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Aim: Since an interaction between binocular disparity and the vergence system takes place in order to reduce retinal disparity, it is likely that vergence control, as measured with the near point of convergence (NPC), will be better if the target used for measurement has 3-dimensional (3-D) features in its most central parts. The aim of the present study was therefore to investigate if the NPC would give a better result using a fixation target with centrally placed 3-D features when compared with a two-dimensional (2-D) target., Methods: Twenty-three asymptomatic subjects (2 men, 21 women; average age 30.0 years ± 7.36 SD) who experienced diplopia when a fixation target was brought close to the eyes had their break point NPC measured using a modified RAF-ruler. A metal cube and a printed image of the cube were used as a 3-D and 2-D stimuli. The measurements were repeated 3 times in each subject for each test condition, for a total of 6 randomized NPC measurements., Results: On average a significant difference in NPC (p = 0.0172) was found for break point NPC with a 3-D stimuli (mean: 7.27 cm ± 2.37 SD), giving the better result as compared with a 2-D stimuli (mean: 8.02 cm ± 2.82 SD). Comparing the most remote recorded NPC values of the 3 repeated measurements under each stimulus condition, a significant difference was found (p = 0.0159, t = 2.612) with 3-D stimuli giving the better result., Conclusion: The results of this study demonstrate the influence of binocular disparity stimuli on the vergence control as NPC was better if the target used for measurement had 3-D features in its most central parts.

Background: Dyslexia affects 5%-8% of the population of the Western world. While reading, different eye movements are required. Compared to other persons, dyslexics have more and longer fixations, shorter saccade amplitude, a higher percentage of regression, and more fixation disparity when reading. In non-reading situations, dyslexics do not have more binocular problems than others. The aim of the present study was to investigate whether computerized orthoptic vergence training could improve reading ability for dyslexic children., Methods: The study was conducted at Ängkärrskolan, Solna, an elementary school exclusively for dyslexic children. Twelve subjects, aged 13-14 years, were trained with RetCorr, a computerized vergence training program. Reading speed was assessed before and after treatment. The results were compared with an age-matched control group., Results: The dyslexic subjects conducted on average 11.75 sessions (±2.53 SD) of orthoptic training over a 5-week period. On average, the number of words read per minute before training were 87.83 (±16.80 SD) and after training 95.58 words (±18.08 SD). The difference was statistically significant (p=0.0066). In the control group, the change was from 85.00 (±19.68 SD) words to 89.37 words (±19.71 SD) over the same time period. This difference was not significant (p=0.1235)., Discussion: Most scientists agree that dyslexia is mainly a phonological impairment. Nevertheless, the results show that vergence treatment might help dyslexics. Larger studies are required to provide guidance in this area.

Background: Prevalence of dyslexia is 5%-10% of the population. Opinions differ on how binocular function affects dyslexia. The aim of the present study was to evaluate the binocular function in dyslexic children and compare it with a group of age-matched control children., Methods: The study was performed at Ängkärrskolan and at Kungsholmen elementary schools in Stockholm, Sweden. Sixty-three children with dyslexia and 60 control children between fourth and ninth grade participated. Monocular and binocular visual acuity, refractive error, best corrected visual acuity at distance and near, near point of convergence, amplitude of accommodation, stereopsis, phorias, and fusional reserves were evaluated in all of the children., Results: The results show that there was no difference in the visual functions tested except for the amplitude of accommodation, which was found to be reduced both monocularly and binocularly in the dyslexic children., Conclusion: This study showed that only the amplitude of accommodation seems to differ in children with dyslexia as compared with the control children; however, the ability to accommodate was still good and is unlikely to hamper reading and learning ability. The results therefore support that the recent findings of binocular deficits in dyslexic children are a result of the phonological deficit of dyslexia and not an underlying cause of dyslexia.

Purpose: It is accepted practice to use a spherical equivalent power as an alternative contact lens correction for those patients with lower amounts of astigmatism, allowing for an easier fit, but the blur caused by one diopter of uncorrected astigmatism can reduce acuity of 6/6 to that of about 6/8. This is usually deemed acceptable monocularly, often retaining a good binocular acuity. The purpose of this study is to explore how monocular astigmatic blur may also affect the patient's binocular vision function., Methods: A trial frame was outfitted with full correction for 20 healthy subjects (mean age 25.5 years, range 19-36 years) and a baseline horizontal fixation disparity was measured at a distance of 1 m. Thereafter, fixation disparity was measured with induced monocular astigmatic blur in the right eye, creating an astigmatic error in the amounts of -0.75 and -1.25 in axis 90 and axis 45., Results: It was determined that the differences among full correction and the 4 different types of astigmatic blur were not significant when analyzed as one group (P = 0.5445), nor when separated into groups according to whether the subject had naturally occurring astigmatism or not, (astigmatic group, P = 0.3801; non-astigmatic group, P = 0.5899)., Conclusions: Monocular astigmatic blur in the amounts of -0.75 and -1.25 did not have a significant effect on tested subjects with regard to the amount of blur or axis orientation. This low amount of blur is likely within the range of compensation for the subjects, proving that spherical equivalent contact lenses are a viable option for low amounts of astigmatic error.

The main purpose of this study was to evaluate the vergence adaptive ability in subjects diagnosed with convergence excess (CE) phoria (ie, subjects with an esophoric shift from distance to near but without an intermittent tropia at near). Vergence adaptation was measured at far and near with both base-in and base-out prisms using a "flashed" Maddox rod technique in 20 control subjects and 16 subjects with CE. In addition, accommodative adaptation and the stimulus AC/A and CA/C cross-links were measured. The AC/A and CA/C ratios were found to be high and low, respectively, and accommodative adaptation was found to be reduced in CE subjects as compared with the controls (P<0.005), all as predicted by the present theory. However, vergence adaptive ability was found to be reduced in the CE subjects at both distance and near and in response to both base-in and base-out prisms (P=0.002). This finding is not in accordance with and is difficult to reconcile with the present theory of CE.

Purpose: The aim of the present study was to evaluate if +2.00 D lens reading addition has the same effectiveness as +1.00 D reading addition in the treatment of accommodative insufficiency (AI)., Methods: Initially 22 subjects (mean age 11.8 years, +/-3.54 SD) with AI were included in the study. The treatment was given according to a randomization list; 11 subjects were given +1.00 D reading addition and the other 11 were given +2.00 D reading addition, for 8 weeks of treatment. The Visual Analogue Scale (VAS) was used to evaluate the subjective degree of asthenopia before and after treatment., Results: The results showed a statistical significant improvement of the accommodative amplitude with +1.00 D reading addition after 8 weeks of treatment. In the +2.00 D reading addition group the improvement of accommodative amplitude was not significant. The reduction in VAS score was significant in both groups., Discussion: The results indicate that +2.00 D reading addition does not exercise the accommodative system in the same amount as +1.00 D reading addition to improve the accommodative amplitude. We therefore recommend that +2.00 D reading addition is not used for treatment of AI.

Purpose: The aim of the present study was to investigate which mode of therapy, plus lens (+1.00D) reading addition (PLRA) or spherical flipper (+/- 1.50D), is the most effective in the treatment of accommodative insufficiency (AI)., Methods: Initially, 24 subjects (mean age 10.3 years, +/- 2.5 SD) with AI were included in the study. Ten subjects completed 8 weeks of PRLA treatment whereas 9, out of 14, subjects completed 8 weeks of spherical flipper treatment., Results: There was a statistically significant improvement in the accommodative amplitude with both regimes of treatment [F(1, 17) = 18.84, p = 0.0004). Spherical flipper treatment was found to have an overall larger effect on accommodative function as compared with PLRA treatment. However, accommodation did not reach normal values after only 8 weeks of treatment., Discussion: The results indicate that both methods improve the accommodative amplitude, but that overall accommodative function reaches higher levels of improvement with spherical flipper as compared with PLRA treatment. However, the accommodative function did not gain normal values in 8 weeks of treatment with either regime.