Pachymetry map of corneal epithelium in patients wearing orthokeratology contact lenses

Abstract

 

Purpose

 

To investigate the characteristics of corneal epithelial pachymetry map in patients wearing orthokeratology lens (OK lens) using the automatically segmentation function of SD-OCT.

 

Methods

 

60 patients who had been fitted with myopic OK lens for at least one night were included in the study (mean age, 10.6±2.38 years) and 11 patients without any history of contact lens served as controls. Patients were divided into 6 groups according to the duration of orthokeratology lens wearing. An SD-OCT (RTVue SD-OCT, Optovue, Inc, CA) with a pachymetry module was used to measure the central 6mm corneal epithelial topography. The epithelial thickness of the central 3 mm, the average thickness of the 3 to 5mm ring (Peripheral 1, P1), and the average thickness of the 5 to 6mm ring (Peripheral 2, P2) were recorded and compared within individual groups. Munnerlyn’s formula was used to model the expected change in refractive error based on measured changes in topographical corneal epithelial thickness.

 

Results

 

The epithelial thickness of the central cornea was significantly reduced in all ortho-k groups. Except for group one, no significantly difference in the epithelial thickness of 3 to 5mm (P1) was found between the ortho-k group and the control one. For P2, the epithelial thickness increased in group2 to 5, but only group 3 reached significant level. The refractive change predicted by Munnerlyn’s formula based on changes in topographical corneal epithelial thickness was much less than the measured refractive changes found in all groups.

 

Conclusions

 

Epithelial pachymetry map automatically generated by the SD OCT could provide object and comprehensive information of epithelial change caused by overnight wearing of OK lens. OK lens can cause significant thinning of central corneal epithelium and thickening of midperipheral corneal epithelium. Changes induced by overnight orthokeratology can not be wholly explained by the induced changes in corneal epithelial thickness. Change in stromal thickness or the bending of the corneal tissue may also play a role.

 

 

Figure 1. Epithelial map generated and corneal topography of same patient who have worn OK lens for 11 months. Both map show well centering of the lens.

 

 

Figure 2. Epithelial map and corneal topography of same patient who have worn OK lens for 3 weeks. Both map show slight decentering of the lens toward superior temporal quadrant of the cornea.

 

Keywords: 482 cornea: epithelium • 477 contact lens