Abstract
Purpose :
The posterior pole of the eye is well known to expand in myopic eyes and is accompanied by scleral remodelling, although collagen degradation takes some time to emerge. Less attention has been directed to other regions of the eye. We employed high resolution scanning acoustic microscopy (SAM) to scan the whole globe during the early phases of myopia in form-deprived guinea pigs (GPs) and mapped the location of changes in peripheral scleral biomechanical parameters to gain insight into precursor mechanisms.
Methods :
14 eyes from seven 2-week-old GPs (after 1-week of monocular form deprivation myopia (FDM)) were cryosectioned (6µm, horizontal or vertical) and scanned with SAM (4µm resolution). Whole eye maps of the bulk modulus (K) were derived using a model-based approach. Key sections were selected, and sclera layer segmented and analyzed.
Results :
K values were generally lower in myopic eyes compared to control eyes, but the largest differences tended to occur in the peri-equatorial area rather than the posterior pole. In control eyes, K increased by 0.117 GPa for every 1mm (p<0.001) away from the equator (marked as “0 mm”) within the nasal posterior-equatorial subregion (PES, from -2 mm posterior eccentricity), reaching a maximum at the equator, beyond which K decreased by 0.090 GPa/mm in the nasal anterior-equatorial subregion (AES, p=0.008) towards the limbus. The temporal, superior and inferior AESs followed a similar trend with K decreasing by 0.089, 0.013 and 0.192 GPa/mm (p=0.009, 0.002 and <0.001, respectively). In contrast, within temporal, superior and inferior PESs, K did not change with eccentricity (all p>0.05).
After 1 week of myopia, significant trends were seen in the AES with K decreasing by 0.152, 0.261 and 0.081 GPa/mm in the nasal, temporal and superior AES (p=0.002, <0.001 and <0.001) but increasing by 0.197 GPa/mm (p=0.03) in the inferior AES. In the PES, K changes in the PES were smaller in magnitude and more varied.
Conclusions :
Scleral bulk modulus measures compressibility, with lower K values implicating a more compressible sclera, and we show this tends to occur about the eye equator early during myopia development. This surprising result suggests that peripheral scleral factors are important precursors to the ultimate changes at the posterior pole and may direct targeted therapies to halt early stage myopization.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.