Reducing variability in visual field assessment for glaucoma through filtering that combines structural and functional information

Factors Associated with Midterm Visual Field Variability in Patients with Stable Glaucoma

Purpose

To evaluate factors associated with midterm visual field (VF) variability in stable glaucoma patients in Brazil.

Methods

This retrospective observational study included 59 eyes of 39 stable glaucoma patients. Baseline data assessed were age, gender, educational level, intraocular pressure (IOP), central corneal thickness, best-corrected visual acuity, spherical equivalent, number of hypotensive eye drops, type of glaucoma, number of VFs performed, follow-up in years, lens status, visual field index (VFI) values from the last 5 VF (standard automated perimetry (SAP)) tests, the presence or absence of central scotoma in the VF test, and the level of glaucomatous damage according to the VF mean deviation (MD) index of the last VFs. The 5 latest VFI scores were used to calculate the mean, the standard deviation (SD), and the coefficient of variation (CV). We divided the eyes into 2 groups, being group 1 comprised by the 29 eyes presenting the lowest CV values and group 2 comprised by the 30 eyes presenting the highest CV values. GEE models were used to compare the CV and demographic and clinical parameters of all participants.

Results

Mean age of all subjects was 65.8 ± 10.1 years. 54.0% were women. Average SAP MD values for groups 1 and 2 were −2.8 ± 3.1 dB and −6.2 ± 4.1 dB, respectively (P=0.006). Average SAP VFI values for groups 1 and 2 were 95.6 ± 5.9% and 85.9 ± 11.3%, respectively (P=0.002). There was a statistically significant association between CV and SAP MD values (P=0.006). A worse SAP MD and VFI were associated with a higher CV. In addition, even adjusting for potential confounding factors (age and level of education), the association between CV and the SAP MD and between CV and VFI remained significant (P ≤ 0.010).

Conclusion

Glaucomatous patients with worse VF sensitivity scores (both MD and VFI indices) present higher VF test variability.

Reducing Variability of Perimetric Global Indices from Eyes with Progressive Glaucoma by Censoring Unreliable Sensitivity Data

Purpose

Recent evidence suggests that increasing perimetric contrast all the way to 0 dB may not be clinically useful. This study examines whether raising the floor for point-wise sensitivities affects the ability of global indices to detect change.

Methods

Longitudinal data from eyes with progressive glaucoma were used. Point-wise sensitivities were censored at various cutoffs (12–19 dB). At each cutoff, mean deviations (MD) were recalculated using censored sensitivities, called censored mean deviation (CMD). Both MD and CMD were fitted using a linear model. MD and CMD rate of changes (signal) and the standard deviations (SD) of the residuals (noise) were obtained from the fitted models. The linear signal to noise ratio (LSNR) for MD (LSNR_MD) and CMD (LSNR_CMD) were compared. Additionally, at each cutoff, the ratios of LSNR_CMD to LSNR_MD were calculated and tested.

Results

CMD provided significantly (P <0.05) better LSNR than MD when using any point-wise sensitivity cutoff between 15–19 dB for progressing eyes. Moreover, the ratios of LSNR_CMD to LSNR_MD were significantly (P <0.05) greater than 1 at all cutoffs from 15–19 dB.

Conclusion

This study demonstrates that censoring is an effective tool to reduce variability at low sensitivities for progressing eyes.

Translational Relevance

This study suggests that 15–19 dB could be a more suitable endpoint for perimetric testing algorithms.