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Biomedical subjects

B C Chauhan

Publications and source records attributed to B C Chauhan.

52 records · Page 3Linked to original sources
PubMed1991

[Diffuse and localized glaucomatous visual field changes in light sense, flicker and visual acuity perimetry. Evidence of pressure damage].

75 eyes of 75 patients with different types of glaucoma (21 eyes with normal-tension glaucoma, 49 eyes with primary open-angle glaucoma and 5 eyes with pigmentary glaucoma) were examined by automated light-sense, flicker and resolution perimetry. All fields were classified as being "normal" (N) or having "diffuse loss" (D), "localized loss" (L) and "diffuse plus localized loss" (DL) in masked fashion. The frequency distributions for the various field loss categories against the highest intraocular pressure ever reported in the patients' records were plotted. The frequency distributions for the purely localized defects show a peak at 20 mmHg and are markedly skewed to low pressure values, while the diffuse plus localized damage and the purely diffuse loss, however, show a peak at about 30 mmHg. The data support the hypothesis that diffuse field loss may be an indicator of pressure-induced damage.

Adult↗
PubMed1990

The use of visual field indices in detecting changes in the visual field in glaucoma.

We present results from 64 glaucoma patients and glaucoma suspects followed up for a median period of 7.4 yr who had a median of seven examinations using Program 31 on the Octopus perimeter. The patients also had manual visual fields recorded on either the Tübinger or Goldmann perimeter during the same period. By examining all manual fields over the follow-up, we classified 37 patients as deteriorating and 27 as nondeteriorating by using predetermined field criteria which we believed to be clinically significant. In a masked fashion, the indices mean defect (MD) and corrected loss variance (CLV), in addition to the three cluster analysis indices SIZ, CLUS, and PCLUS were computed for each patient and regressed on time. When a significant positive index/time slope (P less than 0.05) was defined as indication of deterioration, all indices had remarkably poor sensitivities because their slopes did not reach statistical significance in the great majority of patients. When, regardless of statistical significance, positive slopes were defined as indication of deterioration and negative slopes as nondeterioration, the most sensitive index, PCLUS, still had a sensitivity of less than 65%. The indices were better in detecting the presence or absence of visual field deterioration in fields that were initially normal than in those that were initially abnormal. Since the testing modalities of manual and automated perimetry are different, our study was not designed to compare the sensitivity of one technique over the other. Our study does, however, demonstrate that the indices used currently may not be clinically reliable in the assessment of changes in the visual field.

Analysis of Variance↗
PubMed1990

The influence of intraocular pressure on visual field damage in patients with normal-tension and high-tension glaucoma.

There have been several reports to suggest that the type of visual field damage in open-angle glaucoma is influenced by intraocular pressure (IOP). This study was undertaken to determine the extent to which patients with normal-tension (NTG) and high-tension glaucoma (HTG) could be differentiated on the basis of some features of their visual fields. The results from 40 pairs of NTG and HTG patients were matched closely for the extent of visual field damage, pupil size, and visual acuity. Using this pooled material, the authors increased the IOP difference between the two groups in either direction, ie, by either progressively lowering the highest recorded IOP allowed for inclusion in the NTG group or by progressively increasing that required for inclusion in the HTG group. They compared the normal areas of the patients' visual fields by using simple visual field indices designed to quantify the undisturbed field. Using receiver operating characteristics (ROC) analysis, they showed that changing the inclusion criterion in the NTG group resulted in no better separation between the groups. However, when the inclusion criterion was changed in the HTG group, the two groups tended to become more separable. In this case, the degree of separation appeared to be related to the difference in the highest recorded IOP between the two groups although the separation was not complete. These findings show that pressure has a greater influence on the type of visual field damage at the higher end of the IOP spectrum encountered in open-angle glaucoma and suggest that there is no common single pathophysiologic mechanism in this disease.

Cluster Analysis↗
PubMed1989

Visual field damage in normal-tension and high-tension glaucoma.

We studied the ocular characteristics of 40 pairs of normal-tension and high-tension glaucoma patients who matched closely for the extent of field damage, pupil size, and visual acuity. To determine if there were differences in visual field damage between patients with normal-tension and high-tension glaucoma, we studied characteristics of the areas of the patients' visual fields that were undisturbed. We computed the number of normal locations, the number of clustered normal locations, and the size of the largest cluster of normal locations. The results showed that for an equivalent extent of damage, the individuals in the normal-tension group had greater areas with normal sensitivity, hence more localized damage. A comparison of the patient data to control data showed that paired differences were larger when the normal-tension member of a pair had a larger value in any of the parameters. The results support the hypothesis that glaucoma patients with lower intraocular pressures have more localized damage and those with higher intraocular pressures have more diffuse damage.

Female↗
PubMed1989

The time-course of intraocular pressure in timolol-treated and untreated glaucoma suspects.

We studied the behavior of intraocular pressure in glaucoma suspects randomly selected to receive either topical timolol or no treatment over the course of a long-term prospective follow-up study. All patients who after six years of follow-up showed no localized field defects or disk changes, or whose pressures were not dangerously increased (24 treated and 22 untreated patients), were included in the present study. Overall, the two groups showed an increase in pressure followed by a gentle leveling off and a decrease toward the end of the follow-up period. The pressure-time curves of the two groups were parallel and vertically separated by 4.94 mm Hg. When pressure-time relationships were determined in individual patients, the categorical group differences were not statistically significant. Our results suggest that most glaucoma suspects did not exhibit a random time-course of intraocular pressure and that the effect of treatment was simply to lower the pressure-time curve of the treated group by a fixed level throughout the six-year follow-up period.

Drug Evaluation↗
PubMed1989

The glaucoma suspect: differentiation of the future glaucomatous eye from the non-glaucomatous suspect eye. 1. Ultrasonic measurements and eye-wall stress.

We examined the eyes of a group of patients entered into and still continuing in a glaucoma suspect study. Over time, some remained unchanged while others developed chronic open-angle glaucoma (COAG). By comparing the data obtained by ultrasonic measurement of the axial length (A) and central corneal thickness (CCT), along with measurement of intra-ocular pressure (IOP) from these patients and normal control subjects, we found no differences. However, by combining these factors in a calculation of eye-wall stress we found a significant difference between the glaucoma suspect and the future glaucomatous eye.

Adult↗
PubMed1989

A cluster analysis for threshold perimetry.

Cluster analysis in perimetry is a technique used in the evaluation of localised visual field loss. It has previously been applied to suprathreshold data and, unlike the indices currently available to indicate localised loss, it is influenced by the relative positions of individual defects. This paper describes a cluster analysis for use with data from Program 31 of the Octopus perimeter. To demonstrate the technique, sensitivity values of normal 60-year-old subject were altered to simulate localised loss. Illustrative examples of clinical cases are given, showing differing degrees of localised loss that do not influence the corrected loss variance (CLV) but influence the computed cluster parameters. It is hoped that the value of this form of analysis will be demonstrated in clinical follow-up of glaucoma patients.

Humans↗
PubMed1988

Cluster analysis in visual field quantification.

The central visual fields of 2165 normal and 106 glaucoma eyes were measured using a threshold related suprathreshold strategy. The effects of altering the cluster radius in normals and glaucoma eyes sheds light on the nature of defects in these two groups. It is estimated that approximately 13% of normals have clusters; the great majority of these individuals have one cluster of two defects. Most clusters in normals are formed artefactually due to angioscotoma and/or physiological variations in the blind spot position. Clusters due to other factors occur rarely. Clusters are found with equal frequencies in the superior and inferior fields in normal eyes, but with a greater frequency in the superior field in glaucoma eyes. The use of clusters in quantification is both sensitive and specific. Using results from this large sample and looking at other visual field properties, it is possible to devise weighted probability indices to score visual fields.

Adult↗
PubMed1988

Clinical evaluation of the Non-Contact Tonometer Mark II.

The purpose of this investigation was to test the reliability of the American Optical Non-Contact Tonometer Mark II (NCT II) using the Goldmann Applanation Tonometer (GAT) as the validating instrument. The sample contained 102 consecutive patients from our University Eye Clinic, of whom one-half had 4 NCT II measurements first, followed by 4 GAT measurements; the other one-half had 4 GAT measurements first, followed by 4 NCT II measurements. No significant change in intraocular pressure (IOP) was noted over the measurement sequence with either instrument. There was no significant difference between paired NCT II and GAT readings when the NCT II was used first; however, a highly significant difference between paired readings was obtained when the GAT was used first, indicating that the GAT measurement produced a delayed reduction in the IOP. This effect did not occur with the NCT II. Although the NCT II is shown to have a good overall reliability when compared to the GAT in both protocols, the agreement between any two tonometers may be influenced greatly by the very process of taking a measurement and by the dynamic nature of the IOP.

Adult↗
PubMed1988

Screening for glaucomatous visual field defects: the relationship between sensitivity, specificity and the number of test locations.

The visual field results from 104 eyes with early glaucomatous loss and 1860 normal eyes have been used to derive the relationship between sensitivity, specificity and the number of test locations in a visual field screening test. A logarithmic relationship was found between sensitivity and the number of test locations and a linear relationship between specificity and the number of test locations. The results indicate that large numbers of test locations are not required to reach high levels of sensitivity and that clinically it might be better to screen all patients with a few stimuli quickly than to examine carefully those patients who meet a precondition such as raised intraocular pressure or abnormal disc appearance.

Computers↗
PubMed1988

The effect of long-term intraocular pressure reduction on the differential light sensitivity in glaucoma suspects.

This study was undertaken to observe the effect on the differential light sensitivity in glaucoma suspects produced by a long-term reduction in intraocular pressure (IOP) with timolol maleate. The results are taken from an ongoing 6 year follow-up study of glaucoma suspects randomly selected for treatment and nontreatment. We present fine-grid meridional data, recorded every 4 months by automated perimetry, of all 46 patients (24 treated and 22 untreated) who completed the 6 year follow-up without developing localized visual field defects, acquired optic disc changes and whose IOP was not judged clinically dangerous during the follow-up. Methods of analyzing the profile sensitivity, the profile slope and the sensitivity of specific locations over the follow-up are described. The results show that the long-term fluctuation in differential light sensitivity in the two groups was not significantly different (P = 0.395) and that the sensitivity at most of the locations remained stable. The number of stable locations was not significantly different in the two groups (P = 0.412) and there was also no difference in the number of locations where the sensitivity appeared to decrease (P = 0.193) or increase (P = 0.540). Analysis of covariance showed no group difference in the profile sensitivity or the profile slope and that these variables remained stable in both groups over the 6 year period. Although the treated group maintained a consistently lower IOP than the untreated controls, our results showed that long-term pressure reduction with timolol in glaucoma suspects appeared not to influence the differential light sensitivity in the tested meridian.

Humans↗
PubMed1988

An evaluation of the Hyde surgical astigmatic ruler.

The Hyde Ruler, a semi-quantitative intraoperative keratometric device, was compared with the Bausch and Lomb keratometer by taking 50 paired measurements of induced astigmatism on a model cornea. The correlation between the two instruments was 0.884, and regression of the Hyde Ruler estimates on the Bausch and Lomb keratometer readings produced a slope of 0.732 with an intercept of -0.150 D. From the regression equation, a correction was applied to the Hyde Ruler estimates, resulting in 68.2% of the latter falling within 1.22 D or less of the Bausch and Lomb readings. We consider this accuracy to be acceptable for a semi-quantitative intraoperative keratometer, and should allow appropriate suture tensioning during cataract surgery to aid in early visual rehabilitation of the patient.

Astigmatism↗
PubMed1986

City tests and information theory.

The responses of 455 male subjects on both editions of the City University Colour Vision Tests (City 1 and City 2) were recorded after the establishment of each subject's criterial status using the Nagel anomaloscope. Based on the Information Theory, each plate was assigned a contributory weighted score to the total test score. Using informational analysis, a cut-off point in test score separating normals and defectives was also determined for each test. This scoring system is an improvement on the existing (or manufacturer's) system. The analysis has also shown that the second edition (City 2) is a considerable improvement on the first (City 1). Despite this, even the improved City 2, like its origin, the D-15, is shown to be poorer than most of the commonly used PIC tests.

Adolescent↗
PubMed1985

Informational content of visual field location in glaucoma.

Information Theory has been applied to produce estimates of how valuable each stimulus location on the Friedmann Visual Field Analyser mk. II is in detecting early glaucomatous visual field defects. The results indicate that stimuli in the superior arcuate region of the visual field and in the inferior nasal quadrant give the maximum amount of information. Stimuli in the extreme superior field (beyond 20 degrees), the inferior temporal quadrant and around the physiological blind spot give the least amount of information. It is suggested that these results can be used to develop computerised techniques for the analysis of visual field data.

Adult↗
PubMedDate not supplied

Newer visual function tests in the evaluation of glaucoma.

Conventional visual field testing, with a uniform white-on-white stimulus, is used routinely to diagnose and follow patients with chronic open-angle glaucoma. Many investigators, however, believe that conventional perimetry may not detect the earliest visual dysfunction in patients with chronic open-angle glaucoma. Consequently, much research has been performed over the past decade to develop a visual function test which might diagnose chronic open-angle glaucoma earlier than conventional perimetry. This review discusses the mechanisms, clinical studies and the current usefulness of the most common new visual function techniques. These tests attempt to detect early glaucomatous visual loss, generally by placing the visual system under stress and by minimizing the influence of extensive functional redundancy in the retinal ganglion cell network due to widely overlapping receptive fields. Success of new visual function tests depends on the specificity and the sensitivity of the instrument, excellent patient acceptance, short test duration, standardization of techniques, and limited expense. In addition to searching for newer visual function tests to evaluate glaucoma, we should continue efforts to improve the diagnostic capability and shorten the test duration of conventional perimetry.

Electroretinography↗