Role of the blue mechanism in wavelength discrimination

The role of blue cones as well as the pathways they supply (collectively called the "blue mechanism") is evaluated by comparing ordinary wavelength discrimination functions with those obtained using two methods designed to inhibit the blue mechanism selectively. These methods use a just-noticeable-border criterion (JNB), instead of the usual one of just-noticeable-difference, and a yellow preadapting field to induce transient tritanopia. Without transient tritanopia, the data obtained using the just-noticeable-border criterion reveal a small contribution of the blue mechanism to wavelength discrimination. Transient tritanopia, with JNB, produces an additional selective loss of wavelength discrimination in a spectral region flanking 460 nm, which yields a function resembling those for tritanopes previously examined.     

Reduction of red-green discrimination by dopamine D1 receptor antagonists and retinal dopamine depletion

Reduction of wavelength discrimination ability in the 560–640 nm range, but not in the 404–540 nm range, has been demonstrated in goldfish after intravitreal injection of D1-dopamine receptor antagonists. Intravitreal injection of the dopaminergic neurotoxin 6-OH-dopamine severely reduced wavelength discrimination ability in the 540–661 nm range within 3 days. Discrimination ability could be reconstituted by the Dl-agonist SKF 38393. Animals recovered from injection of 6-OH-dopamine within 14–16 days. No change of wavelength discrimination was induced by 6-OH-dopamine in the 461–540 nm range. We conclude that under photopic conditions dopamine modulates retinal mechanisms involved in red-green colour coding via D1-dopamine receptor-like binding sites.     

Notes on the use of low magnification telescopes in low vision care

Several areas related to the use of telescopes in low vision are reviewed. These include: contrast sensitivity function; eccentric viewing through a telescope; field of view; telescope used in reverse; and IOL-spectacle lens telescopic systems. Experimental data are included to support selected clinical observations routinely made by low vision clinicians.     

Influence of retinal vascular perfusion pressure on macular photostress recovery time

The photostress recovery time (PSRT) was used as an index of macular function under conditions of altered retinal vascular perfusion pressure (RVPP) in 10 healthy human observers. RVPP was decreased by scleral indentation and increased by body inversion. All 10 subjects showed prolonged PSRTs with decreased RVPP. The change in PSRT, associated with increased RVPP, varied among subjects allowing a sub-classification into two groups. Group 1 (n = 4) showed significant increases in PSRT whereas Group 2 (n = 6) showed no significant change in PSRT. This group difference in PSRT could not be related to test procedure-induced changes in vascular dynamics, such as IOP, or diastolic and systolic brachial and ophthalmic artery pressures. Three possible interpretations are presented to account for the significant increase in PSRT demonstrated by some individuals. Results from this preliminary study suggest that the assessment of a subject's PSRT, subsequent to short-term alterations in RVPP, may provide a non-invasive provocative test for the detection of systemic vascular disease.     

Reproducibility of central field results using the Humphrey Field Analyser in normal subjects

Repeated measurements of threshold for the central 10^o visual field were made on normal subjects with the Humphrey Field Analyser. Two examiners repeated the visual field measurement for each subject, giving four readings in all. Visual field results were divided into concentric zones, where each zone area was double the area of the preceding zone, and also into quadrants. There was no significant difference between the results obtained from each examiner and, after the four trials, there was not a significant learning effect. The results showed no significant difference between quadrant divisions for each zone, but there were significant differences between zones and between subjects.     

Axial length and radius of rotation of the eye

Notwithstanding the advent of ultrasound, there remain clinical difficulties in measuring axial length. One alternative method, using a radius of rotation (r) of the eye, has been proposed. However, there are deficiencies in the technique and doubt concerning its reliability. In our pilot study we developed simple slit lamp techniques for measuring r. For two groups of 40 and 14 adult eyes r correlated significantly (p <0.01) with axial lengths measured with ultrasound. Furthermore, r provided a better index of axial length than low degree ametropia. However, the clinical use of r remains in doubt: Axial lengths of 17 eyes were at least 1 mm more or less than the value of r would indicate. Nevertheless, with refinements to the techniques established in this study, further research may indicate more precisely the nature of the relationship between r and axial length.     

Clinical trial of Optolax II: a pilot study

We tested a device to train the facility of accommodation (Optolax II) over a two week period to determine if the training reduced manifest myopia and improved unaided and aided distance visual acuities. Objectively and subjectively measured myopia was reduced on average after training; unaided visual acuity improved by 0.05-0.08 log units (three to four letters) after the two week training period. These preliminary findings indicate that a more prolonged and more controlled trial of the device is warranted.     

A clinical evaluation of the Topcon RM6000 autorefractor

The Topcon RM6000 autorefractor was evaluated by assessing the repeatability of its results and the extent of their agreement with the findings of conventional subjective refraction. The repeatability of the autorefractor results gives an indication of their reliability. This was determined for the Topcon instrument by comparing the right eye results of 93 patients taken before and after their eye examinations. In 95 per cent of cases the test and retest results of equivalent sphere, cylinder power and cylinder axis differed by less than 0.46 DS, 0.34 DC and 14° respectively. The validity of the autorefractor results differed depending on the age of the patient. In pre-presbyopic patients, the autorefractor gave a more minus (or less plus) result compared with conventional subjective refraction in some cases. This difference could be greater than 1.00 DS. For presbyopic patients, more accurate results were obtained, with approximately 95 per cent of results for equivalent sphere and cylinder being within ±0.50 D.     

Prediction of response to treatment in patients with scleritis using a standardised scoring system

Scleritis is a severe chronic inflammation of the eye wall. High-dose corticosteroids and other immunosuppressive drugs are often required to control the inflammatory process. With the development of new and potentially more effective treatment modalities for scleritis has emerged the need for an accurate and reproducible system for quantifying the severity of scleritis and evaluating the response of individual patients to treatment.
We have developed a quantitative scoring system, based on common clinical signs of scleritis, and evaluated it in 24 patients with scleritis. Our results indicate that this system is simple, rapid, reproducible and useful in grading the severity of scleritis and in predicting the response of patients to systemic immunosuppressive therapy.     

Case report: The morning glory syndrome

This is a report of a single case of morning glory syndrome. The morning glory syndrome is a rare congenital optic disc anomaly which has received scant attention in the ophthalmologic literature. The aetiology of the disorder remains controversial, although it would appear to be related to an isolated coloboma of the optic nerve. The association between morning glory syndrome and a variety of ocular (most notably non-rhegmatogenous retinal detachment) and systemic defects makes its recognition and correct management important; this is discussed in some detail.     

Rates of childhood myopia progression as a function of type of astigmatism

This study examines the relation of rate of childhood myopia progression to the type of astigmatism exhibited. Longitudinal records of myopia progression were collected from five optometry practices in the USA. Patients were classified as having with-the-rule (WTR) astigmatism, zero astigmatism or against-the-rule (ATR) astigmatism. Rates of myopia progression for both principal meridians in the right eye were calculated by linear regression. Rates of myopia progression were not significantly different in the three astigmatism groups. Rates of astigmatism change were much less in magnitude than rates of myopia progression, but were significantly different in the three astigmatism groups. WTR astigmats are likely to change in the WTR direction, while ATR astigmats are likely to change in the ATR direction.     

A survey of symptoms and eye safety practices among welders

Welding is a task which is potentially hazardous to the eyes. In this study we have administered a questionnaire to 128 welders to investigate ocular symptoms and eye safety practices when welding. The welders demonstrated high levels of discomfort symptoms which were correlated with the length of unprotected exposure to nearby welding, the number of welding flashes received and the length of time spent welding. Dust and fumes in the workplace were also a frequent cause of ocular discomfort. Foreign body injuries were common among the welders, many of whom also reported after-images persisting following welding.     

Symptoms associated with VDT use

Symptoms associated with the eyes were recorded by a group of 92 video display terminal (VDT) users over five days. A diary was maintained for the symptoms and other task related factors such as the type of work performed. Diary entries were recorded approximately every two hours. Symptoms were classified as either ocular (a range of discomfort symptoms), visual (blur or double vision) and systemic (headache or postural symptoms). Tired eyes and headaches were the most frequently reported symptoms. Comparing the symptoms reported during VDT work sessions and the clerical (non-VDT) work sessions, there was a small but consistent trend towards more frequent symptoms during VDT sessions. Almost all types of symptoms showed a significant increase in frequency over the day (time of day effect).     

Presbyopia – effect of refractive index

The causes of presbyopia are discussed in terms of the possible influences of the optical parameters of power: the shape as well as the refractive index variations. From this and other studies it would appear that with age the human lens becomes more curved and yet the refractive index does not decrease correspondingly to explain the loss of accommodative power. A synchrony between growth and refractive index distribution is advanced as a possible explanation for the ‘lens paradox’.     

A survey of low vision patients in Hong Kong

This report provides some statistical information based on clinical data gathered on low vision patients who attended the low vision clinic of the Hong Kong Society for the Blind in the first three years of its operation. In this period, low vision devices were prescribed for 393 patients (46.5 per cent of the sample). The most commonly prescribed aids were simple magnifiers and distance telescopes. Cataract was the major cause of low vision.     

Reading improvement with tinted lenses: a report of two cases

There have been numerous anecdotal reports of an improvement in reading in dyslexic children fitted with tinted spectacle lenses. Few of these cases have been subjected to scientific scrutiny. We report the findings in two dyslexic brothers each of whom showed a marked improvement in reading facility when reading print material either through a semi-transparent tinted plastic sheet (overlay) or through tinted spectacle lenses. Other observed effects of the tinted overlays and/or tinted lenses were improved visual acuity, improved figure/ground perception and reduction in apparent distortions and fragmentation of print. Such improvements were noted in either one or both of the boys. A speculative explanation for this effect is that the lenses act by altering the transmission of impulses along the primary visual pathway.     

IOP elevation in different phases of sleep

Large and significant increases in intraocular pressure (IOP) have previously been demonstrated after as little as 30 minutes of sleep.¹² The present experiment tests the hypothesis that the lack of eye movements during sleep is responsible for this increase in IOP. Nine subjects slept in the laboratory on two separate nights. IOP was measured (with subjects in the supine position) using a Keeler Pulsair noncontact tonometer. Eye movements were monitored using electro-oculography. Subjects were woken from sleep after 60–90 minutes, on one night when they were in rapid eye movement (REM) sleep, and on one night when they were not. IOP increased significantly on both nights, but the differences between these increases was not significant. Thus, mechanical factors associated with lack of eye movements do not appear to contribute to the increase in IOP after sleep.