Myopia control by atropine and latanoprost in a guinea pig model: impact on refraction, biometry and scleral mechanics

Abstract

Purpose : Form-deprivation (FD) has been shown to produce myopia in a guinea pig model. In this pilot study, we quantified changes in refractive error, axial length, and scleral biomechanical properties in FD guinea pigs, followed by atropine and latanoprost treatments, which have been proposed/used as pharmacological alternatives for myopia control.

Methods : FD model was induced in three tricolor guinea pigs (2-12 weeks-old) with a diffuser placed in one eye for 10 weeks (from postnatal day 14). The deprived eye of each animal was treated (from postnatal day 21) by a daily drop of Latanoprost (LA, 0.005%), Atropine (AT, 1%) or Balanced Salt Solution (BSS). Refractive errors and axial lengths were measured by retinoscopy and with custom Swept Source Optical Coherence Tomography (SS-OCT, 1060nm), respectively. Animals were euthanized and the scleral elastic properties (24h post-mortem) characterized. Elastic waves on the scleral surface were generated in custom ACUS-OCT (Air-Coupled Ultrasonic (3.5kHz) SS-OCT, 1300nm). Shear modulus (G) was estimated from wave speeds. Subsequently, scleral strips (1x3 mm, 4 strips per eye) were cut and used to measure stress-strain (uniaxial stretcher). Young's modulus (YM) at 14% strain was calculated from stress-strain curves fitting.

Results : After 10 weeks of FD, the deprived eye was 0.15mm(LA), 0.33mm(AT), 0.30mm(BSS) longer and its refraction was -3.3D(LA), -7.5D(AT), -8.3D(BSS) higher than its fellow non-deprived eye. Elastic waves (from ACUS-OCE) propagated by -1.4m/s(LA), +3.2m/s(AT) and +0.6m/s(BSS) faster, which resulted in G reduction by 10.7MPa(LA) and increase by 20.3MPa(AT) and 10.8MPa(BSS) in the myopic than in the fellow eye. YM was reduced by 1.2MPa(LA), 1.8MPa(AT) and 3.1MPa(BSS) in the myopic in comparison with the fellow eye.

Conclusions : During the study period, Latanoprost inhibited myopia progression in form-deprived guinea pigs, with a 55%/56% higher effectiveness in axial length/refractive error reduction than Atropine (which did not show differences from a BSS-treated control). Both treatments attenuated the stiffness (Young's Modulus) reduction in myopic eyes, but only Atropine increased shear modulus. OCT-based technologies allow quantification of eye geometry and biomechanics and provide insights on the mechanisms underlying pharmacological myopia treatments and their ocular tissue modulation.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.