Field of View of Modified Osteo-Odonto Keratoprosthesis

Abstract

 

Purpose:

 

To calculate the field of view provided by Modified Osteo-Odonto Keratoprosthesis (MOOKP) as a function of the optical (curvature) and mechanical (cylinder length) design parameters.

 

Methods:

 

Calculations were done using paraxial geometrical optics equations for a plano-convex cylindrical MOOKP made of PMMA (n=1.491) with the convex surface exposed to air. The diameter of the optical cylinder was 3.8mm. The field of view (FOV) was defined as the smallest of the angle subtended by the anterior surface of the MOOKP with respect to the object nodal point and the angle subtended by the posterior surface of the MOOKP with respect to the image nodal point. The FOV was calculated for values of the preoperative axial eye length ranging from 15 to 30mm. For each value of the eye length, we calculated the anterior MOOKP radius of curvature required to produce an emmetropic eye. The FOV was then calculated for the resulting implant.

 

Results:

 

See graphs below. The graph on the left shows the relationship between the radius of curvature of the optic (in red), the axial length and the optical power of the MOOKP (in black). The graph on the right shows the relationship between the full FOV and the anterior radius of curvature. In subjects with normal eye length (23mm), the MOOKP radius is approximately 11mm, and a full FOV of approximately 30 degrees can be expected. The field of view decreases with increasing radius of curvature or increasing eye length.

 

Conclusions:

 

The field of view provided by MOOKP is strongly dependent on the power of the implant, which is determined by the eye length.  

 

Keywords: keratoprostheses • visual fields • optical properties