Optical Properties and Fundus Imaging Through a PMMA

Keratoprosthesis

Rony R. Sayegh1

Linda Avena Diaz1

Fernando Vargas-Martín2

Robert H. Webb2

Claes H. Dohlman1

Eli Peli2

1 Massachusetts Eye & Ear Infirmary, Boston, MA2 The Schepens Eye Research Institute, Boston, MA

Correspondence: rsaye001@umaryland.edu

EP and FVM were supported in part by NIH grants EY05957 and EY12890

Introduction

• Better understanding of the visual function of the Boston Keratoprosthesis (KPro) may lead to design and practice modifications that could further improved outcomes.

• Here, we address the– (1) effect, sources, and control of glare– (2) binocular vision benefits of implanting a KPro in a patient with

a fellow healthy eye– (3) feasibility of wide-angle fundus imaging through the KPro

Methods• Optical Analysis

– Zemax (Focus Software Inc, San Diego, CA) was used to derive theoretical optical parameters of the KPro.

• Artificial Eye– An optical bench setup was used to assess the optical quality

and the effect of glare on the retinal image.

Methods• Glare sensitivity

– Measurements using a BAT (Mentor O&O Inc,Norwell,MA) were obtained with:

• (1) a standard transparent contact lens (CL) in place • (2) a dark iris CL, 4-mm pupil (Kontur Kontact Lens, Richmond, CA)

• Additional tests– Goldmann kinetic perimetry (V4e). – Stereo acuity measured in patients with intact fellow eye (Writ

Stereo Fly Test).

• Fundus imaging– Obtained using a Topcon TRC 50DX (Topcon, Tokyo, Japan)

fundus camera and Optos Panoramic 200MA system.

Results

• Computed MTF and PSF show that the system was close to diffraction-limited.

Results - Glare

• In the optical bench setup with the KPro installed in a metal iris, an image of a distant point-source was consistent with the computed high quality optics.

• A halo of scattered light could be eliminated by decreasing the aperture of the iris down to a 3-mm pupil.

• An opaque CL decreased the size of the scatter halo, but did not eliminate it.

Results - Glare

T II S1: African american patient implanted with type-2 Kpro

T II S2: Asian patient implanted with type-2 Kpro

T I: Patient implanted with a type-1 KPRO (n=8)

T I Dark CL: Same type-1 patients fitted with the dark contact lens

Visual Fields - 95°&90° for types I & II respectively

Results - Photography

• Stereopsis ranged from 400 to 800 sec of arc, reflecting minimal stereo vision

• Fundus Photography

Optos®Optomap

Conclusions

• The hazy cornea surrounding the KPro is a major source of glare

• A tinted soft lens can markedly reduce glare and improve vision up to about 40 percent

• The beneficial effect of a painted CL could potentially be mimicked by keeping as much of the natural iris intact during the surgery.

• KPros provide patients with a good field of view.• Little benefit to stereo vision is derived from implanting a

KPro in the presence of an undiseased contralateral eye with conserved vision.

• Adequate Optos wide-angle fundus imaging of around 150 degrees can be obtained