Abstract
Purpose :
There is no unifying postulate that explains how and why two eyes within the same environment and identical genetic influences develop asymmetrically and produce different refractive errors, sometimes leading to amblyopia and loss of binocularity. This unique pilot study analysed extraocular muscle (EOM) characteristics of the more emmetropic globe acting as an intrinsic control for the more myopic globe in subjects with non-strabismic myopic anisometropia (anisomyopia) of 1D or more by high resolution fast spin echo T2 weighted (T2FSE) surface coil orbital magnetic resonance imaging {(MRI), 3T Siemens Skyra}.
Methods :
5 subjects (10 orbits) of average age 20±7.2 years (3 males) with anisomyopia were imaged with the subject fixating at a central target. 2mm thick contiguous quasi-coronal image planes perpendicular to the orbital axis were analysed for EOM pulley locations, EOM cross sections and LR-SR band length while quasi-sagittal and axial planes were used to measure rectus EOM and optic nerve (ON) length, all by Image J software as per published norms (Figure 1A-E). A comprehensive ophthalmic evaluation was performed in all subjects.
Results :
The average refractive error and axial length (AL) in the more myopic eye was -7±3.6D, 26.1±0.4mm versus -1.5±2.4D,24.1±1.7mm in the more emmetropic eye (p=0.02, 0.04).None of the subjects were amblyopic in either eye. The average stereopsis was 520±455 arcseconds (TNO test). 2 subjects with moderate anisomyopia of 2D demonstrated 100 arcseconds stereopsis. There was marked effacement and lengthening of the LR-SR band in the more myopic eye (10.4±0.8mm) versus the more emmetropic eye (8.6±0.6mm, p=0.003). The antero-posterior extent of the LR-SR band was seen in 1.4±0.5 slices in the more myopic eye versus 3.2±0.4 slices in the more emmetropic eye (p=0.0004). The rectus EOM and ON length was similar in both eyes.
Conclusions :
Anisomyopia provides a unique biological control to evaluate structural and biomechanical ocular and adnexal differences in the same individual.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.