A Novel Nomogram Based On The Total Corneal Astigmatism For Paired Anterior Penetrating Femtosecond Laser Arcuate Keratotomy

To develop a nomogram for paired anterior penetrating femtosecond laser arcuate keratotomy (FLAK) based on the total corneal refractive power (TCRP) astigmatism (CA_tot) during femtosecond laser-assisted cataract surgery (FLACS)

 

Shanxi Eye Hospital, Taiyuan, Shanxi Province, China

Paired anterior penetrating FLAKs were created at an 8.0 mm optical zone with a depth of 90% by LenSx laser. CA_tot measurements were obtained preoperatively and after 1 year with Scheimpflug tomography (Pentacam HR; Oculus, Wetzlar, Germany) for 3- and 5-mm diameter zones respectively. Vector analysis using the Alpins method to describe the surgically induced astigmatism (SIA) and correction index (CI). Holladay-Cravy-Koch formula was used to calculate the corneal net changes in 3-mm diameter zone caused by the FLAKs. Multiple regression analysis with generalized estimating equations was used to develop the nomogram.

The study included 64 eyes of 64 patients. The mean preoperative CA_tot (3-mm: 1.50 ± 0.59 D; 5-mm: 1.45 ± 0.52 D) were significantly reduced to 0.73 ± 0.46 D and 0.76 ± 0.49 D respectively at 1-year follow-up period (both P<0.05). The 3-mm and 5-mm SIA was 1.16 ± 0.61 D and 1.03 ± 0.56 D respectively (P<0.01). The 3-mm and 5-mm CI was 0.72 and 0.64 (P>0.05). The mean corneal net changes were -0.97 D in 3-mm zone, -0.85 D in 5-mm zone respectively. A nomogram is established based on age, length, and location of the FLAKs.

Paired anterior penetrating FLAKs showed efficient and stable corneal astigmatism reduction 1 year postoperatively. The nomogram is proposed according to the CA_tot, which considers the effect of posterior astigmatism of the cornea, may further improve correction accuracy.