Abstract
Background and Objectives
High energy loss of 1,319 nm laser due to pre‐retinal water absorption makes the ocular axial length more critical, while the relative low absorbance of melanin makes retinal pigmented epithelium less contributing, to retinal damage threshold. However, both have never been illustrated experimentally. Here we determined and compared the retinal damage thresholds at this wavelength in three species with different axial lengths and retinal pigmentations. The corneal damage threshold was also determined for further comparative analysis.
Materials and Methods
The retinal damage thresholds of albino rat, non‐pigmented and pigmented rabbit, and the corneal damage threshold of non‐pigmented rabbit were determined for 0.2 and/or 0.4‐second exposure durations. The incident beam diameter on cornea was 5 mm for rabbit retinal and 2 mm for rat retinal and rabbit corneal lesion. Minimum visible lesions were examined 1‐ and 24‐hour post‐exposure. Probit analysis was used to establish the estimated damage threshold for 50% of exposures (ED~50~). The direct transmittance of pre‐retinal eye media was used for further comparative analysis.
Results
The retinal ED~50~ of albino rat for 0.2 seconds, non‐pigmented rabbit for 0.2 seconds, 0.4 seconds, pigmented rabbit for 0.4 seconds was 8.8, 12.1, 22.5, 18.5 J/cm^2^ (0.28, 2.4, 4.4, 3.6 J in total intraocular energy (TIE)). The corneal ED~50~ was 86.1 J/cm^2^. Under the condition of 5 mm beam diameter and 0.4‐second exposure duration, the calculated retinal ED~50~ of human was higher, while that of rhesus monkey was lower than the corneal ED~50~.
Conclusion
For 1,319 nm laser radiation, the ocular axial length has great, while the retinal pigmentation has only slight influence on retinal damage threshold. The relative lower direct transmittance of human eye media makes the retina more resistant to laser lesion, which should be considered when deriving human maximum permissible exposure (MPE). Lasers Surg. Med. 43:306–312, 2011. © 2011 Wiley‐Liss, Inc.