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This prospective study investigated the magnitude and pattern of variation in choroidal optical coherence tomography angiography (OCT-A) indices every 4 h over 24 h in healthy young myopic (n = 24) and non-myopic (n = 20) adults. Choriocapillaris and deep choroid en-face images from macular OCT-A scans were analysed from each session to extract magnification-corrected vascular indices including choriocapillaris flow deficit number, size and density and deep choroid perfusion density in the sub-foveal, sub-parafoveal, and sub-perifoveal regions. Choroidal thickness was also obtained from structural OCT scans. Significant variations over 24 h (P

To assess the effect of changing anterior eye refractive power with contact lenses on the transverse magnification of en face images and associated vascular indices from optical coherence tomographic angiography (OCT-A).Prospective crossover study.Spherical soft contact lenses (-6 diopter [D] to +6 D in 2 D steps) were used to induce anterior eye refractive power changes in 11 healthy young adults and 3 × 3-mm macular scans were captured using OCT-A (Zeiss AngioPlex, software version 11.0; Cirrus HD-OCT 5000, Carl Zeiss Meditec Inc). Image transverse magnification was predicted based on refraction and biometry measurements and compared with empirical changes in the en face images measured with image analysis. Linear regression analysis was performed to assess the relationship between induced refractive ametropia and foveal avascular zone (FAZ) area, perimeter, circularity, and vessel density and perfusion density.The predicted transverse magnification was linearly related to induced refractive ametropia and to the empirical transverse magnification changes (average slope: 1.02, 95% CI: 0.90-1.34). All the OCT-A indices showed linear relationships with induced refractive ametropia (P.05) with the 12 D tested range altering the indices by 7% to 12%. After correcting for transverse magnification, all OCT-A indices except FAZ area were linearly related to induced refractive ametropia (P.05) and were reduced to 1% to 9%.This study is the first to show that induced refractive ametropia can affect OCT-A image magnification and indices. These changes are clinically important and need to be considered along with biometry effects when interpreting OCT-A indices. Transverse magnification changes can affect the ability of OCT-A to precisely measure linear dimensions of blood vessels.

PURPOSE This article aims to illustrate the principles of bearing fixing, a new computer-controlled procedure for subjective determination of astigmatism, and to compare it with conventional clinician-controlled Jackson crossed-cylinder refraction. METHODS The principles and method for bearing fixing are described. Astigmatism was measured using bearing fixing and Jackson cross-cylinder twice on 20 visually normal participants aged between 18 and 34 years. After final sphere adjustment, acuity measurements were made with each refraction estimate. RESULTS Bearing fixing results could be obtained for all participants. Mean bearing fixing cylinder magnitude was slightly higher than Jackson cross-cylinder measures of cylinder magnitude, by 0.05D. Using vector analysis to take into account cylinder power and axis, mean bearing fixing astigmatism was not significantly different from cross-cylinder astigmatism, but did have higher test-retest variability (p

To evaluate changes in the retinal microvasculature of young adults over 24 hours using optical coherence tomography angiography (OCT-A).Participants (n = 44, mean age 23.2 ± 4.1 years, 24 myopes and 20 nonmyopes) with normal ophthalmological findings were recruited. Two macular OCT-A and OCT scans, systemic blood pressure, intraocular pressure (IOP), and biometry measurements were taken every four hours over 24 hours. Superficial and deep retinal layer en face images were analyzed to extract magnification-corrected vascular indexes using image analysis including foveal avascular zone metrics, vessel density, and perfusion density for the foveal, parafoveal, and perifoveal zones.Significant diurnal variations (P0.001) were observed in the vessel and perfusion density in the three superficial retinal layer regions, with acrophase between 4:30 PM and 8:30 PM. Only foveal and parafoveal regions of the deep retinal layer exhibited significant diurnal variations with acrophase between 9 AM and 3 PM. Myopes and nonmyopes had different acrophases but not amplitudes in the parafoveal perfusion density of superficial retinal layer (P = 0.039). Significant correlations were observed between diurnal amplitudes or acrophases of superficial retinal layer indexes and systemic pulse pressure, IOP, axial length and retinal thickness.This study shows, for the first time, that significant diurnal variation exists in OCT-A indexes of macular superficial and deep retinal layer over 24 hours and were related to variations in various ocular and systemic measurements. Myopes and nonmyopes showed differences in the timing but not in amplitude of the superficial retinal layer parafoveal perfusion density variations but not in deep retinal layer.

PURPOSE To investigate the effects of computer monitor pixel density on Landolt C visual acuity measurements and to provide appropriate pixel density recommendations for Landolt C vision chart design. METHODS Participants were 10 healthy observers aged 18-31 years (mean 21.7 ± 3.6). Logarithmic progression charts were used, consisting of eight rows of five Landolt C optotypes ranging from -0.40 logMAR to 0.30 logMAR. Monitor pixel angular subtense varied from 0.10 min arc to 1.97 min arc, achieved by changing the chart test distance. Testing took place with two filtering conditions: unfiltered optotypes, (pixels rendered either black or white) and anti-aliased optotypes with pixel luminance averaged for a pixel square and rendered as grey levels. RESULTS Each participant's acuity versus pixel size data sets were fitted by a nonlinear relationship with acuity equal to an asymptotic threshold visual acuity (VAas ) for small pixel sizes below a critical pixel size (Pcrit ). For pixel sizes larger than Pcrit there was a linear relationship between acuity thresholds and pixel size. For anti-aliased Landolt Cs, mean Pcrit was 1.23 min, and for unfiltered Landolt Cs average Pcrit was 0.65 min. For anti-aliased LandoltCs, Pcrit was 2.01xVAas , and for unfiltered Landolt Cs Pcrit was 1.05xVAas . CONCLUSION These results are quantitatively very similar to previous research on pixellation and Sloan optotype acuity. We have demonstrated that spatially filtering Landolt C optotypes acts as anti-aliasing, to make them more robust to the degradation effects of pixellation. Previous recommendations for maximum pixel size on Sloan letter vision charts can be applied safely to Landolt C charts.

Purpose The effects of image doubling on logarithmic progression chart visual acuity were investigated by simulating diplopia on a computer monitor. Methods Ten participants (6M, 4F) aged 21-28 years (mean 22.4 ± 2.3) were assessed viewing with their left eye while wearing their best correction. Stimuli were eight rows of five Sloan letters, from 0.4 to -0.3 logMAR (6/15 to 6/3) arranged in logarithmic progression format, generated on an HD monitor. Stimuli were generated with different magnitudes of doubling, different directions of doubling, and different intensity ratios between the ghost image and main images. Results When the ghost image had the same intensity as the main image, there was a significant effect of doubling magnitude on visual acuity, with the mean acuity being -0.11 logMAR (6/4.7) for no doubling. Acuity thresholds (logMAR) increased when doubling exceeded 1 min of arc, reaching a level of 0.12 logMAR (6/7.9) for doubling of 16 min of arc. There were no significant effects of orientation on acuity, nor were there significant orientation-doubling magnitude interaction effects of visual acuity. Image doubling magnitude level affected visual acuity differently for different ghost image intensities, with the highest acuity elevation occurring when ghost and main images were equal or nearly equal. For faint ghost image intensities (10% and 20%) image doubling did not significantly affect visual acuity. Conclusions Image doubling will degrade visual acuity if doubling is greater than 1 min of arc, and ghost images are sufficiently intense. However, even with very obvious visually-disturbing image doubling, visual acuity remains only slightly reduced.

Aim: To evaluate feasibility, safety, and clinical efficiency of optometrists in conducting diabetic retinopathy screening and ocular health screening. Methods: This was a prospective observational trial study of newly developed optometric service pathways established at a community health clinic for diabetic retinopathy screening and a hospital ophthalmology clinic for ocular health screening. The study was carried out to assess the feasibility and safety of eye examinations conducted by optometrists. Patients were examined by optometrists using a standard eye examination at both clinics and re-examined by ophthalmologists as the reference standard. Optometrists recorded diagnoses of ocular conditions and classified referral urgency for each patient and these were compared with the diagnoses made by ophthalmologists, who were masked to the optometrists’ findings. Results: There was a high concordance of 87.0% (95% CI 80.4%-93.6%) for the diagnoses between the optometrists and ophthalmologists. Of 26 patients considered by the optometrists to need ophthalmology referral, 23 were agreed as such by the ophthalmologists, giving good agreement, κ = 0.76 (95% CI 0.53 -0.94) between the optometrists and ophthalmologists on referral classification. Agreement by the ophthalmologists for referral urgency classifications (very urgent/urgent or non-urgent) was very good (κ = 0.85, 95%CI 0.62-1.00). Conclusions: Ocular health examination by optometrists using optometric-eyecare pathways is feasible and safe. Optometrists showed strong agreement with ophthalmologists when diagnosing patients who had a range of ocular conditions. Optometrists were also able to triage referrals and their urgency accurately, suggesting that they could play an extensive role as primary eye care providers, thus reducing unnecessary referrals to ophthalmology clinics.

Significance Confidence intervals are still seldom reported for Bland-Altman 95% limits of agreement. When they are reported, 50% of articles use approximate methods and 50% use exact methods. Purpose Bland-Altman limits of agreement can be unreliable estimates, especially for small sample sizes. However, authors seldom use confidence intervals for limits of agreement. This article reviews their use in Optometry and Vision Science. Methods A keyword search for "Bland," "Altman," "Bland-Altman," "LoA," and "limits of agreement" was conducted on the Optometry and Vision Science website within a time range from January 2016 to December 2018. Results Fifty articles were reported or were judged to use Bland-Altman analysis; sample sizes ranged from 3 to 2072. Eight of these article reported confidence limits for limits of agreement, four of which used exact methods and four used Bland and Altman's approximate method. Conclusions Use of confidence intervals for limits of agreement has increased in Optometry and Vision Science but is far from universal. To assist researchers in calculating exact confidence limits for Bland-Altman limits of agreement, spreadsheets are included for performing the calculations and generating Bland-Altman plots with the confidence intervals included.

SIGNIFICANCE This is the first report of monocular ghost image offset thresholds measured using O optotypes. Monocular diplopia is a complaint of patients and is the result of a variety of etiologies. Furthermore, monocular image doubling also can be a confounding variable of vectographic stereoacuity tests, warranting an investigation of ghost image offset thresholds. PURPOSE To measure ghost image offset thresholds of normal observers and how they are affected by offset orientation, target size, and ghost image relative luminance. METHODS Participants were five individuals without ocular abnormalities aged 21 to 32 years. Stimuli were viewed monocularly and consisted of Sloan "O" optotypes generated on a computer monitor with varying levels of image doubling. Ghost image offset thresholds were determined using a spatial 2-alternative forced-choice paradigm and probit analysis of the frequency of seeing data. RESULTS Under close-to-optimal conditions, monocular ghost image offset thresholds ranged between 14 and 22 arc seconds, a level that might be considered a hyperacuity. Ghost image offset detection thresholds demonstrated a U-shaped relationship with optotype size, with optimum thresholds occurring for optotypes sizes of approximately -0.15 logarithmic minimum angle of resolution. There was no measurable effect of offset orientation on ghost image offset detection thresholds. Monocular ghost image offset detection thresholds decreased as ghost image relative luminance increased. CONCLUSIONS Ghost image offset detection thresholds can be quite low even when viewing under monocular conditions and relatively low ghost image relative luminance. This should be considered when designing and interpreting the results of vectographic stereoacuity tests.

Purpose: The Enright phenomenon describes the distortion in speed perception experienced by an observer looking sideways from a moving vehicle when viewing with interocular differences in retinal image brightness, usually induced by neutral density filters. We investigated whether the Enright phenomenon could be induced with monocular pupil dilation using tropicamide. Methods: We tested 17 visually normal young adults on a closed road driving circuit. Participants were asked to travel at Goal Speeds of 40 km/h and 60 km/h while looking sideways from the vehicle with: (i) both eyes with undilated pupils; (ii) both eyes with dilated pupils; (iii) with the leading eye only dilated; and (iv) the trailing eye only dilated. For each condition we recorded actual driving speed. Results: With the pupil of the leading eye dilated participants drove significantly faster (by an average of 3.8 km/h) than with both eyes dilated (p = 0.02); with the trailing eye dilated participants drove significantly slower (by an average of 3.2 km/h) than with both eyes dilated (p

PURPOSE To assess whether the slopes of psychometric functions for measuring low contrast letter acuity were different from those for measuring high contrast letter acuity. METHODS Ten participants, wearing their best spectacle correction, were assessed monocularly. Stimuli were logarithmic progression charts, generated on a computer monitor, with nine rows of five randomised Sloan letters generated in either high contrast format (Weber contrast 99.2%) or low contrast format (Weber contrast 18.7%). For each participant, psychometric functions were generated by probit analysis of the data on each of 16 attempts at a low contrast chart and 16 attempts at a high contrast chart. Each of these probit fits yielded an estimate of Probit Size which provided information about how steep or flat the psychometric function was, along with an estimate of Probit Acuity Threshold. RESULTS Probit Size was significantly larger (p < 0.001) for low contrast charts than for high contrast charts, indicating that psychometric functions were flatter for low contrast charts. Mean Probit Sizes in logMAR were 0.099 (SEM 0.022) for low contrast charts and 0.071 (SEM 0.009) for high contrast charts if a guess rate of 1/26 was assumed, or were 0.086 (SEM 0.019) for low contrast charts and 0.064 for high contrast charts if a guess rate of 1/10 was assumed. Monte Carlo analysis showed that these means were likely to be biased estimates, with true Probit Size probably being larger (i.e. slightly flatter fits) by 0.016-0.019 logMAR. As expected, Probit Acuity Thresholds were poorer for low contrast charts than for high contrast charts (p < 0.001). CONCLUSION Our Monte Carlo modelling showed that such differences in acuity psychometric functions would be expected to give greater intra-subject variability in low contrast letter-by-letter acuity thresholds than for high contrast letter-by-letter acuity thresholds, and that this difference would depend on the termination rule used when measuring acuity. Likewise the variation in letter-by- letter acuity thresholds with termination rule will be different for high and low contrast charts. For low contrast and high contrast Sloan letter charts in a standard logarithmic format, a termination rule of four mistakes on a row, will give close to optimum sensitivity-to-change.

Purpose Ocular diurnal rhythms have been implicated in myopia, glaucoma, diabetes, and other ocular pathologies. Ocular rhythms have been well described in adults; however, they have not yet been fully examined in children. The goal of this study was to investigate ocular and systemic diurnal rhythms over 24 h in children. Methods Subjects, ages 5 to 14 years (n = 18), wore a light, sleep, and activity monitor for one week to assess habitual sleep/wake patterns, then underwent diurnal measurements every 4 h for 24 h. Measurements included blood pressure, heart rate, body temperature, intraocular pressure (IOP), ocular biometry, and optical coherence tomography imaging. Saliva was collected for melatonin and cortisol analysis. Mean ocular perfusion pressure was calculated from IOP and blood pressure. Central corneal thickness, corneal power, anterior chamber depth, lens thickness, vitreous chamber depth, and axial length were determined from biometry. Total retinal thickness, retinal pigment epithelium (RPE) + photoreceptor outer segment thickness, photoreceptor inner segment thickness, and choroidal thickness were determined for a 1 mm diameter centred on the fovea. Subjects' amplitude and acrophase of diurnal variation for each parameter were determined using Fourier analysis, and mean acrophase was calculated using unit vector averaging. Results Repeated measures analysis of variance (ANOVA) showed that all parameters except anterior chamber depth exhibited significant variations over 24 h (p ≤ 0.005 for all). Axial length underwent diurnal variation of 45.25 ± 6.30 μm with an acrophase at 12.92 h, and choroidal thickness underwent diurnal variation of 26.25 ± 2.67 μm with an acrophase at 1.90 h. IOP was approximately in phase with axial length, with a diurnal variation of 4.19 ± 0.50 mmHg and acrophase at 11.37 h. Total retinal thickness underwent a significant diurnal variation of 4.09 ± 0.39 μm with an acrophase at 15.04 h. The RPE + outer segment layer was thickest at 3.25 h, while the inner segment layer was thickest at 14.95 h. Melatonin peaked during the dark period at 2.36 h, and cortisol peaked after light onset at 9.22 h. Conclusions Ocular and systemic diurnal rhythms were robust in children and similar to those previously reported in adult populations. Axial length and IOP were approximately in phase with each other, and in antiphase to choroidal thickness. These findings may have important implications in myopia development in children.

Stand magnifiers are still one of the most commonly prescribed classes of low vision devices. Their performance can be difficult to understand because stand magnifiers usually do not give an image at infinity. This review summarises the methods of describing image enlargement for stand magnifiers, emphasising their relationship to equivalent viewing distance (EVD). This is done in terms of the underlying optical equations, and measurement methods, and methods of prescribing. In the past, methods of determining EVD have been somewhat indirect, requiring accurate measurement of lens power, and image position. The use of digital photography provides an alternative, more direct, simpler method of determining EVD, which can be accomplished in-office. This method is described and it is demonstrated how it gives comparable results to older methods with small, clinically non-meaningful differences, that may be due to differences in image distance reference planes. Describing the performance of stand magnifiers in terms of their dioptric power, or in terms of 'nominal magnification' or 'trade magnification', is imprecise and misleading. It is better to use indices such as equivalent viewing power and EVD, which take into account the magnifier dioptric power, the image position of the magnifier and the distance a patient is from the magnifier. While EVD is a useful index for prescribing stand magnifiers, manufacturers do not always provide sufficient technical details to determine EVD for their stand magnifiers, and available tables of EVDs are more than a decade old and are likely to need updating. Photographic comparison provides a method for determining EVD, and this method can also be applied to other low vision devices.

Purpose To assess the effects of changing computer monitor pixel density on visual acuity measurements made using Sloan optotypes. Methods Acuity was measured on 10 participants aged 19 to 38 years (mean 27.9 ± 7.0) measured binocularly wearing their best spectacle correction. Stimuli were eight lines of five Sloan letter optotypes in logarithmic progression, ranging in size from -0.4 to 0.3 logMAR. Test distance was varied so that pixels on the monitor ranged in size from 0.125 mins of arc to 1.97 mins of arc. Two sampling approaches were used: (1) unfiltered sampling, with each pixel rendered either black or white; and (2) filtered sampling with pixel luminance averaged across a pixel aperture, giving grey-scale smoothing of letter edges. Results A broken line fit was made to each data set, with acuity being stable at an asymptotic threshold VAas for small pixels sizes, with thresholds increasing linearly when pixel sizes exceeded a critical pixel size Pcrit . For unfiltered stimuli, Pcrit averaged 1.1 mins of arc and for unfiltered stimuli averaged 0.69 mins of arc. For filtered stimuli, Pcrit was 1.79xVAas , and for unfiltered Pcrit was 1.05xVAas . Conclusion The results show that grey-scale filtering makes acuity measurement more resistant to the effects of pixellation. Based on a conservative interpretation of these findings, we make the recommendation that charts be constructed with, for filtered optotypes, a maximum pixel size of 0.6 x of the smallest MAR used and, for unfiltered optotypes, 0.35 x the smallest MAR used.

This paper presents the case study of the project EARS Ind developed in the Dominican Republic (DR) with the purpose of increasing access and affordability of hearing aid technology for the hearing impaired. This case study demonstrates how a program can fit hearing aids to patients with hearing impairments can be developed in low and middle income countries.The project planning documents and project statistics and reports were reviewed. A questionnaire and follow-up interviews were used to gain a clear understanding of the situation in the EARS Inc. DR hearing aid project.The case study is presented of the development and services in the DR with a particular focus on the choices made in regard to hearing aid services including manufacturer choices, procurement, distribution, pricing and service delivery. The development of these services included the simultaneous development of a training program, ear mould laboratory, hearing aid repair services, also sales of batteries and accessories as well as the development of calibration services.The development of comprehensive diagnostic and rehabilitation services requires equipping and training local staff.A good hearing aid fitting is more than technology--patient education and the clinician fitting the hearing aid are important. Access to follow-up services including battery supplies, hearing aid adjustments and hearing aid repairs is essential to any hearing aid fitting program in low and middle income countries. Check the WHO guidelines for hearing aid provision in developing countries when planning a program. When working in a country co-ordinate with local professional involved in hearing health where available.

Purpose To investigate ocular and systemic diurnal rhythms in emmetropic and myopic adults and examine relationships with light exposure. Methods Adult subjects (n = 42, 22–41 years) underwent measurements every 4 hours for 24 hours, including blood pressure, heart rate, body temperature, intraocular pressure (IOP), ocular biometry, and optical coherence tomography imaging. Mean ocular perfusion pressure (MOPP) was calculated. Saliva was collected for melatonin and cortisol analysis. Acrophase and amplitude for each parameter were compared between refractive error groups. Subjects wore a light, sleep, and activity monitor for 1 week before measurements. Results All parameters exhibited significant diurnal rhythm (ANOVA, P < 0.05 for all). Choroidal thickness peaked at 2.42 hours, with a diurnal variation of 25.8 ± 13.44 μm. Axial length peaked at 12.96 hours, with a variation of 35.71 ± 6.6 μm. Melatonin peaked at 3.19 hours during the dark period, while cortisol peaked after light onset at 8.86 hours. IOP peaked at 11.24 hours, with a variation of 4.92 ± 1.57 mm Hg, in antiphase with MOPP, which peaked at 22.02 hours. Amplitudes of daily variations were not correlated with light exposure, and rhythms were not significantly different between emmetropes and myopes, except for body temperature and MOPP. Conclusions Diurnal variations in ocular and systemic parameters were observed in young adults; however, these variations were not associated with habitual light exposure. Emmetropic and myopic refractive error groups showed small but significant differences in body temperature and MOPP, while other ocular and systemic patterns were similar.

Bland and Altman described approximate methods in 1986 and 1999 for calculating confidence limits for their 95% limits of agreement, approximations which assume large subject numbers. In this paper, these approximations are compared with exact confidence intervals calculated using two-sided tolerance intervals for a normal distribution. The approximations are compared in terms of the tolerance factors themselves but also in terms of the exact confidence limits and the exact limits of agreement coverage corresponding to the approximate confidence interval methods. Using similar methods the 50th percentile of the tolerance interval are compared with the k values of 1.96 and 2, which Bland and Altman used to define limits of agreements (i.e. [Formula: see text]+/− 1.96Sd and [Formula: see text]+/− 2Sd). For limits of agreement outer confidence intervals, Bland and Altman’s approximations are too permissive for sample sizes

Although comparison phakometry has been used by a number of studies to measure posterior corneal shape, these studies have not calculated the size of the posterior corneal zones of reflection they assessed. This paper develops paraxial equations for calculating posterior corneal zones of reflection, based on standard keratometry equations and equivalent mirror theory. For targets used in previous studies, posterior corneal reflection zone sizes were calculated using paraxial equations and using exact ray tracing, assuming spherical and aspheric corneal surfaces. Paraxial methods and exact ray tracing methods give similar estimates for reflection zone sizes less than 2 mm, but for larger zone sizes ray tracing methods should be used.

A clinical study was conducted to investigate the dose response and metabolism of strawberry anthocyanins. In a crossover study design, 12 healthy adults consumed each of 3 strawberry treatments. The treatments were 100 g, 200 g, and 400 g of pureed strawberries, delivering 15 mmol, 30 mmol, and 60 mmol anthocyanin, respectively. Urine samples were collected for 24 h after each dose and samples were analyzed by HPLC with diode array detection and ion trap MS. Pelargonidin 3-glucoside was the major anthocyanin form in the treatments, and pelargonidin 3-glucoside and 3 metabolites of pelargonidin 3-glucoside (detected as monoglucuronides) were excreted in urine after ingestion. One predominant monoglucuronide form was detected in urine in masses 10-fold higher than the other 2 monoglucuronide forms. Increasing dose resulted in increasing appearance of anthocyanins in urine, and the mass of each pelargonidin monoglucuronide increased in urine with increasing dose. These results suggest that pelargonidin 3-glucoside absorption and metabolism are not saturated at masses # 60 mmol, thus showing that more strawberry anthocyanin can be absorbed with increasing dose. J. Nutr. 138: 897–902, 2008.

Many tropical fruits are rich in anthocyanins, though limited information is available about the characterization and quantification of these anthocyanins. The identification and quantification of anthocyanin pigments in four tropical fruits were determined by HPLC-MS/MS. Fruits studied included acerola (Malphigia emarginata), jussara (Euterpe edulis), jambolão (Syzygium cumini), and guajiru (Chrysobalanus icaco). All four fruits were found to contain anthocyanin pigments. Anthocyanidin backbones included cyanidin, delphinidin, peonidin, pelargonidin, petunidin, and malvidin. Guajiru contained several acylated forms, while acerola, jussara, and jambolão contained only nonacylated glycosides. These results demonstrate that these tropical fruits are rich in anthocyanins and that the anthocyanins are widely ranging in anthocyanidin backbone, glycosylation, and acylation.

Purpose The previous literature on Bland-Altman analysis only describes approximate methods for calculating confidence intervals for 95% Limits of Agreement (LoAs). This paper describes exact methods for calculating such confidence intervals, based on the assumption that differences in measurement pairs are normally distributed. Methods Two basic situations are considered for calculating LoA confidence intervals: the first where LoAs are considered individually (i.e. using one-sided tolerance factors for a normal distribution); and the second, where LoAs are considered as a pair (i.e. using two-sided tolerance factors for a normal distribution). Equations underlying the calculation of exact confidence limits are briefly outlined. Results To assist in determining confidence intervals for LoAs (considered individually and as a pair) tables of coefficients have been included for degrees of freedom between 1 and 1000. Numerical examples, showing the use of the tables for calculating confidence limits for Bland-Altman LoAs, have been provided. Conclusions Exact confidence intervals for LoAs can differ considerably from Bland and Altman’s approximate method, especially for sample sizes that are not large. There are better, more precise methods for calculating confidence intervals for LoAs than Bland and Altman’s approximate method, although even an approximate calculation of confidence intervals for LoAs is likely to be better than none at all. Reporting confidence limits for LoAs considered as a pair is appropriate for most situations, however there may be circumstances where it is appropriate to report confidence limits for LoAs considered individually.

The presence of interface debris is commonly reported in patients having undergone LASIK refractive surgery. The patient described here had numerous large particles believed to be plastic and metal artefacts from the surgery at the level of the stroma/flap interface, along with a corneal scar consistent with a foreign body injury. The aetiology and possible sequelae of the particles and scar are discussed.

AIM: The objective of this study was to find a relationship between goblet cell density (GCD) and other diagnostic tests of dry eye in a group of normal healthy Chinese subjects. The capability of using GCD as a tear function test was assessed. METHOD: A total of 42 optometry students with no contact lens wear history were recruited. Subjects were required to fill in a dry eye questionnaire. The non-invasive tear break-up time (NITBUT) of each subject was measured, followed by phenol red thread test (PRTT) and tear break-up time (TBUT) tests. Conjunctival epithelial cells from the inferior nasal bulbar conjunctiva were harvested by the impression cytology technique. The specimens collected were labelled and stained with PAS (Periodic Acid Schiff)-haematoxylin. The goblet cells and the conjunctival epithelial cells were counted under a light microscope of 100x magnification. Spearman's rho (rho) correlation test was used to analyse the relationship between GCD and the other tear function tests. RESULTS: With a probability level of 0.0051 (corrected for a cumulative familywise error rate of p = 0.05), GCD was found to have no correlation with NITBUT (rho = -0.193, p = 0.222), McMonnies Dry Eye Scores (MCDES) (rho = -0.052, p = 0.742), PRTT (rho = - 0.188, p = 0.234) and TBUT (rho = 0.246, p = 0.117). CONCLUSION: There was no correlation between GCD and MCDES, NITBUT, PRTT and TBUT. The GCD alone is not a useful diagnostic test for tear film instability in normal eyes although it is a good indicator in the diagnosis of ocular surface diseases.

Most of the histopathological and psychophysical studies in glaucoma reveal a preferential damage to the magnocellular (M) pathway although a few of them support a damage to the parvocellular (P) pathway as well. In glaucoma, the visual fields are usually evaluated by conventional perimetry. However, it has been demonstrated that 20-40% of ganglion cells are lost before field defects are detected using conventional perimetry. Therefore, new psychophysical tests have recently been designed in order to specifically isolate and evaluate the visual mechanisms that are impaired at the early stages of glaucoma. In this context, several authors have addressed the issue of motion perception under the hypothesis of a predominant damage of the M pathway in glaucoma, and that motion perception is mediated mainly by M pathway. The results of these studies depict a large variation in the percentage of patients showing anomalous motion perception. Overall, motion thresholds are elevated in both glaucoma and ocular hypertensive patients as compared to control subjects, irrespective of the stimulus size and eccentricity. The test which discriminates best between patients and normal subjects is motion perimetry. The visual field defects in glaucoma patients identified by conventional perimetry and motion perimetry are similar, but the sizes of the defects are usually larger with motion perimetry. However, motion tests in central vision have no correlation with visual field defect on conventional perimetry. In glaucoma, loss of performance on motion perception tests does not necessarily support the existence of a specific deficit in the M pathway, because some behavioral studies suggest that the P pathway can also mediate motion perception. It is also difficult to conclude that motion perception is specifically affected in glaucoma because most of these studies do not yield a comparison with other visual functions. Despite these difficulties, localized motion perception tests at eccentricities of more than 15 degrees can be considered as a promising diagnostic tool.

Objective To examine the risk factors for variations in ocular biometry parameters in Singapore Chinese children, a population with a known high prevalence rate of myopia at an early age. Design Cross-sectional study. Participants Children aged 7 to 9 years (n = 1453) from three schools in Singapore. Methods The children underwent A scan biometry and cycloplegic autorefraction measurements. Questions were asked regarding number of books read per week, night lighting, and parental myopia. Main outcome measures Axial length, vitreous chamber depth, lens thickness, anterior chamber depth, refraction, and corneal curvature radius measurements were made. Results After controlling for several factors, the axial lengths were found to be longer and vitreous chambers deeper in children who were older, male, read more than two books per week, or taller, and those who had at least one parent who was myopic. In these models, children who read more than two books per week had axial lengths that were 0.17 mm longer and vitreous chambers that were 0.15 mm deeper compared with children who read two or fewer books per week. Anterior chambers were deeper in males and taller children, whereas corneal curvature was steeper in female, older, and shorter children. Conclusions Increases of axial length and vitreous cavity depth were associated with older age, being male, reading more than two books per week, increased height, and parental history of myopia. Of these risk factors, however, neither reading nor parental myopia history were associated with values for anterior chamber depth, corneal curvature, or lens thickness. These findings confirm that conventional risk factors for myopia associated with the vitreous cavity, but suggest that anterior segment parameters such as corneal curvature and lens thickness may be subject to unrelated postnatal growth control mechanisms.

PURPOSE: To examine the optimal cutoff point for the use of the visual acuity test to screen for refractive errors in schoolchildren. METHODS: In a sample of schoolchildren between 7 and 9 years old, visual acuity testing was performed using modified ETDRS charts monocularly without optical aids by trained personnel. Cycloplegic autorefraction was performed in each eye. The screening efficacy of using various cutoff points for referring children for further optometric/ ophthalmic assessment was studied. Myopia was defined as a spherical equivalent of at least -0.5 D, hyperopia a spherical equivalent of at least +2.0 D, and astigmatism a cylinder of at least -1.0 D in at least one eye. The sensitivity, specificity, and predictive values were calculated using each patient as a case; a receiver operator curve was plotted. RESULTS: A total of 1,028 children were tested. A satisfactory sensitivity/specificity profile was obtained using a referral criterion of visual acuity worse than or equal to 0.28 logarithm of the minimum angle of resolution in at least one eye. In this scenario, the sensitivity and specificity of this screening test were 72% (95% confidence interval [CI], 68 to 76) and 97% (95%CI, 95 to 98), respectively. The positive and negative predictive values were 96% (95%CI, 93 to 98) and 78% (95%CI, 75 to 82), respectively. CONCLUSIONS: The modified ETDRS visual acuity chart can be used to predict refractive errors in schoolchildren in Singapore in a sensitive and specific manner using a referral criterion of worse than or equal to 0.28 logarithm of the minimum angle of resolution.

The ability of beta-carotene to deliver bioactive retinoids to tissues is highly variable. A clearer understanding of the environmental and genetic factors that modulate the vitamin A potential of beta-carotene is needed.Assess the vitamin A value of orally administered beta-carotene relative to a co-administered reference dose of preformed vitamin A.Equimolar doses (30 micromol) of hexadeuterated D6 beta-carotene and D6 retinyl acetate were orally co-administered in an emulsified formulation to a male subject. The plasma concentration time courses of D6 retinol (derived from D6 retinyl acetate) and bioderived D3 retinol (from D(6) beta-carotene) were determined for 554 h postdosing using gas chromatography/mass spectrometry. Intact D6 beta-carotene plasma concentrations were determined by high-pressure liquid chromatography. The ratio of the two forms of vitamin A, D6 retinol/D3 retinol, at any single time point is postulated to reflect the quantity of vitamin A derived from beta-carotene relative to preformed vitamin A. Additionally, a minute amount of 14C beta-carotene (50 nCi; 0.27 microg) was included in the oral dose and cumulative 24-h stool and urine samples were collected for two weeks to follow absorption and excretion of the b-carotene. The 14C nuclide was detected using accelerator mass spectrometry (AMS). Results During the absorption/distribution phase (3-11 h) the D6/D3 ratio of the two retinols was not stable and ranged between a value of 3 and 16. Between 11 and 98 h postdosing the ratio was relatively stable with a mean value of 8.5 (95 % CI: 7.5, 8.7). These data suggest that in this subject and under these conditions, 8.5 moles of beta-carotene would provide a vitamin A quantity equivalent to 1 mole of preformed vitamin A. On a mass basis, 15.9 microg of beta-carotene was equivalent to 1 microg of retinol. The total administered beta-carotene was found to be 55 % absorbed by AMS analysis of cumulative stool.The co-administration of D6 beta-carotene and D6 retinyl acetate provides a technique for assessing individual ability to process beta-carotene to vitamin A. The results indicate that a single time point taken between 11-98 h after dose administration may provide a reliable value for the relative ratio of the two forms of vitamin A. However, results from more subjects are needed to assess the general utility of this method.

EARS Inc. is a faith based not-for-profit organization established in 1998. As an organization, it has consistently maintained a goal to provide both short-term and long-term projects in low and middle income countries. One specific project undertaken by EARS Inc involved developing a hearing health program in the Dominican Republic.This article is a review of the challenges and successes encountered on the road to establishing improved access and affordability of hearing aid technology for the hearing impaired in Domincan Republic.Despite the challenges, after 12 years of local programming, the hearing health services in the Dominican Republic were successfully implemented. The development of these services included the simultaneous development of a training program, earmould laboratory, hearing aid repair services as well as calibration services and sales of batteries and accessories.As demonstrated in this review, it is possible to develop sustainable and comprehensive diagnostic and rehabilitation hearing services in a developing country. It is clear that training, equipping and empowering local staffs are instrumental to the success of the program.A good hearing aid fitting is more than supplying technology. Patient education and the clinician fitting the hearing aid are important. Access to follow-up services including battery supplies, hearing aid adjustments and hearing aid repairs is essential for a hearing aid fitting program in low and middle income countries to be sustainable. Check the WHO guidelines for hearing aid provision in developing countries when planning a program. When working in a country, co-ordinate with local professionals involved in hearing health where available.

McAlinden et al.[1] have described various statistical tools for assessing repeatability of, and agreement between clinical measurements. One of the methods they described is that of Bland and Altman.[2] The method is well known and often used in health science, with the 1986[2] publication having been cited more than 24 000 times. As part of this method, differences d between each pair of measures are plotted against the mean of each pair of measures. This is illustrated in Figure 1, modified from figure 2 of McAlinden et al.,[1] for 10 pairs of measurements of spherical aberration using different instruments. The mean of the differences math formula is shown (in this case 0.04 μm). The standard deviation of the differences (s diff ) was 0.16 μm. For this 95% Limits of agreement (LoAs) were calculated as ...

Motion is frequently incorporated in stimuli used for psychophysical testing of vernier acuity in infants and young children. In such stimuli, detection of the vernier offset is necessary in order to perceive the motion. Research described in this report tested whether the perception of a vernier offset is sufficient to signal the stimulus motion in adults. We measured how motion detectability changed as a function of vernier offset for two adult subjects, using a stimulus similar to that employed by other authors to measure vernier acuity in infants and children. Motion visibility varied with offset size, achieving a detectability of motion (d') of 0.95 (comparable to two-alternative forced-choice thresholds) at stimulus offsets of 16-19 s arc. In comparison to the motion, the stimulus offset itself was much easier to see, being detectable on 95-100% of trials with the smallest offset, 6.6 s arc. This distinction, between the visibility of motion and the visibility of the vernier offset itself, should be considered when interpreting vernier results using such displays, especially in infants and children for whom motion may be the attractive cue.

When competition pistol shooters aim, they perform four basic visual alignment tasks. With optimal stimuli such tasks can be performed with exquisite sensitivity. However, pistol sights and the target may not constitute the optimal stimuli, and this may impose limits on how well shooters perform. By simulating pistol sights and targets on a computer monitor, we investigated how the vernier task of aligning the top edges of the front and rear pistol sights was affected by the proximity of the target aiming mark. Alignment random error in this task, an analogous measure to vernier acuity, was unaffected by the proximity of the aiming mark; however, alignment systematic error did change significantly as the proximity of the aiming mark changed. This effect was unlikely to significantly change pistol shooting performance as shooters can adjust their sights to compensate for systematic errors. Likewise, compared to the vertical spread of shots on the pistol target, alignment random error was extremely small (only 10 s arc), which implies that other sources of variation limit pistol shooting performance.

PURPOSE: Orthokeratology procedures suffer from lack of predictability in the response of individuals. To identify factors contributing to this, we have retrospectively studied a range of ocular parameters in patients with varying outcomes from orthokeratology lens wear. EXPERIMENTAL DESIGN: Three groups were studied: an experimental group (9 subjects wearing Contex OK-3 design orthokeratology contact lenses), and 2 control groups [10 rigid gas permeable (RGP) contact lens wearers and 10 non-contact lens wearers]. Three categories were identified among the orthokeratology group: those responding well, moderately, or poorly to orthokeratology lens wear. Measurements included subjective refraction, intraocular distances, corneal thickness, ocular rigidity, and epithelial fragility. RESULTS: When comparing the three orthokeratology categories, there was no significant difference for central and peripheral epithelial fragility and ocular rigidity. There was also no significant difference for any of the biometric characteristics measured. The prefitting spherical equivalent power was found to be significantly different between categories of responders (p = 0.0228), with the poor responders having the highest initial level of myopia. None of the measured characteristics differed significantly among the orthokeratology group and the two control groups. CONCLUSIONS: In this pilot study, the success of orthokeratology lens wear was not related to ocular biomechanical or biometric attributes, but it was related to prefitting refractive error.

This report describes a case of central retinal vein occlusion (CRVO) which was classified as papillophlebitis in a young female adult. In this age group, CRVO is relatively rare and tends to be mild in both its short-term and long-term visual consequences. The patient in this case showed a concurrent episode of bilateral intra-ocular pressure (IOP) elevation and the presence of cilio-retinal arteries in the affected eye. Despite extremely poor vision at presentation and the poor prognostic sign of cilio-retinal arteries, the patient made an excellent visual recovery with only mild paracentral field change.

The compatibility of scleral lens wear with the physiological requirements of the cornea was assessed by measuring corneal thickness changes. Lenses made of either poly(methyl methacrylate) (PMMA) (effectively nonoxygen permeable) or itafluorocon B (Equalens II) material (oxygen permeability of 121 × 10−11 cm 2 ml O 2 /sec ml mmHg) were directly compared by fitting one lens type to each eye of eight subjects. The rate of corneal thickness increase was 0.98 ± 3.33 microns/hour for gas permeable lenses and 14.84 ± 14.93 microns/hour for PMMA lenses. This difference was statistically significant (p = 0.039).

Introduction: An observer, looking sideways from a moving vehicle, while wearing a neutral density filter over one eye, can have a distorted perception of speed, known as the Enright phenomenon. The purpose of this study was to determine how the Enright phenomenon influences driving behaviour. Methods: A geometric model of the Enright phenomenon was developed. Ten young, visually normal, participants (mean age = 25.4 years) were tested on a straight section of a closed driving circuit and instructed to look out of the right side of the vehicle and drive at either 40 Km/h or 60 Km/h under the following binocular viewing conditions: with a 0.9 ND filter over the left eye (leading eye); 0.9 ND filter over the right eye (trailing eye); 0.9 ND filters over both eyes, and with no filters over either eye. The order of filter conditions was randomised and the speed driven recorded for each condition. Results: Speed judgments did not differ significantly between the two baseline conditions (no filters and both eyes filtered) for either speed tested. For the baseline conditions, when subjects were asked to drive at 60 Km/h they matched this speed well (61 ± 10.2 Km/h) but drove significantly faster than requested (51.6 ± 9.4 Km/h) when asked to drive at 40 Km/h. Subjects significantly exceeded baseline speeds by 8.7± 5.0 Km/h, when the trailing eye was filtered and travelled slower than baseline speeds by 3.7± 4.6 Km/h when the leading eye was filtered. Conclusions: This is the first quantitative study demonstrating how the Enright effect can influence perceptions of driving speed, and demonstrates that monocular filtering of an eye can significantly impact driving speeds, albeit to a lesser extent than predicted by geometric models of the phenomenon.

Binocular summation for a contrast detection task was measured as a function of eccentricity and target size along the horizontal and vertical meridians for ten young normal subjects. Binocular summation at the fovea was of the order of 1.4 for all target sizes, although there was some intersubject variation. Binocular summation was highest along the vertical meridian. With increasing eccentricity from the fovea, binocular summation for target size I (0.108 degrees projected diameter) decreased, remained relatively constant for target size III (0.431 degrees projected diameter) and increased with increasing eccentricity from the fovea for target size V (1.724 degrees projected diameter). For target sizes I and III, binocular summation was present only when interocular differences in sensitivity were under 5 dB, for target size V this relationship did not hold. Influences such as stimulation of corresponding retinal points and cortical representation are considered.

Purpose: Although the effect of spatial sampling on the visibility of grating stimuli is well described and well understood, little research has been conducted into the effects of spatial sampling on the visibility of letter optotypes. The purpose of this study was to investigate whether thresholds for spatially sampled Sloan letters were equal to or significantly smaller than the spacing between spatial samples.----- Methods: For four visually normal subjects, we measured Sloan letter acuity thresholds, presented on a computer monitor, after the letters had been sampled by sampling arrays with 6.285 elements per square degree, (23.9 min of arc between samples for a square packed array). We used four different sampling arrays: square packed; hexagonally packed; a cone-like array with positive contrast; and a cone-like array with negative contrast. Thresholds were assessed using letter-counting rules and also Probit analysis.----- Results: Although results depended on array type, and the definition of sample spacing, letter acuity thresholds were substantially less than estimates of sample spacing by between 0.290 log units (49% less) (hexagonally sampled Probit thresholds compared with spacing between hexagonal samples) to 0.136 log units (27% less) (positive contrast cone-like sampled letter-counting thresholds compared with spacing between rows of hexagonal samples).----- Conclusions: Sample spacing is not an absolute limit for Sloan letter thresholds. By comparison with previous measurements of human foveal cone sampling of space, our findings suggest that cone sampling limits for Sloan letters could be as small as 20/4.

We have investigated the effects of a range of workstation factors upon the visual symptoms experienced by a group of 92 visual display terminal (VDT) users. Subjects in the study kept a diary over five consecutive working days in which they recorded the types of visual and postural symptoms which occurred and the types of work tasks being performed. Each subject's workstation was analysed for screen legibility and stability, discomfort and disability glare, and required head postures. By the use of multiple regression analysis techniques we have considered the relative contribution of these factors to the symptoms reported by the users of these workstations. Screen legibility significantly influenced the occurrence of symptoms of ocular discomfort and vertical head movements significantly affected the incidence of postural/headache symptoms.

We conducted eye examinations on 79 subjects who used visual display terminals (VDTs) for a significant portion of their normal working day. The examination included the detection of ocular pathology, near and intermediate visual acuity, accommodative facility, fusional vergences, near point of convergence, fixation disparity, near horizontal heterophoria and colour vision. Each subject maintained a diary over five working days in which they recorded the frequency and intensity of symptoms experienced. Symptoms were classed as either ocular (discomfort) or visual (blur) symptoms. Multiple regression analysis techniques were used to investigate the relationship between symptoms and eye examination results and demographic characteristics of subject gender, age and experience with VDTs. None of the eye examination findings were significantly associated with symptoms and of the demographic variables, only VDT experience was significantly associated with symptom rates. Statistical associations were limited in a number of measures by the relatively small population of VDT users sampled.

Corrinoid (vitamin B 12 -like) cofactors contain various α-axial ligands, including 5,6-dimethylbenzimidazole (DMB) or adenine. The bacterium Salmonella enterica produces the corrin ring only under anaerobic conditions, but it can form “complete” corrinoids aerobically by importing an “incomplete” corrinoid, such as cobinamide (Cbi), and adding appropriate α- and β-axial ligands. Under aerobic conditions, S. enterica performs the corrinoid-dependent degradation of ethanolamine if given vitamin B 12 , but it can make B 12 from exogenous Cbi only if DMB is also provided. Mutants isolated for their ability to degrade ethanolamine without added DMB converted Cbi to pseudo-B 12 cofactors (having adenine as an α-axial ligand). The mutations cause an increase in the level of free adenine and install adenine (instead of DMB) as an α-ligand. When DMB is provided to these mutants, synthesis of pseudo-B 12 cofactors ceases and B 12 cofactors are produced, suggesting that DMB regulates production or incorporation of free adenine as an α-ligand. Wild-type cells make pseudo-B 12 cofactors during aerobic growth on propanediol plus Cbi and can use pseudo-vitamin B 12 for all of their corrinoid-dependent enzymes. Synthesis of coenzyme pseudo-B 12 cofactors requires the same enzymes (CobT, CobU, CobS, and CobC) that install DMB in the formation of coenzyme B 12 . Models are described for the mechanism and control of α-axial ligand installation.

Every year in the United States, more than 4500 pedestrians are killed and more than 75,000 pedestrians injured by motor vehicles. Worldwide, annually, one quarter of a million pedestrians are killed by motor vehicles. The vast majority of these deaths (70% or more) occur at night. Therefore, research into night-time pedestrian visibility is highly valuable...

There is a need for an improved test of human ability to assimilate dietary vitamin B 12 . Assaying and understanding absorption and uptake of B 12 is important because defects can lead to hematological and neurological complications. Accelerator mass spectrometry is uniquely suited for assessing absorption and kinetics of carbon-14 ( 14 C)-labeled substances after oral ingestion because it is more sensitive than decay counting and can measure levels of 14 C in microliter volumes of biological samples with negligible exposure of subjects to radioactivity. The test we describe employs amounts of B 12 in the range of normal dietary intake. The B 12 used was quantitatively labeled with 14 C at one particular atom of the dimethylbenzimidazole (DMB) moiety by exploiting idiosyncrasies of Salmonella metabolism. To grow aerobically on ethanolamine, Salmonella enterica must be provided with either preformed B 12 or two of its precursors, cobinamide and DMB. When provided with 14 C-DMB specifically labeled in the C2 position, cells produced 14 C-B 12 of high specific activity (2.1 GBq/mmol, 58 mCi/mmol) (1 Ci = 37 GBq) and no detectable dilution of label from endogenous DMB synthesis. In a human kinetic study, a physiological dose (1.5 μg, 2.2 kBq/59 nCi) of purified 14 C-B 12 was administered and showed plasma appearance and clearance curves consistent with the predicted behavior of the pure vitamin. This method opens new avenues for study of B 12 assimilation.