The Study Of Posterior Vitreous Detachment And Subconjunctival Hemorrhage After LASIK By Different Corneal Flaps Creating

Objective1. To compare the incidence and change of posterior vitreous detachment (PVD) early after femtosecond laser and microkeratome-assisted LASIK and study the difference of the incidence and change of PVD and analyze the risk factors.2. To observe the clinical features of LASIK-induced subconjunctival hemorrhage (SCH) and compare the extent and distribution characteristics of SCH after femtosecond laser and microkeratome-assisted LASIK and analyze associated risk factors of LASIK-induced subconjunctival hemorrhage.Methods1. A prospective study was proceeded with patients who accepted LASIK in Tianjin Medical University Eye Hospital from October2011to March2012. According to the patients’ choices, the patients were divided into two groups:the femtosecond laser group and microkeratome group.2. There are40cases (80eyes) in femtosecond laser group and40cases (80eyes) in microkeratome group. The occurrence and changes of PVD in two groups were compared by B ultrasound and OCT examination preoperatively, one week, one month and three month postoperatively. One eye of a patient for statistical analysis was randomly selected.3. A total of54patients (108eyes) were in femtosecond laser group and44patients (88eyes) were in microkeratome-assisted group. The site and extent of hemorrhage, the grade of hyperemia were determined in all subjects. The conjunctiva was divided into the following8equal areas:superior, superior/nasal, nasal, inferior/nasal, inferior, inferior/temporal, temporal, and superior/temporal. Severity of hyperemia was classified as follows:grade0, no hyperemia; grade1, mild; grade2, moderate, and grade3, severe.Results1. In femtosecond group18eyes (45%) had previously existing partial PVD before surgery.11eyes (27.5%) with no preoperative signs of PVD developed partial PVD or original parts of PVD developed. In microkeratome group21eyes (52.5%) had previously existing partial PVD preoperatively,8eyes (20%) with no preoperative signs of PVD developed partial PVD or original parts of PVD developed. There were no statistically significant differences between the incidence and change of PVD in the2groups (χ2=2.257, P=0.133).2. Logistic regression analysis indicated the suction time was associated with the postoperative development of PVD in femtosecond group and long axial length was a significant risk factor in microkeratome group. No serious posterior segment complications such as retinal breaks or retinal detachment were observed postoperatively.3. Hyperemia in microkeratome group was more serious. SCH was more common in femtosecond laser group and the extent of SCH was more serious than microkeratome group (all P<0.05). In femtosecond laser group, SCH was most often localized to the temporal and superior/nasal areas of the conjunctiva (28.7%and29.5%respectively). In microkeratome group, typically, SCH affected the temporal conjunctiva (45.5%).4. Correlations analysis shows hyperemia was correlated with the size of the suction press at the suction time (P=0.02) in femtosecond laser group and spherical equivalent (P=0.003) in microkeratome group. Multivariate logistic regression analysis revealed that the suction time and spherical equivalent were significantly associated with an increased risk of SCH in femtosecond laser group (all P<0.05).Conclusions1. The femtosecond laser does not increase the incidence of PVD compared to microkeratome-assisted LASIK. The long axial length was more likely to occur. No serious posterior segment complications were observed during the3months follow-up period.2. The major risk factor for LASIK-induced subconjunctival hemorrhage is the suction time. The size of the negative pressure during the suction time was significantly associated with an increased risk of hyperemia. LASIK-induced SCH is not associated with the extent of hyperemia.