Theoretical model of the contributions of corneal asphericity and anterior chamber depth to peripheral wavefront aberrations

Influence of Overhanging Bleb on Corneal Higher-Order Aberrations after Trabeculectomy

Recent advances in ocular aberrometry have revealed that ocular surgery increases ocular and corneal higher-order aberrations. This retrospective single-center study aimed to examine the effects of the overhanging bleb on corneal higher-order aberrations using a wavefront analyzer. We included 61 eyes from 50 patients with overhanging bleb after trabeculectomy with a fornix-based conjunctival flap using mitomycin C (overhanging bleb group) and 65 eyes from 54 glaucoma patients with no history of glaucoma surgery (control group). Corneal higher-order aberrations (total higher-order aberrations, coma aberrations, coma-like aberrations, spherical aberrations, and spherical-like aberrations) on a 4 mm pupil diameter were measured using the TOPCON KR-1W wavefront analyzer. Corneal coma aberrations were higher in the overhanging bleb group than in the control group (0.16 ± 0.13 μm and 0.10 ± 0.05 μm, respectively; p = 0.042). Corneal coma-like aberrations were also higher in the overhanging bleb group than in the control group (0.31 ± 0.32 μm and 0.16 ± 0.09 μm, respectively; p = 0.022). With an increasing ratio of cornea covered by the bleb to the entire cornea, all corneal higher-order aberrations increased except for corneal coma-like aberrations. Overhanging bleb after trabeculectomy with a fornix-based conjunctival flap using mitomycin C and its size influenced corneal higher-order aberrations.

Corneal Eccentricity in a Rural Japanese Population: The Locomotive Syndrome and Health Outcome in Aizu Cohort Study (LOHAS)

PURPOSE

To determine normal corneal eccentricity in a rural Japanese population and to examine factors associated with eccentricity value.

METHODS

This used data from the Locomotive Syndrome and Health Outcome in Aizu Cohort Study (LOHAS) project between 2009 and 2012. Residents of Minamiaizu and Tadami in Fukushima, Japan, who were aged 40 years or over, were invited for a comprehensive eye examination. For 1371 patients with no history of internal eye surgery, corneal eccentricity was measured using a Pentacam.

RESULTS

Of 1371 people recruited to the study, 1215 (1215 eyes) met the inclusion criteria. The overall mean eccentricity was 0.46 (SD = 0.18; range, -0.85 to 0.88). Corneal eccentricity was significantly associated with age, spherical equivalent, pupil diameter, anterior chamber angle, anterior chamber volume, and central corneal thickness, but not with gender or body mass index.

CONCLUSIONS

In this study, the normal cornea in this Japanese population was prolate. Corneal eccentricity was likely to decrease with increasing age. Also, spherical equivalent and other anterior segment parameters had an influence on corneal eccentricity. Corneal eccentricity measurements might be helpful in the diagnosis of corneal diseases and in calculations for intraocular lens implantation and corneal refractive surgery.

Retinal contour modelling to reproduce two-dimensional peripheral spherical equivalent refraction

Reproduction of the peripheral spherical equivalent refraction (SER) in the eye model is critical for investigations in myopia control. Based on the derivation of a linear relationship between SER and the vergence of the wavefront at exit pupil center, a computing method is proposed to locate the retinal points to reproduce the two-dimensional (2D) distribution of SER. The method is validated by reproducing SER maps measured on both emmetropic and myopic eyes in a realistic eye model based on measurement data. By fitting the retinal points to a general ellipsoid, the limited capability of the general ellipsoid model in reproducing the 2D map of SER is calculated and compared with original data. The high accuracy in SER reproduction and low time-cost of the proposed retinal-locating method can help significantly improve the precision and accuracy of customized wide-angle eye modelling.

Relative Peripheral Myopia Induced by Fractal Contact Lenses

PURPOSE

To assess the peripheral refraction induced by Fractal Contact Lenses (FCLs) in myopic eyes by means of a two-dimensional Relative Peripheral Refractive Error (RPRE) map.

MATERIALS AND METHODS

This study involved 26 myopic subjects ranging from -0.50 D to -7.00 D. FCLs prototypes were custom-manufactured and characterized. Corneal topographies were taken in order to assess correlations between corneal asphericity and lens decentration. Two-dimensional RPREs were measured with an open-field autorefractor at 67 points, covering the central 60 × 30 degrees of the visual field. The bidimensional RPRE vector components: M, J₀ and J₄₅ of the difference between the values obtained with and without the FCLs in the eye were obtained. Additionally, the FCL-induced peripheral refraction in tangential and sagittal planes was computed along the horizontal meridian.

RESULTS

Induced by the FCLs, significant differences for all vector components were found in the peripheral retina. FCLs were decentered a mean of 0.7 ± 0.19 mm to the temporal cornea. The two-dimensional RPRE maps manifested the FCLs decentration. In particular, M varied asymmetrically between nasal and temporal retina after fitting the FCLs with a significant increment of the myopic shift beyond 10º (p < 0.05). No correlations were found between the amount of lens decentration and the asphericity of the cornea along temporal and nasal sides. However, significant correlations were found between the corneal asphericity and vector components of the RPRE in naked eyes. FCLs produced an increasing myopic shift in tangential and sagittal power errors along the horizontal meridian.

CONCLUSIONS

As predicted by ray-tracing simulations, FCLs fitted in myopic eyes produce a myopic shift of the RPRE. The two-dimensional RPRE maps show information about the lens performance that is hidden in the conventional one-dimensional meridional representations.

A Model of the Effect of Lens Development on Refraction in Schoolchildren

SIGNIFICANCE

The study provides a new theory on the mechanism underlying myopia development, and it could be useful in clinical practice to control myopia development in schoolchildren.

PURPOSE

To model the effect of the crystalline lens on refractive development in schoolchildren.

METHODS

The Zemax 13 was used to calculate Zernike aberrations and refractions across 50° horizontal visual fields. Optical effects of the anterior chamber depth, lens thickness, and radii of curvature of the lens surfaces on refractions were modeled. Refractive changes induced by lens development in emmetropic and myopic eyes, based on a previous longitudinal study from literature, were calculated.

RESULTS

A lens thickness reduction with an anterior chamber depth deepening caused a hyperopic shift over the visual fields and even more at the periphery. Opposite effects were found when the lens was thinned without any change of the anterior chamber depth. While a flattening of the anterior lens surface produced hyperopic refractions overall, a posterior lens flattening caused a myopic shift at the periphery, but a hyperopic shift of the central refraction. In the myopic eye, lens development induced refractive change toward more hyperopic over the visual fields and more at the periphery.

CONCLUSIONS

Lens thinning and lens axial movement participate in peripheral refractive development in schoolchildren, and lens development with a deeper anterior chamber depth and a flatter lens surface in the myopic eye could generate extra hyperopia over visual fields. The myopic lens development could be due to a backward movement of the lens, driven by a backward growth of the ciliary process, which might be a causative factor of myopia development.

Ocular Aberrations and Corneal Shape in Adults with and without Astigmatism

PURPOSE

To characterize and compare the corneal shapes and monochromatic aberrations in Chinese myopic adults with and without astigmatism.

METHODS

Forty-six Hong Kong Chinese aged 50 to 70 years with compound against-the-rule myopic astigmatism (n = 18) or simple myopia (n = 28) were recruited. Corneal shapes were measured by a Scheimpflug-based corneal topographer: the semimeridian corneal shape factors at the nasal, temporal, inferior, and superior corneal quadrants measured from the corneal apex to 3 mm midperiphery were analyzed. The ocular aberrations were measured by the COAS (Complete Ophthalmic Analysis System) Shack-Hartmann wavefront aberrometer; the corneal aberrations were computed using the corneal topographic map data measured by the Medmont E300 corneal topographer; and the internal aberrations were calculated from the ocular and corneal aberrations.

RESULTS

Compared with simple myopia, myopic astigmatism had more oblate nasal and temporal corneal shapes and showed significantly more negative Y trefoil and more positive vertical coma. The asymmetry in corneal shape along the vertical principal meridian (inferior - superior) was significantly associated with the Y trefoil and vertical coma of the cornea, suggesting that this regional asymmetry in corneal shape may contribute to the ocular aberrations.

CONCLUSIONS

The significant relationships found between astigmatism, corneal shapes, and monochromatic aberrations underscore the importance of taking corneal shape into account when correcting the optical defects in myopic Chinese adults with astigmatism.