Quantitative Classification of Visual Field Defects in Early Glaucoma.

OBJECTIVE

While qualitative visual field (VF) grading systems enable the classification and description of VF defects in glaucoma, they may be prone to subjective interpretation and interobserver disagreement. In this study, we characterize the types and frequencies of VF defects in a large cohort of subjects with early glaucomatous loss, using a quantitative method based on the Ocular Hypertension Treatment Study (OHTS) VF classification system.

DESIGN

Cross-sectional study.

SUBJECTS

One thousand three hundred thirty eyes of 733 subjects with healthy, suspect or early glaucoma.

METHODS

We translated the OHTS system into an objective, quantitative method to classify the VF of each eye into nerve fiber bundle (bundle) and nonbundle defects comprising 14 patterns. This was applied to VF tests from subjects who received two 24-2 Swedish Interactive Thresholding Algorithm-Faster VF tests per eye on the same visit.

MAIN OUTCOME MEASURES

Distribution of initial and repeatable VF patterns across cohort and the relationship with mean deviation (MD) and test reliability.

RESULTS

The mean baseline MD and pattern standard deviation (SD) was -1.08 (SD, 1.83) and 2.26 (SD, 1.26), respectively. The most common repeatable pattern was the inferior nasal step (22.6%), followed by the inferior enlarged blind spot (19.1%), superior nasal step (12.6%), and superior enlarged blind spot (11.6%). The frequency of occurrence of initial defects was significantly higher than repeatable defects for the majority of patterns. The frequency of nasal step defects decreased as MD worsened, with a corresponding increase in the frequency of arcuate defects. There was a consistently higher frequency of bundle and nonbundle defects in unreliable versus reliable tests based on a false-positive rate above 15%, including an inferior enlarged blind spot (30.0% vs. 20.8%, P < 0.001), superior central defect (13.7% vs. 5.5%, P < 0.001), and partial superonasal quadrant (14.4% vs. 7.2%, P < 0.001) defects.

CONCLUSIONS

In a large cohort of suspect and early glaucoma, the most common VF defects were nasal step, enlarged blind spot and arcuate defects, with a significant difference in distribution between initial versus repeatable defects and reliable versus unreliable tests. Application of quantitative criteria may improve the accuracy and consistency of classifying VF defects. FINANCIAL DISCLOSURE(S): The authors have no proprietary or commercial interest in any materials discussed in this article.