Kittichai Akrapipatkul1, Grobgarn Wichitnark1 1Department of Ophthalmology, Thammasat University, Thailand Purpose: To compare the residual gas volume of perfluoropropane C 3 F 8 after two different methods of air gas exchange procedures, namely fixed-concentration and fixed-volume, used in rhegmatogenous retinal detachment surgery. Methods: A prospective, randomized clinical trial in 56 patients whose eyes were diagnosed as rhegmatogenous retinal detachment and underwent 23-gauge pars plana

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... rectomy combined with laser endophotocoagulation and air-perfluoropropane gas exchange. In 28 patients whose eyes were in fixed-concentration group, air-perfluoropropane gas exchange were performed using 20% C 3 F 8 50 cc. replacing air within eye globe and the 28 eyes in fixed-volume group, 0.8 cc. of 100% C 3 F 8 was injected into the eyes. We followed up at 1 day, 1 week, and 1 month postoperatively to measure outcomes including postoperative intraocular gas volume (in percent), anatomical retinal reattachment rate and post-operative complications such as ocular hypertension and endophthalmitis. Results: A total of 56 eyes (56 patients) with 23-gauge pars plana vitrectomy combined with laser endophotocoagulation and air-perfluoropropane gas exchange were performed in this study. The patients consisted of 34 men (60.7%) and 22 women (39.3%). Patient ages were between 33-84 years with a mean of 59.84 ± 10.4 years. The mean postoperative residual intraocular gas volume for the fixed-volume method after 1 day, 1 week, and 1 month were 81.25 ± 8.57%, 62.14 ± 12.87%, and 31.25 ± 11.52% respectively. And the mean postoperative residual intraocular gas volume for the fixed-concentration method after 1 day, 1 week, and 1 month were also 85.36 ± 10.71%, 70.36 ± 17.74% and 38.93 ± 16.18% respectively. There was no significant difference in residual intraocular gas volume between the two groups in 1 day and 1 week postoperatively. After 1 month, there was a difference of mean postoperative residual intraocular gas volume between 2 groups; 31.25 ± 11.52% for the fixed-volume method and 38.93 ± 16.18% for the fixed-concentration method (p<0.05). The anatomical retinal reattachment rates were 85.7% and 89.3% for the fixed-volume method and fixed concentration method respectively. There was no significant difference in the rates of ocular hypertension between two groups, and none of the patients developed postoperative endophthalmitis. Conclusions: Both techniques of air-perfluoropropane gas exchange in 23-gauge pars plana vitrectomy combined with laser endophotocoagulation were comparable when considering the anatomical retinal reattachment rate, though there was a smaller intraocular gas volume in fixed-volume technique when compared to fixed-concentration technique. Conflicts of interest: The authors report no confilcts of interest.