Search PubMed⌕ Search

Biomedical subjects

G B Arden

Publications and source records attributed to G B Arden.

At least 19 recordsLinked to original sources
PubMed1992

The pattern electroretinogram in glaucoma and ocular hypertension.

Thirty one eyes with established glaucoma, 61 high risk ocular hypertensive (OHTs) eyes, 66 medium risk OHT eyes, 58 low risk OHT eyes, and 47 control eyes have been followed for up to 2 years by clinical examination and pattern electroretinography (PERG). The study was 'masked' so electrophysiological and clinical data were kept separate. Criteria have been devised which enable PERG measurements to distinguish all established glaucomatous eyes from all normal controls; these criteria demonstrate abnormalities in some OHT eyes, particularly those at high risk. The PERG abnormality is greatest in eyes with established glaucoma in which the intraocular pressure has been lowered by treatment. The PERG becomes smaller as the degree of clinical abnormality increases. Test-retest variability of the PERG is sufficiently low to ensure that most of those first described as abnormal continue to be so.

Adult↗
PubMed1992

Abnormal dark adaptation kinetics in autosomal dominant sector retinitis pigmentosa due to rod opsin mutation.

The time course of dark adaptation was measured in 10 subjects from three families with autosomal dominant sector retinitis pigmentosa (RP) due to mutations in the first exon of the rod opsin gene. In each subject cone adaptation and the early part of the recovery of rod sensitivity followed the normal time course, but the later phase of rod adaptation was markedly prolonged. The recovery of rod sensitivity is much slower than that reported in any other outer retinal dystrophy. Using a model based upon primate data of rod outer segment length and turnover, we have calculated that the delayed phase of the recovery of rod sensitivity in the RP patients tested following strong light adaptation could be due in part to formation of new disc membrane with its normal concentration of rhodopsin rather than in situ regeneration of photopigment.

Adolescent↗
PubMed1992

Electrode comparison in pattern electroretinography.

In recent years, there has been great interest in recording the pattern electroretinogram (PERG) in glaucomatous and diabetic populations. The Dawson, Trick, and Litzkow thread electrode (DTLTE) and the gold foil electrode (GFE), commonly used for recording PERGs, were compared for variations in amplitude of response, test-retest variability, and patient comfort. Two study centers collected data on a total of 32 normal subjects. The subjects from the London center showed a slight (but not significant) preference for the DTLTE, and the Houston subjects also found the DTLTE to be significantly more comfortable (chi-square = 39, P less than 0.001). In both study groups, the GFE was found to produce a statistically larger amplitude of response than that obtained with the DTLTE. Significant differences were found regardless of the slow (transient, 3.1 Hz; F = 6.24; P = 0.0192) or fast (steady state, 8.3 Hz; F = 18.38; P = 0.0001) stimulus-presentation rate. Larger differences between the two electrodes occurred under steady-state conditions. Although there is no consensus as to the optimum recording conditions to obtain the subtle PERG, it appears the the GFE records larger responses than the DTLTE. However, test-retest data confirmed that the GFE records twice the amplitude of the DTLTE, and it also produced twice the variability (average percent difference over time for GFE, 15%; for DTLTE, 8%).

Adolescent↗
PubMed1991

Colour contrast sensitivity changes caused by peripheral retinal laser photocoagulation.

Macular phototoxicity is known to occur with laser use, and there is evidence that the wavelength of the light used influences this effect. In this study, a computer based colour contrast sensitivity test was used to assess the immediate macular effects of photocoagulation of peripheral flat retinal holes in otherwise normal retinas, using blue-green (488 and 514 nm), yellow (577 nm), orange (595 nm) or red (647 nm) laser light. The laser aiming beam was not allowed to traverse the macula at any stage during treatment. No protan or deutan axis threshold changes were noted in the 17 patients tested irrespective of the laser wavelength used. Tritan axis sensitivity was significantly reduced one hour after treatment with the blue-green laser, but no tritan axis change was found after treatment with longer wavelength lasers. The effect was no longer present the day after treatment in the subjects tested. The results show that even peripheral retinal treatment with blue-green laser can cause acute macular phototoxicity.

Color Perception↗
PubMed1991

Macular colour contrast sensitivity in ocular hypertension and glaucoma: evidence for two types of defect.

Colour contrast sensitivity (CCS) of a large cohort of glaucomatous patients, ocular hypertensive patients (OH), and normal persons was measured at six-month intervals during a two-year period. The OHs were graded into high, medium, and low risk groups. 69% of glaucomatous patients and 32% of all OHs had CCS thresholds greater than the mean plus 2 SDs of the controls. Satisfactory specificity and sensitivity could not be obtained by adjusting the criterion of threshold. In abnormal eyes, progressive small increases of threshold occurred during the study, but glaucomatous eyes with normal thresholds on the first visit retained normal thresholds in the subsequent visits. Although our system is very sensitive and precise, the proportion of abnormalities detected is no greater than with other techniques. In some glaucomatous patients there is a true preservation of colour vision which does not merely reflect the limitations of the test employed.

Color Perception↗
PubMed1991

Peripheral color contrast. A new screening test for preglaucomatous visual loss.

A new test of peripheral color contrast is described. A high-definition color monitor driven by a personal computer with a graphics interface card displays an annulus subtending 25 degrees at the eye. The color contrast between the annulus and the background can be varied. Forty-five degrees of the annulus is randomly removed in one of four quadrants. Patients are asked to identify the position of the gap while fixating a central spot. The minimum color contrast between annulus and background at which the identification is possible is between 13-16% for the protan, deuteran, and tritan axis in normal subjects. This threshold value changes little with age, refractive error, or pupillary aperture, and test-retest variability is low. Testing one eye takes only 1-2 min. The test was applied to ocular-hypertensive and glaucomatous patients. All patients with glaucoma had thresholds greater than two standard deviations (SD) above the normal mean. In addition, 97% of glaucoma patients had thresholds greater than four SDs, and 95% had thresholds more than five SDs above the normal mean. Most patients with ocular hypertension and clinical signs indicating a low or medium risk of conversion to glaucoma had thresholds under the upper limit of normal. High-risk patients with ocular hypertension fell into two groups. One approximated to normal; the other had elevated thresholds, which in many cases were more than four SDs above the normal mean. The epidemiologic consequences of this test are discussed.

Adult↗
PubMed1979

Abnormal cilia.

Explore the source record for details and available documents.

Cilia↗
PubMed1979

Effect of occlusion on the visual evoked response in amblyopia.

Average normal values for the VER were obtained in children aged 4 to 11 years. There are slight but significant differences between the values obtained and those found in adults (an increase in the time to peak of P1). In amblyopic eyes the time to peak is increased, and the amplitude reduced, roughly in proportion to the loss of visual acuity and binocularity. The VER is normal in the better eyes of children who have never been treated by occlusion therapy. Occlusion increases the time to peak of the VER, both in serial studies on individuals, and in lateral population studies, so that the response of the better eye is delayed beyond that of the amblyopic eye. After the end of occlusion, the VER change usually returns to normal. In a subgroup of patients with prolonged occlusion, the changes had not completely reversed one year later. In children in whom occlusion therapy had improved visual acuity, the VER returned towards normal.

Amblyopia↗
PubMed1979

A gold foil electrode: extending the horizons for clinical electroretinography.

A gold foil ERG electrode is described. The device is inexpensive and simple to fabricate. Since it is hooked over the lower lid and makes minimal touch contact with the inferior limbal area, it can be used in circumstances which require prolonged testing of retinal function or in eyes with corneal pathology. Because the optics of the eye are not compromised, it is possible, with the use of appropriate stimuli and response-averaging techniques, to record local EFGs from relatively small retinal areas.

Child↗
PubMed1978

Grating test of contrast sensitivity in patients with retrobulbar neuritis.

A retrospective study of 57 patients with retrobulbar neuritis (RBN) was carried out with a new test of contrast sensitivity that utilizes printed sinusoidal gratings. For 21 patients suffering from multiple sclerosis, visual abnormality was detected in 18 "affected" eyes and 12 apparently unaffected eyes. For the 36 patients with RBN, abnormalities were detected in 29. In seven of these cases, the grating test showed bilateral impairment. The grating test seemed to be a more sensitive indicator of demyellinization than other psychophysical tests. In 24 of the patients with the least severe disease, the grating test was compared with the visual evoked response. The probability of making a positive diagnosis was .54 for the evoked potential alone, and .71 for the grating test alone.

Cerebral Cortex↗
PubMed1978

Changes in pigeon cone photocurrent caused by reduction in extracellular calcium activity.

1. Photocurrents have been recorded from the red spot of the isolated superfused pigeon retina. The technique used was to record photovoltage gradients and extracellular fluid resistivity in a direction parallel with the long axes of the receptors. 2. Cone and rod responses were identified, and experiments designed so that only the former were elicited. 3. In the outer portion of the receptor layer, the wave form of the cone photoresponse lacks the initial transient (the 'nose') seen in the portions of the receptor layer nearer the synapses. It is argued that this observation permits the use of a simple equivalent circuit for the generation of the extracellular photocurrent, to infer membrane properties from extracellular recordings. 4. When the superfusing Ringer is changed to one which has a very low calcium activity (2 X 10(-7)M) the first result is that photoresponses increase in magnitude (X 7.7) but the relationship between light intensity and response amplitude and the light intensity (sigma) required to produce a half maximal response remains unchanged. 5. This increase in photocurrent in low calcium also occurs if the superfusing fluid is cooled to 10 degrees. 6. After 2--3 min, the photoresponses in low calcium begin to decrease in amplitude, and the value of sigma is progressively reduced, tenfold in 10 min. 7. During this time, the wave form of the photocurrent alters, the rate of increase and decrease of the responses being slowed. 8. The relationship between peak photocurrent and duration of light flash is modified. 9. The response to a step of light is not well maintained in higher calcium, but is well maintained in low calcium. 10. In higher calcium, the current overshoots during recovery from a flash to below the previous dark level. This does not happen in low calcium. 11. In low calcium, a light adapting background illumination desensitizes the cones. All changes in wave form of the response can be accounted for in terms of the membrane non-linearities. The calculated time course of the change in concentration of the 'internal transmitter' is unaffected. The same is true of desensitization, in the dark, following exposure to intense illumination.

Animals↗
PubMed1978

The importance of measuring contrast sensitivity in cases of visual disturbance.

A description is given of a practical clinical test of contrast sensitivity and of the results obtained on a normal population. An account is given of recent physiological work which illustrates the potential usefulness of the method in ophthalmology, and the clinical results obtained by the author and others are summarised.

Adult↗
PubMed1978

A simple grating test for contrast sensitivity: preliminary results indicate value in screening for glaucoma.

Using a new test, in which patients are asked to view printed sinusoidal gratings of varying contrast, we have established normal population values and have investigated a small series of glaucomatous patients. In these, test scores are higher than the normal range and increase with the severity of the disease. Patients with raised intraocular tension, normal discs, and no field loss may give abnormal results. The test can be scored so that a very sharp distinction may be made between normal and glaucomatous eyes. The test is simple, quick to perform, portable, and can be done in almost any situation.

Adolescent↗