Microperimetry is a specialized eye diagnostic test that combines visual field testing with retinal imaging to assess central vision and how well different parts of the retina function. This technique provides a detailed map of light sensitivity across the macula, the central part of the retina responsible for sharp, detailed vision. It helps eye care professionals gain a comprehensive understanding of an individual’s visual capabilities, especially in conditions affecting the macula. The test is non-invasive.
Understanding Microperimetry
Microperimetry measures two specific aspects of visual function: retinal sensitivity and fixation stability. Retinal sensitivity indicates how well different retinal areas detect light stimuli. Results are displayed using a decibel (dB) scale, where higher dB values mean better sensitivity.
The test’s ability to correlate functional information, like light sensitivity, directly with specific anatomical points on the retina is a unique feature. This is done through real-time retinal imaging, often using scanning laser ophthalmoscopy (SLO) technology. The device constantly tracks eye movements, ensuring light stimuli are precisely mapped to the intended retinal location. This eye-tracking also assesses fixation stability, which is how steadily a person holds their gaze. For patients with central vision loss, microperimetry can identify a “preferred retinal locus” (PRL), an eccentric retinal area used for vision when the central macula is compromised.
The Microperimetry Procedure
The microperimetry test is generally comfortable and non-invasive. Patients sit in front of a device that projects light stimuli onto their retina. Pupil dilation is usually not needed, allowing patients to resume normal activities immediately.
During the test, the patient focuses on a central target while small light spots are projected onto different retinal areas. Each eye is tested separately. The patient presses a button when they perceive a light stimulus. The device’s eye-tracking system monitors eye movements, ensuring measurement accuracy. The entire procedure for both eyes typically lasts 25 to 30 minutes.
Conditions Evaluated by Microperimetry
Microperimetry is valuable for evaluating and monitoring conditions affecting the macula and central vision. Age-related macular degeneration (AMD) is a primary example; the test assesses vision quality, identifies central blind spots (scotomas), and tracks disease progression by detecting subtle changes in retinal sensitivity. It can also help predict AMD progression risk, with a mean retinal sensitivity below 24.7 dB potentially indicating higher risk.
Diabetic macular edema (DME), a diabetes complication, also benefits from microperimetry. It correlates diminished macular sensitivity with fluid buildup, helping doctors determine if treatments like anti-VEGF injections or laser therapy are improving retinal function. Inherited retinal diseases, such as Stargardt disease, retinitis pigmentosa, and choroideremia, cause complex vision loss patterns. Microperimetry allows for detailed mapping and monitoring of these changes, even detecting impairments before they are apparent on retinal images. The test is also useful in assessing central serous retinopathy, where macular sensitivity below 20 dB can predict persistent subretinal fluid.
Distinct Advantages of Microperimetry
Microperimetry offers significant advantages over conventional perimetry and other general vision tests due to its precision and integrated capabilities. Its eye-tracking system ensures light stimuli are projected onto the exact same retinal points during testing and retesting, compensating for involuntary eye movements. This leads to highly accurate and repeatable measurements of retinal function, even in patients with unsteady or eccentric fixation.
The ability of microperimetry to directly correlate functional data with structural retinal images is another unique strength. By superimposing the retinal sensitivity map onto a high-resolution fundus image, clinicians can precisely identify vision loss areas and link them to specific anatomical changes, such as macular scars or drusen. This combined structural and functional information provides a more comprehensive understanding of the disease, allowing for more accurate diagnoses and tailored treatment plans. Furthermore, microperimetry can quantify the location and stability of fixation, which is particularly useful for low vision rehabilitation by helping patients learn to use their remaining vision more effectively.