Intraexaminer repeatability and agreement in stereoacuity measurements made in young adults

·AIM: To determine the repeatability and agreement of stereoacuity measurements made using some of the most widely used clinical tests: Frisby, TNO, Randot and Titmus. ·METHODS: Stereoacuity was measured in two different sessions separated by a time interval of at least 24h but no longer than 1wk in 74 subjects of mean age 20.6y using the four methods. The study participants were divided into two groups: subjects with normal binocular vision and subjects with abnormal binocular vision. ·RESULTS: Best repeatability was shown by the Frisby and Titmus [coefficient of repeatability (COR): 依13 and 依12s arc respectively] in the subjects with normal binocular vision though a clear ceiling effect was noted. In the subjects with abnormal binocular vision, best repeatability was shown by the Frisby (COR: 依69s arc) and Randot (COR: 依72s arc). In both groups, the TNO test showed poorest agreement with the other tests. ·CONCLUSION: Therepeatabilityof stereoacuitymeasures was low in subjects with poor binocular vision yet fairly good in subjects with normal binocular vision with the exception of the TNO test. The reduced agreement detected between the tests indicates they cannot be used interchangeably.

Phenomenological model of visual acuity

We propose in this work a model for describing visual acuity (VV) as a function of defocus and pupil diameter. Although the model is mainly based on geometrical optics, it also incorporates nongeometrical effects phenomenologically. Compared to similar visual acuity models, the proposed one considers the effect of astigmatism and the variability of best corrected VV among individuals; it also takes into account the accommodation and the “tolerance to defocus,” the latter through a phenomenological parameter. We have fitted the model to the VV data provided in the works of Holladay et al. and Peters, showing the ability of this model to accurately describe the variation of VV against blur and pupil diameter. We have also performed a comparison between the proposed model and others previously published in the literature. The model is mainly intended for use in the design of ophthalmic compensations, but it can also be useful in other fields such as visual ergonomics, design of visual tests, and optical instrumentation.

Accommodative changes produced in response to overnight orthokeratology

Background To evaluate short-term (3 months) and long-term (3 years) accommodative changes produced by overnight orthokeratology (OK). Methods A prospective, longitudinal study on young adult subjects with low to moderate myopia was carried out. A total of 93 patients took part in the study. Out of these, 72 were enrolled into the short-term follow-up: 21 were on a control group, 26 on a Paragon CRT contact lenses group, and 25 on a Seefree contact lenses group. The other 21 patients were old CRT wearers on long-term follow-up. Accommodative function was assessed by means of negative and positive relative accommodation (NRA / PRA), monocular accommodative amplitude (MAA), accommodative lag, and monocular accommodative facility (MAF). These values were compared among the three short-term groups at the follow-up visit. The long- and short-term follow-up data was compared among the CRT groups. Results Subjective accommodative results did not suffer any statistically significant changes in any of the accommodative tests for any of the short-term groups when compared to baseline. There were no statistically significant differences between the three short-term groups at the follow-up visit. When comparing the short- and long-term groups, only the NRA showed a significant difference (p = 0.0006) among all the accommodation tests. Conclusions OK does not induce changes in the ocular accommodative function for either short-term or long-term periods.