There is quite a bit of ground to cover when explaining to patients with glaucoma how visual field tests illustrate certain areas of loss. Due to compensation by the other eye, the patients may not notice some of these early changes. A novel method to evaluate binocular fields using a formula applied to right and left visual field indices (VFIs) may make patient education easier and more straightforward, according to researchers. A pair of new models that employ VFI compare well with the integrated visual field (IVF) model, according to a study published in Journal of Glaucoma.
IVF — widely used since 2005 — determines binocular fields based on 52 matching central points of the Humphrey Field Analyzer (HFA), a “best location” model. In contrast, combined average VFI (CaVFI) uses an average of individual VFI index values. Binocular summation VFI (BiSumVFI) requires more steps: the left eye’s visual field index squared plus the right eye’s visual field index squared, followed by calculating the square root of this sum.
Investigators compared IVF, CaVFI, and BiSumVFI in 58 patients with primary glaucoma. Using statistical Spearman rank order correlation (rho), the analysis found significant correlation between IVF and the 2 VFI-determined models (both P <.001).
Participants also took the 9-question glaucoma activity limitation questionnaire (GAL-9), a patient-reported outcome measure. IVF, CaVFI, and BiSumVFI each significantly correlated with the GAL-9 total score (all P <.001). The models also were significantly associated with several individual questions; for example, walking on uneven ground and adapting to low light. Indeed, CaVFI and BiSumVFI were more sensitive than IVF for questions regarding walking after dark, managing stairs, and seeing objects arriving from the side — actions using aspects of binocular vision.
Previous research has found a visual field score based on calculations from the 2 monocular fields may be better than a both-eye-open Estermann test on HFA to ascertain patients’ perception of their vision and assess details of glaucomatous loss. In the IVF model, it is possible 1 eye compensates for a damaged region of the other. In an asymmetric case where the better eye displays nearly normal fields, an IVF may read more normal. In contrast, CaVFI and BiSumVFI may be more discerning for regions of loss.
Participants in this study were diagnosed with open or closed angle glaucoma, and had repeatable HFA field loss in at least 1 eye. Patients’ mean age was 62.9 years, and the population sample exhibited a wide range of field damage. A limitation of this investigation was that the cohort sample resided in a single rural region.
Because glaucoma is “a binocular disease,” understanding its impact on a patient’s daily life may help a clinician manage treatment. “Having VFI models of binocular field might make it easier to explain to the patient about the nature of the disease and the magnitude of damage,” researchers explain.
Kuzhuppilly NIR, Pai VH, Daruka R, et al. A novel approach to measuring binocular visual fields in glaucoma. J Glaucoma. 2021;30(8):656-660. doi:10.1097/IJG.0000000000001845