Microperimetry is a visual function test that integrates retinal imaging and perimetry. It is also called fundus-controlled perimetry (FCP) or macular perimetry.
This test directly maps light stimuli onto regions of interest on the retina and measures light sensitivity (in decibels, dB) at each location. Because an eye-tracking system corrects eye movements in real time, accurate testing is possible even in patients with unstable fixation, which was difficult with conventional standard automated perimetry (SAP).
The first microperimeter (SLO101) was manufactured in 1982 by Rodenstock Instruments (Germany). It used scanning laser ophthalmoscope (SLO) technology and semi-automatically measured the central visual field of 33×21° with a 633 nm helium-neon laser, but it did not have an eye-tracking function.
Microperimetry has become an essential tool for analyzing the structure-function correlation of the retina 1). Combined with structural imaging such as fundus autofluorescence (FAF) and OCT, it allows precise evaluation of the spatial distribution of functional impairment in retinal diseases.
Conventional standard automated perimetry assumes stable foveal fixation, and test accuracy decreases in patients with unstable fixation. Microperimetry uses eye tracking to correct eye movements in real time, accurately projecting stimuli onto the same retinal location, resulting in high test-retest reproducibility. Additionally, overlay with fundus images enables direct structure-function correlation analysis.
Similar to conventional perimetry, light stimuli are presented at specific retinal locations, and the minimum light intensity (threshold) perceived by the patient is measured. Sensitivity at each test point is expressed in decibels (dB).
During the examination, eye tracking continuously compensates for retinal movement and simultaneously evaluates fixation status. After measurement, a sensitivity map is overlaid on the fundus image, enabling functional assessment of the region of interest.
An important caution is that comparison of results between different devices requires careful consideration. This is because the maximum luminance differs between devices, and the dB scale is defined relative to that value1).
Fixation data obtained by microperimetry are presented in the following two ways.
The classification of fixation location and fixation stability is shown below.
| Classification of fixation location | Percentage of fixation points within 2° of the fovea |
|---|---|
| Predominant central fixation | >50% |
| Poor central fixation | 25–50% |
| Eccentric fixation predominant | <25% |
| Fixation stability | Criteria |
|---|---|
| Stable | >75% within 2° circle |
| Relatively unstable | Less than 75% within 2° circle, more than 75% within 4° circle |
| Unstable | Less than 75% within 4° circle |
There are several types of microperimetry1).
Scotopic microperimetry is a test that evaluates rod function and can detect decreased rod sensitivity even in early age-related macular degeneration patients who maintain good visual acuity 2). Even at stages where mesopic microperimetry shows no abnormalities, scotopic testing may reveal decreased sensitivity, and it is attracting attention as an early progression indicator for age-related macular degeneration.
Currently, there are three main types of microperimeters commercially available1).
Nidek MP-3
Manufacturer: Nidek Technologies (Padua, Italy)
Retinal imaging: Built-in color fundus camera
Features: Supports scotopic microperimetry. It is an improved version of the older MP-1, overcoming ceiling effects and filter selection limitations.
MAIA 3
Manufacturer: CenterVue (Padua, Italy)
Retinal imaging: Scanning laser ophthalmoscope (SLO)
Features: Dynamic range 0–36 dB. Supports scotopic microperimetry (S-MAIA). Dual-color stimuli (cyan and red) allow separate assessment of rod and cone function2).
Optos OCT-SLO
Manufacturer: Optos (Marlborough, USA)
Retinal image: SLO
Features: Equipped with a function to overlay functional defects on OCT tomographic images. Enables three-dimensional structure-function correlation analysis, not just en face images.
Microperimetry is an optimal method for evaluating residual visual function and is applied to a wide range of retinal diseases.
The usefulness of microperimetry in age-related macular degeneration has been widely studied1)2).
In a scoping review by Madheswaran et al. (2022), 10 out of 12 studies (83.3%) used a cross-sectional design to evaluate photopic and scotopic microperimetry, reporting significant reduction in scotopic sensitivity even in early AMD patients with good visual acuity. Longitudinal analysis showed that in RPD cases, both photopic and scotopic sensitivity significantly decreased over 3 years2).
The application of microperimetry in GA is also attracting attention as a clinical trial endpoint 1).
In diabetic macular edema, the decrease in macular sensitivity correlates with the degree of edema, and it is also used to evaluate the effects of different laser treatments on macular function.
In cases of silicone oil (SO) tamponade after vitrectomy for rhegmatogenous retinal detachment (RRD), microperimetry is useful for functional evaluation 3).
According to a narrative review by Dunca et al. (2025), retinal sensitivity during SO tamponade decreases by approximately 5–10 dB, and after SO removal, an improvement of 1–2 dB is observed, but it often does not return to normal levels. There is a correlation between the duration of tamponade and the degree of sensitivity loss 3).
For patients with central scotoma, rehabilitation using the microperimetry biofeedback function is performed. By identifying the preferred retinal locus (PRL) and moving it to a clinician-determined trained retinal locus (TRL), improvements in fixation stability, visual function, and quality of life have been reported.
It is particularly useful for patients with macular disease who have impaired foveal function and unstable fixation. Conventional perimetry assumes stable central fixation, but microperimetry uses eye tracking to enable accurate measurement even in cases of unstable fixation. It is used not only for macular diseases such as age-related macular degeneration, diabetic macular edema, and macular dystrophy, but also for developing rehabilitation plans for low vision patients.
Defect-mapping microperimetry is a new technique that has gained attention in recent years, and its principle differs from conventional threshold-based methods1).
A fixed-intensity stimulus (typically 10 dB) is presented once on a high-density retinal grid, and at each test point, whether the stimulus is perceived is determined as binary (seen/not seen). While conventional methods measure sensitivity thresholds at each point stepwise, defect mapping is a technique that detects the presence of deep scotomas at high density1).
| Item | Conventional threshold method | Defect mapping method |
|---|---|---|
| Measurement content | Sensitivity threshold at each point | Perception/non-perception of stimulus |
| Spatial density | Relatively coarse | High density |
| Reproducibility (TRV) | 3.3%1) | 1.8%1) |
In a 24-month study, defect-mapping microperimetry demonstrated superior detection of changes over time compared to conventional best-corrected visual acuity (BCVA) measurement, and showed equivalent performance to GA area assessment. The required sample size was reduced by 46% compared to GA area assessment and by 94% compared to best-corrected visual acuity, with a median examination time of 5.6 minutes per eye 1).
Defect-mapping microperimetry is a promising visual function endpoint in clinical trials, showing more robust reproducibility than conventional methods for tracking deep scotomas 1).
The test-retest variability (TRV) of microperimetry is relatively well maintained due to co-registration with structural images and eye tracking.
A fully automated AI-based microperimetry system is under development and is being evaluated in the FirstOrbit study for Stargardt disease1).
To maximize the utility of microperimetry in GA clinical trials, the following standardization has been proposed1).
In studies of patients with age-related macular degeneration, a positive correlation has been reported between macular sensitivity and self-assessed vision-related quality of life (VFQ-39 questionnaire)1). This indicates that microperimetry can serve as an endpoint reflecting patients’ subjective visual function.
Scotopic microperimetry can detect rod dysfunction in early age-related macular degeneration that is not captured by photopic microperimetry2). Decreased scotopic sensitivity may precede structural changes, and it is expected to be established as a functional biomarker predicting the progression of age-related macular degeneration. However, evidence is mainly limited to European studies (Germany 75%, Italy 16.7%, UK 8.3%), and validation in diverse populations remains a future challenge2).
