Abstract
The fundamental transverse mode (TEM00) is preferable for experimental and theoretical study on the laser-induced retinal injury effect, for it can produce the minimal retinal image and establish the most strict laser safety standards. But actually lasers with higher order mode were frequently used in both earlier and recent studies. Generally higher order mode leads to larger retinal spot size and so higher damage threshold, but there are few quantitative analyses on this problem. In this paper, a four-surface schematic eye model is established for human and macaque. The propagation of 532-nm laser in schematic eye is analyzed by the ABCD law of Gaussian optics. It is shown that retinal spot size increases with laser transverse mode order. For relative lower mode order, the retinal spot diameter will not exceed the minimum laser-induced retinal lesion (25 ~ 30 μm in diameter), and so has little effect on retinal damage threshold. While for higher order mode, the larger retinal spot requires more energy to induce injury and so the damage threshold increases. When beam divergence is lowered, the retinal spot size decreases correspondingly, so the effect of mode order can be compensated. The retinal spot size of macaque is slightly smaller than that of human and the ratio between them is independent of mode order. We conclude that the laser mode order has significant influence on retinal spot size but limited influence on the retinal injury effect.
Highlights
This is an Open Access article published by World Scientic Publishing Company
Based on the study of thermal damage model by Zuclich et al.,[4] the dependence of retinal damage threshold on the retinal spot size varies with injury mechanism which is determined by exposure duration
For a pulse ranging from microseconds to seconds, the retina damage is induced by thermal e®ect, and the thresholds, in terms of total intraocular energy (TIE), are proportional to the retinal spot diameter.[5,6,7]
Summary
This is an Open Access article published by World Scientic Publishing Company Based on the study of thermal damage model by Zuclich et al.,[4] the dependence of retinal damage threshold on the retinal spot size varies with injury mechanism which is determined by exposure duration. The earlier thresholds were found to be generally larger than the recent values, which probably resulted from underestimation of the retinal spot size.[12,13] Nowadays, with signicant advances in laser technology, lots of lasers can export a beam with TEM00 mode. A question is raised that whether the higher order modes can be used in the experimental study on the laser injury thresholds. The laser wavelength in our calculation is 532 nm which is widely used for the study on the laser-retina injury e®ect
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