Refractive Outcomes of Non-Toric and Toric Intraocular Lenses in Mild, Moderate and Advanced Keratoconus: A Systematic Review and Meta-Analysis

Abstract

Background: To perform a systematic review and meta-analysis of the refractive outcomes of non-toric and toric intraocular lenses (IOLs) in keratoconus (KC) using different IOL power calculation formulas. Methods: A systematic search was conducted to identify studies that report on refractive outcomes of different IOL power calculation formulas in KC patients undergoing cataract surgery. Inclusion criteria were primary posterior chamber non-toric and toric monofocal intraocular lens implantation, data on the degree of KC, explicit mention of the formula used for each stage of KC, and the number of eyes in each category. We calculated and compared the absolute and mean prediction errors, percentage of eyes within 0.5 D and 1 D from target, and the weighted absolute prediction errors of IOL formulas, all were given for KC degrees I–III. Results: The bibliographic search yielded 582 studies published between 1996 and 2020, 14 of which (in total 456 eyes) met the criteria: three studies on non-toric IOL (98 eyes), eight studies on toric IOLs (98 eyes) and three studies of unknown separation between non-toric and toric IOLs (260 eyes). The lowest absolute prediction error (APE) for mild, moderate, and advanced KC was seen with Kane’s IOL power formula with keratoconus adjustment. The APE for the top five IOL power formulas ranged 0.49–0.73 diopters (D) for mild (83–94%) of eyes within 1 D from the target), 1.08–1.21 D for moderate (51–57% within 1 D), and 1.44–2.86 D for advanced KC (12–48% within 1 D). Conclusions: Cataract surgery in eyes with mild-to-moderate KC generally achieves satisfactory postoperative refractive results. In patients with advanced KC, a minority of the eyes achieved spherical equivalent refraction within 1 D from the target. The Kane’s formula with keratoconus adjustment showed the best results in all KC stages.

Clinical Outcomes of Toric Intraocular Lenses in Patients with Fuchs Endothelial Corneal Dystrophy

“…In this study, we found similar results for toric IOLs in FECD eyes compared with healthy eyes. The expanding indications for the implantation of toric IOLs in eyes with comorbidities such as AMD and even corneal ectasias such as keratoconus enables more patients to be spectacle independent and enjoy a higher quality of vision [6][7][8].…”

“…However, toric IOL implantation is more predictable and precise, can fix a higher corneal astigmatism, can achieve more spectacle independence, and can provide a higher quality of vision without image distortion compared to the other methods [1,2,5,6]. Recently, the implantation of toric IOLs in eyes with comorbidities has burgeoned, and patients with age-related macular degeneration (AMD), as well as patients with mild to moderate corneal ectasias, are being offered toric IOLs and spectacle independence with satisfactory refraction results [6][7][8]. However, the implantation of toric IOLs in patients with corneal dystrophies such as FECD is still considered by some surgeons to be contraindicated, which lacks supporting clinical evidence [6].…”

Factors Predictive of Refractive Error After Toric Lens Implantation

“…28 A meta-analysis revealed that the percentage of eyes with keratoconus and a toric lens implant achieving within 1 D of target SE was 1818 between 57% and 100% for stage I keratoconus and 50 to 100% in stage II keratoconus. 29 Irregular corneal astigmatism in keratoconus can increase the chance of inaccurate keratometry measurements. 30 Conventional biometry often will overestimate corneal power, leading to an underpowered IOL and hyperopic surprise.…”

Current concepts in the management of cataract with keratoconus

“…Advanced KCN has shown variable results owing to the large amount of irregular corneal astigmatism in these eyes. [ 61 72 ] Therefore, toric IOLs are recommended only for mild-to-moderate stages of KCN. Patients with advanced KCN where keratoplasty is anticipated in the future are not ideal candidates for toric IOL implantation.…”