Evaluation of a Direct Image Fundus Lens for Indirect Ophthalmoloscopy

Abstract

Abstract: : Purpose: To evaluate a compact hand–held direct image lens, that provides a correctly oriented retinal view when used in conjunction with binocular indirect ophthalmoloscope during ophthalmoscopy. Methods: The lens system consists of three coaxial air–spaced double aspheric lenses (lens A, lens B, lens C). They are non symmetric double aspheric lenses with axial length lens A 9.69 mm, lens B 9.69 mm and lens C 21.27 mm. The lens A and B are seperated by a distance of 19.38 mm while lens B and C are 30.96 mm apart. The total length of the lens system is 79.63 mm. All the lenses in the system are mounted co–axially in a plastic housing (Figure). Results: The lenses in the system are designed and positioned to converge the illuminating light beam from the light source to form the image of the source on to the pupil of the examined eye. This light diverges to illuminate the fundus. The emerging light from the eye through its pupil is refracted by the optical system to form an upright aerial real image of the fundus between the lens system and the indirect ophthalmoscope. Conclusions: This lens system is a useful adjunct to indirect ophthalmoscopy and facilitates panretinal examination by providing true erect real image of the fundus compared to the conventional indirect convex lens.  

Keywords: retina • imaging/image analysis: clinical • optical properties