Sir,
I read with interest the paper by Al-Hussainy et al.1 In their paper, the authors concluded that reducing the exposure time and increasing the laser power while performing PRP can reduce pain significantly without compromising the long-term results of the treatment.
It has been our experience that using scatter retinal laser application with shorter duration setting, as described by the author, yields uneven and much smaller sized scars than the traditionally used longer duration laser setting (the scars have less than intended treatment spot size and with larger untreated retina in between). This can be explained by both insufficient time available for heat conduction into surrounding tissue to cause thermal damage and the Gaussian distribution of the energy across laser beam.2 Additionally, it can be calculated from data provided by the authors that with reduced exposure setting, the mean laser energy necessary to achieve visible retinal reaction was much less (0.02 ms × 489 mW=9.78 mJ vs 0.1 ms × 178 mW=17.8 mJ) and, hence, expectedly lesser associated tissue damage and subsequent scaring.
Although the immediate visible retinal burns were apparently similar, the authors failed to mention the difference in the scar appearances between the groups in their study. In our experience, spaced smaller retinal scars produced by shorter duration laser setting are usually indicative of inadequate treatment and necessitates further laser application to control the proliferative process.
As the end point of their study has not been clarified, it is difficult to gain any knowledge regarding the time scale as well as the number of the sessions that were required to achieve regression of neovasculrization in their series and conclude effectiveness of their setting, compared with any published data.
Finally, their treatment setting using Volks lens, 300-μm spot size and high power requirement (mean 0.47 W, no SD was mentioned) is likely to breach laser safety to the anterior segment, where the laser energy fluence is much higher than the retinal plane due to smaller laser beam size at the corneal plane.3
References
Al-Hussainy S, Dodson PM, Gibson JM . Pain response and follow-up of patients undergoing panretinal laser photocoagulation with reduced exposure times. Eye 2008; 22: 96–99.
Walsh Jr JT, Flotte TJ, Anderson RR, Deutsch TF . Pulsed CO2 laser tissue ablation: effect of tissue type and pulse duration on thermal damage. Lasers Surg Med 1988; 8 (2): 108–118.
Shiraki K, Moriwaki M, Kohno T, Yanagihara N, Miki T . Inadvertent corneal burn by using indirect wide-field contact lenses and different laser beam delivery systems during experimental fundus photocoagulation. Lasers Surg Med 2000; 27 (1): 43–48.
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Toufeeq, A. Pain response and follow-up of patients undergoing panretinal laser photocoagulation (PRP) with reduced exposure times. Eye 23, 491 (2009). https://doi.org/10.1038/eye.2008.111
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DOI: https://doi.org/10.1038/eye.2008.111
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