ASCRS News: EyeWorld Journal Club
December 2023

by Timothy Grosel, MD, Mung Yan Lin, MD, Samera Ahmad, MD, and Jared Raabe, MD*
Emory Eye Center residents
*All authors contributed equally to this work.

Eyes that have undergone pars plana vitrectomy (PPV) have worse refractive outcomes compared to eyes that have not undergone PPV.¹ Several new IOL calculation formulas have improved refractive outcomes in these eyes²; however, the optimal IOL calculation formula is still under debate. Further, risk factors for a poor refractive outcome are unknown. Zhang et al. sought to determine the optimal IOL calculation formula to use preoperatively in eyes that have previously undergone PPV.

Methods

This was a retrospective chart review study including 974 patients with prior PPV who underwent phacoemulsification and IOL implantation at Zhongshan Ophthalmic Center, Guangzhou, China, from July 2018 to August 2022. Demographic data, biometric measurements, surgical details, as well as postoperative refraction and best-corrected visual acuity (BCVA) were collected. The study evaluated 11 formulas: Barrett Universal II, Emmetropia Verifying Optical, Hoffer QST, Kane, Ladas Super Formula, Pearl-DGS, Radial Basis Function (RBF), Haigis, Hoffer Q, Holladay 1, and SRK/T. The predicted postoperative spherical equivalent refraction was derived. To assess the predictive accuracy of the formulas, five parameters were assessed for each formula: the mean absolute prediction error (MAE), the median absolute prediction error (MedAE), the root-mean-square absolute prediction error (RMSAE), the percentage of eyes within ±1 D of prediction error (PE), and the formula performance index (FPI).

Results

Included in the study were 947 eyes with an average patient age of 56.81 years. The most common primary retinal pathology was retinal detachment (64.4%). In the study, 7.1% of eyes had a scleral buckle, and 33.9% of eyes had silicone oil tamponade (with the remaining eyes having balanced salt solution tamponade). The majority of implanted IOLs were one-piece (69.4%) hydrophobic acrylic (84.7%) IOLs. Of the included eyes, 178 (18.3%) had a hyperopic predictive error greater than 1 D. The most significant risk factors for hyperopic refractive predictive error were silicone oil tamponade (OR 1.82) and higher axial length (OR 1.55 per 1 mm increase of axial length). In the study, 106 eyes (11.2%) were found to have a myopic predictive error greater than 1 D, with the highest risk factors being sulcus IOL placement (OR 6.65), history of scleral buckle (OR 2.43), and shallower anterior chamber depth (OR 1.79 per 1 mm decrease). When the performance of the IOL calculation formulas was analyzed based on the five parameters (MAE, MedAE, RMSAE, FPI, percentage of eyes within ±1 D of predictive error), the Kane formula was found to the most accurate formula for post-vitrectomy eyes (MAE 0.49 D, MedAE 0.36 D, FPI 0.85, RMSAE 0.67 D). The Barrett Universal II formula was found to be the most accurate in eyes with prior scleral buckle (MAE 0.63 D, FPI 0.69, highest percentage within ±1 D of PE 82.81%). In long eyes (AL>26 mm), the Holladay 1 with the nonlinear version of the Wang-Koch AL adjustment (WKn) was most accurate (MAE 0.52 D, RMSAE 0.69 D, FPI 0.75, highest percentage within ±1 D of PE 88.14%). The Kane was also found to be the most accurate in eyes with flat corneas (K<42 D; MAE 0.44 D, FPI 0.84, highest percentage within ±1 D of PE 95.83%).

Several new IOL calculation formulas have improved refractive outcomes in [eyes that have undergone PPV]; however, the optimal IOL calculation formula is still under debate.

Discussion

In their retrospective review, Zhang et al. identified risk factors for refractive prediction error using a large sample size and included two formulas (Hoffer QST and Pearl-DGS) that had not been previously reported in post-vitrectomy eyes. A history of scleral buckling or sulcus IOL placement increased the risk of myopic error, while long axial length (>26 mm) and silicone oil tamponade increased the risk of hyperopic prediction error. Post-vitrectomy eyes overall had significantly lower accuracy with respect to refractive prediction than eyes that had not undergone vitrectomy. The Kane formula had the best overall performance in vitrectomized eyes; however, other formulas performed well in specific situations, such as the Barrett Universal II in eyes that had undergone scleral buckling, which may be due to the inclusion of corneal diameter in the calculation. The authors stated the risk of hyperopic prediction error is too high when traditional formulas are used in post-vitrectomy eyes with long axial length, so they suggested using the Emmetropia Verifying Optical or Holladay 1 with WKn if the tamponade is with balanced salt solution and using the SRK/T with the first version of the Wang-Koch AL adjustment (WK1) if silicone oil was used. Limitations of the study included its retrospective nature, variations in scleral buckling technique, and the intrinsic inaccuracy of manifest refraction measurement in patients with lower visual acuity, which is prevalent in their post-vitrectomy patient population. 

---

Choice of intraocular lens calculation formula for cataract patients with prior pars plana vitrectomy

Zhang J, et al. J Cataract Refract Surg. 2023;49:956–963.

• Purpose: To determine the optimal intraocular lens (IOL) calculation formula for vitrectomized eyes with diverse surgical and biometric characteristics
• Setting: Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China.
• Design: Retrospective consecutive case series study.
• Methods: This study included 974 vitrectomized eyes (974 patients) scheduled for phacoemulsification with IOL implantation. Eleven formulas were evaluated: Barrett Universal II (BUII), Emmetropia Verifying Optical, Hoffer QST, Kane, Ladas Super Formula, Pearl-DGS, Radial Basis Function (RBF), Haigis, Hoffer Q, Holladay 1, and SRK/T. Risk factors for prediction error (PE) exceeding 1 diopter (D) were determined using multiple logistic regression. Subgroup analyses were performed based on surgical history and biometric parameters.
• Results: The risk of hyperopic PE (>1 D) was higher in patients with silicone oil tamponade (odds ratio [OR], 1.82) and longer axial length (AL) (OR, 1.55), while patients with previous scleral buckling (OR, 2.43) or ciliary sulcus IOL implantation (OR, 6.65) were more susceptible to myopic PE (<–1 D). The Kane formula had the highest overall prediction accuracy and the best in silicone oil-filled eyes and the flat cornea subgroup. The BUII and RBF displayed the optimal performance in eyes with previous scleral buckle and steep cornea, respectively. In eyes with an AL ≥26 mm, the Holladay 1 with the nonlinear version of the Wang-Koch AL adjustment (Holladay 1-WKn) showed the lowest absolute PE and highest percentage within ±1.0 D
  of PE.
• Conclusions: The Kane achieved the highest overall prediction accuracy in vitrectomized eyes. The optimal formula for eyes with previous scleral buckle, steep cornea, or long AL was BUII, RBF, and Holladay 1-WKn, respectively.

---

References

1. Xu Y, et al. Refractive outcomes and anterior chamber depth after cataract surgery in eyes with and without previous pars plana vitrectomy. Curr Eye Res. 2021;46:1333–1340.
2. Tan X, et al. Accuracy of new generation intraocular lens calculation formulas in vitrectomized eyes. Am J Ophthalmol. 2020;217:81–90.

Contact 

Ahmad: samera.ahmad@emory.edu
Grosel: tgrosel@emory.edu
Jones: jjones2@emory.edu
Lin: mung.yan.lin2@emory.edu
Raabe: jared.raabe@emory.edu