Open-angle glaucoma, the most common form of the disease in the United States, is insidious, chronic and progressive. Effective management requires early detection, followed by careful evaluation and monitoring to identify those likely to have rapid progression and need aggressive intervention. Unfortunately, the classic methods of glaucoma evaluation — optic disc examination and visual field testing — have limited reliability due to their subjective nature. Visual field abnormality tends to be detected later than structural defect. Furthermore, as Dr. Brian Francis’ article in this issue points out, three years of semi-annual visual field testing are needed to detect significant progression, even in those with the most rapid “catastrophic” rate of disease worsening.
Fortunately, more precise objective evaluation is now available with optical coherence tomography (OCT). Dr. Brad Fortune describes a new OCT-based disc parameter called “Bruch’s membrane opening minimum rim width” that enhances early detection. Drs. Don Hood and Gustavo De Moraes use macular imaging to identify patients with early paracentral damage who need to be followed with central 10-2 visual field testing in addition to the standard 24-2 field. While Dr. Francis describes the role of visual fields for monitoring glaucoma progression patients, part two of his article (in a coming issue) will describe how to use OCT to monitor the thinning of both the peripapillary retinal nerve fiber layer (NFL) and the macular ganglion cell complex (GCC).
Finally, the recent introduction of OCT angiography (OCTA) gives us a way to assess retinal perfusion, which is tightly linked to tissue metabolism and function, with greater precision. OCTA can measure vessel density in retinal layers associated with the NFL and GCC. These angiographic parameters have been shown to be more highly correlated with visual field results than structural parameters such as NFL and GCC thickness. Thus, OCTA may finally offer us something close to an objective surrogate for visual field. Another plus: Analytic software providing automated measurement of OCT angiographic parameters relevant to glaucoma has recently become commercially available. Large clinical studies are needed, though, to determine whether it will improve diagnosis and monitoring of glaucoma. Based on the excellent correlation between vessel density and visual field, I believe OCTA may be most valuable as a way to monitor progression in moderate- to advanced-stage glaucoma, where structural measures reach a floor and lose the ability to follow worsening.
Some bemoan that the practice of glaucoma has shifted from the art of observation to the science of measurements. But, the greater reliance in technology is well justified in the increased confidence and timeliness with which we can intervene in the disease process. The need for nuance and judgment persists. The clinician has been, and remains, essential in observing the whole human being and in recommending the best treatment options for the patient. OM