Insights for mfVEPs from perimetry using large spatial frequency-doubling and near frequency-doubling stimuli in glaucoma.

PURPOSE: To compare two forms of perimetry that use large contrast-modulated grating stimuli in terms of: their relative diagnostic power, their independent diagnostic information about glaucoma and their utility for mfVEPs. We evaluated a contrast-threshold mfVEP in normal controls using the same stimuli as one of the tests. METHODS: We measured psychophysical contrast thresholds in one eye of 16 control subjects and 19 patients aged 67.8 ± 5.65 and 71.9 ± 7.15, respectively, (mean ± SD). Patients ranged in disease severity from suspects to severe glaucoma. We used the 17-region FDT-perimeter C20-threshold program and a custom 9-region test (R9) with similar visual field coverage. The R9 stimuli scaled their spatial frequencies with eccentricity and were modulated at lower temporal frequencies than C20 and thus did not display a clear spatial frequency-doubling (FD) appearance. Based on the overlapping areas of the stimuli, we transformed the C20 results to 9 measures for direct comparison with R9. We also compared mfVEP-based and psychophysical contrast thresholds in 26 younger (26.6 ± 7.3 y, mean ± SD) and 20 older normal control subjects (66.5 ± 7.3 y) control subjects using the R9 stimuli. RESULTS: The best intraclass correlations between R9/C20 thresholds were for the central and outer regions: 0.82 ± 0.05 (mean ± SD, p ≤ 0.0001). The areas under receiver operator characteristic plots for C20 and R9 were as high as 0.99 ± 0.012 (mean ± SE). Canonical correlation analysis (CCA) showed significant correlation (r = 0.638, p = 0.029) with 1 dimension of the C20 and R9 data, suggesting that the lower and higher temporal frequency tests probed the same neural mechanism(s). Low signal quality made the contrast-threshold mfVEPs non-viable. The resulting mfVEP thresholds were limited by noise to artificially high contrasts, which unlike the psychophysical versions, were not correlated with age. CONCLUSION: The lower temporal frequency R9 stimuli had similar diagnostic power to the FDT-C20 stimuli. CCA indicated the both stimuli drove similar neural mechanisms, possibly suggesting no advantage of FD stimuli for mfVEPs. Given that the contrast-threshold mfVEPs were non-viable, we used the present and published results to make recommendations for future mfVEP tests.

Estimates of visual impairment and its causes from the National Eye Survey in Malaysia (NESII).

BACKGROUND: Population-based data on prevalence, causes of blindness and extent of ophthalmological coverage is required for efficient implementation and evaluation of ocular health programs. In view of the scarcity of prevalence data for visual impairment and blindness in Malaysia, this study aims to estimate the prevalence and causes of visual impairment (VI) in the elderly, using Rapid Assessment of Avoidable Blindness (RAAB) survey technique. METHODS: Malaysia was divided into six regions, with each region consisting of 50 clusters. Multistage cluster sampling method was used and each cluster contained 50 residents aged 50 years and above. Eligible subjects were interviewed and pertinent demographic details, barriers to cataract surgery, medical and ocular history was noted. Subjects had visual acuity assessment with tumbling 'E' Snellen optotypes and ocular examination with direct ophthalmoscope. The primary cause of VI was documented. Results were calculated for individual zones and weighted average was used to obtain overall prevalence for the country. Inter-regional and overall prevalence for blindness, severe VI and moderate VI were determined. Causes of VI, cataract surgical coverage and barriers to cataract surgery were assessed. RESULTS: A total of 15,000 subjects were examined with a response rate of 95.3%. The age and gender-adjusted prevalence of blindness, severe visual impairment and moderate visual impairment were 1.2% (95% Confidence Interval: 1.0-1.4%), 1.0% (95%CI: 0.8-1.2%) and 5.9% (5.3-6.5%) respectively. Untreated cataract (58.6%), diabetic retinopathy (10.4%) and glaucoma (6.6%) were the commonest causes of blindness. Overall, 86.3% of the causes of blindness were avoidable. Cataract surgical coverage (CSC) in persons for blindness, severe visual impairment and moderate visual impairment was 90%, 86% and 66% respectively. CONCLUSION: Increased patient education and further expansion of ophthalmological services are required to reduce avoidable blindness even further in Malaysia.

Long-term results of primary trabeculectomies and Molteno implants for primary open-angle glaucoma.

OBJECTIVE: To describe the long-term outcomes of primary trabeculectomies and primary Molteno implants performed in cases of primary open-angle glaucoma at Dunedin Hospital. METHODS: Prospective comparative case series of 718 eyes (500 patients) and 260 eyes (195 patients) that had trabeculectomy and Molteno implants, respectively, at Dunedin Hospital as the first drainage operation for primary open-angle glaucoma between 1976 and 2007, and followed up for a mean of 7.7 (range, 0.0-28.0) and 5.0 (range, 0.0-27.4) years, respectively. RESULTS: The probability of intraocular pressure (IOP) control at 21 mm Hg or less following trabeculectomy at 1, 2, 5, 10, 15, and 20 years was 0.95 (95% confidence interval [CI], 0.94-0.97), 0.93 (95% CI, 0.91-0.96), 0.89 (95% CI, 0.86-0.92), 0.82 (95% CI, 0.78-0.86), 0.74 (95% CI, 0.68-0.80), and 0.68 (95% CI, 0.59-0.77), respectively. There were 96 (13%) failures (using the >21-mm Hg definition of failure) in the trabeculectomy group by the final follow-up. The probability of IOP control at 21 mm Hg or less following Molteno implant insertion at 1, 2, 5, 10, 15, and 20 years was 0.98 (95% CI, 0.97-1.0), 0.97 (95% CI, 0.96-1.0), 0.96 (95% CI, 0.92-0.99), 0.96 (95% CI, 0.92-0.99), 0.91 (95% CI, 0.81-1.00), and 0.91 (95% CI, 0.81-1.00), respectively. In the Molteno implant group, there were 8 (3%) failures (using the >21-mm Hg definition of failure) by the final follow-up. CONCLUSION: Insertion of a Molteno implant provided superior IOP control to trabeculectomy when carried out as a first operation in cases of primary glaucoma.