Retinal nerve fibre layer characteristics with vigabatrin-associated visual field loss--could scanning laser polarimetry aid diagnosis?

PURPOSE: To describe the retinal nerve fibre layer (RNFL) characteristics in patients suffering vigabatrin-associated visual field loss or behaviour consistent with field loss. METHODS: Eight patients with visual field loss attributed to vigabatrin use had their RNFL evaluated by scanning laser polarimetry. RESULTS: All eight patients managed to perform the test reliably. The mean length of vigabatrin treatment was 81 months with a mean cumulative dose of vigabatrin being 5.4 kg. All patients had significantly reduced RNFL parameters; mean TSNIT=36.5 microm, mean nerve fibre indicator=63.1, mean superior average=42.7 microm, and mean inferior average=39.2 microm. There was no correlation between cumulative dose or time on treatment and RNFL thickness. CONCLUSION: Scanning laser polarimetry can be performed safely and reliably on patients with vigabatrin-associated field loss. RNFL thickness is reduced in these patients with vigabatrin-associated field loss. RNFL loss concentrates on the long nerve fibres, which explains the nasal pattern of field loss seen in these patients. This investigation shows promise in the screening of vigabatrin patients, especially in those patients that may not tolerate formal field testing well.

Effectiveness of optometrist screening for diabetic retinopathy using slit-lamp biomicroscopy.

PURPOSE: To assess the effectiveness of optometrists as screeners for diabetic retinopathy using slit-lamp binocular indirect ophthalmoscopy through dilated pupils. METHODS: Prospective study of a screening scheme. Screening was performed by 27 locally accredited optometrists in their practice. The referral protocol used a new simple grading system of retinopathy, especially designed for use in an optometrist screening programme. All positive referrals and 10% of negative referrals were reexamined by an ophthalmologist. Sensitivity, specificity, likelihood ratios and technical failure rates were calculated. RESULTS: The optometrists screened 4904 people with diabetes in 18 months. 'Subthreshold' (screen negative) reports accounted for 4438 (90.5% of 4904); 429 (9.67%) of these were re-examined at secondary screening. There was disagreement regarding grading in 13 patients, of whom 5 (1.16% of 429) had sight-threatening retinopathy (STDR); this extrapolates to 52 patients if all the 4438 test-negatives had been examined. Of the 371 'threshold' patients, 112 (30.18%) were false positives; the commonest cause for false positive referral was drusen in patients with background diabetic retinopathy. The sensitivity for identification of STDR was 76% (95% CI 70% to 81%) and specificity 95% (95% CI 95% to 96%). The likelihood ratio of a positive test indicating STDR was 16.54 (95% CI 14.17 to 19.23) and that of a negative test 0.25 (95% CI 0.20 to 0.32). The technical failure rate was 0.2%. CONCLUSIONS: Suitably trained and accredited community optometrists performed well when screening for diabetic retinopathy using slit-lamp biomicroscopy through a dilated pupil. This was facilitated by the use of simple grading and referral criteria. The sensitivity, positive likelihood ratio and specificity were high.

Prevalence of blindness and visual impairment in a population of people with diabetes.

PURPOSE: To assess the prevalence of visual impairment and the underlying causes in a population of people with diabetes. METHOD: A population-based study of a defined population of people with diabetes in a district in the North West of England was done. There were 7652 known people with diabetes, representing 2.12% of target general population of 361050. The main outcome measures were the prevalence of blindness and significant visual impairment (less than 6/18 corrected vision in their better eye) and the underlying causes. RESULTS: Visual acuity data on 6482 (84.7%) of the 7652 individuals were obtained. Of these, 184 had significant visual impairment (prevalence 2.84%) including 49 who were blind (vision of less than 3/60 in their better eye, prevalence 0.75%); if blindness was defined as vision less than or equal to 6/60, prevalence was 1.13% (n = 73). Details of 3 individuals could not be ascertained. Only 67 were registered, either as partially sighted (n = 42) or as blind (n = 25). In the majority (n = 133; 68%) of these 181 individuals the visual impairment was due to causes other than diabetic retinopathy. CONCLUSIONS: The prevalence of blindness and visual impairment in our population of people with diabetes was low. Non-diabetic eye disease accounted for the majority of this visual impairment. This provides essential baseline data against which future progress can be assessed. Screening and treatment can greatly reduce the incidence of visual impairment due to diabetic retinopathy, but its impact on overall visual impairment rates in the population of people with diabetes will be more modest.

Rapid onset of ptosis indicates accurate intraconal placement during retrobulbar anaesthetic injection.

BACKGROUND: Anecdotal evidence has previously suggested that retrobulbar local anaesthetic (LA) injection is accompanied by the rapid onset of ptosis. Here the validity of this potentially valuable sign is tested. METHODS: 25 patients received a retrobulbar injection and the times for development of ptosis and akinesia in other extraocular muscle groups were recorded and compared. The effects of retrobulbar injections were also studied on posterior orbital structures in 10 patients using low frequency ultrasound. RESULTS: The mean time of onset of ptosis was 4.76 seconds, an order of magnitude less than times recorded for akinesia in other muscle groups. Ultrasonography revealed a significant distension of the extraocular muscle cone during retrobulbar injection. CONCLUSION: Ptosis develops significantly more rapidly than other motor effects in retrobulbar anaesthesia and can therefore be taken as an indicator of accurate intraconal placement. Retrobulbar injection is associated with significant distension of the extraocular muscle cone.

Digital fundus imaging: a quality and cost comparison with 35-mm film.

PURPOSE: This study compares 35-mm transparencies with colour digital fundus images. METHODS: Colour fundus photos were acquired simultaneously on a digital system and on 35-mm film on 32 consecutive patients. These were assessed independently by two ophthalmologists who graded overall picture quality and granularity of the images. They also assessed if the images were adequate for the purpose of making a diagnosis. An analysis of the costs of the two systems was performed. RESULTS: The film images had significantly better scores for overall picture quality (p=0.0001, 95% CI 0.5 to 1.5) and granularity (p<0.0001, 95% CI 1.5 to 2). However, both digital and film images were considered adequate for diagnosis (p=0.052, 95% CI 0.12 to 8.32). CONCLUSION: The quality of digital images is acceptable for diagnostic purposes although resolution is limited. Other advantages and developing technologies will make it increasingly attractive in the future.

Pulsatile ocular blood flow measurements in healthy eyes: reproducibility and reference values.

PURPOSE: To determine the reproducibility and the normal reference range of pulsatile ocular blood flow (POBF) values in healthy subjects using the Ocular Blood Flow Tonograph (OBF Laboratories, UK Ltd., Wiltshire, England). METHOD: Pulsatile ocular blood flow was measured in one eye of each of 83 patients. Coefficient of reliability was determined by calculation of intraclass correlation coefficient via one-way analysis of variance. Mean difference between measurements was calculated for bias and first exposure effects. Pulsatile ocular blood flow from 163 healthy individuals were analyzed to determine the distribution, mean, standard deviation (SD), range, and the 5th and 95th percentile values. The influence of age, blood pressure, pulse rate, and intraocular pressure on pulsatile ocular blood flow was determined by regression analysis. RESULTS: Reliability coefficient for pulsatile ocular blood flow values ranging from 290 microliters/min to 2,196 microliters/min was 0.92. Variation in bias and first exposure effect were not significant. Pulsatile ocular blood flow values were normally distributed. Mean values were 669.90 +/- 233.0 microliters/min in men and 841.90 +/- 254.6 microliters/min in women. Fifth and ninety-fifth percentile values were 364.75 microliters/min and 1,266.10 microliters/min in men and 397.18 microliters/min and 1,346.10 microliters/min in women. Pulsatile ocular blood flow was significantly influenced by pulse rate. CONCLUSION: This study confirms the reliability of the Ocular Blood Flow Tonograph in repeated measurements of POBF within individuals over short time intervals. The high interindividual variation in POBF may invalidate comparison of POBF between individuals, and the wide range of normal values may limit the value of using a low POBF as a possible indicator of disease.

Surgically induced diffuse scleritis following cataract surgery.

We report 21 cases, representing 3.1% of a total of 682 cataract patients, of surgically induced diffuse scleritis (SIDS) following planned extracapsular cataract extraction with intraocular lens insertion. The mean age was significantly lower in the patients with SIDS (mean 62.5 years; SD 13.68) when compared with the non-scleritic group (mean 73.6 years; SD 10.2; Mann-Whitney U-test, p = 0.0003). There was an association of SIDS with general anaesthetic (chi-squared test, p = 0.0008). Twenty of 21 patients responded to oral non-steroidal anti-inflammatory agents with good visual result.