Biomedical subjects

M Yap

Publications and source records attributed to M Yap.

31 records · Page 2Linked to original sources

PubMed1989

Causes of blindness and partial sight in the Bradford Metropolitan District from 1980 to 1985.

A retrospective review of the BD8 forms submitted for the period 1980-85 in the Bradford Metropolitan District was conducted to ascertain the incidence and causes of blindness and partial sight. A total of 1485 cases were registered in this period of which 755 (50%) were included in the Blind register and 730 (49.2%) in the Partially Sighted register. Age-related macular degeneration was the most important cause of visual handicap, accounting for 43.9% of all registrations, followed by glaucoma (16.2%), diabetic retinopathy (6.3%), myopic degeneration (6.1%), optic atrophy (4.4%), cerebrovascular disease (3.8%), cataracts (3.6%), retinal vascular occlusive disease (3.2%), corneal opacities (3.0%), congenital anomalies (2.7%), retinitis pigmentosa/tapeto-retinal degeneration (1.9%), retinal detachment (1.8%) and others (3.1%). The ratio of female to male registrations was 1.8:1. Eighty-four per cent of this sample population was above the age of 60 years at the time of registration.

Adolescent↗

PubMed1989

Do intraocular lenses with ultraviolet absorbing chromophores protect against macular oedema?

In a prospective study, designed to test the effect of intraocular lenses containing an ultraviolet absorbing chromophore on the incidence of post-operative cystoid macular oedema, 55 patients undergoing extracapsular cataract extraction were randomly allocated to receive intraocular lenses with or without an ultra-violet absorbing chromophore. Post-operative fluorescein angiography showed no difference in the incidence of macular oedema in those patients receiving an intraocular lens with an ultraviolet absorbing chromophore compared with patients receiving a standard posterior chamber intraocular lens.

Aged↗

PubMed1987

Contrast sensitivity and pattern ERG in Waldenstrom's macroglobulinaemia.

Patients with Waldenstrom's macroglobulinaemia (WM) and age matched controls have been examined using tests of contrast sensitivity and pattern electroretinography. The patients with WM were in remission on maintenance treatment and had only moderately elevated plasma viscosity. They showed evidence of abnormal contrast sensitivity but there was no significant difference in amplitude of the pattern ERG between patients and controls.

Blood Viscosity↗

PubMed1987

Performance of amblyopic children on printed contrast sensitivity test charts.

Forty consecutive amblyopic patients between the ages of 3 and 12 years attending the Orthoptic Clinic for assessment and treatment were tested on the AO Contrast Sensitivity System [Arden grating test (AGT)] and the VISTECH Contrast Sensitivity Charts. Recordings were unsuccessful in more than 50% of these patients on both test systems. Of those who could successfully complete the AGT, false negative results were noted in 62.5% of the amblyopic eyes and false positive results were found in 25% of the normal fellow eyes. On the near VISTECH chart, all normal and amblyopic eyes produced results that were outside the specified limit of normality. On the distance VISTECH chart, 25% of the normal fellow eyes gave false positive results and 25% of the amblyopic eyes gave false negative results. From these findings, it is doubtful whether either test system has a role in the routine clinical assessment of amblyopia.

Amblyopia↗

PubMed1987

Edge contrast sensitivity in optometric practice: an assessment of its efficacy in detecting visual dysfunction.

The utility of the Melbourne Edge Test (MET) in optometric practice was evaluated by screening 293 consecutive patients who presented for routine eye examination. The MET identified ocular abnormalities in 37 eyes. Of these, 36 also manifested a reduction of visual acuity. The incidence of "false positives" was 1.0%. The MET test failed to detect ocular abnormalities revealed by conventional examination techniques in 29 eyes (4.9%), of which 28 exhibited Snellen acuity losses.

Adolescent↗

PubMed1987

Psychophysical measurement of the foveal avascular zone.

The size of the foveal avascular zone (FAZ) reflects the condition of the microcapillary circulation in the foveal area. A number of studies have shown a significant increase in FAZ size in conditions of vascular pathology including diabetes. A non-invasive method of estimating FAZ size may be a valuable addition to a psychophysical test battery. We used a blue-light field to reveal the activity of the retinal leucocytes to two groups of normal subjects with average ages 24 and 61 years. Two methods were used to estimate the FAZ size, making use of the fact that subjects could see their own FAZ as the area free of leucocyte activity. The first method required subjects to indicate when leucocyte activity stopped as the field size was decreased and when it reappeared as field size was increased. The second required subjects to match the size of the leucocyte-free area with a white circle superimposed on the field. A search algorithm was used to change circle size according to subjects' responses. Results show a significant difference in FAZ size between the two age groups with both methods of measurement, and estimates were comparable to those reported using angiographic methods.

Adult↗

PubMed1986

Influence of lid position on astigmatism.

The influence of 3 different lid positions on the astigmatism of 50 young healthy eyes was investigated with an autorefractor. The results showed that a significant amount of astigmatism may be induced when the palpebral aperture is voluntarily narrowed.

Adolescent↗

PubMed1986

Visual performance in pseudophakia with standard and ultraviolet-absorbing intraocular lenses: a preliminary report.

There is currently considerably interest in the vulnerability of the pseudophakic eye ultraviolet light. Contrast sensitivity was measured in patients receiving UV-absorbing and standard posterior chamber intraocular lenses (IOLs) and in normal age-matched observers. The results suggest that in the relative short-term there is no difference in visual performance with either type of IOL. Modulation Transfer Function studies on 3 batches of IOLs (2 standard and 1 UV-absorbing) showed slight variations in optical performance within and between batches. Spectral sensitivity testing demonstrated increased macular protection from short wave-length blue light by the crystalline lens when compared with both types of IOL.

Aged↗

PubMed1986

Contrast sensitivity in pseudophakia and aphakia.

Contrast sensitivity was measured in pseudophakic and aphakic patients. No difference could be demonstrated between the contrast sensitivities of patients with anterior chamber/iris-supported and posterior chamber intraocular lenses (IOLs). Little difference was found between pseudophakics and aphakics. Interocular contrast ratios in five pseudophakic patients with normal fellow eyes revealed a range of contrast attenuation characteristics which may be attributed to the IOL and corneal and posterior capsule transmission.

Adult↗

PubMed1985

Recovery of contrast sensitivity following bilateral orbital decompression: a case report.

Contrast sensitivity (CS) was measured in a patient with bilateral optic nerve compression resulting from thyroid ophthalmopathy. Initially both right and left contrast sensitivity functions (CSF's) were markedly attenuated over the spatial frequency range measured. CS improved significantly after surgical decompression although distance visual acuities remained unchanged during most of the period of observation. Sensitivity to medium- and high-spatial frequencies remained attenuated compared to the level achieved by a normal group of subjects of a similar age decade.

Differential Threshold↗

PubMed1985

The Arden gratings in optometric practice.

The use of the Arden gratings (AO contrast sensitivity system) in optometric practice is evaluated. A total of 320 patients presenting for eye examination were screened with the gratings. Sixty-four eyes (10%) gave abnormal grating scores although results from conventional examination techniques revealed no abnormality. Of the 110 abnormal eyes detected by routine examination techniques, 8 presented with normal grating scores, 6 with "borderline suspect" scores and 96 with abnormal scores. Used in isolation, the failure rate of the Arden gratings to detect ocular abnormality in the patient population was 1.3% and the "false positive" referral rate was 10%.

Adolescent↗

PubMed1984

The effect of a yellow filter on contrast sensitivity.

Most previous studies have found no visual advantage for the use of yellow filters. This study reports the effect of wearing a long-pass yellow filter on monocular spatial contrast sensitivity under photopic and mesopic conditions. Contrast sensitivity was improved with the yellow filter under photopic conditions but not significantly at most spatial frequencies under mesopic conditions.

Adult↗

PubMed1983

Selective thalamic degeneration--report of a case with memory and mental disturbances.

A selective thalamic degeneration is described in a 21-year-old Chinese female patient. Clinical history was characterized by a 3-year evolution of severe memory loss, progressive dementia, amenorrhea, emaciation, and short terminal coma. Neuronal losses were maximal in the thalamic anterior and medialis formations, but they were also noted in the pulvinar, the nuclei ventralis anterior, reticularis polaris, and dorsalis superficialis. The microneurons were generally spared. All other thalamic nuclei and the rest of the central nervous system were intact but for discrete changes in the bulbar olives. The clinical features and the classification of this case of selective thalamic atrophy are discussed.

Adult↗