Refractive Development and Choroidal Vascularity in the Form-Deprivation Pigmented Rabbit Model

Abstract

Purpose: This study assessed the characteristics of refractive development and choroidal vasculature in the form-deprivation (FD) pigmented rabbit model.

Methods: Monocular FD was performed in three-week-old pigmented rabbits (n = 18 for FD, n = 12 for control). Throughout the eight-week rearing period, refractive errors, corneal curvature radius (CCR), ocular biometric parameters, retinal thickness (RT), and choroidal thickness (ChT) were measured every two weeks using cycloplegic retinoscopy, keratometer, A-scan ultrasonography, and optical coherence tomography (OCT). The choroidal vascularity index (CVI) was calculated from OCT images by measuring the total choroidal area (TCA), stromal area (SA), and luminal area (LA). At the end of the form deprivation, the vitreous dopamine level was measured using an enzyme-linked immunosorbent assay kit.

Results: Relatively myopic refraction was induced in FD eyes after two, four, six, and eight weeks (interocular differences: -1.48 ± 0.88, -1.92 ± 0.90, -1.95 ± 0.80, and -2.00 ± 0.83 diopter; P < 0.001). Furthermore, FD eyes showed significantly longer axial length (AL) and vitreous chamber depth after eight weeks, with mean differences of 0.32 ± 0.03 and 0.32 ± 0.05 mm, respectively (P < 0.001). There were no significant differences in anterior chamber depth, lens thickness, CCR, and RT among the three groups through the intervention (all P > 0.05). After eight weeks, the average ChT of FD eyes was thinner than contralateral eyes (-19.37 ± 7.01 µm; P < 0.001). Additionally, the TCA, SA, and LA in FD eyes were smaller after four, six, and eight weeks (all P < 0.05, week 8: 0.3697 ± 0.0639 vs. 0.4272 ± 0.0968, 0.1047 ± 0.0221 vs. 0.1233 ± 0.0328, and 0.2650 ± 0.0459 vs. 0.3039 ± 0.0659 mm2, respectively). However, the CVI showed no significant difference among the three groups (P > 0.05). Finally, the concentration of vitreous dopamine was lower in the FD eyes, compared with contralateral and control eyes: 0.18 ± 0.20, 0.40 ± 0.67, and 0.33 ± 0.06 ng/mL, respectively (P < 0.05).

Conclusions: Form deprivation led to a relatively myopic shift in pigmented rabbits and a decrease in vitreous dopamine levels. In addition, with the lengthening of AL, the choroid thinned, but CVI remained unchanged.

Translational relevance: Our study offered data about the refractive characteristics of pigmented rabbits to investigate myopia mechanisms. The modified method imaged the choroid of the inferior species more clearly, achieving in exploring the changes of choroidal vasculature in vivo.

Figure 1.

(A) The laboratory photographs of the experimental subjects, including the special occluders in pigmented rabbits. (B) The dopamine levels of vitreous in the FD eyes of pigmented rabbits showing a significant reduction at week 8. ^NSP > 0.05, *P < 0.05.

Figure 2.

Measurements of the RT and ChT in the temporal, central, and nasal positions of the OCT image in vivo. (A) En face fundus image of pigmented rabbit right eye; The temporal, central, and nasal locations in the visual streak (approximately one pupil distance below the optic nerve head). (B) The corresponding measurements of ChT and RT in the OCT image.

Figure 3.

The analysis of the choroidal vascularity index of the right eye in a pigmented rabbit in vivo. (A) The area of the middle two-thirds of the OCT image (3000 µm on either side of the center) was added to calculations of CVI, TCA, LA, and SA. (B) The binarized OCT image after Niblack's auto local threshold tool. (C) The overlay of the binarized image to the raw OCT image shows the choroidal structure components. The whole area represents TCA, the light area (surrounded by yellow lines) represents SA, the dark area represents LA, and CVI is the ratio of LA to TCA.

Figure 4.

Changes in ocular parameters from week 0 to 8. (A) The spherical equivalent was more myopic in the FD eyes than contralateral and control eyes from week 2 to 8. (B) The cornea became more flattened over time and the corneal curvature radius showed no significance among the FD, contralateral, and control eyes. (C) Axial length in the FD eyes was longer than the contralateral and control eyes from week 2 to 8. (D) Vitreous chamber depth in the FD eyes was elongated than the contralateral and control eyes from week 2 to 8. *P < 0.05, **P < 0.01, ***P < 0.001 between the FD and contralateral eyes; ^#P < 0.05, ^##P < 0.01, ^###P < 0.001, between the FD and control eyes.

Figure 5.

Changes in the choroidal thickness in the temporal, central, and nasal position below one pupil distance from the optic nerve head from week 0 to 8. (A) The choroidal thickness in the temporal side of FD eyes was significantly thinner than those of contralateral and control eyes from week 2 to 8. (B) The choroidal thickness in the center of FD eyes was significantly thinner than those of contralateral and control eyes from week 2 to 8. (C) The choroidal thickness in the nasal side of FD eyes was significantly thinner than those of contralateral and control eyes from week 2 to 8. (D) Changes in the average choroidal thickness of the temporal, central, and nasal positions from week 2 to 8. T: temporal; C: center; N: nasal. *P < 0.05, **P < 0.01, ***P < 0.001 between the FD and contralateral eyes; ^#P < 0.05, ^##P < 0.01, ^###P < 0.001, between the FD and control eyes.

Figure 6.

The comparison of changes in choroidal vascularity parameters from week 0 to 8. (A) The total choroidal area in the FD and contralateral eyes was enlarged, and the area in the FD eyes was smaller than that in the contralateral and control eyes. (B) The stromal area in the FD eyes was smaller than in the contralateral and control eyes. (C) The luminal area in the FD eyes was smaller than in the contralateral and control eyes. (D) There was no significance in the choroidal vascularity index between the FD and contralateral eyes. *P < 0.05, **P < 0.01, ***P < 0.001 between the FD and contralateral eyes; ^#P < 0.05, ^##P < 0.01, ^###P < 0.001, between the FD and control eyes.