Enables view of fundus through cloudy media or around partial intra-ocular opacities which make direct ophthalmoscopy more difficult.
Excellent survey technique allowing large field of view and stereopsis.
Allows easier examination of peripheral fundus than direct ophthalmoscopy.
Greater working distance increased safety for examiner and less restraint of patient.
Facilitates determination of fundus depressions and elevations.
Both hands are on patient's head with binocular indirect technique, so fundus examination is faster and comparison between eyes is easier.
A supplemental mirror can be attached to many binocular indirect models, permitting simultaneous visualization by examiner, student, colleague or client.
Disadvantages
Low magnification (2-4 times).
Inverted, virtual image.
Equipment is expensive with binocular models, but simple bupe lens and pen torch inexpensive for monocular indirect technique.
Technical problems
Requires time and patience to master technique.
Alternative techniques
Direct ophthalmoscopy where greater magnification is required.
The monocular indirect ophthalmoscope (American Optical Co.) combines advantages of both systems: simplicity of use, production of erect image, but is expensive.
Pen torch or transilluminator plus condensing lens can be used as cheap indirect ophthalmoscope, but more difficult to use and examiner cannot restrain patient's head.
Time required Preparation
20 min for mydriatics to work if being used.
Procedure
10 min should be adequate for detailed examination of both eyes.
Head light illuminates eye, permitting examination from eyelids to anterior vitreous body.
Core Procedure
Step 1 - Diagnostic information
Ocular opacities can frequently be localized by direct and angled illumination.
Opacities anterior to posterior lens nucleus move with eye movements, whereas opacities caudal to posterior lens nucleus move in opposite direction.
Partial or complete mobile opacities are in vitreous humor or anterior chamber.
Fixed opacities are in cornea or lens.
Step 2 - Fundus examination
Interpose hand lens between light source and patient's eye, held about 2" from eye.
Fundus magnification is dependent on dioptic power of lens. +20 lens or 2.2 panretinal is most versatile but other sizes are available, eg +14, 18, 20, 28 and 30 diopters.
Slight tilting of hand lens will remedy annoying light reflections.
Scleral depressor used to facilitate peripheral fundus examinations -a dificult technique which can only be carried out in sedated or anesthetized animals.
If using focal light source and hand lens, hold light source (pen torch) next to examiner's head and aim at animal's eye.
Petersen-Jones S & Crispin S (2002) BSAVA Manual of Small Animal Opthalmology. 2nd edn. British Small Animal Veterinary Association.
Mould J R B (1993) Approach to an ophthalmic examinatonBSAVA Manual of Small Animal Ophthalmology Chapter 2. eds. Peterson-Jones S M, Crispin S M. (BSAVA publications Cheltenham).
Bistner S I (1971) Examination of the eye.Veterinary Clinics of North AmericaVolume 1 (Jan 1971). pp 29-52.
Gelatt K N (1970) Examination of the eye.Scientific Presentations and Seminar Synopses37th AAHA meeting. pp 326-333.
Vetstream contributor(s)
Dennis E Brooks DVM PhD DipACVO , College of Veterinary Medicine, 2015 SW 16th Ave, University of Florida, PO Box 100126, Gainesville, FL 32610-0126, USA.
P W Renwick MA VetMB DVOphthal MRCVS , Willows Referral Practice, 78 Tanworth Lane, Solihull, West MIdlands B90 4DF, UK.
David L Williams MA VetMB CertVOphthal PhD MRCVS , Department of Clinical Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK.
increased safety for examiner and less restraint of patient.
