Abstract
We enrolled 500 highly myopic eyes and 50 controls in this hospital-based prospective cohort study. The fixation ellipse angle and area in terms of the bivariate contour ellipse area (BCEA) were measured with Macular Integrity Assessment microperimetry. Optic disc tilt and rotation were evaluated with retinal images. The associations between fixation and optic disc changes were assessed. Both 63% and 95% BCEA correlated positively with axial length (AL) (both r = 0.230, P = 0.001) in highly myopic group, and were significantly higher than the control group (both P < 0.001). The direction of fixation ellipse presented clockwise rotation in the right eyes and anti-clockwise rotation in the left eyes with the increase of AL in highly myopic group (AL ≥30 vs <30 mm: OD 76.12 ± 51.17°: vs 90.60° ± 51.28°, P = 0.029; OS 94.73 ± 57.45° vs 87.82 ± 55.15°, P = 0.371). The angle between the long axis of the fixation ellipse and the long axis of the optic disc (AngleF−D) distributed in various directions: 0–30° (34.6% almost parallel) ≈60–90° (34.4% almost vertical) >30–60° (31% oblique). AngleF−D increased slightly with the AL (r = 0.105, P = 0.024). In highly myopic eyes, fixation stability decreased with the AL, and superior rotation of the fixation ellipse increased with AL. The long axis of fixation ellipse and the long axis of optic disc became less parallel to each other with increasing AL. Our data may provide clues for improvement of fixation evaluation designs of biometric instruments.
Highlights
A poor fundus can result in poor visual function, and the ability to maintain steady fixation may be impaired in high myopes
Previous studies of myopic disc changes have mainly focused on glaucomatous eyes, in which disc torsion and parapapillary atrophy (PPA) are often used as predictors of visual field defects
Previous studies have managed to judge the direction of corneal astigmatism from the features of the optic disc[16], as the latter is easier to visualize with a funduscope, and we speculate if there are some correlations between the fixation ellipse direction and the optic disc direction, as the two seems anatomically and functionally related
Summary
A poor fundus can result in poor visual function, and the ability to maintain steady fixation may be impaired in high myopes. Healthy eyes use central fixation to maintain the target, and the magnitudes of the eye movements are small These eye movements are larger in highly myopic eyes, as indicated by the fixation ellipse area, according to our previous study[7,8]. The direction of fixation ellipse calculated by MAIA microperimetry may provide us with extra information on the trace of those most frequently used macular loci during fixation, which will be useful in those with poor fundus, such as highly myopic cases According to this direction of fixation ellipse, we may be able to correct data measured by the IOLMaster in the future, or to obtain the “most frequently used macular loci corrected AL” in eyes with high myopia. The aims of this study were to characterize the fixation in high myopes with the MAIA microperimetry system and to investigate its anatomical association with optic disc changes
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