Xinjie Mao

Vertical and Horizontal Thickness Profiles of the Corneal Epithelium and Bowman's Layer after Orthokeratology

PURPOSE To investigate thickness profile changes of the corneal epithelium and Bowmans layer at the vertical and horizontal meridians with overnight myopia orthokeratology (OK) lenses. METHODS Twenty subjects (age range: 19-33 years) wore reverse-geometry rigid gas-permeable OK lenses in both eyes for 30 days. Before lens wear and after 1, 7, and 30 days of overnight lens wear, evaluation of lens fitting, visual acuity examination, corneal topography, and ultra-high resolution optical coherence tomography (UHR-OCT) were performed. The central, midperipheral, and peripheral cornea were imaged in both the horizontal and vertical meridians. Custom software was produced to acquire the thickness profiles of the epithelium and Bowmans layer. RESULTS Unaided visual acuity and refraction were improved significantly after OK lens wear. The central corneal epithelium thinned in the horizontal and vertical meridians after one night of lens wear (P < 0.05). In the horizontal meridian, the epithelium thickened at the temporal and nasal midperipheries (P < 0.05), while the superior midperipheral epithelium thinned in the vertical meridian. There were no changes in the thickness profile of Bowmans layer during the study period. CONCLUSIONS Overnight wear of OK lenses caused the central corneal epithelium to thin in both the vertical and horizontal meridians, while the midperipheral nasal and temporal epithelium became thicker and the superior midperipheral epithelium became thinner. The thickness of the central or midperipheral Bowmans layer in either meridian did not change. Improved vision acuity after overnight OK lens wear can be attributed to changes in the corneal epithelium and not Bowmans layer.

Corneal reshaping and wavefront aberrations during overnight orthokeratology.

Purpose: To investigate changes of corneal thickness at the vertical and horizontal meridians and of wavefront aberrations (WA) over a 30-day period of overnight myopia orthokeratology (OK) lens wear. Methods: Sixteen subjects (11 women, 5 men, 26.3±3.2 years) were enrolled and fitted for OK lenses. Long scan depth optical coherence tomography was used to measure corneal thickness profiles at both horizontal and vertical meridians at baseline and on days 1, 7, and 30 days. Corneal and ocular WA of a 6-mm pupil were measured and the root-mean-square (RMS) of the astigmatism, coma, spherical aberration (SA), and total higher-order aberrations (HOAs) were determined. Results: During the 30-day period, the central cornea thinned in the horizontal and vertical meridians, whereas corneal thickening occurred in the temporal, nasal, and inferior mid-peripheries. In contrast, the cornea thinned in the mid-peripheral superior. There were significant increases in RMS for astigmatism, SA, coma, and positive horizontal coma during the study period. After OK, there were significant positive correlations between the midperipheral-central thickness change difference and the changes in corneal and ocular RMS of total HOAs and SA (r range: 0.281 to 0.492, P<0.05). Only the change of corneal coma RMS was correlated with midperipheral-central thickness change difference (r=0.270, P<0.05). The change in corneal horizontal coma was correlated with the temporal-nasal thickness change difference (r=−0.289, P<0.05). Conclusions: Overnight OK caused unique changes in corneal thickness profiles at the vertical and horizontal meridians and increased corneal and ocular HOAs related to corneal reshaping.

The impact of eyelid and eye contour factors on a toric soft contact lens fitting in Chinese subjects.

Purpose: To evaluate eyelid and eye contour factors that can influence the fitting of toric soft contact lenses (TSCLs). Methods: Thirty-two subjects (64 eyes) were enrolled and fitted with Lo-Torque design TSCLs. One eye of each subject was randomly selected. High-resolution digital images were acquired after the subjects had worn the lens for 20 minutes, and the images were then processed with Adobe Photoshop. The palpebral aperture (PA), various angles of the eyelid, horizontal visible iris diameter (HVID), and lens parameters were obtained. Finally, lens fitting was evaluated. Results: During the assessment of the correlations between the eyelid and eye contour factors and the lens fitting, there were four pairs of significant correlations: (1) the PA and rotational direction of the lens: larger eye PA was associated with a greater possibility of nasal rotation of the corresponding lens (P=0.03); (2) the angle of the central lower lid (&thgr;3) and the rotational stability of the lens: the larger the angle was, the worse the rotational stability was (P=0.02); (3) the lower lid angle of the medial canthus (&thgr;5) and temporal rotational recovery: the smaller the angle was, the more quickly the lens recovered (P=0.05); and (4) HVID and routine fitting assessments: the larger the HVID was, the looser the lens fitting (P=0.00). Finally, when assessing correlations between some lens parameters and the orientation of the lens, we found that lower sphere values were associated with quicker lens recovery (P=0.04). Conclusion: Several eye factors, as well as lens characteristics, had impacts on the TSCLs fitting, including the PA, the angle of the central lower lid (&thgr;3), the lower lid angle of the medial canthus (&thgr;5), and the sphere of the lens. These factors should receive particular attention when fitting TSCLs.