Keratometric Index in Keratoconus and in Keratoconus With Intracorneal Ring Segments
Narrative Responses:
Purpose
To compare the curvature of the anterior and posterior surface of the cornea between healthy control eyes (C), keratoconus (KC) and keratoconus with intracorneal ring segments (KC-ICS).
Methods
Retrospective study in which the following eyes were included: 30 control eyes, 30 keratoconus before and after intracorneal ring segment implantation. Using the anterior segment Scheimpflug analyzer the mean anterior (Rant) and posterior radii (Rpost) of the cornea and True Net Power (TNP) were measured. Using those data, the ratio between anterior and posterior radius (Rant/Rpost) and the keratometric index (KI) in each group were calculated.
Results
Mean Rant and Rpost were 7.82±0.31mm y 6.42±0.37mm en C, 6.94±0.46mm and 5.51±0.5mm en KC and 7.18±0.5mm and 5.5±0.49mm en KC-ICS, being Rant significantly different between all groups (p=0.0001), Rpost significantly different between C and KC and between C and KCSIC (p=0.0001), but not between KC and KC-ICS (p=0.846). Rant/Rpost corneal ratio was significantly different between all groups (p= 0.0001). IK was significantly different between C, KC y KC-SIC (p=0.0001 KC vs KC-SIC, KC.SIC vs C; p=0.012 KC vs C).
Conclusion
The curvature of the anterior and posterior corneal surfaces and the Rant/Rpost ratio are significantly higher in KC than KC-SIC. After ICS implant, the anterior surface flattens without significant changes in the posterior one. These findings invalidate the use of the standard KI in KC and KC-ICS for IOL calculations.