Abstract
Purpose :
While abnormal visual manipulations can influence refractive development, the specific impacts of astigmatic blur on the initial stages of ocular development are not fully understood. This study aimed to determine the effects of astigmatic blur on early eye growth.
Methods :
White Leghorn chicks were randomly assigned to the treatment or normal group (n=15 per group) at post-hatching day 5 (P5). Astigmatic blur, either With-The-Rule (WTR) or Against-The-Rule (ATR), was imposed by attaching crossed-cylinder lenses (+4.00DS/-8.00DC) with axis oriented at 90° (WTR) or 180° (ATR) over the orbit of the right eyes for 3 days. Ocular axial dimensions were measured for all birds on a daily basis using a custom-made high-resolution A-scan ultrasonographer. For a subset of birds (n≥11 per group), the corneal shape was measured at P8 using a custom-built Placido-based corneal topographer. The acquired corneal parameters were decomposed using power vector analysis to derive J0 and J45 corneal astigmatism. ANOVAs were used to compare ocular parameters across groups. All data were expressed as mean±SD.
Results :
As short as three days of exposure to astigmatic blur induced significant corneal astigmatic changes. The two treated groups developed significantly higher magnitudes of corneal astigmatism than the normal group (WTR: 2.18±0.89D; ATR: 2.44±0.72D; Normal: 1.18±0.64D, p<0.001). In addition, both treated groups exhibited more negative J45 compared to the normal group (WTR: -0.72±0.66D; ATR: -0.50±0.58D; Normal: +0.12±0.38D, p=0.001), and the ATR-treated group developed more positive J0 than the normal group (WTR: -0.11±0.63D; ATR: +0.77±0.52D; Normal: -0.40±0.33D, p<0.001). Significant effects of astigmatic blur were also found in the anterior segment: ATR-treated birds exhibited longer anterior chamber depth (ACD) compared with that of the other two groups at P8 (p≤0.041) and thinner crystalline lens thickness (LT) than normal birds at P7 (p=0.044) and P8 (p=0.021).
Conclusions :
Even a brief 3-day exposure to astigmatism can induce compensatory changes in corneal shape in WTR- and ATR-treated chicks. ATR-treated birds also developed longer ACD and thinner LT than normal birds. This study provides new insights into the influential role of astigmatic blurs on early anterior segment development.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.