Introduction to the Ophthalmoscope
One must be familiar with the following key elements of ophthalmoscopy:
- How to switch a standard ophthalmoscope on and off. The importance of using the lowest illumination necessary. Advantage of low room illumination if possible.
- The focusing dial: clockwise (yellow/green/white) for plus lenses (+1 to +20), anti-clockwise (red) for minus lenses (-1 to –35). Importance of focusing – dialling in lenses compensates for both the observer’s and the patient’s refractive errors, eg if the observer has no refractive error and the patient is myopic, minus lenses will be required to focus on the retina.
- Observer should remove glasses unless astigmatic (and patient should remove glasses unless very myopic) to enable the ophthalmoscope to be held as close as possible to the observer’s eye.
- Right eye, right hand and right fore-finger on dial of ophthalmoscope should be used to examine the patient’s R eye, and vice versa for left. Keep top of ophthalmoscope close to observer’s brow such that the ophthalmoscope aperture is close to the eye.
- Patients must be given clear instructions. Ask patient to look directly ahead or ask patient to look at a target – be aware that this may be confusing since the observer may well block the target causing patient confusion and eye movement and make allowances.
- Dial up a 0 lens and stand back at arm’s length from the patient with your free hand on their shoulder, to examine the red reflex (R/R) through each pupil. Compare each R/R.
- Once the R/R has been examined, dial up a plus 10 lens.
- Stand to the side of the patient (not in front), place hand on patient’s forehead (or shoulder) and whilst keeping pupil aligned, move closer to eye from a slightly temporal approach - coming in from approximately 45 degrees should help you to land on the optic disc. Commence with a +10 lens and this focuses on the anterior of the lens of the eye. Dial through the lenses towards 0 to bring retina into focus.
- The patient’s pupil is like a keyhole, the nearer you are the more you see, the observer should bring the ophthalmoscope very close to the patient’s eye (3-5 cm) whilst keeping it close to their own. The importance of pupil dilatation will be noted from lectures and practicals.
- Magnification is approximately x15 and the first object encountered is usually the optic disc which will fill much of the undilated view. If the optic disc is not visualised, the vessels should be followed to the disc, remembering that the ‘V’ created by the branching of vessels always points to the disc.
- Students should follow a methodical pattern of examination. A six point fundal examination routine should be followed: a) disc, b) superior temporal arcade vessels and retina, c) inferior temporal arcade vessels and retina, d) inferior nasal arcade vessels and retinae, e) superior nasal arcade vessels and nasal retina, f) macula. Always ask the subject to look in the direction of the portion of retina you are examining, ie look up for superior retina, look left for nasal aspect of right retina, etc.