Risk Factors for Opaque Bubble Layer in Small Incision Lenticule Extraction (SMILE).

PURPOSE: To assess the independent effect of myopia and astigmatism on the risk of the occurrence of opaque bubble layer (OBL) in small incision lenticule extraction (SMILE) and further investigate the relationship between scanning depth and OBL.

METHODS: Twenty-two cases and 317 controls were included in a case-control study from the database of Tianjin Eye Hospital from April 2015 to July 2016. Baseline characteristics were recorded and all of the eyes were manually reviewed by two different observers masked to preoperative refractive status. Multiple regression analysis was used to assess the independent relationship between the attempted correction in diopters and the risk of OBL and to further analyze the association between scanning depth and the risk.

RESULTS: The risk of OBL significantly decreased with increasing myopia (diopters) (odds ratio [OR] = 0.44; 95% confidence interval [CI]: 0.30 to 0.64; P < .0001). The risk of OBL also significantly decreased with increasing astigmatism (diopters) (OR = 0.10; 95% CI: 0.02 to 0.42; P = .0017). Lenticular thickness changed by 14.86 μm per diopter for myopia (β =14.86; 95% CI = 14.56 to 15.15; P < .0001) and 15.10 μm per diopter for astigmatism (β = 15.10; 95% CI = 13.96 to 16.24; P < .0001), respectively.

CONCLUSIONS: A low correction was a significant independent risk factor for OBL during SMILE and the effect of astigmatism on OBL was greater than that of myopia. Deepening the photodisruption plane appropriately may reduce the risk of OBL. [J Refract Surg. 2017;33(11):759-764.].