abduction deficit. We report a plication augmentation of the Hummelsheim procedure for the management of esotropia and severe abduction deficit due to abducens nerve palsy or type 1 Duane syndrome., Methods: The medical records of patients operated on using the plication augmentation Hummelsheim procedure at two tertiary centers were retrospectively reviewed. The surgery involved ipsilateral lateral rectus plication, half muscle transposition of the vertical rectus muscles to the paralytic plicated lateral rectus, Foster augmentation sutures, and ipsilateral medial rectus recession or botulinum toxin injection if it was found to be tight on intraoperative forced duction testing. Pre- and postoperative deviations, ocular motility findings, and complications were noted., Results: A total of 13 patients were included, all of whom had an esotropia with profound abduction deficit (-4 or more). Postoperative deviations ranged from 14(Δ) of esotropia to 14(Δ) of exotropia, with significant improvement of the abductive motion. No patient developed anterior segment ischemia., Conclusions: The plication augmentation Hummelsheim procedure resulted in correction of even very large esodeviations and improvement of the abduction force. This procedure may also better preserve the blood supply to the anterior segment compared to other surgical approaches., (Copyright © 2015 American Association for Pediatric Ophthalmology and Strabismus. Published by Elsevier Inc. All rights reserved.)

Purpose: To test the hypothesis that the topical carbonic anhydrase inhibitor brinzolamide (Azopt) has beneficial effects versus placebo on measures of nystagmus and visual acuity in adult subjects with infantile nystagmus syndrome (INS)., Design: Prospective, cross-over, double masked clinical trial., Setting: Single centre., Study Population: Five subjects ≥18 years old with typical INS and best-binocular visual acuity in their primary position null zone ETDRS 55 letters to 85 letters (20/200 to 20/50) and had no previous treatment for nystagmus., Intervention: In a randomised order, each subject received one drop of Azopt or placebo in both eyes three times a day separated by a washout period of at least a week followed by Azopt or placebo in both eyes three times a day; thus each subject got the drug and placebo, each acting as his or her own control., Outcome Measures: The nystagmus acuity function and INS waveforms obtained from eye movement recordings, binocular optotype visual acuity, using the ETDRS protocol analysed individually and as a group before and after Azopt and placebo., Results: Versus placebo and baseline measures, topical Azopt significantly improved; INS waveform characteristics in the primary position null zone, group mean values of the nystagmus acuity function across gaze (p<0.01) and group mean ETDRS binocular letter visual acuity (p<0.05). There was a predictable decrease in intraocular pressure (IOP) without any systemic or ocular adverse events., Conclusions: Although a prospective large-scale clinical trial is needed to prove effectiveness, an eye-drop-based therapy for INS may emerge as a viable addition to optical, surgical, behavioural and systemic drug therapies for INS., Trial Registration Number: NCT01312402., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.)

Oculocutaneous albinism (OCA) is a genetically inherited autosomal recessive condition. Individuals with OCA lack melanin and therefore are susceptible to the harmful effects of solar ultraviolet radiation, including extreme sun sensitivity, photophobia and skin cancer. OCA is a grave public health issue in sub-Saharan Africa with a prevalence as high as 1 in 1000 in some tribes. This article considers the characteristics and prevalence of OCA in sub-Saharan African countries. Sun-induced adverse health effects in the skin and eyes of OCA individuals are reviewed. Sun exposure behavior and the use of photoprotection for the skin and eyes are discussed to highlight the major challenges experienced by these at-risk individuals and how these might be best resolved., (© 2014 The American Society of Photobiology.)

Purpose: To investigate the effect of an artificial scotoma on open-loop disparity vergence responses (DVRs) and vergence control mechanisms, we examined open-loop DVRs to disparity stimuli using monocular artificial scotomas in normal subjects., Methods: Using a mirror haploscope with two computer monitors, we delivered disparity stimuli on a pair of random dot patterns subtending 40 by 30 degrees at 47 cm from each eye. The scotomas were black circles located in the center of a random dot pattern for the left eye. Eye movements of both eyes were recorded with a magnetic search coil system., Results: We first found that the amplitudes of DVRs were gradually decreased and the latency of DVRs was moderately increased as the size of the scotomas was increased. Second, monocular responses from each eye were symmetrical although the stimuli to each eye were asymmetrical., Conclusions: The results suggest that the monocular eye movements in disparity vergence are controlled by a binocular central mechanism, not driven separately by monocular inputs in the open-loop window.

We report a case of bilateral bifid insertion of superior rectus muscles, in a patient with oculocutaneous albinism as an incidental intraoperative finding during eye muscle surgery. The muscle was successfully operated on and the patient did well postoperatively. To our knowledge, this is the first report of this anomaly.

The purpose of this report is to summarize an understanding of the ocular motor system in patients with albinism. Other than the association of vertical eccentric gaze null positions and asymmetric, (a) periodic alternating nystagmus in a large percentage of patients, the ocular motor system in human albinism does not contain unique pathology, rather has "typical" types of infantile ocular oscillations and binocular disorders. Both the ocular motor and afferent visual system are affected to varying degrees in patients with albinism, thus, combined treatment of both systems will maximize visual function.

We have observed dramatic effects of tactile tongue stimulation on nystagmus eye movements in patients with acquired blindness, and we report these results. Six adult subjects (3 subjects with light perception or worse vision and 3 normal subjects) were included in this study. Causes of blindness included traumatic explosion, anterior ischemic optic neuropathy, and central retinal artery occlusion. Duration of blindness was 15, 3 and 1.5 years, respectively. A video eye tracking system (Eyelink 1000) was used to record eye movements. The eye movement recording (EMR) was repeated four times in a span of 20 min. Two of the EMRs were performed without tongue stimulation and two with tongue stimulation in randomized order. A tongue stimulus was applied to the surface of the tongue using a Brainport device that produces an electrical tactile stimulus. The nystagmus waveform characteristics and frequency were analyzed. We found that all blind subjects showed continuous jerk nystagmus with slow and quick phases, mainly in horizontal plane in their primary eye positions. The recorded nystagmus waveforms were jerk with linear velocity slow phases. When the tongue stimulus was applied, the frequency of nystagmus was significantly reduced by 47, 40, and 11%, and relative amplitude was reduced by 43, 45, and 6% for three blind subjects, respectively. In conclusion, we think our results that tongue stimulation influences nystagmus eye movements support a link between non-visual sensory input and ocular motor activity.

Background: Many children treated for cataracts develop strabismus and nystagmus; however, little is known about the critical period for adverse ocular motor outcomes with respect to age of onset and duration., Methods: Children who had undergone extraction of dense cataracts by the age of 5 years were enrolled postoperatively. Ocular alignment was assessed regularly throughout follow-up. Fixation stability and associated ocular oscillations were determined from eye movement recordings at ≥5 years old. Multivariate logistic regression was used to evaluate whether laterality (unilateral vs bilateral), age at onset, and/or duration of visual deprivation were associated with adverse ocular motor outcomes and to determine multivariate odds ratios (ORs)., Results: A total of 41 children were included. Of these, 27 (66%) developed strabismus; 29 (71%) developed nystagmus. Congenital onset was associated with significant risk for strabismus (OR, 5.3; 95% CI, 1.1-34.1); infantile onset was associated with significant risk for nystagmus (OR, 13.6; 95% CI, 1.6-302). Duration >6 weeks was associated with significant risk for both strabismus (OR, 9.1; 95% CI, 1.9-54.2) and nystagmus (OR, 46.2; 95% CI, 6.0-1005). Congenital onset was associated with significant risk for interocular asymmetry in severity of nystagmus (OR, 25.0; 95% CI, 2.6-649), as was unilateral cataract (OR, 58.9; 95% CI, 5.1-2318)., Conclusions: Laterality (unilateral vs bilateral) and age at onset were significant nonmodifiable risk factors for adverse ocular motor outcomes. Duration of deprivation was a significant modifiable risk factor for adverse ocular motor outcomes. The current study demonstrated that reduced risk for nystagmus and strabismus was associated with deprivation ≤6 weeks., (Copyright © 2012 American Association for Pediatric Ophthalmology and Strabismus. Published by Mosby, Inc. All rights reserved.)

Purpose: Nystagmus eye movement data from infants and young children are often not suitable for advanced quantitative analysis. A method was developed to capture useful information from noisy data and validate the technique by showing meaningful relationships with visual functioning., Methods: Horizontal eye movements from patients (age 5 months-8 years) with idiopathic infantile nystagmus syndrome (INS) were used to develop a quantitative outcome measure that allowed for head and body movement during the recording. The validity of this outcome was assessed by evaluating its relation to visual acuity deficit in 130 subjects, its relation to actual fixation as assessed under simultaneous fundus imaging, its correlation with the established expanded nystagmus acuity function (NAFX), and its test-retest variability., Results: The nystagmus optimal fixation function (NOFF) was defined as the logit transform of the fraction of data points meeting position and velocity criteria within a moving window. A decreasing exponential relationship was found between visual acuity deficit and the NOFF, yielding a 0.75 logMAR deficit for the poorest NOFF and diminishing deficits with improving foveation. As much as 96% of the points identified as foveation events fell within 0.25° of the actual target. Good correlation (r = 0.96) was found between NOFF and NAFX. Test-retest variability was 0.49 logit units., Conclusions: The NOFF is a feasible method to quantify noisy nystagmus eye movement data. Its validation makes it a promising outcome measure for the progression and treatment of nystagmus during early childhood.

Objective: To determine whether age at initiation of treatment for amblyopia influences the response among children 3 to less than 13 years of age with unilateral amblyopia who have 20/40 to 20/400 amblyopic eye visual acuity., Methods: A meta-analysis of individual subject data from 4 recently completed randomized amblyopia treatment trials was performed to evaluate the relationship between age and improvement in logMAR amblyopic eye visual acuity. Analyses were adjusted for baseline amblyopic eye visual acuity, spherical equivalent refractive error in the amblyopic eye, type of amblyopia, prior amblyopia treatment, study treatment, and protocol. Age was categorized (3 to <5 years, 5 to <7 years, and 7 to <13 years) because there was a nonlinear relationship between age and improvement in amblyopic eye visual acuity., Results: Children from 7 to less than 13 years of age were significantly less responsive to treatment than were younger age groups (children from 3 to <5 years of age or children from 5 to <7 years of age) for moderate and severe amblyopia (P < .04 for all 4 comparisons). There was no difference in treatment response between children 3 to less than 5 years of age and children 5 to less than 7 years of age for moderate amblyopia (P = .67), but there was a suggestion of greater responsiveness in children 3 to less than 5 years of age compared with children 5 to less than 7 years of age for severe amblyopia (P = .09)., Conclusions: Amblyopia is more responsive to treatment among children younger than 7 years of age. Although the average treatment response is smaller in children 7 to less than 13 years of age, some children show a marked response to treatment.

Purpose: To report the effect of the abnormal head posture (AHP) correcting procedures on the visual acuity improvement in patients with infantile nystagmus syndrome (INS) and the visual acuity improvement outcomes in different AHP correcting surgeries in INS., Methods: This was a prospective, non-randomized, interventional study. Twenty-eight patients underwent the Anderson-Kestenbaum procedure or the modified Anderson procedure with or without tenotomy of at least one horizontal recti for correction of AHP. Best-corrected binocular null zone acuity and degree of AHP was recorded preoperatively and compared with those done 1 month postoperatively., Results: The average null zone logarithm of the minimum angle of resolution acuity was 0.42 preoperatively, which improved significantly to 0.33 postoperatively (P = .002). The AHP ranged from 10° to 40° (mean: 20.89°), which improved significantly to a mean of 3.21° (P = .000). No significant difference (P = .65) was found in the visual acuity improvement among patients who underwent the Anderson-Kestenbaum procedure or the modified Anderson procedure with or without tenotomy. No significant difference in the visual acuity improvement was seen in patients who underwent tenotomy of at least one horizontal rectus muscle along with the modified Anderson procedure compared to those who underwent the modified Anderson procedure alone (P = .28)., Conclusion: The procedures used mainly for correction of AHP in INS do yield significant improvement in the visual acuity. This improvement is seen in patients undergoing surgery for both horizontal and vertical AHP., (Copyright 2011, SLACK Incorporated.)

Background: Recent advances in infantile nystagmus syndrome (INS) surgery have uncovered the therapeutic importance of proprioception. In this report, we test the hypothesis that the topical carbonic anhydrase inhibitor (CAI) brinzolamide (Azopt) has beneficial effects on measures of nystagmus foveation quality in a subject with INS., Methods: Eye movement data were taken, using a high-speed digital video recording system, before and after 3 days of the application of topical brinzolamide 3 times daily in each eye. Nystagmus waveforms were analyzed by applying the eXpanded Nystagmus Acuity Function (NAFX) at different gaze angles and determining the longest foveation domain (LFD) and compared to previously published data from the same subject after the use of a systemic CAI, contact lenses, and convergence and to other subjects before and after eye muscle surgery for INS., Results: Topical brinzolamide improved foveation by both a 51.9% increase in the peak value of the NAFX function (from 0.395 to 0.600) and a 50% broadening of the NAFX vs Gaze Angle curve (the LFD increased from 20° to 30°). The improvements in NAFX after topical brinzolamide were equivalent to systemic acetazolamide or eye muscle surgery and were intermediate between those of soft contact lenses or convergence. Topical brinzolamide and contact lenses had equivalent LFD improvements and were less effective than convergence., Conclusions: In this subject with INS, topical brinzolamide resulted in improved-foveation INS waveforms over a broadened range of gaze angles. Its therapeutic effects were equivalent to systemic CAI. Although a prospective clinical trial is needed to prove efficacy or effectiveness in other subjects, an eyedrops-based therapy for INS may emerge as a viable addition to optical, surgical, behavioral, and systemic drug therapies.

Aims: We developed a new data analysis algorithm called the automated nystagmus acuity function (ANAF) to automatically assess nystagmus acuity function. We compared results from the ANAF with those of the well-known expanded nystagmus acuity function (NAFX)., Methods: Using the ANAF and NAFX, we analysed 60 segments of nystagmus data collected with a video-based eye tracking system (EyeLink 1000) from 30 patients with infantile or mal-development fusional nystagmus. The ANAF algorithm used the best-foveation positions (not true foveation positions) and all data points in each nystagmus cycle to calculate a nystagmus acuity function., Results: The ANAF automatically produced a nystagmus acuity function in a few seconds because manual identification of foveation eye positions is not required. A structural equation model was used to compare the ANAF and NAFX. Both ANAF and NAFX have similar measurement imprecision and relatively little bias. The estimated bias was not statistically significant for either methods or replicates., Conclusions: We conclude that the ANAF is a valid and efficient algorithm for determining a nystagmus acuity function.

Purpose: Infantile nystagmus syndrome (INS) can be idiopathic or associated with ocular or systemic disease. The ocular oscillation of INS directly contributes to loss of visual acuity. In this study, visual acuity development in patients with INS was examined., Methods: Children with INS were classified as having idiopathic INS (n = 84) or INS with an associated sensory deficit: INS and albinism (n = 71), bilateral optic nerve hypoplasia (ONH; n = 23), or congenital retinal disorder (n = 36). Visual acuity was assessed with Teller cards and/or optotypes, and the data were analyzed for three age groups (<24 months, 24-48 months, and >48 months)., Results: Patients with idiopathic INS showed mildly reduced visual acuity early in life and gradual maturation with age that paralleled a normative curve. Patients with albinism also showed a mild visual deficit early in life but failed to keep pace with the normative curve, showing a gradual increase in visual acuity deficit. Patients with ONH and congenital retinal disorders exhibited more severe visual acuity deficits during infancy. The ONH group displayed slow improvement of visual acuity with a plateau at 24 months through >48 months, with a small increase in visual acuity deficit. The congenital retinal disorder group had no significant change in visual acuity across age and had a rapid increase in visual acuity deficit., Conclusions: The pattern of visual acuity development differs among children with INS, depending on the presence or absence of associated sensory system deficits. Careful characterization of visual system differences in patients with INS is important if visual acuity is an outcome in clinical trials.

Periodic alternating nystagmus consists of involuntary oscillations of the eyes with cyclical changes of nystagmus direction. It can occur during infancy (e.g. idiopathic infantile periodic alternating nystagmus) or later in life. Acquired forms are often associated with cerebellar dysfunction arising due to instability of the optokinetic-vestibular systems. Idiopathic infantile periodic alternating nystagmus can be familial or occur in isolation; however, very little is known about the clinical characteristics, genetic aetiology and neural substrates involved. Five loci (NYS1-5) have been identified for idiopathic infantile nystagmus; three are autosomal (NYS2, NYS3 and NYS4) and two are X-chromosomal (NYS1 and NYS5). We previously identified the FRMD7 gene on chromosome Xq26 (NYS1 locus); mutations of FRMD7 are causative of idiopathic infantile nystagmus influencing neuronal outgrowth and development. It is unclear whether the periodic alternating nystagmus phenotype is linked to NYS1, NYS5 (Xp11.4-p11.3) or a separate locus. From a cohort of 31 X-linked families and 14 singletons (70 patients) with idiopathic infantile nystagmus we identified 10 families and one singleton (21 patients) with periodic alternating nystagmus of which we describe clinical phenotype, genetic aetiology and neural substrates involved. Periodic alternating nystagmus was not detected clinically but only on eye movement recordings. The cycle duration varied from 90 to 280 s. Optokinetic reflex was not detectable horizontally. Mutations of the FRMD7 gene were found in all 10 families and the singleton (including three novel mutations). Periodic alternating nystagmus was predominantly associated with missense mutations within the FERM domain. There was significant sibship clustering of the phenotype although in some families not all affected members had periodic alternating nystagmus. In situ hybridization studies during mid-late human embryonic stages in normal tissue showed restricted FRMD7 expression in neuronal tissue with strong hybridization signals within the afferent arms of the vestibulo-ocular reflex consisting of the otic vesicle, cranial nerve VIII and vestibular ganglia. Similarly within the afferent arm of the optokinetic reflex we showed expression in the developing neural retina and ventricular zone of the optic stalk. Strong FRMD7 expression was seen in rhombomeres 1 to 4, which give rise to the cerebellum and the common integrator site for both these reflexes (vestibular nuclei). Based on the expression and phenotypic data, we hypothesize that periodic alternating nystagmus arises from instability of the optokinetic-vestibular systems. This study shows for the first time that mutations in FRMD7 can cause idiopathic infantile periodic alternating nystagmus and may affect neuronal circuits that have been implicated in acquired forms.

Purpose: To report the repeatability of a digital head-posture measuring system when used to record anomalous head postures in children., Design: Prospective study and clinical laboratory investigation., Methods: Using a digital head-posture measuring system, we measured 36 different anomalous head postures in 27 children with infantile nystagmus syndrome. Repeatability values and 95% limits of repeatability of measurements were generated for anomalous head postures., Results: Among the 27 children, 3 had 2 head postures (right and left head turns) in 2 different directions; 6 had 2-dimensional head postures that were considered 2 different head postures; and 18 had a 1-dimensional head posture. There were 5 chin-up or chin-down postures, 23 head-turn postures, and 8 head-tilt postures in a total of 36 anomalous head postures. The repeatability value for all anomalous head postures was less than 10 degrees. Ninety-five percent limits of repeatability yielded ranges of less than 10 degrees for all anomalous head postures., Conclusions: The digital head-posture measuring system is a valid and reliable device for measuring 3-dimensional head postures in children with nystagmus., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Background: The study of the clinical and electrophysiological effects of eye muscle surgery on patients with infantile nystagmus has broadened our knowledge of the disease and its interventions., Design: Prospective, comparative, interventional case series., Participants: Twenty-four patients with a vertical head posture because of electrophysiologically diagnosed infantile nystagmus syndrome. The ages ranged from 2.5 to 38 years and follow up averaged 14.0 months., Methods: Thirteen patients with a chin-down posture had a bilateral superior rectus recession, inferior oblique myectomy and a horizontal rectus recession or tenotomy. Those 11 with a chin-up posture had a bilateral superior oblique tenectomy, inferior rectus recession and a horizontal rectus recession or tenotomy., Main Outcome Measures: Outcome measures included: demography, eye/systemic conditions and preoperative and postoperative; binocular, best optically corrected, null zone acuity, head posture, null zone foveation time and nystagmus waveform changes., Results: Associated conditions were strabismus in 66%, ametropia in 96%, amblyopia in 46% and optic nerve, foveal dysplasia or albinism in 54%. Null zone acuity increased at least 0.1 logMAR in 20 patients (P < 0.05 group mean change). Patients had significant (P < 0.05) improvements in degrees of head posture, average foveation time in milliseconds and infantile nystagmus syndrome waveform improvements., Conclusions: This study illustrates a successful surgical approach to treatment and provides expectations of ocular motor and visual results after vertical head posture surgery because of an eccentric gaze null in patients with infantile nystagmus syndrome., (© 2010 The Authors. Clinical and Experimental Ophthalmology © 2010 Royal Australian and New Zealand College of Ophthalmologists.)

Introduction: The lure of studying the ocular motor system stems from its anatomic and physiological accessibility, ease of measurement and analysis of function, as well as the promise of providing a direct window into the brain. There is an increasing body of knowledge on how the brain responds to peripheral eye muscle manipulation (surgery, medications, denervation, genetic therapy). Investigations in both animals and humans have established that plasticity within the brain occurs after peripheral neuromuscular (medical or surgical) disruption and repair., Purpose: This paper will review and summarize neurophysiological concepts resulting from recent investigations of the ocular motor system and treatment of involuntary oscillations such as nystagmus., Methods: Review of both a multidisciplinary literature and the authors 25 years experience evaluating, treating and investigating the ocular motor system., Conclusions: The ocular motor system in man is a continuously controlled, malleable brain-eye system, which is genetically programmed, environmentally modified and contains powerful reparative processes. It begins during development, extends throughout life and is subject to external manipulation in both health and disease. These ideas challenge the historically significant axiom, i.e., that there is eventual (and a final maturing to an end state) "hard-wiring" of much of both the ocular motor and afferent visual systems. Rather, they now are shown to maintain some degree of plasticity throughout life.

Purpose: To discuss the common characteristics of infants and children with nystagmus and review treatments and their evidence., Methods: The NEI-sponsored classification of eye movement abnormalities and strabismus and a PubMed search for papers from 1995 through 2005 on interventions for Infantile Nystagmus Syndrome (INS) are reviewed., Results: The review of treatments revealed 18 papers on surgical or pharmacological interventions and six papers describing other interventions. There is only one randomized controlled trial, with all the other studies being uncontrolled trials/case series., Conclusions: Previous science and studies on interventions for nystagmus in infancy and childhood have laid an important foundation for future work in this field, which should include a randomized clinical trial.

Purpose: To report a systematic approach to, and the visual and electrophysiological effect of, eye muscle surgery in 100 patients with infantile nyustagmus syndrome (INS)., Methods: Prospective, interventional case cohort analysis of clinical and eye movement data in 100 patients with INS who had virgin extraocular eye muscles operated on for nystagmus with or without combinations of strabismus and an anomalous head posture. All patients were followed at least 9 months after surgery. Outcome measures, part of an IRB approved study, included binocular visual acuity, head position, strabismic deviation, and eye movement recordings, from which waveform types and an Automated Nystagmus Acuityn Function (ANAF) was calculated. Computerized parametric and non-parametric statistical analysis of data were performed using standard software on both individual and group data., Results: There were 9 consistent surgical procedures used with the most common being that for a horizontal head posture alone (22%). Age at surgery averaged 14 years with 11 months followup. Sixty-eight percent had associated eye disease (optic nerve, retinal, amblyopia, cataracts). Group means in binocular acuity, strabismic deviation, head posture, abd ANAF measures from eye improved for all procedures. There were 12 (12%) reoperations without any serious surgical complications. Individual analysis revealed only age and head posture differences in outcome measures between the 9 procedures., Conclusions: Using this approach, surgery on the extraocular muscles in patients with INS results in improvements in multiple aspects of ocular motor and visual function.

Data regarding the pupillary responses in very premature neonates is scarce; what data exist, moreover, is not recent. The purpose of this pilot study is to collect data on direct and consensual pupillary light responses before 30 weeks postmenstrual age. Six neonates were studied. Mean pupillary size at rest was 3.6 +/- 0.4 mm. No direct or consensual responses to light were present in any of 12 eyes. Accurate information about pupillary reflexes in very premature neonates provides relevant information about the development of the visual and neurologic systems. Available information about the development of the Edinger-Westphal nucleus, sphincter pupillary muscle, optic nerve myelinization, and autonomic nervous system is briefly reviewed.

Purpose: To evaluate the feasibility of spectral domain optical coherence tomography (SD-OCT) macular scanning as a means of studying the afferent visual system in nystagmus patients., Methods: Nystagmus patients who underwent SD-OCT, clinical evaluation, and eye movement recordings were recruited for this prospective, single-center, noncomparative study. Three SD-OCT macular three-dimensional cube scans per eye (200 x 200 x 1024 samplings in a 6 x 6 mm region) were obtained for qualitative retinal morphology analysis., Results: Nineteen patients (6-68 years; average, 19 years) were analyzed. Of these, 17 patients had infantile nystagmus syndrome, and 2 had fusion maldevelopment nystagmus; 17 patients (89%) had associated sensory system abnormalities, including 9 (47%) with albinism. Macular images were successfully obtained in all but 1 patient (95%). Of the 8 successfully imaged oculocutaneous patients, 7 patients demonstrated "fovea plana," and all demonstrated abnormal morphology., Conclusion: SD-OCT reliably provides detailed structural imaging of the fovea in nystagmus patients.

Purpose: To report the accuracy and repeatability of a new digital head posture measuring system., Design: Prospective study, clinical laboratory investigation., Methods: The digital head posture measuring system consists of a head-mounted motion tracker, a standard personal computer, and customized software to sample and display 3-dimensional (3D) head posture in real-time. Using a mechanical head posture measuring device as a reference, 3D head positions of an artificial head and 12 human subjects were recorded with the digital head posture device. Accuracy of the digital device outputs, relationship between digital outputs and actual head rotations, and repeatability of the tests were analyzed., Results: The digital head posture device showed consistent outcomes when compared to the mechanical one. The digital outputs of 3D rotations are very close to actual artificial head and human head rotations. The correlation coefficients of the linear relationship between the digital outputs and actual head movements were greater than 0.99. Repeatability tests for the artificial head and human subjects for all 3D rotations had 95% limits of agreement angles less than +/-6 degrees and +/-8 degrees, respectively., Conclusions: The digital head posture device is an acceptable device with high accuracy, repeatability, and validity in measuring head posture in 3 dimensions.

Purpose: To determine the effectiveness of weekend atropine for severe amblyopia from strabismus, anisometropia, or both combined among children 3 to 12 years of age., Methods: We enrolled children into 2 prospective, randomized multicenter clinical trials of amblyopia therapy. Herein we report the results for severe amblyopia, 20/125 to 20/400. In Trial 1, 60 children 3 to 6 years of age (mean, 4.4 years) were randomized to weekend atropine plus a plano lens or weekend atropine plus full spectacle correction for the sound eye. In Trial 2, 40 children 7 to 12 years of age (mean, 9.3 years) were randomized to weekend atropine or 2 hours of daily patching. The visual acuity outcome was assessed at 18 weeks in Trial 1 and 17 weeks in Trial 2., Results: In Trial 1, visual acuity improved by an average of 4.5 lines in the atropine plus correction group (95% CI, 3.2-5.8 lines) and 5.1 lines in the atropine plus plano lens group (95% CI, 3.7-6.4 lines). In Trial 2, visual acuity improved by an average of 1.5 lines in the atropine group (95% CI, 0.5-2.5 lines) and 1.8 lines in the patching group (95% CI, 1.1-2.6 lines)., Conclusions: Weekend atropine can improve visual acuity in children 3 to 12 years of age with severe amblyopia. Improvement may be greater in younger children.

Background: This study identifies the clinical and ocular motility characteristics of the periodic and aperiodic forms of infantile alternating nystagmus (IAPAN) and establishes the range of electrophysiological and clinical characteristics while providing clues to its presence and pathophysiology., Methods: Seventy-eight patients with ocular oscillations consistent with IAPAN were reported. Outcome variables were: age, follow-up in months, vision, strabismus, other eye and systemic abnormalities, head position, periodicity, cycle and null period duration, foveation time, waveforms, and cycle symmetry., Results: Age range was 1 to 67 years, 50% had pure periodic and aperiodic forms, 46% had albinism, 26% had binocular acuity of 20/40 or greater, 72% had strabismus, 35% had amblyopia, 31% had other eye disease, 14% had systemic disease, 87% had an anomalous head posture, and 65% had binocular directional asymmetry. The periodic cycle averaged 224 seconds and the aperiodic cycle ranged from 2 to more than 300 seconds. One in three patients with strabismus and nystagmus periodicity had a static head posture., Conclusion: Fifteen percent of the infantile nystagmus syndrome population had either the periodic or aperiodic form. A changing null period is often clinically missed because of long or irregular cycles, decreased acuity, associated strabismus, and either a nonexistent or inconsistent head posture. The changing null period is easier to recognize using eye movement recordings or if the non-preferred eye is occluded and the preferred eye is examined with the head straight and gaze in primary position for at least 5 to 7 minutes. The recognition of this variant has profound treatment implications.