Clinical Observation Of The Shammas-PL Formula In Predicting Intraocular Lens Power After Excimer Laser Surgery

BackgroundAs the rapid development of the refractive surgery over the past decades, since the radial keratotomy(RK) in 1970 s to excimer and femtosecond laser surgery nowadays, a large number of patients with refractive error receive the operations in order to pursue a better quality of life. However with the passage of time, this part will also have to face the cataract surgery which disease is complicated or age-related. At present the phacoemulsification is gradually perfect on technique aspect that the operation effect on postoperative vision has gradually decreased. But for the patients who have received the myopia operation before, there often appears farsightedness after cataract surgery because of the error of predicted low intraocular lens power and is difficult to achieve the expected effect. Therefore, accurate prediction of intraocular lens power became the hotspot in present study, it is also a new challenge for cataract surgery. ObjectiveTo explore the accuracy of the Shammas-PL formula in predicting intraocular lens power after excimer laser surgery. MethodsCollected 12 patients(18 eyes) with cataract after excimer laser surgery whom were treated in our hospital during July 2014 to December 2015. And retrospective analyzed them. These patients consist of 2 case with 4 eyes after PRK+ALK, 10 case with 14 eyes after LASIK. Measured the anterior chamber depth, axial lengths and corneal curvature with Al-scan, calculated the intraocular lens power by the SRK/T formula, Shammas-PL formula and Haigis formula. Predicted a intraocular lens power according to age, profession, coordination and experience method. Following up 3 months to 1 year, compared the uncorrected visual acuity(UCVA) and the best corrected visual acuity(BCVA) before operation with those 1w, 3m after operation respectively. And compare the predicted refractive power with the actual refractive power 1w, 3m after operation respectively. Explored and analyzed the accuracy of the calculate method. T test was used for statistical analysis. ResultsThe preoperative UCVA and the UCVA 1w after operation were 3.81±0.66 and 4.60±0.25, respectively(p<0.01). The preoperative BCVA and the BCVA 1w after operation were 4.24±0.45 and 4.66±0.28, respectively(p < 0.01). The actual refractive power 1w after operation was-1.83±1.47 D. The predicted refractive powers of the SRK/T formula, Shammas-PL formula and Haigis formula were-3.99±1.76D(p<0.01),-1.74±1.31D(p>0.05) and-2.63±1.67D(p>0.05), respectively. The refractive error values of the SRK/T formula, Shammas-PL formula and Haigis formula were 2.07±1.50 D, 0.89±1.20 D and 1.19±1.15 D, respectively. If treat the error value<1.0D as the standard, the accuracy rates of the SRK/T formula, Shammas-PL formula and Haigis formula were 16.67%, 77.78% and 61.11%, respectively. If treat the error value<0.5D as the standard, the accuracy rates were 11.11%, 50.00% and 27.78%, respectively. The UCVA and the BCVA 3m after operation were 4.61±0.27 and 4.77±0.23, respectively(p>0.05). The actual refractive power 3m after operation was-2.04±1.10D(p>0.05). The refractive error values of the SRK/T formula, Shammas-PL formula and Haigis formula were 1.94±1.40 D, 0.89±0.66 D, 1.13±0.99 D, respectively. If treat the error value<1.0D as the standard, the accuracy rates were 22.22%, 72.22% and 50.00%, respectively. If treat the error value<0.5D as the standard, the accuracy rates were 11.11%, 38.89% and 33.33%, respectively. Conclusions1. The UCVA and BCVA improved generally after cataract operation;2. The SRK/T formula was not applicable in predicting intraocular lens power after excimer laser surgery;3. The Shammas-PL formula has the better accuracy than the Haigis formula in predicting intraocular lens power after excimer laser surgery, but it always shows overcorrection;4. The experience method can be used for reference.