• Journal of Korean Ophthalmic Optics Society
• /
• v.16 no.3
• /
• pp.273-281
• /
• 2011

Purpose: In order to provide the fundamental information for the design development of RGP lenses and its clinical prescription, the corneal types of Korean twenties were analyzed according to corneal shapes, astigmatic degree, and the certain distance from the corneal apex. Methods: Corneal types of total 252 eyes in 20s were firstly classified, then their corneal radii from the certain distance from the corneal apex were measured by corneal topography and further analyzed based on the astigmatic degree. Results: Korean 20s' corneal types were classified as 14.3%(36 eyes) of round, 31.3%(79 eyes) of oval, 28.6%(72 eyes) of symmetric bow tie, 17.5%(44 eyes) of asymmetric bow tie, 8.3%(21 eyes) of irregular shapes. The round and oval typed corneas had mild astigmatic degree whereas the higher astigmatic degree in symmetric and asymmetric bow tie typed corneas were shown. The relative corneal radii of round and oval typed corneas at each distance from corneal apex were shown to consistently increase regardless of astigmatic degrees when they measured at certain distances from the corneal apex. However, the relative corneal radii of symmetric and asymmetric bow tie typed corneas within 1.0-1.5mm from the corneal apex were decreased, which showed steeper slope than it within 1.0 mm and somewhat different based on astigmatic degrees. Bigger change of corneal radii outer 3.5 mm from the corneal apex in symmetric bow tie typed corneas with astigmatism of 1.50-2.00 D and 2.25-2.75 D appeared. Conclusions: The consideration of radial change from the central cornea to peripheral cornea is necessary for manufacturing RGP lens and its prescription since they showed different change in corneal radii by corneal patterns and astigmatic degrees.

• Journal of Biomedical Engineering Research
• /
• v.20 no.1
• /
• pp.45-51
• /
• 1999

The purpose of this study is to investigate the effects of various factors in keratotomy for astigmatism correction on surgical outcomes by finite element method as well as animal experiments. Three kinds of surgical techniques were mechanically investigated : arcuate, straight, and inverse arcuate keratotomy. Among the three techniques the arcuate keratotomy is the most popular one while the other two techniques are being investigated in this area. The arcuate keratotomy was found to be more controllable and effective in reducing the refractive power than the others. In arcuate keratotomy it was found most effective when the incision was located in the middle position between the apex and the edge of the cornea from the results of experiment as well as finite element study. Regarding to the range of the corneal incision in arcuate keratotomy, the incision angle of 90$^{\circ}$ was found th be most effective in reducing refractive power than other angles even it was incised up to 150$^{\circ}$. Therefore, it was concluded that 90$^{\circ}$ of incision angle results in the largest decrease in refractive power in arcuate keratotomy. However, other important findings were that the effect of the surgery decreased with time so the visco-effect of the cornea and auto-healing process. Therefore, these factors should be considered in future studies.