P. T. K. Chew

Intraocular pressure and visual field loss in primary angle closure and primary open angle glaucomas.

Aim: To compare the correlation between visual field loss and the pretreatment intraocular pressure (IOP) in primary angle closure glaucoma (PACG) and primary open angle glaucoma (POAG). Methods: In a cross sectional observational study of 74 patients (43 PACG, 31 POAG), pretreatment IOP was measured at presentation, before treatment was initiated. The severity of visual field loss was assessed by AGIS score, mean deviation (MD), pattern standard deviation (PSD), and corrected pattern standard deviation (CPSD). Glaucomatous optic neuropathy was assessed from simultaneous stereo disc photographs. Results: There was a stronger correlation between pretreatment IOP and the extent of visual field loss in PACG subjects than in those with POAG for both MD (PACG: Pearson correlation coefficient (r) = 0.43, p = 0.002; r2 = 0.19), (POAG: r = 0.21, p = 0.13; r2 = 0.04) and AGIS score (PACG: r = 0.41, p = 0.003; r2 = 0.17), (POAG: r = 0.23, p = 0.19; r2 = 0.05 respectively). No such associations were seen for pattern standard deviation (PSD) or corrected pattern standard deviation (CPSD) in either group (p> 0.29). Both horizontal and vertical cup-disc ratio were well correlated with severity of field loss but not with presenting IOP for either diagnosis. Conclusions: This is consistent with the hypothesis of a greater IOP dependence for optic nerve damage in PACG than POAG and, conversely, a greater importance of other, less pressure dependent mechanisms in POAG compared to PACG.

Randomised controlled trial comparing the effect of brimonidine and timolol on visual field loss after acute primary angle closure

Aim: To compare the effect of brimonidine and timolol in reducing visual field loss in patients with acute primary angle closure (APAC). Methods: In addition to standard acute medical treatment, patients presenting with APAC were randomised to either brimonidine 0.2% or timolol 0.5% upon diagnosis, then twice daily for 4 weeks. After laser peripheral iridotomy (LPI), subjects underwent three baseline perimetry tests during the first week, and then at weeks 4, 8, 12, and 16. Pointwise linear regression analysis was applied to the field series of each of these subjects starting with the third test (total of five tests per subject). Progression was defined as a significant regression slope (p<0.05) showing 1 dB per year or more of sensitivity loss at the same test location in the series. Patients were also compared for prevalence of abnormal fields at 16 weeks, which was defined as an abnormal glaucoma hemifield test result and/or corrected pattern standard deviation outside the 95% confidence limits. Results: 59 subjects (31 in the brimonidine group; 28 in the timolol group) completed the study. There were 47 females (79.7%), the majority of subjects (94.9%) were Chinese and the mean age was 59.2 (SD 7.2) years. There were no significant differences between the two groups with respect to demographic features, presenting intraocular pressure (IOP), duration of symptoms, time from presentation to LPI, or mean IOP at each study visit. Over the 16 week study period, despite adequate statistical power, no difference was found between groups in terms of the number of patients with progressing locations, the mean number of progressing locations per subject, or the mean slope of the progressing locations. Nine (29%) subjects in the brimonidine group and 10 (35.7%) in the timolol group were found to have significant visual field defects at 16 weeks (p = 0.58). 15 out of these 19 subjects (78.9%) already had these visual field defects in the first week. Conclusions: In the first 16 weeks after APAC, there was no difference in the prevalence of visual field defects or rate of visual field progression between brimonidine and timolol treated groups.

Interocular asymmetry of visual field defects in primary open angle glaucoma and primary angle-closure glaucoma

AbstractAim To compare the interocular asymmetry in visual field loss of patients with primary open-angle (POAG) and primary angle-closure glaucoma (PACG).Methods Subjects entering a prospective, randomised, controlled trial of intraoperative 5-fluorouracil in glaucoma surgery in Singapore were included. Preoperative visual field testing was performed using automated white-on-white perimetry (24-2 test pattern, threshold program, Mk II, Model 750, Zeiss-Humphrey, San Leandro, CA, USA). A minimum of two tests were required with mean deviation within 2 dB on two tests, fixation losses <20%, false positives <33%, and false negatives <33%. The second field was scored using AGIS II criteria and the ‘mean asymmetry score’ defined as the mean difference between eyes for both AGIS scores and global indices.Results In 230 subjects assessed (128 POAG, 102 PACG), mean interocular asymmetry of visual field loss was greater for the PACG group. The mean AGIS asymmetry scores for total (PACG=9.21±6.87 vsPOAG=6.48±5.58, P=0.001), superior (PACG=4.31±3.39 vsPOAG=3.35±3.13, P=0.035), and inferior (PACG=4.43±3.31 vsPOAG=2.64±2.77, P<0.0001) areas and mean deviation (MD) asymmetry scores (PACG=6.89±13.22 vsPOAG=1.66±16.97, P=0.012) were all significantly different. Interocular correlation of visual field loss for POAG was significant; total AGIS, r=0.27 (P=0.003), superior field AGIS, r=0.24 (P=0.008), inferior field AGIS, r=0.34 (P=0.0001), and MD, r=0.27 (P=0.003). In PACG, there was no significant correlation between eyes; total AGIS, r=−0.02 (P=0.85), superior field AGIS, r=−0.02 (P=0.82), inferior field AGIS, r=−0.17 (P=0.87), and MD, r=0.015 (P=0.89).Conclusion There was a greater asymmetry of visual field loss between eyes, as measured by AGIS scores and MD, in PACG than that in POAG.

Effect of cataract extraction and intraocular lens implantation on nerve fibre layer thickness measurements by scanning laser polarimeter (GDx) in glaucoma patients

AbstractPurpose To assess the influence of visually significant cataract on the measurement of nerve fibre layer thickness by scanning laser polarimetry (GDx) in glaucoma patients undergoing phacoemulsification cataract extraction.Method and Subjects All subjects with primary glaucoma participating in a prospective trial of glaucoma surgery who subsequently underwent cataract extraction were eligible. A single trained observer using the GDx nerve fibre layer analyser (LDT) performed pre- and post-operative measurements of nerve fibre layer thickness (NFLT). NFLT parameters, best-corrected LogMAR visual acuity, and automated visual fields were assessed before and after phacoemulsification cataract extraction with implantation of an acrylic intraocular lens.Results A total of 49 subjects were assessed: 22 (45%) had POAG and 29 (55%) PACG; all were Asian (36 (73%) were Chinese), with mean age 67.1 (±7.6 SD) and mean ‘LOCS III’ lens opacity grading 11.4 (±3.1 SD). Visual acuity significantly improved (mean LogMAR 0.5 vs0.15, P<0.0001). Corrected pattern standard deviation (6.1 vs6.4, P=0.2) and mean deviation (−17.7 dB vs-17.0 P=0.91) were little changed after cataract removal. Pseudo-phakic measurements of NFLT were significantly different from pre-op values. Measures of absolute thickness (including the average thickness, ellipse, ellipse average, superior and inferior averages, superior integral) were significantly greater than preoperative values (all P<0.01), whereas ratios and measures of symmetry (symmetry, superior/nasal) were unchanged (all P>0.1) and ‘the number’ was smaller (P=0.04). Differences in measured NFLT were most strongly correlated with posterior subcapsular cataract (average thickness, P=0.01).Conclusions Removal of cataract resulted in greater absolute measurements of NFLT but ratio values were unchanged. Scanning laser polarimetry measurements can change significantly after cataract extraction. New baseline measurements may be required.