[The relationships between ocular optical components and implications in the process of emmetropization]. / Relación entre los componentes ópticos oculares e implicaciones en el proceso de emetropización.

PURPOSE: To report the relationship between different optical ocular components and the influence of axial length on emmetropization. METHODS: 109 young university students, divided into five groups, were enrolled in this study: emmetropes, hyperopes, low myopes, moderate myopes and high myopes. Intraocular parameters and topographic corneal analyses were performed by ultrasonography and videokeratoscopy respectively. RESULTS: Anterior chamber depth and axial length were found to correlate significantly in eyes with axial lengths less than 24 mm (r = 0.441; p < 0.001) However this correlation was not found in eyes with longer axial lengths (r = 0.098; p = 0.527). Lens thickness showed an inverse correlation with axial length for shorter eyes (r = 0.391; p < 0.001), whereas any correlation in longer eyes was associated with moderate to high levels of myopia. Anterior corneal curvature only correlated, although weakly, with vitreous chamber depth for shorter eyes (r = 0.363; p < 0.003). CONCLUSION: Differences in optical parameters of the human eye displayed different associations in longer eyes. A lack of correlation was seen between ocular components in eyes with higher myopia, corresponding to myopia in excess of 2.00 D.

[Diurnal variations of central and paracentral corneal thickness and curvature]. / Variaciones diurnas de espesor y curvatura corneal central y paracentral.

OBJECTIVE: Corneal topography and thickness has clinical importance in contact lens fitting and refractive surgery, however repeated measurement of corneal thickness and curvature is complicated by the natural phenomenon of diurnal variation. Our aim was determine diurnal variations of central and paracentral corneal thickness and curvature over a period of ten hours. MATERIALS AND METHODS: Corneal thickness and curvature of 10 right eyes of 10 young healthy men were determined by Orbscan Topography System and EyeSys videokeratoscope respectively. Both parameters were determined for central and paracentral regions 1 mm and 2 mm from the centre of the cornea at 2-hour internals for ten hours. RESULTS: The cornea was thickest and flattest on awakening. There was a difference in corneal thickness (ANOVA, Schfféc method p< 0.05) and curvature (ANOVA, Tamhane method p< 0.05) over time for all the corneal locations studied, with greater changes observed in the peripheral corneal data. The minimum value was 10 and 8 hours after eye opening for central and paracentral zones, respectively. Change in central and paracentral corneal thickness was strongly correlated with corneal curvature, except for the 2 mm nasal and superior semi-meridians. CONCLUSIONS: These data indicate a shift in corneal thickness and curvature that can be of clinical relevance as individual changes vary greatly.

Performance on three-point vernier acuity targets as a function of age.

With certain (but not all) vernier acuity (VeA) stimulus displays observers exhibit no or slight performance decrements with aging. Because three-point VeA test displays are much more easily applied experimentally and clinically, we examined visual performance on this task as a function of age. Ages of groups tested ranged from 20 to 70+ years (some individuals were 90+ years old). Eyes were examined monocularly. We tested three- and two-point sharply defined VeA arrays and a three-point ground-glass-degraded display (simulating a 20/100 nuclear cataract). Gap or feature separations were varied. Results obtained with the three-point display showed little alteration with age. Image degradation resulted in reduction in performance when small gap separations were used between the test points, but only slight decrements for large gap separations were recorded. The finding that performance with certain VeA targets is largely unaffected by age is confirmed and is expanded.

Hyperacuity test to evaluate vision through dense cataracts; research preliminary to a clinical study. I. Studies conducted at the University of California at Berkeley before travel to India.

BACKGROUND. Patients with dense ocular media disorders retain the ability to project or point to an intense source of light. Using this response capability and high luminance points of light as stimuli, Vernier judgments (a hyperacuity test) can be made by these patients, even without the presence of a "window" through a leucoma, cataract, or bleed. Without coaching, these individuals are able to locate the centers of the individual degraded point images if the individual light sources are adequately separated (i.e., if sufficient "gaps" exist between the individual stimuli), and they can spatially align the degraded images. Advanced cataracts are the main cause of blindness in the developing world, and this is a treatable condition. In these nations, only a modest proportion of affected patients receive surgery, and only 5% or less of these individuals obtain treatment in two eyes. There are incredibly large and rapidly growing backlogs of advanced cataract patients requiring care (many millions). Because of the 20 to 30% failure rates that occur after treatment (all causes) in many developing world settings, a test performed before surgery, which offers a meaningful estimate of postsurgical visual outcome, can be valuable. Using the principle defined above, we seek to determine before surgery those individuals who will derive most benefit from cataract removal, and which of two cataractous eyes has the better postsurgical visual prognosis. EXPERIMENTAL. In Berkeley, we performed a series of preliminary studies on a Vernier acuity test before initiating a clinical study in a developing world setting. These studies were conducted upon young adult normal subjects wearing their usual vision corrections, with and without induced refractive errors, and/or with or without simulated dense nuclear cataracts. We sought (1) to determine the number of repeat trials necessary for reliable outcomes; (2) to compare a two-point and a three-point Vernier acuity display; (3) to determine the shape of the measured response function at large gap separations between test points; (4) to define optimal test distance and stimulus size; (5) to assess the effect(s) of a broad range of uncorrected refractive errors upon outcomes; and (6) to consider means to minimize refraction-based errors by using a pinhole, a refractive correction, and/or selective spatial filtering. We compared responses obtained using the current CRT/VDT-based, computer-driven (Berkeley) instrument with a new precision optical/mechanical computer-driven (India) instrument. The India instrument is needed to determine design parameters for a next stage simpler, cheaper, more rugged field instrument(s).(ABSTRACT TRUNCATED AT 400 WORDS)