Repeatability and Reproducibility of Anterior Segment Measurements in Normal Eyes Using Dual Scheimpflug Analyzer

Corneal Curvature: the Influence of Corneal Accommodation and Biomechanics on Corneal Shape

Purpose

Variation in the presence and magnitude of corneal conformational changes during accommodation may predict postoperative ectasia following refractive surgery and assist in the early diagnosis of corneal ectatic disorders. The current study aimed to establish a baseline for corneal refractive changes during ocular accommodation and to clarify the role of biomechanical factors in predicting these changes in a population without corneal pathology.

Methods

GALILEI G2 corneal tomography was assessed in 63 participants in both the accommodated and unaccommodated states. Four diopters (D) of physiological accommodation were induced using near-acuity calibrated words viewed through an externally mounted beam splitter mounted on a three-dimensional-printed frame. Corneal biomechanical characteristics were assessed with the CorVis-ST instrument, and statistical analysis was completed in R software.

Results

Anterior chamber depth was reduced by 0.10 ± 0.07 mm with accommodation (P < 0.01). Areas of statistically significant change in corneal curvatures were seen in all participants with accommodation. Mean anterior instantaneous corneal power increased in the superior-nasal periphery (0.1 D, 95% confidence interval [CI] = 0.05–0.2 D) and decreased in the inferior-temporal periphery (0.1 D, 95% CI = −0.05 to −0.15 D). Corneal stiffness and the corneal deformation amplitude ratio predicted peripheral corneal curvature changes with accommodation (P < 0.05).

Conclusion

Corneal conformational changes occur during accommodation in normal subjects. Further studies are required to assess the magnitude of corneal changes during accommodation in patients with corneal ectasia.

Translational Relevance

An externally mounted beam splitter can be used to modify the visual target presented by clinical ocular imaging instruments. Corneal conformational changes during accommodation may be useful in the diagnosis of corneal ectasia.

Analysis of Corneal Spherical Aberrations in Cataract Patients with High Myopia

To evaluate the corneal spherical aberrations in cataract patients with and without high myopia, we conducted a retrospective case series of 502 cataract eyes with high myopia and 1500 age-related cataract eyes and measure their corneal biometric data and axial length using Pentacam and IOLMaster. Both the anterior and total corneal primary spherical aberrations were lower in the high myopia group than that in the control group (0.317 ± 0.215 vs 0.338 ± 0.148 μm, P = 0.043; and 0.281 ± 0.207 vs 0.314 ± 0.153 μm, P < 0.001). The incidence of eyes with negative total corneal primary spherical aberration increased as axial length increased in the high myopia group, and the overall incidence was higher in the high myopia group than that in the control group (2.59% vs 1.47%). These were mainly contributed to the younger age of cataract patients with high myopia (55.76 ± 13.10 vs 60.18 ± 15.72 years, P < 0.001), along with the positive correlations between age and anterior and total corneal primary spherical aberrations. In clinical practice, an aspheric IOL with a low negative or zero primary spherical aberration is recommended for cataract patients with high myopia. Negative total ocular primary spherical aberrations resulting from aspheric IOL implantation should be avoided in extremely high myopic eyes.

Analysis of corneal higher-order aberrations in cataract patients with high myopia

PURPOSE

To evaluate the differences in corneal higher-order aberrations (HOAs) between cataract patients with high axial myopia and normal cataract patients, and to identify the associated factors.

SETTING

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

DESIGN

Retrospective case series.

METHODS

Corneal aberrations and axial lengths (ALs) were measured using a rotating Scheimpflug camera (Pentacam) and partial coherence interferometry (IOLMaster) in the high myopia group and the control group.

RESULTS

The study comprised 287 patients (520 eyes). There were 194 eyes in the high myopia group and 326 eyes in the control group. The 5 anterior corneal aberrations-vertical coma, vertical trefoil, horizontal coma, oblique trefoil, and primary spherical aberration-in the high myopia group were 0.07 μm ± 0.38 (SD), -0.11 ± 0.23 μm, 0.07 ± 0.28 μm, -0.02 ± 0.18 μm, and 0.39 ± 0.19 μm, respectively. No negative primary spherical aberrations of the total or anterior corneal surface were found in the high myopia group. Differences between the 2 groups were found in terms of central corneal thickness, astigmatism, primary spherical aberration, vertical coma, and oblique trefoil; however, these differences were not consistent between different age subgroups. Higher-order aberrations were correlated with age. Posterior corneal vertical coma was correlated with AL (Pearson correlation = -0.188, P = .047).

CONCLUSIONS

Negative primary spherical aberrations of the anterior or total corneal surface were not found in the high myopia group. Age showed a strong relationship with HOAs. For cataract patients with high myopia, aspheric intraocular lens implantation is recommended.