Predicting progression of glaucoma from rates of frequency doubling technology perimetry change

Abstract

Purpose: To evaluate the ability of longitudinal frequency doubling technology (FDT) to predict the development of glaucomatous visual field loss on standard automated perimetry (SAP) in glaucoma suspects.

Design: Prospective, observational cohort study.

Participants: The study included 587 eyes of 367 patients with suspected glaucoma at baseline selected from the Diagnostic Innovations in Glaucoma Study (DIGS) and the African Descent and Glaucoma Evaluation Study (ADAGES). These eyes had an average of 6.7 ± 1.9 FDT tests during a mean follow-up time of 73.1 ± 28.0 months.

Methods: Glaucoma suspects had intraocular pressure (IOP) >21 mmHg or an optic disc appearance suspicious of glaucoma. All patients had normal or nonrepeatable abnormal SAP at baseline. Humphrey Matrix FDT (Carl Zeiss Meditec, Inc, Dublin, CA) testing was performed within 6 months of SAP testing. The study end point was the development of 3 consecutive abnormal SAP test results. Joint longitudinal survival models were used to evaluate the ability of rates of FDT pattern standard deviation (PSD) change to predict the development of visual field loss on SAP, adjusting for confounding variables (baseline age, mean IOP, corneal thickness, and follow-up measurements of SAP PSD).

Main outcome measures: The R(2) index was used to evaluate and compare the predictive abilities of the model containing longitudinal FDT PSD data with the model containing only baseline data.

Results: Sixty-three of 587 eyes (11%) developed SAP visual field loss during follow-up. The mean rate of FDT PSD change in eyes that developed SAP visual field loss was 0.07 dB/year versus 0.02 dB/year in those that did not (P < 0.001). Baseline FDT PSD and slopes of FDT PSD change were significantly predictive of progression, with hazard ratios of 1.11 per 0.1 dB higher (95% confidence interval [CI], 1.04-1.18; P = 0.002) and 4.40 per 0.1 dB/year faster (95% CI, 1.08-17.96; P = 0.04), respectively. The longitudinal model performed significantly better than the baseline model with an R(2) of 82% (95% CI, 74-89) versus 11% (95% CI, 2-24), respectively.

Conclusions: Rates of FDT PSD change were highly predictive of the development of SAP visual field loss in glaucoma suspects. This finding suggests that longitudinal FDT evaluation may be useful for risk stratification of patients with suspected glaucoma.

Figure 1

A. Longitudinal trajectory of frequency doubling technology (FDT) pattern standard deviation (PSD) raw measurements in progressors (right) and nonprogressors (left). B. Longitudinal trajectory of SAP PSD raw measurements in progressors (right) and nonprogressors (left). SAP = standard automated perimetry

Figure 2

Distribution of rates of frequency doubling technology (FDT) pattern standard deviation (PSD) change in eyes that developed standard automated perimetry (SAP) visual field loss versus eyes that did not develop SAP visual field loss. Eyes that developed SAP visual field loss had considerably faster rates of FDT PSD change when compared to eyes that did not developed SAP visual field loss.

Figure 3

Predicted survival probabilities for two eyes, one that showed a relatively fast rate of frequency doubling technology (FDT) pattern standard deviation (PSD) change during follow-up (A) and another that showed stable measurements over time (B). A comparison of the predicted survival probabilities shows that the eye with fast progression had much lower predicted probabilities of survival, i.e., retaining a normal standard automated perimetry (SAP) visual field. The former in fact showed development of visual field loss during follow-up whereas the eye with stable FDT PSD measurements did not develop any SAP field defect.

Figure 4

Example of how survival probabilities can be updated as more information on predictive factors becomes available during follow-up. A. Left panel shows survival probabilities after considering only the baseline data. The model estimated that the probability of retaining a normal standard automated perimetry (SAP) visual field over time was relatively high. As more information became available (middle and right panels), the survival probabilities were updated. The estimated survival probabilities became much lower as the result of progressive increase of frequency doubling technology (FDT) pattern standard deviation (PSD) over time. B. Corresponding FDT pattern deviation plot showing progressive deterioration. C. SAP visual fields for the same eye showing development of a repeatable defect at the end of follow-up.