George C. Woo

Effect of magnification and field of view on reading speed using a CCTV

Reading speeds were measured in 18 subjects with normal vision and 10 with low vision for each of 20 experimental conditions with different magnifications and field sizes on the Closed Circuit Television System (CCTV). There was a significant difference between the results for the two groups of subjects. These results suggested that in low‐vision patients with faster reading speeds, minimum magnification for maximum field size on the CCTV would be valid advice. For low‐vision patients who read more slowly, reading speed may improve at higher magnifications despite reduced field size.

A PILOT STUDY OF CONTRAST SENSITIVITY ASSESSMENT OF THE CAM TREATMENT OF AMBLYOPIA

Contrast thresholds of varying spatial frequencies were obtained on 3 amblyopic patients before and after the CAM treatment of amblyopia. Results of this study confirm previous findings that in the absence of change of visual acuity, contrast sensitivity function can be changed with the use of this technique. Improvement of contrast sensitivity can occur in older patients and that the sensitivity sometimes can deteriorate when treatment is stopped.

Notch in contrast sensitivity function of optical origin: diffraction effects of acrylic filters

A series of retinal image degrading filters was evaluated by measuring the contrast sensitivity function of four human subjects through the litters (residual CSF). The acrylic filters, with regularly spaced cross‐hatches, produced progressively more reduction in the residual CSF as the density of the cross hatching increased. For some of the fillers there was a selective toss of a narrow band of spatial frequencies as a result of diffraction effects. This experiment serves to further emphasize the need to rule out optical causes of such notches in the CSF before making a diagnosis of neurological dysfunction.

EFFECT OF FRESNEL PRISM DISPERSION ON CONTRAST SENSITIVITY FUNCTION

Abstract— Fresnel prisms are often used in orthoptics for binocular anomalies and in low vision for visual field defects. These prisms are made of optical polyvinyl chloride (PVC) and this material increases chromatic dispersion and produces a loss of contrast. In this study, the effect of chromatic dispersion on contrast sensitivity is determined. Contrast thresholds over a wide range of spatial frequencies are obtained on a number of subjects with the use of Fresnel prisms ranging from 5 to 30 prism dioptres. As predicted there is a decrease in visual acuity and cut‐off spatial frequency threshold as prism power increases. Similarly, a decrease in contrast sensitivity at high and medium spatial frequencies is recorded.

The non-amblyopic eye of a unilateral amblyope: a unique entity

The non‐amblyopic eye of a unilateral amblyope is generally thought of as a ‘normal’ eye. Recently differences in sensitivity, visual acuity, fixation and eye movements, between a ‘normal’ eye and the non‐amblyopic eye of unilateral amblyopes were reported in the literature. Two separate studies were conducted fifteen years apart, with two distinctly different samples in which both gave similar results regarding the distribution of ametropia within the sample populations. This distribution was found to be significantly different for amblyopic eyes, non‐amblyopic eyes of unilateral amblyopes and ‘normal’ eyes. Amblyopia training, whether employing the CAM vision stimulator or occlusion therapy, appears to have a positive effect on the contrast sensitivity function of both the amblyopic and non‐amblyopic eyes of the unilateral amblyope, although there may be no improvement in the visual acuity. On the other hand, age‐matched normal undergoing identical treatment programs show no change in their contrast sensitivity function.

FRESNEL PRISM CORRECTION FOR TRAUMA-INDUCED DIPLOPIA

Abstract— Fresnel prisms placed on the spectacle lenses of a patient with optic atrophy resulting from an accident eliminated constant diplopia in the remaining visual field. A reduction in vision due to Fresnel prisms was found to be more tolerable than diplopia.

THE SPECTACLE MAGNIFICATION OF FOCAL TELESCOPES

A generalized expression for spectacle magnification is derived and used to determine the magnification of focal telescopes used to correct ametropia and/or to view objects at finite distances. When applied to low‐powered hand‐held telescopes, the expression predicts a clinically negligible difference between spectacle and nominal magnification.

A clinical assessment of the Storz Omega A-scan biometer

We investigated factors which affect values of axial length, anterior chamber depth and lens thickness measurements made with the Storz ophthalmic ultrasound system. We found that reliable measures of axial length can be made with the instrument; for a reasonable approximation of axial length, not more than 10 measurements appear to be necessaIy. The instrument should not be used in continuous mode for measurements of anterior chamber depth or lens thickness. When used in continuous mode the measures of anterior chamber (AC) depth and lens thickness (LT) given by the system are highly correlated, even for an artificial eye system supplied by the manufacturer. When used in this mode, the instrument appears insensitive to changes of lens thickness with accommodation. Compression of the probe of the Storz instrument affects the measured values of AC depth and LT; presumably, efforts should be made to minimise probe compression during measurements.

The Effect of CAM Treatment and Occlusion Therapy on Contrast Sensitivity Function in Amblyopia

Assessment of visual function has traditionally involved only measurement of the limit of resolution. This has been obtained by use of letters or gratings at a specific contrast. This rather restrictive method has limited our appreciation of vision in general. CAMPBELL and GREEN [1] in 1965 used a completely new approach that assessed not only the resolution limit but more importantly the visibility of objects within the resolution limit. These measurements typically involve determining contrast sensitivity over a wide range of grating sizes by means of sinusoidal luminance profiles, thus measuring the contrast sensitivity function. It mirrors the now familiar modulation transfer function measurements of optical and photographic devices.

Maurice KH Yap: academic, administrator, innovator in myopia research and public health

Maurice KH Yap was born in Sabah, East Malaysia and went to school in Jessleton (now Kota Kinabalu). After attending an English-medium Christian Brothers’ secondary school, he entered the University of Bradford in the UK to read Optometry. In 1985, Maurice completed a PhD in Optometry and Physiological Optics at Bradford, as well as a Diploma in Ophthalmic Optics from the UK’s College of Optometrists. Maurice was very well regarded and liked by his peers at Bradford where he also spent his post-doctoral years. One of his earliest projects was the use of yellow filters to increase contrast sensitivity. It must have come from his experience in flying as his colleagues remember him spending many Sundays at the airfields. He started flying at an early age and became very fond of it. During his time at Bradford and in collaboration with John Weatherill, who was a consultant ophthalmologist at the Bradford Royal Infirmary, Maurice set up one of the first shared-care schemes between optometrists and ophthalmologists for cataract referral to a hospital. This model soon became the standard followed in Bradford. On a lighter note, he introduced his graduate students to his love of Chinese food by taking them to Leeds for yum cha on Sundays. It was deemed to be a civilised way of conducting post-graduate research supervision. Maurice joined the then Hong Kong Polytechnic in 1987 as a Senior Lecturer. As the Head of the then Department of Diagnostic Sciences, it was during this period that I got to know him. I remember Marion Edwards, the program leader of the Optometry Section at the time and I met him at Kai Tak airport in October 1987. He had hardly any luggage but, as an avid sportsman, he did bring along his tennis racquet. Maurice took his assigned teaching tasks seriously and I observed that he was quite keen on joint research with colleagues even then. After four years at the Hong Kong Polytechnic, he moved to the University of Auckland’s Department of Optometry and Vision Science in 1991, where he stayed for the next seven to eight years. He returned to The Hong Kong Polytechnic University (PolyU) in December 1998 as a Professor and as the Head of the Department of Optometry and Radiography as they had become. After the department was restructured in 2005, he continued being the Head of the new School of Optometry for the remaining two years of his headship. Let me first relay some of his activities as the Head of the Department of Optometry and Radiography. At the time, the Radiography Section was not as well developed as the Optometry Section. He challenged all academics in the department that they must possess a PhD if they wished to remain as faculty members. This policy sent academics scrambling to attain doctorates in Hong Kong or from abroad. In the end, the PolyU became, I believe, the only university in the world to have a Radiography Section that requires this qualification of all its academics. This has enabled colleagues in radiography to adopt the culture of publishing their research findings in top-tier international medical science journals and today, thanks to Maurice, the undergraduate degree program in radiography has become one of the top five at PolyU in terms of student admission scores. In the Optometry Section, Maurice was known to have strict rules for research. He decided that the section’s research should be focused on myopia or the ageing eye. All faculty members in optometry were to conduct research in one of those two areas; no departmental funds would be allocated for research that did not comply. At the time, it was rather difficult for some staff to accept this policy, as they felt their own research goals were being somewhat compromised; however, in hindsight, almost all faculty members now appreciate the direction established by Maurice, with the research foci aligning well with the School’s academic programs. Years later and with limited human resources, the School is enormously proud to have been singled out by Hong Kong’s University Grants Committee in its last report on PolyU for its vision science research program’s achieving international distinction. BSc (Hons) PhD MCOptom FAAO K.B. Woo Family Professor in Optometry, Chair Professor of Optometry, Dean, Faculty of Health and Social Sciences, The Hong Kong Polytechnic University.