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PubMed1992

A prospective study examining the changes in factors that affect visual acuity following trabeculectomy.

Many patients report subjective changes in vision following trabeculectomy. In a prospective study of 16 eyes, we have tried to determine the causes of these visual changes. Ninety-four per cent of eyes showed a change in uncorrected Snellen acuity 1 week following surgery. This change was due to a myopic shift in refraction secondary to changes in the anterior chamber depth. A 1 mm change in anterior chamber depth results in approximately a 2 dioptre change in refractive sphere. Visual acuity starts to return to pre-operative levels by the third post-operative week, from which point no eyes showed a deterioration in corrected acuity of more than one line of Snellen. The vertical corneal radius of curvature is reduced in the early post-operative period and there is a with-the-rule change in corneal astigmatism. This resolves over longer follow-up and the possible causes of this are discussed. No changes were noted in corneal thickness and there was no evidence of macular oedema over the follow-up period. Patients should be warned of these possible visual changes pre-operatively as many will have normal acuity prior to surgery.

Aged↗
PubMed1994

Visual acuity and pupillary responses to spatial structure in infants.

PURPOSE: To determine the age of onset of the pupil grating response (PGR). To compare estimates of resolution acuity obtained by pupillometric and behavioral methods in early infancy. METHODS: Dynamic infrared pupillometry was undertaken on 19 newborn infants while they fixated a uniform background upon which a 0.1 c/deg sine wave grating was briefly presented. Pupillary responses were also recorded to an increment in luminance of a spatially homogeneous target. Longitudinal measurements of PGRs were obtained from a subset of eight infants between 3.5 and 38 weeks of age. In this group, behavioral estimates of visual resolution obtained using the acuity card procedure were compared with the highest spatial frequency grating to elicit a PGR. RESULTS: When presented with the pattern stimulus, newborn infants did not show any pupil reaction indicative of a PGR. This finding could not be attributed to immaturity of pupillomotor function: All infants showed marked pupillary construction to diffuse light stimulation. By 1 month of age, pupillary responses to pattern stimuli were reliably present. For these and older infants, the spatial frequency of the finest grating to elicit a PGR was comparable to the behaviorally determined resolution threshold: mean difference (+/- 95% confidence interval) = 0.28 +/- 0.23 octaves. CONCLUSIONS: A PGR could not be detected in newborn infants. From 1 month of age, responses to spatial structure can provide objective estimates of visual acuity comparable to those determined by established methods.

Age of Onset↗