How fundus perimetry detects changes in progression that may go unnoticed.
Age-related macular degeneration (AMD) is a leading cause of visual impairment. As many as 11 million Americans have some form of AMD, and that number is expected to double by 2050. Fortunately, we now have therapies that can help stabilize or even reverse vision loss in “wet” AMD, including EYLEA (aflibercept), Lucentis (ranibizumab), Avastin (bevacizumab) and Macugen (pegaptanib), as well as laser photocoagulation. Unfortunately, the wet form accounts for only 10% of AMD cases. Dry AMD is typically managed with high-dose antioxidant vitamins and zinc in an effort to delay or prevent the condition—and vision—from worsening. These measures are no guarantee against progression, however, and therefore careful monitoring is critical.
Enter, microperimetry (fundus perimetry). This technology permits the simultaneous correlation of function with structural changes at the level of the macula. While standard perimetry detects the ability to perceive light in different aspects of one’s visual field, microperimetry utilizes projected light directly onto focal areas of the retina and combines those sensitivity measurements with a corresponding retinal image, thereby precisely associating functional data with anatomical information. Through the use of an automated eye-tracking system, microperimeters ensure repeatability and even account for eccentric fixation. In AMD, microperimetry can detect small, localized functional changes due to atrophy or neovascularization that might otherwise go undetected. It also has the ability to track progression over time by determining which changes are statistically significant and which represent an inherent disease variation. Here are two microperimeters available in the U.S.:
MP-3 Microperimeter from NIDEK employs a digital fundus camera and computerized perimeter that uses stimulus projection within the region of interest. An infrared light source allows testing to be done under non-mydriatic conditions. Automatic image registration ensures accurate test-to-test repeatability. As a means of reliability, an analysis of fixation stability (stable or unstable) and location (central or eccentric) is generated for each exam. Results of these analyses can be viewed as either a numerical representation (in dB) for each stimulus point or as an interpolated color map. The MP-3 has a 10.4-inch color touch screen testing display and requires a dedicated computer and monitor.
MAIA Macular Integrity Assessment from CenterVue, Inc. utilizes a confocal scanning laser ophthalmoscope (SLO) rather than a digital camera to obtain its retinal image. The SLO is better able to penetrate cloudy ocular media with less degradation than traditional photography. MAIA also uses infrared lighting and is therefore non-mydriatic and boasts many of the same features as the MP-3, such as precision eye tracking, numerical and colorimetric sensitivity representation, and fixation stability assessment. It compares results to a normative database, rating assessments as “normal,” “suspect” or “abnormal.” It also has the ability to compare prior and subsequent examinations. In terms of size, MAIA is roughly equivalent to the MP-3, but because it is self-contained (with a touch screen interface) and requires no external computer or monitor, it maintains a smaller office “footprint.” MAIA is also available with scotopic test capability and offers a FDA-approved biofeedback module to help train patient fixation stability and eccentric vision. OO
Alan G. Kabat, OD, FAAO, is professor, Southern College of Optometry in Memphis, TN.