Form Deprivation Myopia in the Guinea Pig and Chick: Influence of Ambient Lighting Parameters

Abstract

Aims: To determine the effects of periodic, white or quasi-monochromatic, high intensity ambient illumination on the development of form-deprivation myopia (FDM) in the guinea pig and chick. Methods: Experiment (i): FDM was induced in one week old guinea pigs by monocular diffuser wear. Experimental animals (n = 10) were raised for 14 days under a periodic lighting regime where 15 minutes of 300 lux white fluorescent lighting was alternated with 15 minutes 10,000 lux halogen lighting (50% duty cycle) in a 12:12 hour light:dark cycle. Control animals (n = 10) were raised under 300 lux fluorescent ambient lighting in a 12:12 hour light:dark cycle. Cycloplegic refraction was measured with an IR optometer, corneal curvature with an IR videokeratometer, and axial length with high-frequency A-scan ultrasound. Retinal tissue samples were collected for dopamine concentration (DAC) analysis by high performance liquid chromatography - mass spectrometry (HPLC - MS). Experiment (ii): FDM was induced in 4 day old chicks by monocular diffuser wear. Experimental animals were raised for 3 days under a periodic lighting regime where 15 minutes of 300 lux white LED lighting was alternated with 15 minutes of 10,000 lux white (n = 11), or equivalent irradiance blue (n = 12), green (n = 10) or red (n = 13) LED lighting (50% duty cycle) in a 12:12 hour light:dark cycle. Control animals (n = 10) were raised under 300 lux LED ambient lighting on a 12:12 hour light:dark cycle. Non-cycloplegic refraction and biometric measurements were made as for experiment (i). Results: Experiment (i): Guinea pigs raised under the periodic high intensity halogen lighting paradigm exhibited a significant reduction in the degree of relative myopia induced (-2.38 ± 0.41 D) when compared to the 300 lux condition (-4.01 ± 0.61 D; p = 0.038). While this difference in refractive outcome was not significantly correlated with either vitreous chamber depth (VCD) or axial length (AXL), the absolute anterior chamber depth (ACD) of the deprived eyes exposed to high intensity lighting exhibited significantly smaller ACD (p = 0.012). No significant difference was found in retinal DAC by lighting condition. Experiment (ii): No significant difference in relative refraction was found for any of the periodic high intensity white, blue, green or red LED ambient lighting conditions when compared to the 300 lux white LED condition. However, when compared to a previously published control group of chicks (Backhouse, Collins et al. 2013) raised under 300 lux fluorescent lighting (-9.73 ± 0.96 D), significantly less myopia (-5.21 ± 1.47 D, p = 0.017) was induced in the chicks raised under white LED-based 300 lux illumination in this study. The degree of FDM induced was strongly correlated with an increase in VCD under all lighting conditions (R2 = 0.594, p < 0.0001). Conclusions: (i) Daily exposure to periodic high intensity white halogen light (10,000 lux) suppresses development of FDM in pigmented guinea pigs. (ii) Conversely, no significant difference was found in the degree of FDM induced in chicks under the white or quasi-monochromatic high intensity LED lighting conditions. However significantly less FDM (54%) was induced under the 300 lux white LED ambient light condition, when compared to an equivalent control group previously raised under 300 lux fluorescent light in the same laboratory (Backhouse, Collins et al. 2013). Analysis showed that the differing spectral irradiance distributions of white LED and fluorescent lights may explain this outcome.