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Biomedical subjects

M E Tytla

Publications and source records attributed to M E Tytla.

6 recordsLinked to original sources
PubMed1993

Stereopsis after congenital cataract.

PURPOSE: The authors determined whether stereopsis can be demonstrated in children treated for congenital cataract after compensating for their amblyopia and strabismus. METHODS: A custom-made set of large stereograms was used to compensate for amblyopia and presented in a synoptophore to facilitate motor fusion. Each pair of stereograms contained five wide vertical bars of high contrast, of which two or three were in crossed disparity. The authors aligned the stimuli in the synoptophore, then decreased the disparity until the child could no longer identify which bars appeared to be "in front." RESULTS: In normal children (n = 25), stereo acuity on this test (Tytla-Lewis-Maurer-Brent [TLMB] test) correlated well with the Titmus and Randot results within the ranges measured by those tests. Seven children in whom a traumatic cataract had developed after 6 yr of age (four with no clinical stereopsis) had TLMB test stereo acuities ranging from 225 to 28 arc-sec. Of 30 children treated for congenital cataract with no clinical stereopsis, 5 regularly achieved a TLMB stereo acuity of up to 225 arc-sec, and 2 with Titmus stereo acuities up to 200 arc-sec, each had a TLMB stereo acuity of 112 arc-sec. These seven congenital cases (two unilateral and five bilateral) with measurable TLMB acuities are among those with the shortest deprivation, the highest minimum resolvable acuity, and the highest contrast sensitivity. CONCLUSIONS: By compensating for amblyopia and strabismus, stereopsis can be demonstrated in some form-deprived amblyopic patients.

Adolescent↗
PubMed1992

Vision in the "good" eye of children treated for unilateral congenital cataract.

PURPOSE: The authors examined linear acuity and contrast sensitivity in the "good" (fellow) eye of children treated for unilateral congenital cataract to determine (1) whether there were subtle deficits like those described for the good eye of patients with strabismic amblyopia and (2) whether any deficits were related to the degree to which the good eye had been patched. METHODS: The authors tested patients treated for unilateral congenital cataract who had a well-documented history of patching. The good eye was physically normal with minimal refractive error. The measures were linear acuity at far (n = 15) and contrast sensitivity (n = 9). RESULTS: Compared with age-matched control subjects, the good eyes of patients had subtle deficits in linear acuity and in contrast sensitivity at high spatial frequencies. These deficits occurred even in eyes that had received minimal patching, and their severity was not related systematically to the duration of patching, which varied widely across the group. CONCLUSION: The visual sensitivity of the good eye of children treated for unilateral congenital cataract is, on average, slightly reduced, even in cases of minimal patching. Consequently, any deficits discovered after aggressive patching may not have been caused by occlusion amblyopia.

Adolescent↗
PubMed1990

Recovery of spatial vision following shunting for hydrocephalus.

Individuals with papilledema due to intracranial hypertension often exhibit a loss of contrast sensitivity confined to low spatial frequency (coarse detail), which can disappear following treatment of the intracranial hypertension. The basis of the initial loss may be revealed by the rate of sensitivity recovery. We monitored the contrast sensitivity of seven patients immediately before and after surgical treatment in which a shunt was placed for intracranial hypertension. Compared with normal controls, the 13 of 14 eyes with papilledema exhibited the characteristic preshunt loss of sensitivity. For the first 3 days after shunt placement, sensitivity remained approximately equal to preshunt levels. By postshunt days 4 through 6, sensitivity rapidly normalized and remained normal for up to 1 year. Based on the rate and pattern of sensitivity normalization, we conclude that the initial loss represents an interaction of axoplasmic stasis with ischemia at the level of the optic nerve.

Adolescent↗
PubMed1990

Flicker sensitivity in treated ocular hypertension.

Reductions in flicker sensitivity in ocular hypertension are thought to precede manifest glaucomatous damage, but the proportion of patients with ocular hypertension reported to have losses in flicker sensitivity (50-90%) is far out of step with the proportion of ocular hypertensive patients in whom clinically defined glaucoma will develop (5-30%). The authors examined the possibility that the flicker losses in some of these patients represent not early glaucomatous damage, but instead a transient influence of raised intraocular pressure (IOP) on an otherwise normal eye. Temporal contrast sensitivity was measured in 26 patients with ocular hypertension and in 22 patients with primary open-angle glaucoma (POAG) before and after hypotensive treatment (timolol). Compared with normotensive controls, all POAG patients exhibited sensitivity losses before treatment which remained unchanged after treatment. The ocular hypertensive patients were divided into three groups, which may reflect differing risks of glaucoma conversion. Group I patients (8/26) had normal flicker sensitivity, and thus appear to be resistant to high IOP. Group II patients (9/26) showed initial losses which disappeared with lowered IOP. They probably have not yet suffered damage but appear to be sensitive to high IOP. Group III patients (9/26) had losses that persisted despite lowered IOPs. The similarity of their response to that of the POAGs suggests that group III patients have already suffered early glaucomatous damage.

Adult↗
PubMed1981

Evaluation of the CAM treatment for amblyopia: a controlled study.

Single letter and linear acuity (near and distance) and contrast sensitivity were measured in 15 amblyopes (ages 5 to 12) before, during, and after four weekly 7 min sessions of CAM treatment. Six of the children, however, played games over a homogeneous grey disc having the same space-averaged luminance as that of the striped stimuli. Experimental and controls results were indistinguishable. In a few subjects from both groups, contrast sensitivity and slight linear acuity improvement was observed. We conclude that these vision changes can be attributed to the short-term occlusion experienced by all subjects during treatment and that grating stimulation did not contribute to this improvement.

Amblyopia↗