Effect of Cataract Extraction on Visual Field in Patients with Open Angle Glaucoma

The aim of the study was to retrospectively analyze changes in the results of automated perimetry in open angle glaucoma patients, including Mean Defect (MD), Loss Variance (LV) and Corrected Loss Variance (CLV) before and after cataract surgery, and also to note how the presence of dense scotoma preoperatively could influence postoperative results. MD is mean of all local visual field defects. LV and CLV are indexes of localized field damages. Increased values of these indicators are even more specific for glaucomatous damage than MD. We investigated 18 eyes of 14 patients with open angle glaucoma who were scheduled for cataract extraction with intraocular lens implantation. The diagnosis of open angle glaucoma was based on the presence of glaucomatous optic disk cupping and abnormal results on glucoma field testing. The intraocular pressure (IOP) criterion was IOP higher than 21 mm Hg. On gonioscopy, all angles of the anterior chamber were open. All patients underwent Octopus Field Analyzer dG2 testing within two months before and three months after cataract surgery. The eyes were divided into two groups based on the presence of absolute or near absolute (dense) scotomata before surgery. Dense (absolute or near absolute) scotomata noted on automated perimetry were found not to be caused by the cataract. Their existance before surgery could be explained by glucomatous visual field defects. Cataract can induce various degrees of relative scotoma, which can induce worstening of local field defects (LV and CLV) after surgery. This implies that the real size of glaucomatous damage (expressed as difference between LV and CLV before and after cataract surgery) can only be seen and properly measured after cataract extraction. Therefore, it is concluded that LV and CLV can be used as reliable indicators in distinguishing the role of coexisting cataract in glaucomatous damage, however, additional studies in the area are needed.