Shifting of the Line of Sight in Keratoconus Measured by a Hartmann-Shack Sensor

Purpose: To evaluate ocular wavefront aberrations owing to keratoconus compared with normal controls and to describe the changes in the axis of line of sight (LoS) among keratoconic patients. Design: Prospective case- control study. Participants: Fifty- five eyes of 30 patients with keratoconus and 100 eyes of 50 refractive surgery candidates with normal corneas. Methods: Ocular aberrations over a 4.5 mm (undilatated) pupil were measured with a Hartmann- Shack sensor. Corneal topographic measurement was performed with a Tomey corneal topographer. The axis of the displacement of LoS was calculated by vector analysis. Main Outcome Measures: Root mean square (RMS) and higher order RMS values, ocular aberrations up to the 6th Zernike order and the distance of the LoS from the pupillary center (x and y offset values) in keratoconic and normal eyes were measured with aberrometry. The steepest and average keratometric values and the axis of the steepest meridian were measured in keratoconic eyes with topography. Correlations were made between the size and the direction of the shift in the LoS and ocular aberrations. Results: The following parameters were significantly higher in the keratoconus group compared to the control group: higher order RMS (P <0.001), Z(3)(-1) (P <0.001), Z(3)(-3) (P <0.002), Z(3)(3) (P = 0.001), Z(4)(-2) (P <0.001), Z(4)(2) (P <0.001), Z(4)(4) (P = 0.016), Z(5)(-5)(P = 0.03), Z(5)(-1) (P = 0.04), Z(5)(3) (P = 0.01), and y offset value (P<0.001). In keratoconic patients there was a significant correlation between the axis of the shift in the LoS and the steepest keratometric axis on topography (r = 0.59; P <0.001), the distance of the LoS from pupil center and vertical coma (r = -0.39; P = 0.004), and spherical aberration (SA; r = 0.29; P <0.04). There was also a significant correlation between the average keratometry value measured by topography and SA (r = = 0.49; P <0.001). A factorial regression model testing the interactive effects of vertical coma and SA on the shift of LoS had a good fit on our data (r(2) = 0.69; P <0.001). Conclusions: A significant displacement of the LoS is observed in keratoconus and relates to the position of the cone on topography and the induced vertical coma measured by aberrometry.