Decreased Fixation Stability of the Preferred Retinal Location in Juvenile Macular Degeneration

Abstract

Macular degeneration is the main cause for diminished visual acuity in the elderly. The juvenile form of macular degeneration has equally detrimental consequences on foveal vision. To compensate for loss of foveal vision most patients with macular degeneration adopt an eccentric preferred retinal location that takes over tasks normally performed by the healthy fovea. It is unclear however, whether the preferred retinal locus also develops properties typical for foveal vision. Here, we investigated whether the fixation characteristics of the preferred retinal locus resemble those of the healthy fovea. For this purpose, we used the fixation-offset paradigm and tracked eye-position using a high spatial and temporal resolution infrared eye-tracker. The fixation-offset paradigm measures release from fixation under different fixation conditions and has been shown useful to distinguish between foveal and non-foveal fixation. We measured eye-movements in nine healthy age-matched controls and five patients with juvenile macular degeneration. In addition, we performed a simulation with the same task in a group of five healthy controls. Our results show that the preferred retinal locus does not adopt a foveal type of fixation but instead drifts further away from its original fixation and has overall increased fixation instability. Furthermore, the fixation instability is most pronounced in low frequency eye-movements representing a slow drift from fixation. We argue that the increased fixation instability cannot be attributed to fixation under an unnatural angle. Instead, diminished visual acuity in the periphery causes reduced oculomotor control and results in increased fixation instability.

Peripheral Visual Fields in ABCA4 Stargardt Disease and Correlation With Disease Extent on Ultra-widefield Fundus Autofluorescence

“…Moreover, although the widefield kinetic perimetry testing followed the same strategy and standards for all patients, we did not account for test-retest variability measurements for each individual patient. 44–46 In addition, by grouping subtypes IIIa, IIIb and IIIc, this study was unable to determine whether the extent or the severity of atrophy in the periphery was responsible for the peripheral visual field loss of our patients.…”

Integrating oculomotor and perceptual training to induce a pseudofovea: A model system for studying central vision loss

“…The saccadic velocity threshold of 30°/s, saccadic acceleration threshold of 8000°/s 2 , and saccadic motion threshold of 0.1° were used to define saccades from fixations (Bethlehem et al, 2014; Lingnau et al, 2008; Smith, Glen, Monter, & Crabb, 2014; Van der Stigchel et al, 2013). Note that previous studies (Aguilar & Castet, 2011; Bernard et al, 2007) reported the unwanted triggering of slow eye movements (smooth pursuits) in the absence of a target for tracking (as if the scotoma becomes an actual moving target).…”

The retinal locus of fixation in simulations of progressing central scotomas

“…The fixations were separated from other events (blinks and saccades) using the Eyelink parsing algorithm. The algorithm classified fixations, saccades, and blinks using a saccadic velocity threshold of 308/s, a saccadic acceleration threshold of 80008/s 2 , and a saccadic motion threshold of 0.18 (Lingnau, Schwarzbach, & Vorberg, 2008;Van der Stigchel et al, 2013;Bethlehem et al, 2014;Smith, Glen, Monter, & Crabb, 2014;Liu & Kwon, 2016). If the eye movement was below the velocity and acceleration thresholds criteria, then it was categorized as a fixation eye movement; otherwise, it was categorized as a saccade eye movement.…”