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Biomedical subjects

R V North

Publications and source records attributed to R V North.

28 records · Page 2Linked to original sources
PubMed1991

Atropine occlusion in the treatment of strabismic amblyopia and its effect upon the non-amblyopic eye.

A total of 189 cases with amblyopia, where atropine sulphate 1% had been used as a method fo unilateral occlusion, were reviewed. The results show that after atropine had been appropriately applied, permanent reversal of amblyopia is rare, and unwanted side-effects are few and of minor nature. Pupil size, light reflex and accommodation of the atropinized eye appear to be unaffected. The angle of squint was unaffected and fixation of the amblyopic eye either remained unchanged or shifted to a more central point.

Amblyopia↗
PubMed1990

Do long wavelength pass filters improve low vision performance?

It has been suggested that the wearing of band-pass tints may improve the contrast performance in certain ocular conditions. We examined this by measuring grating visual acuity (VA) for targets of various contrasts. The benefits of Corning CPF 511, 527 and 550 lenses, and neutral density (ND) filters were examined with and without the presence of glare. Generally, patients with anterior sector conditions showed improved performance with band-pass filters (not with ND filters). It is suggested that the filter reduces the scatter within the ocular media. People with retinitis pigmentosa or diabetic retinopathy rarely benefited. The CPF 511 most frequently improved VA followed by CPF 527 and 550 respectively. We suggest that a condition of glare is incorporated when assessing suitability with tints.

Adult↗
PubMed1990

Prism adaptation and viewing distance.

Previous studies have shown that subjects with normal binocular vision adapt to prism-induced phorias. However, there are conflicting reports as to the amount of adaptation shown to horizontal prisms. Some investigations found a greater amount of adaptation to base out prisms compared with base in, whilst others found the reverse and one study found no adaptation to base out prism at all. This study investigated the adaptation response to horizontal prisms at distance and near in a larger number of subjects (n = 40). The results confirmed our previous findings and showed that at distance the adaptation responses are asymmetrical, there being a significantly greater amount of adaptation to base out prism compared with base in, whilst at near the responses are virtually symmetrical. Possible reasons for these findings are discussed.

Adaptation, Ocular↗
PubMed1989

Adaptation ability of subjects with different refractive errors.

In previous studies we have shown that subjects with normal binocular vision adapt to prism-induced heterophorias. In this study we have continued the work by investigating the adaptation ability of subjects with different refractive errors to horizontal prisms. The results showed that emmetropes, late-onset myopes (LOM's), and early-onset myopes (EOM's) can adapt to prism-induced phorias at distance and at near. The early-onset myopes demonstrated the greatest amount of adaptation after 3.5 min of binocular viewing in all cases. However, the differences found between the refractive groups in the amount of adaptation after 3.5 min of binocular viewing are not statistically significant.

Adaptation, Ocular↗
PubMed1987

Vergence adaptive changes with varying magnitudes of prism-induced disparities and fusional amplitudes.

Vergence adaptation response monitored with various prism disparities demonstrated that the rates of adaptation decreased as the prismatic effect was increased. However, the amount adapted increased with the increase in the value of the prism until this value fell outside the fusional amplitude; the amount adapted then decreased. However, a large disparity can be adapted to with ease if the prismatic effect is increased gradually in small steps. The clinical implications of these results are discussed.

Adaptation, Ocular↗
PubMed1986

Effects of prolonged forced vergence upon the adaptation system.

In previous studies the ability of the oculomotor system to adapt to prism-induced heterophoria has been shown. The 'phoria that occurs immediately after a prism has been placed before one eye gradually reduces and returns to its original baseline value as the subject is allowed binocular experience while wearing the prism. Little work has been carried out to determine when the adaptation is complete. In this study we report on the results of two experiments designed to determine when adaptation is complete. In the first, the rate of decay of adaptation, i.e. loss of slow fusional vergence, is measured after varying periods of forced vergence. In the second experiment the rate of adaptation to an additional disparity is measured; this should be the same as that before the induced effect if adaptation is complete. The results of this study indicate that although adaptation may appear complete by the criterion that the 'phoria has returned to its baseline value, the adaptation is unlikely to be truly complete for a much longer period of time has passed.

Adaptation, Ocular↗
PubMed1985

The relationship between the extent of visual field and driving performance--a review.

The effect of the extent of visual field upon driving performance has recently received a great deal of interest. With such a volume of traffic on the roads today, peripheral vision would seem to be essential for safe driving and yet past literature is inconclusive as to the relationship between the extent of visual field and driving performance. This paper reviews the research work and gives possible reasons for the lack of relationship reported in most of the studies. Until further research work does determine the minimum visual field required for safe driving, the role of the medical practitioner in advising patients when they are considered unsafe to drive is in question. The provision of a period of adaptation after complete loss of vision in a previously normal eye should also be considered, during which time the motorist is temporarily banned from driving.

Accidents, Traffic↗
PubMed1982

Effect of orthoptics upon the ability of patients to adapt to prism-induced heterophoria.

In a previous study we showed that subjects with abnormal binocular vision either lacked or had a deficient ability to adapt their oculomotor systems to a prism-induced heterophoria. In this study we report on the results of an experiment designed to establish whether the adaptation ability improves in patients who are successfully treated, by means of orthoptics, for convergence insufficiency. In all seven patients examined, we found an improved ability to adapt. Whereas at the beginning of the experiment only two patients fell within the 95% confidence limits of the norm, at the end five patients fell within these limits. These results demonstrate that the success of orthoptics in relieving symptoms is associated with an improved ability to adapt to prism-induced heterophoria.

Adaptation, Ocular↗
PubMed1979

Dark adaptation in diabetes mellitus.

The effect of diabetes mellitus on the normal dark adaptation curve is investigated. It has been found that diabetic patients take longer to adapt and that their absolute thresholds are raised. The degree of elevation in the final threshold correlates with the duration of diabetes.

Adolescent↗