Refractive Outcomes after Cataract Surgery

A post-operative manifest refractive error as close as possible to target is key when performing cataract surgery with intraocular lens (IOL) implantation, given that residual astigmatism and refractive errors negatively impact patients’ vision and satisfaction. This review explores refractive outcomes prior to modern biometry; advances in biometry and its impact on patients’ vision and refractive outcomes after cataract surgery; key factors that affect prediction accuracy; and residual refractive errors and the impact on visual outcomes. There are numerous pre-, intra-, and post-operative factors that can influence refractive outcomes after cataract surgery, leaving surgeons with a small “error budget” (i.e., the source and sum of all influencing factors). To mitigate these factors, precise measurement and correct application of ocular biometric data are required. With advances in optical biometry, prediction of patient post-operative refractory status has become more accurate, leading to an increased proportion of patients achieving their target refraction. Alongside improvements in biometry, advancements in microsurgical techniques, new IOL technologies, and enhancements to IOL power calculations have also positively impacted patients’ refractory status after cataract surgery.

Influence of refractive status and age on corneal higher-order aberration

This study aimed to investigate the influence of refractive status and age of patients on corneal higher-order aberrations (HOAs). Four hundred and twenty-six right eyes of 426 patients were enrolled in this study. The mean and standard deviation of patient age was 47.7 ± 22.1 years. Total HOAs, spherical-like aberration, coma-like aberration, Z^-1₃, Z¹₃, Z^-3₃, Z^-3₃ and spherical aberration (Z⁰₄) for 6-mm pupil were measured using anterior segment optical coherence tomography (AS-OCT). Subjects were classified into three groups according to the amount of spherical equivalent refractive error (SE): myopia (<-0.5 D), emmetropia (-0.5 to 0.5 D), and hyperopia (>0.5 D). The amount of corneal astigmatism was recorded. Relationship between corneal aberrations, refractive status, astigmatism, and age was analyzed. In total, total HOAs, spherical-like aberration and amount of Z^-3₃ and Z⁰₄ were significantly larger in the hyperopia group than in the myopia group. After adjustment for age, however, aberration components did not differ among the three refractive groups. In multiple regression analysis, age and corneal astigmatism showed significant correlation with aberrations, whereas amount of SE and refractive status did not. The current study indicated that age and amount of corneal astigmatism have significant influence on corneal HOAs, but refractive status (myopia, emmetropia, or hyperopia) is not associated with corneal HOAs.

Correlations of Corneal Spherical Aberration with Astigmatism and Axial Length in Cataract Patients

Purpose

To clarify the distribution of corneal spherical aberrations (SAs) in cataract patients with different corneal astigmatism and axial length.

Setting

Department of Ophthalmology and Vision Science of the Eye and ENT Hospital of Fudan University, Shanghai, China.

Design

Retrospective case series.

Methods

The axial length, corneal SAs, and other corneal biometrics were collected in cataract patients with Pentacam HR and IOLMaster 500. The statistical analysis of the corneal SAs was based on the stratification of axial length and anterior corneal astigmatism.

Results

In total, 6747 eyes of 6747 patients were recruited, with 2416 eyes (58.17 ± 16.81 years old) in the astigmatism group (anterior corneal astigmatism ≥1 D) and others (61.82 ± 12.64 years old) in the control group. In patients with astigmatism <2 D, the total and anterior SAs decreased as the axial length increased (P < 0.001). The total corneal SAs of patients with astigmatism of 2-3 D stabilized at around 0.29 μm, whereas those of patients with anterior corneal astigmatism ≥3 D tended to be variable. Age and anterior corneal astigmatism had positive and negative effects, respectively, on SA in the regression model.

Conclusions

Axial length has a negative effect on the anterior and total corneal SAs, which stabled around 0.33 μm and 0.30 μm in patients with axial length of ≥26 mm, respectively. Individualized SA adjustments are essential for patients undergoing aspheric toric IOL implantation with preoperative anterior corneal astigmatism of 1-2 D or ≥3 D. Toric IOLs with a negative SA of −0.20 μm are recommended for patients with anterior corneal astigmatism of 2-3 D if no customized therapy is warranted.

The effect of corneal irregularity on astigmatism measurement by automated versus ray tracing keratometry

The aim of this study was to compare the effect of corneal irregularity on astigmatism assessment using automated keratometry (AK) (IOLMaster) versus ray tracing keratometry (Pentacam). This is an observational case series approved by the institutional review board of Dongguk University Hospital, Goyang, South Korea. A total of 207 eyes of 207 cataract patients were included. Preoperative corneal astigmatism was measured by both IOLMaster and Pentacam. Corneal irregularity index (IR) was calculated in Fourier analysis map of Pentacam. AK by IOLMaster and total corneal refractive power (TCRP, 3 mm and 4 mm zone analysis with pupil centered) by Pentacam were selected and the difference between the 2 measurements (delta Δ) was calculated using vector analysis. Ocular residual astigmatism (ORA) after cataract surgery was calculated by subtracting 6-month postoperative refractive astigmatism (RA) measurements from corresponding preoperative values (AK, TCRP3, and TCRP4). The mean irregularity index measured was 0.042 ± 0.019 mm (mean ± standard deviation) and was positively correlated with age and magnitude of corneal astigmatism (P < 0.001 and P < 0.05). The difference (Δ) between TCRPs and AK (ΔTCRPs-AK) was 0.43 ± 0.37 (TCRP3) and 0.39 ± 0.35 (TCRP4) diopters. Linear regression analysis revealed that age (P < 0.001), IR (P < 0.001), and AK (P < 0.001) were positively correlated with ΔTCRPs-AK. In highly irregular corneas (IR over 0.77 diopters: mean + 2 standard deviation), postoperative ORAs calculated using TCRPs were significantly lower than ORAs calculated using AK. Corneal irregularities significantly impact astigmatism assessment by IOLMaster (AK) and Pentacam (TCRPs). Compared with AK, TCRPs were more accurate in predicting postoperative residual astigmatism in highly irregular corneas.