In glaucoma care, we instinctively reach for functional testing. Visual fields (VF) are indispensable. They’re not just a part of our diagnostic toolbox, they’re a reflex. Any glaucoma clinician knows that a robust VF strategy, coupled with structural measures, such as optical coherence tomography (OCT), provides a richer understanding of a patient’s disease than anatomical structure alone. Yet when it comes to age-related macular degeneration (AMD), I would argue that our diagnostic habits are quite different.
The AMD Approach
We’ve become highly skilled at using structural imaging to diagnose and stage AMD. The Age-Related Eye Disease Study Research Group gave us a common language for grading lesions on color fundus photos.1 As an example, category 1 is characterized by fewer than 5 small drusen, each below 63 µm in size.
Imaging technology now provides resolution of atrophy, drusen, subretinal fluid, and subretinal neovascularization at the earliest stages. I would argue that not many of us reach for a functional test when AMD is suspected or diagnosed. I’d like to propose we take up this habit.
The Argument for Functional Testing
The functional testing for AMD is contrast sensitivity (CS), dark adaptometry (DA), and microperimetry. CS is valuable in AMD in that it reveals the entire visual system’s reaction to both the ranges of light intensity and contrast levels patients encounter on a daily basis. Think ability to identify faces, objects, and signs.2 Additionally, CS can aid in picking up retinal health changes.3 DA helps in identifying subclinical disease or high-risk eyes before structural changes manifest. In fact, a systematic review highlights that DA abnormalities precede many of the clinical changes we identify on exam or imaging.4 What’s more, DA helps the OD to predict conversion to advanced disease.5 Finally, microperimetry is of value in AMD in that it aids in assessing fixation and central VF defects, allowing for the monitoring of the functional natural history and the quantification of beneficial or detrimental effects of different treatments.
The Challenge
Just as we once learned to combine OCT with perimetry to fully appreciate glaucoma, it’s clear that AMD care would benefit from both structural and functional testing. The challenge for us as clinicians is to shift our mindset. If functional testing is indispensable in glaucoma, it is only a matter of time until our AMD patients benefit from it as well. OM
References
1.Age-Related Eye Disease Study Research Group. The Age-Related Eye Disease Study system for classifying age-related macular degeneration from stereoscopic color fundus photographs: the Age-Related Eye Disease Study Report Number 6. Am J Ophthalmol. 2001;132(5):668-681. doi:10.1016/s0002-9394(01)01218-1.
2. Roark MW, Stringham JM. Visual performance in the “real world”: contrast sensitivity, visual acuity, and effects of macular carotenoids. Mol Nutr Food Res. 2019;63(15):e1801053. doi:10.1002/mnfr.201801053.
3. Kleiner RC, Enger C, Alexander MF, Fine SL. Contrast sensitivity in age-related macular degeneration. Arch Ophthalmol. 1988;106(1):55-57. doi:10.1001/archopht.1988.01060130061028
4. Higgins BE, Taylor DJ, Binns AM, Crabb DP. Are current methods of measuring dark adaptation effective in detecting the onset and progression of age-related macular degeneration? A systematic literature review. Ophthalmol Ther. 2021;10(1):21-38. doi:10.1007/s40123-020-00323-0.
5. Owsley C, McGwin G Jr, Clark ME, et al. Delayed rod-mediated dark adaptation is a functional biomarker for incident early age-related macular degeneration. Ophthalmology. 2016;123(2):344-351. doi:10.1016/j.ophtha.2015.09.041.
