When it comes to educating patients about the visual prognosis associated with geographic atrophy (GA), I tend to be a hopeless optimist—I focus on what available treatments can do rather than what they cannot. Based on clinical trial evidence, we know that complement inhibition slows the rate of lesion progression, thereby helping preserve viable retina and retain useful vision. As a result, we cannot promise patients they will restore vision, but we can assure them there is a good chance therapy can extend the time with useful vision to enjoy normal daily activities.

Discussing Visual Prognosis

Many patients we encounter have already experienced some element of vision loss, so they understand this is a pathology with real-world implications. If they have not yet experienced vision loss, it can be a difficult message to convey. Our focus is on having an honest dialogue that properly conveys the appropriate goals and outcomes of initiating therapy. This means being honest that currently available complement inhibitors are not designed to stop the condition; rather they are designed to slow the pathology. Furthermore, it means relaying our goal is to keep them as functional as possible for as long as possible.

While current treatments for GA are not perfect, they are often better than doing nothing. We are still in the nascent era of GA treatment, and I have every confidence the eye care community will learn to utilize the available treatments more effectively in real-world practice. This includes gaining better insights into patient selection and when to start therapy, which should translate to better outcomes. As well, the pipeline of GA treatments is rich and deep—the current modalities may be temporizing agents, but they may also be adequate to stabilize our patients long enough for regenerative and restorative agents to become clinically available.

What Is The Role of Measuring Vision?

Whenever possible, we want to base our clinical management decisions on objective data. The problem we face in real-world practice is the methods for measuring functional visual acuity in the clinic are subjective and unreliable. For example, we use ETDRS charts in our lanes as opposed to Snellen visual acuity charts. The problem is patients can memorize the letters on the ETDRS chart or use eccentric fixation to read the chart. As a consequence, visual acuity measurements are not a good barometer for the risk of progression, nor do they tell us much about what the patient is experiencing in their everyday world.

A number of more objective functional assessments are currently being investigated for potential clinical use (see Functional Testing Modalities). In particular, microperimetry testing is a modality that may highlight areas of functional loss not appreciated by conventional testing. Likewise, low-luminance visual acuity and testing reading speed are much better ways of quantitatively determining functional limitations versus relying on patient reported symptoms.

In our experience, however, functional testing is more valuable as a research tool than as a diagnostic tool to guide clinical decision making. A large issue with functional testing is incorporating it into a busy clinical schedule can be a rate-limiting step: the time it takes to perform such testing does not justify the yield. Fundamentally, the results of functional testing would not affect the decisions we make in the clinic on a daily basis.

FUNCTIONAL TESTING MODALITIES

Microperimetry – A visual field test that incorporates perimetry and retinal imaging to allow direct mapping of the stimulus in the region of interest, thus providing the ability to correlate functional information with structural data.

Low-Luminance Visual Acuity – Visual acuity testing that is performed with a significantly reduced light level, typically using a neutral density filter placed in front of the eye; differences between normal visual acuity and low luminance visual acuity can indicate early signs of retinal damage.

Reading Speed Test – Typically assessed by measuring the number of words an individual can read correctly in a specific timeframe, often using standardized reading charts. Reading speed tests may be more sensitive to functional impairments compared to BCVA alone.

Conclusion

Functional testing in patients with GA, as currently construed, has limited clinical value in terms of guiding management decisions. As more research is done, and perhaps as AI makes inroads into clinical practice, the calculus will change. Certainly, functional testing has the theoretical advantage of picking up nascent GA before objective imaging studies. At the current time, however, what we learn from functional testing is not correlated with the risk of progression or potential for vision loss. Modalities that guide patient conversations in this regard are certainly welcome, but we simply need more data before they are implemented in real-world practice.