Purpose:
To investigate sectorial changes in corneal curvature with myopic orthokeratology lens wear over a period of two weeks.
Methods:
Nineteen eyes of 9 males and 10 females who underwent orthokeratology were analysed retrospectively. Participants with myopia less than -4.50D and astigmatism less than -1.50D were enrolled. Corneal topography from the Medmont E300 was analysed to investigate changes in the central zone and two surrounding annular zones (para-central and peripheral), with each zone sub-divided into four quadrants (nasal, superior, temporal and inferior). All participants wore BE reverse geometry lenses (Boston XO) on an overnight schedule for two weeks in one eye randomly; the other eye underwent orthokeratology treatment with different materials, and these data were not included in this analysis. A custom written Matlab program was used to extract and average all topographic data within each sector. Changes from baseline in each pre-defined sector were calculated and analysed using ANOVA and one tailed paired t tests.
Results:
Participant age ranged from 19 to 40 years (mean 30.1±6.8 years). After two weeks of treatment significant flattening was noted in all central sectors. Central superior (p<0.001) and central temporal (p<0.001) locations showed significantly more flattening than other central sectors. The para-central nasal cornea was significantly steepened compared with para-central superior (p=0.01) and para-central inferior cornea (p<0.001). The peripheral nasal cornea was significantly steepened compared with peripheral superior (p=0.02) and peripheral inferior sectors (p=0.04).
Conclusions:
This retrospective study shows that although central flattening was achieved in all quadrants with orthokeratology, there were significant differences in various sectorial zones. As expected, the para-central and peripheral cornea became steeper; however, there was an area of flattening towards the para-central temporal and peripheral temporal locations, adjacent to the significantly flattened central temporal zone. This is consistent with the known tendency of these lenses to decenter towards the temporal cornea.
Keywords: contact lens • cornea: clinical science • refraction