Comparison of visual field progression in patients with normal pressure glaucoma between eyes with and without visual field loss that threatens fixation

Aim-To compare the frequency and site of visual field progression and chang es in visual acuity in patients with normal pressure glaucoma (NPG) with an d without pre-existing visual field loss. Method-Patients with normal tension glaucoma were selected who had at least 10 visual fields over 5 or more years of follow up and no other condition that might influence the visual field or visual acuity. Alternate left and right eyes were selected from patients in random order. These eyes were the n subdivided according to visual field defect threatening fixation, visual field defect not threatening fixation, and no visual field defect (fellow e yes). Eyes were defined as showing a threat to fixation according to the pr esence of a visual field defect involving one of more of four paracentral v isual field locations. Pointwise linear regression analysis was applied to each visual field series using PROGRESSOR software. Progression of visual f ield loss was defined as the appearance of a regression slope 1 dB per year or more with a significance of p<0.01, which remained consistent with the addition of two of three successive visual fields to the series. The number of patients showing progression and the number where progression occurred in one of the four paracentral visual field locations was noted. The number of eyes losing two or more lines of Snellen visual acuity over the follow up period was also noted. Results-174 eyes of 174 patients were selected. 106 eyes had visual field l oss threatening fixation, 46 eyes had visual field loss that did not threat en fixation, and 22 were fellow eyes with normal visual fields. The median follow up was 7.2 years. Eight eyes (36.4%) in the "normal visual fields" g roup, 31 eyes (67.4%) in the "visual field loss away from fixation" group, and 87 eyes (82.1%) in the "threat to fixation" group showed progression in any part of the visual field. Two eyes (9.1%) in the "normal visual fields " group, nine eyes (19.6%) in the "visual field loss away from fixation" gr oup, and 45 eyes (42.5%) in the "threat to fixation" group showed progressi on at "threat to fixation". The Cox proportional hazards regression model s howed an increased risk of progression at any part of the visual field for female sex and a decreased risk for eyes with normal visual fields. For pro gression at threat to fixation this model showed an increased risk with pre existing threat to fixation. Eyes from older patients and those that went o n to have progressive visual field loss at fixation were more likely to los e two lines of Snellen visual acuity over the follow up period. Conclusion-Since 20-30% of previously field damaged eyes and over 60% witho ut prior field loss fail to demonstrate progressive visual field damage ove r a long follow up it is recommended that normal pressure glaucoma patients be monitored for progression and that potentially harmful therapy be withh eld until progression is demonstrated. Although the presence of visual fiel d loss that threatens fixation does not constitute an increased risk of vis ual field progression it does indicate an increased risk of further loss of visual field close to fixation which is in turn associated with loss of ce ntral acuity. In the light of this finding, patients with visual field loss that threatens fixation should be managed more aggressively.