Optometry & Visual Performance 122 Volume 14 | Issue 2 | June 2026 the attainment of consistent and accurate foveation. Table 2 presents some of the objective approaches to assess fixation. This allows for a more detailed, quantitative, and unbiased appraisal of fixational ability, including the overall pattern and types of abnormal eye movements (e.g., increased amblyopic drift, large saccadic intrusions). An early approach was the infrared, horizontal, limbal technique (Figure 2).1 Basically, the eyes are bathed with safe levels of infrared light, and the two detectors for each eye are aimed at the horizontal nasal and temporal regions to assess the differential light reflection on the sensors: the white sclera reflects more light than the darker iris. This type of system has been used in many laboratories over the past 75 years, as well as in the clinical domain (e.g., ReadAlyzer; https://www. compevousa.com/). Again, the patient is instructed to fixate carefully on a small target on a screen, usually 4057 cm away along the midline in the primary position, for several seconds. The resultant horizontal fixational pattern can be viewed as a function of time, printed out for the record, and even quantified if a prior calibration was performed. Newer technology uses a video-based approach (Figure 3).1 Here, small video cameras are aimed at each eye, and both the horizontal and vertical eye movements are recorded during fixation. Thus, this provides a more complete picture of fixation. These systems are easy for the clinician to use and provide a wide linear range of movement for accurate assessment. This includes various laboratory devices (e.g., Tobii; https://gaming.tobii.com/) as well as clinical devices (e.g., RightEye; https://righteye.com/). However, the latter system does not allow for testing of fixation under monocular conditions, which is critical for both EF assessment in amblyopic eyes, as well as eccentric viewing (EV) assessment in ocular disease/visual field loss situations; furthermore, it does not present the eye movements as a function of time like most instruments do. Rather, it presents each fixational sample in x,y Cartesian coordinate space with disregard for time. The third and newest approach has been the use of microperimetry for fixational testing (Figure 4).7-9 This involves direct visualization of the fundus area of interest (similar to visuoscopy), typically the foveal/ macular region of only one eye. The patient is asked to fixate the target carefully, and the calibrated system samples both the horizontal and vertical eye positions at 25 Hz (i.e., 25 samples per second) or higher for 30 seconds. Once the test is completed, an overlay of the area of fixation is presented as a series of calibrated bivariate ellipses, typically enclosing the retinal regions of fixation 25, 50, 75, and 100% of the time:1 the less fixational scatter, the smaller the ellipse, and the better the fixation. From this, one can obtain the retinal point of maximal fixation and its variability, all objectively documented—that is, either the fovea, the EF point, or the EV point. This approach is so important because the Infrared limbal sensing Video recording Microperimetry Table 2. Objective Approaches to Assess Fixation Figure 2. Infrared limbal eye movement system Figure 3. Tobii eye tracking video system assessing reading eye movements Figure 4. Microperimetry showing eccentric and unsteady fixation in an amblyope
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