Asymmetries and visual field summaries as predictors of glaucoma in the ocular hypertension treatment study

Abstract

Purpose: To evaluate whether baseline visual field data and asymmetries between eyes predict the onset of primary open-angle glaucoma (POAG) in Ocular Hypertension Treatment Study (OHTS) participants.

Methods: A new index, mean prognosis (MP), was designed for optimal combination of visual field thresholds, to discriminate between eyes that developed POAG from eyes that did not. Baseline intraocular pressure (IOP) in fellow eyes was used to construct measures of IOP asymmetry. Age-adjusted baseline thresholds were used to develop indicators of visual field asymmetry and summary measures of visual field defects. Marginal multivariate failure time models were constructed that relate the new index MP, IOP asymmetry, and visual field asymmetry to POAG onset for OHTS participants.

Results: The marginal multivariate failure time analysis showed that the MP index is significantly related to POAG onset (P < 0.0001) and appears to be a more highly significant predictor of POAG onset than either mean deviation (MD; P = 0.17) or pattern standard deviation (PSD; P = 0.046). A 1-mm Hg increase in IOP asymmetry between fellow eyes is associated with a 17% increase in risk for development of POAG. When threshold asymmetry between eyes existed, the eye with lower thresholds was at a 37% greater risk of development of POAG, and this feature was more predictive of POAG onset than the visual field index MD, though not as strong a predictor as PSD.

Conclusions: The MP index, IOP asymmetry, and binocular test point asymmetry can assist in clinical evaluation of eyes at risk of development of POAG.

Figure 1

Cutpoints (in decibels) at each of the 52 visual field locations used to identify an extreme reduction in sensitivity in the OHTS eyes corrected for age 45. Clinically, if the measured asymmetry for a patient at a particular point is larger than that presented at the same point in the figure, then the eye with the lower sensitivity should be flagged for increased risk of POAG.

Figure 2

Predicted survival curves, adjusted for treatment and fellow eye correlation, comparing eyes from a symmetric pair (solid curve), an asymmetric pair with lower IOP (dashed curve), and an asymmetric pair with higher IOP (dotted curve).

Figure 3

Predicted survival curves, adjusted for treatment and fellow eye correlation, comparing eyes from an asymmetric pair with depressed sensitivity with all other eyes in the OHTS.