Intraocular Lens Power Calculation for Combined Cataract and Pterygium Surgeries

Zebin Li,1,2,* Beiling Tan,1,2,* Yanting Chen,2 Rubing Liu,1,2 Han Wang,1,2 Jifa Kuang,2 Furong Luo,2 Mingbing Zeng1,2,* 1State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, Guangdong, People’s Republic of China; 2Hainan Eye Hospital and Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Haikou, Hainan, People’s Republic of China*These authors contributed equally to this workCorrespondence: Mingbing Zeng, State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, Guangdong, People’s Republic of China, Tel +86898-68628583, Fax +86898-68628587, Email zengmingb@mail.sysu.edu.cnBackground: For patients with both cataract and pterygium, combined surgery reduces the burden and cost associated with two separate procedures. However, the accuracy of intraocular lens (IOL) power calculation is compromised in eyes with pterygium, as the lesion disturbs the corneal surface and tear film, leading to erroneous keratometry measurements. This often results in unpredictable postoperative refraction and a tendency toward myopic shift. Therefore, developing a reliable method to determine true corneal power for IOL calculation in such eyes is essential to improve refractive outcomes after combined surgery.Purpose: This study aimed to develop and validate a topography-guided selective keratometry input method to improve the accuracy of intraocular lens power calculation in eyes undergoing combined cataract and pterygium surgery.Methods: In this comparative study, patients were randomly allocated to two groups. In the control group (Uncorrected Corneal Power Group), the IOL power was calculated using the standard keratometry (K1, K2) values obtained directly from the IOLMaster’s integrated Barrett Universal II formula. In the study group (Corrected Corneal Power Group), a novel topography-guided method was employed: the flat keratometry (K1) was derived from the average of simulated keratometry (SimK) readings along the vertical meridian within the central 3mm zone on the Pentacam axial map, while the steep keratometry (K2) was taken from the contralateral (temporal) quadrant. These customized K-values were manually entered into the Barrett Universal II calculator. All patients underwent combined phacoemulsification and pterygium excision. Postoperative outcomes, including visual acuity, refraction, and the Mean Absolute Error (MAE) of the predicted versus actual spherical equivalent, were compared between groups.Results: Postoperative corneal power increased significantly only in the ipsilateral quadrant on the pterygium side, while remained largely unchanged in the vertical and contralateral quadrants. The study group (corrected method) achieved significantly better uncorrected distance visual acuity (UDVA) and a mean spherical equivalent closer to target, compared to the control group. Most importantly, the Mean Absolute Error (MAE) was significantly lower in the study group (0.22 ± 0.18 D) than in the control group (1.18 ± 0.95 D) (P < 0.001), demonstrating superior predictive accuracy of the novel calculation method.Conclusion: The novel topography-guided selective keratometry method, which utilizes the contralateral quadrant and vertical meridians for IOL calculation, significantly improves the predictive accuracy (as evidenced by a markedly lower Mean Absolute Error) and enhances the refractive and visual outcomes in patients undergoing simultaneous cataract extraction and pterygium excision.Keywords: cataract, pterygium, corneal power, surgery, intraocular lens power calculation