Investigative ophthalmology & visual scienceSep 19, 2025

Pigmentation background linked to risk of developing experimentally caused nearsightedness in albino and pigmented guinea pigs

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Updated Apr 2, 2026

Abstract

Choroidal thickness was 100 ± 19 µm in crossbred guinea pigs, thicker than albinos but thinner than pigmented guinea pigs.

Crossbred guinea pigs exhibited intermediate choroidal melanin content and tyrosinase activity compared to albino and pigmented breeds.
Albino guinea pigs showed the largest a-wave amplitudes in electroretinograms among the three breeds, indicating differences in retinal function.
Monocular form deprivation caused a significant myopic shift and axial elongation in albino and crossbred guinea pigs, but only a mild myopic shift in pigmented guinea pigs.
Choroidal thickness was associated with reduced in crossbred guinea pigs and less axial elongation in albinos.
The study suggests that crossbreeding may partially restore inherited mechanisms related to myopia susceptibility.

Simplified

PURPOSE: To investigate how pigmentation heritage affects susceptibility to (FDM) through crossbreeding myopia-susceptible albino and myopia-resistant pigmented guinea pigs (GPs).

METHODS: Ninety GPs (albino: n = 29, pigmented: n = 29, F1 crossbred: n = 32) were studied. Eye parameters were measured using retinoscopy and A-scan ultrasound. Scotopic electroretinograms were recorded by full-field electroretinography in 36 naive GPs at 1 and 5 weeks of age. Monocular form deprivation (FD) was applied from 1 to 5 weeks of age in 27 GPs, with 27 littermates as controls. The retina, choroid, and sclera were imaged using optical coherence tomography. From control GPs at 5 weeks, scleral melanin was assessed histologically; choroidal melanin and tyrosinase activity in the choroid and sclera were quantified biochemically.

RESULTS: Crossbreds had a pigmented appearance, and choroidal thickness (ChT, 100 ± 19 µm) was thicker than in albino GPs (69 ± 12 µm, P < 0.001) but thinner than in pigmented GPs (124 ± 19 µm, P = 0.004). Choroidal melanin content and tyrosinase activity followed similar patterns and were significantly different (one-way ANOVA): highest in pigmented GPs, intermediate in crossbreds, and undetectable in albinos. Albinos exhibited the largest a-wave amplitudes across the intensity-response functions among the three breeds. Crossbreds displayed a monotonic b-wave intensity-response function, similar to but with higher amplitudes than pigmented GPs, whereas albinos showed a bell-shaped response pattern before the second rise. FD induced significant myopic shift and axial elongation in albinos (spherical equivalent [SE]: -7.83 ± 4.74 D, P = 0.001; axial length [AL]: 0.20 ± 0.14 mm, P = 0.003) and crossbreds (SE: -5.42 ± 2.90 D, P < 0.001; AL: 0.17 ± 0.09 mm, P = 0.001). Pigmented GPs showed a mild myopic shift (-2.08 ± 1.93 D, P = 0.01) with no significant AL changes (0.03 ± 0.08 mm, P = 0.357). FDM severity differed across breeds (SE: P = 0.006, AL: P = 0.004); thicker baseline ChT was associated with less FDM in crossbreds (P = 0.027) and reduced axial elongation in albinos (P = 0.004); retinal and scleral thicknesses were nonpredictive.

CONCLUSIONS: Crossbreeding improved retinal function and choroidal morphology, while preserving susceptibility to FDM, suggesting a partial restoration of myopia-inducible mechanisms inherited from the albino lineage. These findings support the value of the crossbred model for investigating retinal and choroidal regulation in myopia.

Key numbers

100 ± 19 µm

Choroidal Thickness Comparison

Crossbred guinea pigs vs. albino and pigmented guinea pigs

-7.83 ± 4.74 D

Myopic Shift in Albino Guinea Pigs

Myopic shift after form deprivation in albino guinea pigs

-5.42 ± 2.90 D

Myopic Shift in Crossbred Guinea Pigs

Myopic shift after form deprivation in crossbred guinea pigs

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Pigmentation background linked to risk of developing experimentally caused nearsightedness in albino and pigmented guinea pigs

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