Abstract:

Objective

To evaluate the accuracy of three corneal astigmatism measurement methods Pentacam SimK＆posterior corneal astigmatism，IOLMaster 700 SimK，and IOLMaster 700 total keratometry（TK）in predicting postoperative refractive outcomes after toric intraocular lens（IOL）implantation.

Methods

A total of 34 patients（34 eyes）with cataracts who underwent phacoemulsification cataract removal combined with Toric IOL implantation at the Ophthalmology Center of Beijing Tongren Hospital affiliated with Capital Medical University from September 2022 to December 2024 were enrolled.Among them，there were15 patients（15 eyes）male and 19 patients（19 eyes）female with an average age of（57.7±16.9）years（ranging from 28 to 83 years）.All patients were examined using three methods：Pentacam measuring SimK combined with posterior corneal surface astigmatism，IOLMaster 700 measuring SimK，and IOLMaster 700 measuring TK.These examinations were conducted for uncorrected distance visual acuity，best corrected visual acuity，subjective refraction results，preoperative axial length，central anterior chamber depth，lens thickness，corneal diameter，and corneal curvature both before surgery and 3 months postoperatively.The obtained corneal astigmatism parameters were substituted into the Barrett Toric IOL calculation formula to compute IOL refractive power and predict postoperative refractive power.The vector method was used to calculate the prediction error（PE），mean absolute error（MAE），centroid error，and error distribution percentage for the three measurement methods 3 months postoperatively.The number and percentage of patients with preoperative with-the-rule（WTR）and against-the-rule（ATR）astigmatism were recorded for the three detection methods.Age，axial length，corneal curvature，IOL refractive power，and MAEall followed a normal distribution and expressed as±s.Paired t test were used for comparisons before and after surgery.Gender，eye side，and error distribution were described using counts（number of eyes）and percentages.One way repeated measures ANOVA was used to compare the three measurement methods.When the difference was statistically significant，further pairwise comparison was made.Chi square test was used to compare the three measurement methods.

Results

Preoperative corneal astigmatism and postoperative residual corneal astigmatism were（2.76±1.10）Dand（0.65±0.51）D，respectively，with a statistically significant difference（t＝15.760，P＜0.05）.MAE of Pentacam measured posterior surface，Master SimK，and Master TK were（0.63±0.36）D，（0.65±0.35）D，and（0.65±0.39）D，respectively.The Pentacam measured posterior surface had a lower MAE compared to Master SimK，with a statistically significant difference（t＝-2.360，P＜0.05）.Three methods showed centroid errors in the WTR direction，with Master SimK having the largest centroid error of（0.19±0.72）D＠119°.The number of cases with prediction errors within±0.50 D were 20 cases（20 eyes），15 cases（15 eyes），and 17 cases（17 eyes），accounting for 58.8%，44.1%，and 50.0%，respectively.

Conclusions

Compared to IOLMaster 700 SimK，both IOLMaster 700 TK and Pentacam-measured SimK combined with posterior corneal astigmatism provided higher accuracy in predicting postoperative refraction after Toric IOL implantation.Incorporating posterior corneal astigmatismdata can optimize total corneal astigmatism assessment，thereby improving refractive prediction accuracy following Toric IOL surgery.

Key words: Cataract, Intraocular lens calculation formula, Toric intraocular lenses, Posterior corneal astigmatism, Predictive error