Central Damage Detection in Glaucoma
Perhaps one of the greatest misconceptions about glaucoma is the concept that glaucoma is a disease of peripheral vision loss. Let’s start with the basics. If a superior nasal step is one of the earliest signs of functional damage in glaucoma, then it would be more accurate to say that the vision loss begins right in front of the patient’s eye. But even more to the point, glaucoma often occurs centrally, even early in the disease. If this is not something that you have encountered frequently, it may be because the standard 24-2 visual field test samples the macular area sparsely, using testing points separated by 6 degrees.
We can now assess the macula with optical coherence tomography (OCT) as well. Spectral-domain and swept source OCT platforms can now evaluate for glaucoma within the macula, either by segmenting the ganglion cell layer, the ganglion cell layer plus the retinal nerve fiber layer, or the total macular thickness.
Work from Donald Hood at Columbia University has demonstrated that glaucoma does affect central vision, even early in the disease. We often say that, by definition, glaucoma with central visual field loss is considered to be advanced glaucoma. So when we say that central vision can be affected in early glaucoma, we need to say that in eyes with modest amounts of retinal nerve fiber layer loss, or modest amounts of mean deviation deficits in the visual field, defects may still be found centrally, and not uncommonly. In one study of moderate glaucoma, up to half of eyes had damage within the central 3 degrees of fixation on closer inspection.
Recently, Dana Blumberg and researchers from Columbia University (including Dr Hood) sought to investigate how the presence of visual field damage within the central 8 degrees of fixation related to patient quality of life. Specifically, they sought to determine whether using the 10-2 visual field algorithm would more closely correlate visual field loss and quality of life disruption than using the 24-2 algorithm. Because visual quality of life (measured with National Eye Institute Visual Function Questionnaire [NEI VFQ-25]) correlates best with binocular visual field loss, binocular visual field sensitivities were calculated for each patient.
When a statistical model was constructed for 113 patients included in the study, the 10-2 visual field results correlated more closely with NEI VFQ-25 scores than the 24-2 binocular visual field tests. The take-home point here is that when patients seem to have functional impairment that would not be expected based on 24-2 testing, look within the macula.
In summary, several lines of research are converging to suggest that whether we are using OCT or perimetry, focusing on central vision or the macula will serve our patients well and help us preserve vision-related quality of life.