Construction of a model eye and its applications

Area of Science:

• Ophthalmic optics
• Biomedical engineering
• Ophthalmology

Background:

• Accurate ophthalmic imaging requires understanding how optical systems, like fundus cameras, interact with ocular structures.
• Schematic eye models are essential for controlled experimentation in visual optics and instrument calibration.
• Axial ametropia, a common refractive error, can significantly impact the perceived size of retinal features in fundus photography.

Purpose of the Study:

• To construct and validate a model eye capable of simulating a wide range of axial ametropia.
• To assess the repeatability and reproducibility of autorefractor measurements using the model eye.
• To investigate the impact of axial ametropia on magnification in two different fundus camera designs.

Main Methods:

• A model eye was constructed based on the Bennett and Rabbetts schematic eye, featuring adjustable vitreous chamber depth via a micrometer screw.
• Axial ametropia was induced from +11 D to -17 D by altering vitreous chamber depth.
• Autorefractor (Topcon RM-A6500) readings were taken to evaluate measurement precision.
• Magnification differences were analyzed using a telecentric Zeiss Oberkochen fundus camera and a Carl Zeiss Jena fundus camera.

Main Results:

• The model eye achieved repeatable and reproducible autorefractor readings within +/- 0.25 D across most of its ametropic range.
• The telecentric Zeiss Oberkochen camera maintained constant magnification regardless of ametropia.
• The Carl Zeiss Jena camera exhibited magnification that varied linearly with the degree of ametropia.

Conclusions:

• The developed model eye is a reliable tool for simulating axial ametropia and evaluating ophthalmic instruments.
• Fundus camera design significantly influences image magnification in the presence of refractive errors.
• Telecentric fundus cameras offer consistent magnification, simplifying the assessment of retinal feature sizes.