Ghee Soon Ang

Corneal biomechanical properties in primary open angle glaucoma and normal tension glaucoma

PurposeTo determine and compare the corneal biomechanical properties between eyes with primary open angle glaucoma (POAG) and eyes with normal tension glaucoma (NTG). Patients and MethodsProspective cross-sectional study. Consecutive eligible POAG and NTG patients attending the Glaucoma Clinic had assessment of their corneal biomechanical properties—corneal hysteresis (CH) and corneal resistance factor (CRF)—using the Ocular Response Analyzer by an observer masked to the diagnosis. Exclusion criteria included previous intraocular surgery, corneal pathology, inflammatory connective tissue disease, and refraction of 5-dimensional or over. If both eyes were eligible, then the right eye was used for analysis. The main outcome measures were corneal hysteresis and CRF measurements. Data analysis was performed using the t test and general linear model. ResultsEighty-one patients (80 whites) were analyzed. Forty had NTG, whereas 41 had POAG. Thirty-five were females. There was a statistically significant difference in mean CH (NTG 9.6±1.3 mm Hg; POAG 9.0±1.4 mm Hg; P=0.01), but not in mean CRF (NTG 9.9±1.4; POAG 10.8±1.7; P=0.06). The highest recorded Goldmann applanation intraocular pressure (IOP) was statistically significantly associated with lower CH (P=0.01) and higher CRF (P=0.02). ConclusionsThere was a small but statistically significant difference in the mean CH between POAG and NTG (CH was higher in NTG). The highest recorded Goldmann applanation IOP was also statistically significantly correlated with lower CH and higher CRF, suggesting that alterations to the corneal biomechanical properties may occur as a result of chronic raised IOP in POAG.

A systematic literature review of surgical interventions for limbal stem cell deficiency in humans.

PURPOSE To evaluate the relative benefits and to identify any adverse effects of surgical interventions for limbal stem cell deficiency (LSCD). DESIGN Systematic literature review. METHODS We searched the following electronic databases from January 1, 1989 through September 30, 2006: MEDLINE, EMBASE, Science citation index, BIOSIS, and the Cochrane Library. In addition, reference lists were scanned to identify any additional reports. The quality of published reports was assessed using standard methods. The main outcome measure was improvement in vision of at least two Snellen lines of best-corrected visual acuity (BCVA). Data on adverse outcomes also were collected. RESULTS Twenty-six studies met the inclusion criteria. There were no randomized controlled studies. All 26 studies were either prospective or retrospective case series. For bilateral severe LSCD, keratolimbal allograft was the most common intervention with systemic immunosuppression. Other interventions included eccentric penetrating keratolimbal allografts and cultivated autologous oral mucosal epithelial grafts. An improvement in BCVA of two lines or more was reported in 31% to 67% of eyes. For unilateral severe LSCD, the most common surgical intervention was contralateral conjunctival limbal autograft, with 35% to 88% of eyes gaining an improvement in BCVA of two lines or more. The only study evaluating partial LSCD showed an improvement in BCVA of two lines or more in 39% of eyes. CONCLUSIONS Studies to date have not provided strong evidence to guide clinical practice on which surgery is most beneficial to treat various types of LSCD. Standardized data collection in a multicenter LSCD register is suggested.

Lower corneal hysteresis in glaucoma patients with acquired pit of the optic nerve (APON)

ObjectiveAcquired pit-like changes of the optic nerve head (APON) are characteristic of glaucomatous damage and may be a sign of a localized susceptibility of the optic nerve. Thus, it is possible that biomechanical properties of the ocular tissues may play a pressure-independent role in the pathogenesis of glaucoma. Corneal hysteresis (CH) appears to provide information of the biomechanical properties of the ocular hull tissues. The purpose of this study was to compare CH of patients with primary open angle glaucoma (POAG) with and without APON.MethodsA prospective case control study was done. POAG patients with and without APON were measured using the Ocular Response Analyzer by masked investigators. Patients in both groups were matched for sex, age, corneal thickness, and type of glaucoma according to maximal IOP (NTG or POAG). Statistical analysis was done using ANOVA.ResultsCorneal hysteresis of 16 glaucomatous eyes with APON and 32 controls (glaucoma without APON) was measured. The mean (±SD) CH in the APON group was 8.89 (±1.53) and 10.2 (±1.05) in the control group. The difference is statistically significant (p = 0.005).ConclusionsCorneal hysteresis in POAG patients with APON was significantly lower than in patients that did not have such structural changes of the optic disc. These findings may reflect pressure-independent mechanisms involved in the pathogenesis of such glaucomatous optic nerve changes.

The influence of the new general ophthalmic services (GOS) contract in optometrist referrals for glaucoma in Scotland

PurposeTo assess the quality of referrals from community optometrists in the northeast of Scotland to the hospital glaucoma service before and after the implementation of the new General Ophthalmic Services (GOS) contract in Scotland.MethodsRetrospective study encompassing two 6-month periods, one before the implementation of the new GOS (Scotland) contract in April 2006 (from June to November 2005), and the other after (from June to November 2006). The community optometrist referral forms and hospital glaucoma service notes were reviewed. Comparisons were performed using the t-test and χ 2-test.ResultsIn all, 183 referrals were made during the first 6-month period from June to November 2005, and 120 referrals were made during the second 6-month period from June to November 2006. After the introduction of the new GOS contract, there was a statistically significant increase in true-positive referrals (from 18.0 to 31.7%; P=0.006), decrease in false-positive referrals (from 36.6 to 31.7%; P=0.006), and increase in the number of referrals with information on applanation tonometry (from 11.8 to 50.0%; P=0.000), dilated fundal examination (from 2.2 to 24.2%; P=0.000), and repeat visual fields (from 14.8 to 28.3%; P=0.004) when compared to the first 6-month period. However, only 41.7% of referrals fulfilled the new GOS contract requirements, with information on applanation tonometry the most commonly missing.ConclusionsAfter the implementation of the new GOS (Scotland) contract in April 2006, there has been an improvement in the quality of the glaucoma referrals from the community optometrists in the northeast of Scotland, with a corresponding reduction in false-positive referrals. Despite the relatively positive effect so far, there is still scope for further improvement.

Postoperative infection in penetrating versus non-penetrating glaucoma surgery

The aim of glaucoma surgery is to lower the intraocular pressure in order to reduce the risk of further glaucomatous progression, particularly in cases refractory to topical therapy. Although effective in reducing intraocular pressure, these procedures are not without complications, with endophthalmitis being one of the most serious. A PubMed review of the literature was performed for trabeculectomy, glaucoma drainage device procedures (Ahmed, Baerveldt and Molteno implants) and non-penetrating glaucoma surgery (deep sclerectomy and viscocanalostomy) for reports of postoperative infection, including blebitis and endophthalmitis. The literature on infections relating to non-penetrating glaucoma surgery is sparse compared with penetrating surgery, but this may be a reflection of the relatively shorter follow-up duration and comparatively smaller body of data available on non-penetrating procedures. Overall, there is not enough evidence, in terms of well-constructed randomised clinical trials with sufficiently large sample sizes and long follow-up durations, to be able to make informed comparisons of the risk of postoperative endophthalmitis and infection between the various glaucoma operations. This review article summarises the incidences of endophthalmitis from the literature and discusses the major risk factors for postoperative infection.

Changes in Caucasian eyes after laser peripheral iridotomy: an anterior segment optical coherence tomography study: Laser peripheral iridotomy in Caucasians

Background:  To evaluate by anterior segment optical coherence tomography (AS‐OCT) the changes in the anterior chamber structures in Caucasian eyes after laser peripheral iridotomy (PI).

Epidemiology of Giant Retinal Tears in the United Kingdom: The British Giant Retinal Tear Epidemiology Eye Study (BGEES)

PURPOSE To determine the incidence of giant retinal tear (GRT) in the United Kingdom and to provide epidemiologic data, clinical characteristics, treatment methods, and short-term outcomes in affected and fellow eyes. METHODS Patients with a newly developed GRT (90 degrees or greater in circumferential extent associated with posterior vitreous detachment) were identified prospectively over a 13-month period (January 2007-January 2008, inclusive) by active surveillance through the British Ophthalmic Surveillance Unit. Questionnaire-based data were obtained from reporting ophthalmologists at baseline and 12 months. RESULTS Sixty patients (62 eyes) developed a new GRT, giving a U.K. annual incidence of 0.094 (95% CI 0.072-0.120) cases or 0.091 (95% CI 0.069-0.117) patients per 100,000. The GRTs were mostly idiopathic (54.8%), affected middle-aged (mean, 42.2 years), white British (93.3%) males (71.7%), with presenting vision worse than 20/40 in 59.7%, foveal detachment in 45.2%, and proliferative vitreoretinopathy of grade C (PVR-C) or worse in 11.3%. Treatment in most was managed by pars plana vitrectomy (93.5%) with laser retinopexy (52.5%) and silicone oil endotamponade (75.8%). Prophylactic 360 degrees laser or cryotherapy was applied to 39.0% of the fellow eyes. At mean follow-up of 11.3 months, eventual retinal reattachment was attained in 94.7%, although only 42.1% achieved vision of >or=20/40. Neither GRT nor RD developed in any of the 19 nontraumatic, noniatrogenic, prophylactically treated fellow eyes. CONCLUSIONS This study is the first population-based prospective effort to evaluate the epidemiology of GRT. Although only a minority presented with PVR-C and high retinal reattachment rates were achieved, fewer than half had vision sufficient for driving in the GRT eye.

Factors influencing laser peripheral iridotomy outcomes in white eyes: an anterior segment optical coherence tomography study.

PurposeTo determine the pre-laser anterior segment optical coherence tomography (AS-OCT) features in White eyes which may predict the outcome after laser peripheral iridotomy (PI). Patients and MethodsConsecutive White patients who underwent laser PI at Capital Eye Specialists over a 25-month period (November 2007 to November 2009) were identified, and the AS-OCT images of the temporal and nasal angles (in light and dark) before laser were analyzed. The PI was considered unsuccessful if there was still iridotrabecular apposition in the dark in ≥2 quadrants at follow up. The parameters studied were anterior chamber depth, trabecular-iris angle (TIA), angle opening distance (AOD), trabecular-iris space area, trabecular-iris contact length (TICL), iris thickness, and maximum iris bow height (MIBH). ResultsImages of 71 eyes (71 patients) were assessed. The mean age at laser PI was 60.3 (±10.0) years. The mean time from laser PI to the follow-up AS-OCT scan was 5.92 (±3.22) weeks. The TIA 500 (P=0.002 temporal; P=0.024 nasal), AOD 500 (P=0.004 temporal; P=0.022 nasal), and TICL (P<0.001 temporal; P=0.013 nasal) in light were significantly different between the successful and unsuccessful groups. The MIBH in light was significant temporally (P=0.021) and approached significance nasally (P=0.052). Iris thickness measurements demonstrated no statistical significance. ConclusionsAn unsuccessful PI outcome is associated with pre-laser greater angle closure (decreased TIA 500 and AOD 500, increased TICL) and less anterior iris bowing (decreased MIBH) in light conditions in the temporal and nasal angles.

The Effect of Thin, Thick, and Normal Corneas on Goldmann Intraocular Pressure Measurements and Correction Formulae in Individual Eyes

OBJECTIVE To evaluate the usefulness of the central corneal thickness (CCT)-based correction formulae for stratified CCT groups, with intraocular pressure (IOP) from the Pascal dynamic contour tonometer (PDCT) as the reference standard. DESIGN Retrospective case series. PARTICIPANTS Two hundred eighty-nine patients attending a specialist glaucoma practice and a mixture of normal subjects and subjects with confirmed glaucomatous optic neuropathy. METHODS Intraocular pressure was measured using PDCT, Goldmann applanation tonometry (GAT), and the Ocular Response Analyzer (ORA; Reichert Corp, Buffalo, NY). The GAT readings were obtained before automated readings and were adjusted for CCT using 4 different correction formulae. Discrepancies between GAT and CCT-corrected GAT readings were evaluated after stratification into thin, intermediate, and thick CCT groups. The IOP measurements from GAT, the ORA, and CCT-adjusted IOP were compared against PDCT IOP measurements using Bland-Altman analysis. MAIN OUTCOME MEASURES Mean, 95% limits of agreement, and proportion of patients with IOP difference of 20% or more between PDCT IOP and each of GAT IOP, Goldmann-correlated IOP (IOPg), corneal-compensated IOP (IOPcc), and adjusted IOP using CCT-based correction formulae. RESULTS Average PDCT IOP values were higher than GAT, IOPg, IOPcc, and CCT-adjusted IOP. The GAT IOP readings demonstrated poor agreement with PDCT IOP (95% limits of agreement, ± 4.7 mmHg); however, IOPg, IOPcc, and adjustment of GAT IOP with CCT-based formulae resulted in even poorer agreement (range of 95% limits of agreement, ± 5.1 to 6.7 mmHg). If PDCT was used as the reference standard, there was a 26% to 39% risk of making an erroneous IOP adjustment of magnitude of 20% or more at all levels of CCT. This risk was greatest in the patients with thicker corneas (CCT, ≥568 μm). CONCLUSIONS Adjusting IOP using CCT-based formulae resulted in poorer agreement with PDCT IOP when compared with unadjusted G AT IOP. If PDCT is the closest measure we have to intracameral IOP, there is a risk of creating clinically significant error after adjustment of GAT IOP with CCT-based correction formulae, especially in thicker corneas. This study suggests that although CCT may be useful in population analyses, CCT-based correction formulae should not be applied to individuals.

Optic disc area and correlation with central corneal thickness, corneal hysteresis and ocular pulse amplitude in glaucoma patients and controls: Optic disc and cornea correlations

Background:  To examine the relationships between optic disc area and parameters measured at the cornea; central corneal thickness (CCT), corneal hysteresis (CH) and ocular pulse amplitude (OPA) in glaucoma subjects and controls.