Search PubMed⌕ Search

Biomedical subjects

S A Vernon

Publications and source records attributed to S A Vernon.

At least 37 records · Page 2Linked to original sources
PubMed2003

Assessing the 'cyclodiode G-probe' using a grey scale test: reproducibility and differences between probes.

AIMS: 1. To determine the number of clinicians performing cyclodiode therapy who reuse the 'G-probe' used for the delivery of cyclodiode therapy. 2. To show a simple method to assess the output of the 'G-probe' that can be used in the clinical setting. METHODS: A total of 71 questionnaires were sent to ophthalmologists who have an Oculight SLx Iris Medical Diode Laser. Ophthalmologists were asked as to whether they performed cycloablative therapy using the 'G-probe' and whether they reused the G-probe. They were also asked as to the frequency of any reuse of probes. To determine the output of the 'G-probe', paper copies of a custom-made grey scale chart containing graded blocks of increasing shades of grey densities were produced. A special probe holder was made so that the G-probe tip could be held at a fixed distance from the grey scale chart. Laser burns were made on the grey scale using this arrangement and measurements of the burn size were made. After using 'standard settings' of 2000 ms and 2000 mW, 'threshold' burns were defined. Five new probes (with two different operators) were tested to assess the interprobe, interoperator, and intersheet variability of test. Probes were then tested for the burn size produced between 1000 and 3000 mW, and 1000 and 3000 ms. RESULTS: Results from the questionnaire showed that of the 44 respondents (62.0% response), 93.2% performed cyclodiode therapy with 58.5% reusing the G-probe. Among them, 56.1% reused probes on more than one occasion. Results from testing a new G-probe on the grey scale chart showed that with 'standard settings', highly reproducible burns at grey density 8 could be produced. No significant interprobe, interoperator, and intersheet variations were noted. Above 3 J of laser energy, the test could detect a 20% increase in energy settings and it was found that at levels of 4 J or above, alterations to the power setting had a greater influence on burn production than alterations to the time setting. CONCLUSIONS: This study demonstrates 1. that many clinicians in the UK reuse G-probes, 2. a simple, quick, and highly reproducible method to assess the laser output from the G-probe used for cyclodiode therapy. The method can help the ophthalmic surgeon to test the G-probe prior to commencement of therapy and with a standard treatment protocol, may produce a more predictable intraocular pressure reduction.

Ciliary Body↗
PubMed2001

Non-enhanced trabeculectomy by non-glaucoma specialists: are results related to risk factors for failure?

PURPOSE: To determine the 1 year success rate of non-enhanced trabeculectomy under the care of non-glaucoma specialists and the effects of risk factors on the surgical outcome as measured by intraocular pressure (IOP) control. METHODS: A retrospective study of 167 patients undergoing trabeculectomy was performed. One hundred and four cases were performed in a teaching hospital and 63 in a district general hospital (DGH). Non-glaucoma specialists performed all the operations, enhanced trabeculectomy with antimetabolites being excluded. Information was recorded from a retrospective review of case notes, and post-operative IOPs at 12 months follow-up were analysed. Risk factors for failure were defined as: (1) age less than 40 years old, (2) black race, (3) diabetes mellitus, (4) miotic therapy > or = 18 months, (5) sympathomimetic therapy > or = 6 months, (6) pseudophakia or aphakia, (7) previous failed filtration procedure, (8) argon laser trabeculoplasty, (9) previous ocular surgery and (10) high-risk glaucoma (angle recession glaucoma, uveitic glaucoma and neovascular glaucoma). A success was defined to be a post-operative IOP at 1 year of less than 21 mmHg and at least 20% less than the presenting IOP on no medication. RESULTS: The overall success rate was 139 of 167 (83.2%). Eighty-seven of 104 eyes (83.7%) were classified as a success in the teaching hospital group and 52 of 63 (82.5%) were classified as a success in the DGH group. There was no significant difference in the number of risk factors between the success and failure groups. Eyes with two or more risk factors had significantly higher IOPs at 1 year when compared with eyes with 0 or 1 risk factor (mean +/- SD: 17.4 +/- 6.34 mmHg vs 14.2 +/- 5.0 mmHg, p = 0.022). When only 'successful eyes' were analysed, those with two or more risk factors still had significantly higher IOPs at 1 year (mean +/- SD: 15.0 +/- 3.0 mmHg vs 12.8 +/- 3.9 mmHg, p = 0.046). There were significantly fewer eyes in the two or more risk factor group with IOPs < 16 mmHg at 1 year (26.1% vs 60.4%, p = 0.021). CONCLUSIONS: Eyes at relatively low risk for failure operated upon by non-glaucoma specialists appeared to have success rates similar to previously published series. Eyes with two or more risk factors for failure have higher IOPs at 1 year in non-enchanced trabeculectomy. Adjunctive anti-scarring agents may be considered for these patients when filtration surgery is scheduled.

Aged↗
PubMed2001

Do locally agreed guidelines for optometrists concerning the referral of glaucoma suspects influence referral practice?

PURPOSE: To assess whether the issuing of local guidelines for glaucoma detection including a protocol for the referral of suspects can improve the quality and accuracy of referrals from optometrists. METHODS: Universally agreed guidelines, which included a protocol for referring glaucoma suspects, were circulated to all optometrists in the catchment area of a major teaching hospital ophthalmic unit. Data on 207 new patients referred to one glaucoma clinic were collected from GOS18 forms and hospital records covering two 12 month periods spanning the guideline dissemination. Referral accuracy was calculated and the reasons for protocol violations and referral of normal individuals were determined. Where possible, data were compared with a similar study relating to referrals made to the same clinic in 1988 and 1993. RESULTS: The mean (SD) intraocular pressure (IOP) at which optometrists referred patients was 22.5 (6.6) in 1997 and 21.9 mmHg (6.6) in 1998/9, both significantly less than in 1988. A statistically significant upward trend with time was found in the number of patients referred with an assessment of cup/disc ratio and in those with details of a visual field assessment. The overall 'true positive diagnosis' was 40% (42/105) in 1997 and 32.3% (33/102) in 1998/9 after the guidelines (p = 0.32), both of which were significantly lower than the 1988 rate of 56% (34/75) (p = 0.03 and 0.003). Fifty per cent of false positive referrals in both 1997 and 1998/9 were associated with an assessment by the optometrist of the optic disc(s) that was at variance with the ophthalmologist's. False positive visual fields were associated with 22% and 35% of non-true positive referrals in 1997 and 1998/9. Protocol violations were observed in 48% of referrals after the guidelines had been disseminated. When the referral was both a false positive and the guideline protocol was not followed, 88% of violations were associated with IOP measurement in 1997 and 73% in 1998/9. The equivalent figures for visual field violations were 70% in 1997 and 76% in 1998/9. Normal individuals referred as suspects were significantly (p = 0.001) less likely to be referred on IOP grounds if their optometrist followed the referral protocol. CONCLUSION: Local dissemination of glaucoma screening guidelines with a protocol for referral did not appear to improve the diagnostic accuracy of optometrists in our area. Optometrists who follow the guidelines refer fewer normal individuals on IOP grounds, but false positive visual fields and optic disc interpretation difficulties remain a factor in such referrals. Additional strategies will be necessary to improve the quality and accuracy of referrals for suspect glaucoma by optometrists.

Aged↗
PubMed2001

Does macular laser alter the refraction in a diabetic with maculopathy? A pilot study.

PURPOSE: To determine whether macular photocoagulation has any effect on refraction in diabetics. METHODS: This was a prospective study of 12 eyes of 12 diabetics with refraction at 2 weeks before and at 4 weeks and 4 months after argon laser. This was combined with a questionnaire survey of attitude among ophthalmologists on prescribing spectacles for diabetics awaiting macular laser. The main outcome measure was the spherical equivalents (SEQ) before and after treatment. RESULTS: Only 36% of ophthalmologists surveyed would prescribe corrective lenses in patients waiting for macular photocoagulation. The median change in magnitude of SEQ at 4-6 weeks post-laser compared to pre-laser was 0.36 D (interquartile range 0.18-0.50 D). The median change in SEQ at 4 months was 0.25 D (interquartile range 0.12-0.56 D). These changes in SEQ from pretreatment values were not statistically significant on Wilcoxon signed-rank test (p = 0.17 and 0.10, respectively). The correlation coefficient between difference and average SEQ was 0.02 (95% CI -0.14 to 0.19, p = 0.75) at 4 weeks and 0.11 (95% CI -0.06 to 0.275, p = 0.17) at 4 months, indicating no tendency for change in refraction with increasing ametropia. CONCLUSION: This pilot study implies that argon laser photocoagulation in diabetic maculopathy does not alter refraction. Prescription of corrective lenses can be performed prior to laser therapy, if required.

Aged↗
PubMed2001

Association of macular involvement with proliferative retinopathy in Type 2 diabetes.

AIMS: To determine whether documented evidence of pre-existing maculopathy is present in Type 2 diabetic patients who require photocoagulation or vitrectomy for proliferative disease. This is a retrospective case notes review. METHODS: The study was performed at Queen's Medical Centre, UK. All patients listed in the laser register and operating theatre register over 5 years (March 1994 to March 1999) who had undergone pan retinal photocoagulation (PRP) for diabetic retinopathy, in one consultant firm, were studied. The medical records of patients who had undergone vitrectomy as their first treatment for proliferative diabetic retinopathy in a vitreo-retinal firm over the 5 years were examined. The proportion of patients with documented maculopathy before development of proliferative retinopathy was determined. RESULTS: All except 1/134 or 0.7% (95% confidence interval 0.1-4.5%) patients had documentation of macular signs in at least one eye prior to the patient's first session of PRP. Of the remaining 133, 104 (78%) had had focal or grid photocoagulation of the macula. The median time between the documentation of maculopathy before the first PRP treatment session was 16 months (interquartile range 7-36). Fourteen patients had vitrectomy and endolaser performed as the initial treatment for proliferative disease. All patients had documented maculopathy before the onset of proliferative disease. CONCLUSIONS: The results of this study suggest that in Type 2 diabetes, proliferative disease occurs relatively late compared with maculopathy. In such patients, maculopathy is almost invariably present when proliferative disease is detected.

Age of Onset↗
PubMed2001

Sensitivity and specificity of a new scoring system for diabetic macular oedema detection using a confocal laser imaging system.

AIM: To assess the use of the Heidelberg retina tomograph (HRT) in screening for sight threatening diabetic macular oedema in a hospital diabetic clinic, using a new subjective analysis system (SCORE). METHODS: 200 eyes of 100 consecutive diabetic patients attending a diabetologist's clinic were studied, all eyes had an acuity of 6/9 or better. All patients underwent clinical examination by an ophthalmologist. Using the HRT, one good scan was obtained for each eye centred on the fovea. A System for Classification and Ordering of Retinal Edema (SCORE) was developed using subjective assessment of the colour map and the reflectivity image. The interobserver agreement of using this method to detect macular oedema was assessed by two observers (ophthalmic trainees) who were familiarized with SCORE by studying standard pictures of eyes not in the study. All scans were graded from 0-6 and test positive cases were defined as having a SCORE value of 0-2. The sensitivity of SCORE was assessed by pooling the data with an additional 88 scans of 88 eyes in order to reduce the confidence interval of the index. RESULTS: 12 eyes in eight out of the 100 patients had macular oedema clinically. Three scans in three patients could not be analysed because of poor scan quality. In the additional group of scans 76 out of 88 eyes had macular oedema clinically. The scoring system had a specificity of 99% (95% CI 96-100) and sensitivity of 67% (95% CI 57-76). The predictive value of a negative test was 87% (95% CI 82-99), and that of a positive test was 95% (95% CI 86-99). The mean difference of the SCORE value between two observers was -0.2 (95% CI -0.5 to +0.07). CONCLUSIONS: These data suggest that SCORE is potentially useful for detecting diabetic macular oedema in hospital diabetic patients.

Adult↗
PubMed2000

Passing the DVLA field regulations following bilateral macular photocoagulation in diabetics.

PURPOSE: At present the Driver and Vehicle and Licensing Agency (DVLA) of the UK requires all diabetic patients with laser treatment in both eyes to undergo a binocular driving field assessment. Increasingly we find that many such patients have undergone only macular laser treatment without panretinal photocoagulation. We aimed to ascertain the frequency and causes of failure of the binocular driving field test after bilateral macular laser treatment performed according to a set protocol. METHODS: A retrospective case notes study was combined with a prospective recall of patients for visual field assessment. All diabetic patients under the care of one consultant who had had bilateral macular laser treatment (without panretinal photocoagulation) over a 4 year period were identified and the case notes studied. Patients who could not achieve a corrected binocular acuity of 6/9 were excluded, as were patients with glaucoma. Patients who had not had the DVLA test were recalled to perform the test, whether or not they had an intention to drive. Failure was defined utilising strict criteria on the Esterman Programme of the Humphrey Analyser. RESULTS: A total of 138 patients were identified. Fifty-four were not eligible (21 because of poor acuity, 29 had died or were too ill to participate and 4 for other reasons). Of the 84 who were eligible, 64 had visual fields performed and 20 declined to attend. Sixty-three of 64 tested passed the Esterman test, the one failure having a previously unknown and relatively mild homonymous field defect. CONCLUSION: Patients undergoing bilateral macular laser can be counselled that, provided their acuity remains adequate, they have a very low chance of failing the DVLA field regulations.

Adult↗
PubMed2000

Improvement of reproducibility of macular volume measurements using the Heidelberg retinal tomograph.

AIMS: To develop a more reproducible method of macular volumetric analysis in order to facilitate serial monitoring of changes in retinal oedema with time. METHODS: The Heidelberg retinal tomography (HRT) machine was used to scan the macula of 20 normal subjects and 40 diabetics with macular oedema. The volume above reference plane (VARP) within a 2 mm diameter and 3 mm diameter circle was measured twice in each eye. The position of the circle to be measured was carefully defined relative to major retinal vessels. As a modification to the previously published technique, fluctuation of the height of the contour line relative to the focal plane of the eye is compensated for by an adjustment of the reference plane. The position of the circle was controlled relative to major retinal vessels using an acetate. The reproducibility of VARP measurement was assessed by three variables-the standard error of the difference on two isolated VARP measurements, the standard error of the difference between the average of three readings on two different occasions, as well as the coefficient of variation (COV). RESULTS: Both the 2 mm and 3 mm circles showed good reproducibility in VARP measurements. In normal subjects, the COV of VARP for 2 mm circles and 3 mm circles were 13% and 12% respectively. In patients with macular oedema, the COV of VARP for 2 mm circles and 3 mm circles were 9% and 11% respectively. CONCLUSION: The modification of VARP measurements between scans of the same eye has improved the COV from 31% to 9% in eyes with diabetic macular oedema.

Diabetic Retinopathy↗
PubMed1999

Reproducibility of volumetric macular measurements in diabetic patients with the Heidelberg Retina Tomograph.

AIMS: To quantify diabetic macular edema by confocal scanning laser ophthalmoscopy and assess its usefulness by determining the reproducibility of topographic measurements at the macula. METHODS: The volumes above reference plane bound by a 2 mm diameter circle centred on the fovea were measured by two observers. The reference plane was adjusted to the lowest point of the height variation of the contour line. The reproducibility of this technique was assessed in 20 eyes of 20 diabetic patients of which 8 eyes had macular edema. Three HRT scans of each eye were obtained. The measurements of volume above reference plane of each scan were repeated three times. RESULTS: For all diabetic eyes, the intra scan coefficients of variability measured 14.71% to 21.21%, the inter scan coefficient of variability was 30.46%. The average standard deviations were 0.053 mm3 for one examination per scan, 0.047 mm3 for two examinations per scan and 0.044 mm3 for three examinations per scan. Linear regression demonstrated an increase in standard deviation with greater volumetric measurements (p < 0.001). We found good correlation (r = 0.959, p < 0.001) and strong agreement between the two observer's findings for all 20 eyes. For the 8 eyes with macular edema, the coefficients of variability were similar to those calculated for all 20 eyes. The average SD for one examination per scan were 0.078 mm3, 0.069 mm3 for two examinations per scan and 0.062 mm3 for three examinations per scan. We found good correlation (r = 0.945, p < 0.001) and strong agreement between the two observer's findings in eyes with edema. CONCLUSION: The reproducibility of this technique has been demonstrated in diabetic eyes. This may have useful clinical applications for the quantification of diabetic macular edema and monitoring of laser therapy.

Adult↗
PubMed1999

Assessment of the Heidelberg Retina Tomograph in the detection of sight-threatening diabetic maculopathy.

PURPOSE: To assess the potential role of the Heidelberg Retina Tomograph (HRT) in screening for sight-threatening macular oedema in diabetes. METHODS: One hundred and thirty-one eyes of 81 consecutive diabetic patients who fitted the inclusion criteria were included in the study. On HRT, the volume above the reference plane bound within a 2 mm diameter circle centred at the fovea was measured. The volumetric indices were compared with the mean measurement index in a group of 20 age-matched controls (mean score = 1, mean +2 SD score = 1.8). We also assessed the sensitivity of the subjective analysis of the intensity image and the addition of the three-dimensional map to the intensity image for detecting macular oedema and clinically significant macular oedema (CSMO). RESULTS: One hundred and twelve eyes of 71 patients had a corrected Snellen visual acuity of 6/9 or better. When considering eyes with 6/9 or better vision only, the system's sensitivity for detecting CSMO was 58.33% 'per eye' examined, and 81.82% 'per patient' examined using a cut-off volumetric index of 1.8. In our study eyes with 6/9 or better vision, we found a 21% prevalence of CSMO. The predictive values of a positive test were 38.89% and 45% (cut-off score 1.8, 'per eye' and 'per patient' respectively) for CSMO. The predictive values of a negative test were 86.84% and 90.48% (cut-off score 1.8, 'per eye' and 'per patient' respectively) for CSMO. CONCLUSIONS: The volumetric assessment of diabetic maculopathy by HRT is a potentially useful method for screening eyes at risk. A larger group of patients with a greater number of eyes with minimal or no maculopathy is required to establish the specificity of this technique.

Adult↗
PubMed1999

"Cyclodiode": results of a standard protocol.

AIMS: To analyse the results of intraocular pressure (IOP) reduction in refractory glaucoma following diode laser cyclophotocoagulation with a repeatable standard protocol. METHODS: 58 eyes of 53 patients were followed for 6-37 months (mean 19 months) after initial cyclodiode treatment. RESULTS: Mean (SD) pretreatment IOP for the 58 eyes was 33.0 mm Hg (10.7) reducing at final index visit to 16.7 mm Hg (7.8) (p < 0.0001). The mean antiglaucoma medication score per eye was significantly reduced from 2.4 (0.8) to 1.4 (1.0) at last index visit (p < 0.0001) with 91% of patients able to stop oral acetazolamide. 45% of eyes required more than one treatment and the overall mean per eye was 1.6 (range 1-5). Of eyes with visual acuity 6/60 or better pretreatment, 12 (32%) lost more than two lines of Snellen acuity and two eyes with poorer acuity initially dropped to NPL. Poor visual outcome was associated with the presence of diabetic retinopathy. Hypotony (IOP < 5 mm Hg) was noted in two eyes at the last index visit although neither had specific signs of the same. No phthisis was seen. CONCLUSION: The simple treatment protocol, repeated if necessary, appears relatively safe and effective at lowering IOP in eyes with refractory glaucoma.

Adolescent↗
PubMed1999

Topographic and keratometric astigmatism up to 1 year following small flap trabeculectomy (microtrabeculectomy).

AIM: To determine the induced corneal astigmatism by measuring the changes in manual keratometry and computerised corneal videokeratoscopy up to 1 year following small flap trabeculectomy (microtrabeculectomy). METHOD: A prospective study of a case series of small flap trabeculectomy procedures performed at the 90 degree meridian on 16 eyes of 16 patients, all followed to 1 year postoperatively. Changes in manual keratometry and computerised videokeratoscopy (Eyesys) readings were analysed by vector analysis and vector decomposition techniques. RESULTS: By vector analysis, the mean surgically induced refractive change (SIRC) cylinder power vectors induced at 1, 3, 6, and 12 months as measured by manual keratometry were 0.68, 0.38, 0.52, and 0.55 dioptres, and by keratography 0.75, 0.66, 0.59, and 0.64 dioptres. Vector decomposition on the induced vector cylinders on manual keratometry resulted in a "with the rule" mean vector of 0.52 and 0.22 dioptres at 1 and 3 months and an "against the rule" mean vector of 0.16 and 0.16 dioptres at the same time points (p=0.03 and 0.28 respectively). Vector decomposition at 6 and 12 months revealed no significant with the rule changes induced. Similar analysis on the videokeratoscopy results revealed significant induced with the rule astigmatism until 3 months, but not at 6 and 12 months postoperatively. CONCLUSION: Small flap trabeculectomy (microtrabeculectomy) produces smaller changes in corneal curvature that resolve sooner than previous reports of larger flap techniques.

Aged↗