ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1990.tb00854.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

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 ti

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1990.tb00855.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A closed circuit television (CCTV) magnifier was used to measure the reading rates of nine fluent low‐vision subjects. Performance was found to be dependent on field width, character size, and the number of characters displayed in line. A field width of 70 degrees and a mean of 24 characters were commensurate with the fastest reading rate. The optimal character size that elicited the fastest reading was determined for each subject. In seven of the nine subjects, this differed from the character size selected by chance at their initial CCTV sessions, prior to these experiments. A clinical procedure is recommended, which avoids inappropriate choice, and guides the examiner in achieving directly the most efficient CCTV reading conditions for each individual patien

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1990.tb00856.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A cross‐sectional study of 753 Melanesian children in Vanuatu and 904 Malay children in Malaysia included measurement of refractive error and ocular dimensions. All children were between the ages of 6 and 17 years. The prevalence of myopia in Malay children was 4.3% at 7–8 years and 25.6% at 15–16 years with corresponding figures of 0.8% and 4.3% for Melanesian children. The range of refractive error was greater for Malay children at all ages. Mean refractive error for Malay children showed greater hypermetropia, together with a shorter axial length at 6 years, than Melanesian children, but at 17 years the situation reversed and Malay children had more myopia and longer axial lengths than their Melanesian counter

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1990.tb00857.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Evidence has accumulated recently which challenges the conventional description of the parasympathetic division of the oculomotor nerve pathway to intraocular smooth muscles. It is claimed that the pathway from the midbrain to the ciliary muscle is direct and uninterrupted by a synapse in the ciliary ganglion. A similar, separate claim has been made regarding the innervation of the sphincter muscle of the iris. The weaknesses in the arguments supporting the revised versions are discussed in this review and they are rejected in favour of the conventional pathway.

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1990.tb00858.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Dark convergence is often measured psychophysically by aligning two dichoptic stimuli, which are briefly flashed in a dark surround. In the present study, the effect of different stimulus parameters on dark convergence measurements was investigated. Chief among these was the effect of viewing distance (50, 100 and 500 cm) of the stimulus. Measured dark convergence was biased towards the actual viewing distance of the stimuli; this effect was stronger with bar stimuli than with point‐and‐line stimuli. Measured dark convergence depended on the viewing distance to a lesser extent if bar stimuli were observed through pin‐holes (open accommodative feedback loop). The subject's knowledge of the viewing distance had a small but significant effect; the size of the nonius bars had none. To reduce artefacts due to the stimulus distance on psychophysical measurement of dark convergence, point‐and‐line stimuli should be used at a viewing distance of about 1 m. In this case, the effect of stimulus distance can be about 0.25 meter angle (ma), averaged over subjects, but it may be as large as 0.5 ma in some in

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1990.tb00859.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The aim of this study was to investigate proximally‐induced accommodation (PIA) at two levels of cognitive demand. PIA was assessed by comparing the open‐loop accommodative responses to stimuli located at viewing distances of 6 m (0.17 D) and 0.33 m (3 D), respectively. The vergence and accommodation loops were opened by subjects monocularly viewing the targets through a 0.5 mm pin‐hole. PIA was measured while subjects either were encouraged to relax and listened to popular music, or performed a relatively demanding mental arithmetic task (counting backwards in sevens). The results indicated that for 4 of the 12 subjects examined, increased cognitive demand produced a marked (>± 1.00 D) change in the magnitude of PIA. This finding suggests the presence of an interaction between the output of proximally‐and cognitively‐induced accommodation in these subjects. Such an interaction may hinder attempts to examine individual, non‐optical components of a

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1990.tb00860.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Monocular and binocular transient visually evoked responses (VER) were recorded on 50 adult subjects using a pattern reversal stimulus (check size 5.5 min arc). The peak‐to‐trough amplitude of the VER wave was measured and compared with the subjective visual acuity (Landolt C). The binocular amplitude enhancement over the monocular amplitude was around 26% across the acuity range studied, whereas the mean binocular subjective visual acuity improvement was around 11.3%, but this varied from 1% at the high acuity end to 17% at the low acuity end of the ra

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1990.tb00861.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Although the Varilux type varifocal has been and still is very popular, research has been carried out on other methods of providing a progressive addition lens. This paper deals with the field of gradient‐index optics. It includes a review of the literature related to the production of a gradient‐index element and the theoretical analysis of concentric varifocals. A procedure is described to construct a varifocal lens, after that described by Wood in 1905, to produce lenses known as ‘non‐homogeneous cylinders’ or ‘pseudo‐lenses’. The method is based on a diffusion process, taking place in half of the lens, and creates steps in the refractive index of the material. Experimental data are also given on the change of the spherical and cylindrical power, which indicate that the lens constructed is an optical system having a rotational symmetry in power, aroun

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1990.tb00862.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The direction of chromostereopsis observed with a natural pupil and the direction of the monocularly perceived disparity between coloured targets (F and C lines—486 and 656 nm) have been measured in a sample of 30 subjects at 10 and 1000 lx. At both illumination levels approximately equal numbers of subjects perceived positive and negative chromostereopsis. When the ambient illumination was increased, a reversal in the direction of the chromostereopsis occurred for 16 subjects. For six of them a change from a positive to a negative chromostereopsis was observed, a pattern not reported in previous studies. In most cases at both high and low illuminance, there was an absence of perception of a monocular disparity (transverse chromatic aberration), although chromostereopsis was reported, indicating that binocular information can be obtained from sub‐threshold monocular disparities. At low illuminance, the lack of correlation between the direction of chromostereopsis and transverse chromatic aberration (TCA) may indicate that there may be a supplementary binocular factor in chromostereop

ISSN:0275-5408    

DOI:10.1111/j.1475-1313.1990.tb00863.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY