Cranial Nerves: The Eye 2 – Fundi

Published on 09/04/2015 by admin

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Last modified 09/04/2015

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Cranial Nerves

The Eye 2 – Fundi

BACKGROUND

The ophthalmoscope provides a light source and an optical system to allow examination of the fundus (Fig. 8.1).

Figure 8.1 The parts of two commonly used ophthalmoscopes

Its moving parts are:

• on/off switch, usually with brightness control

• focus ring (occasionally two)

• sometimes a beam selector

• sometimes a dust cover.

The focus ring is used to correct (1) for your vision and (2) for the patient’s vision.

1. If you are short- or near-sighted (myopic) and not using glasses or contact lenses, you will have to turn the focus dial anticlockwise to focus to look at a normal eye; turn it clockwise if you are long- or far-sighted (hypermetropic). Establish what correction you need before approaching the patient.

2. If the patient is myopic, turn the ring anticlockwise; if hypermetropic, clockwise.

TIP

An oblique view of the patient with his spectacles on tells you if he is long- or short-sighted and gives an idea of severity. If his face is smaller through his glasses, he is myopic; if his face is larger, he is hypermetropic. The degree indicates severity.

Beam selector choices are:

• standard for general use

• narrow beam for looking at the macula

• target (like a rifle sight) to measure the optic cup

• green to look for haemorrhages (red appears as much darker).

COMMON MISTAKES

• Second focus ring, with choices 0, + 20 and − 20, is not set to 0.

• Incorrect beam is chosen, or selection ring is left between two selections.

• Dust cover is not removed.

• Batteries are flat (most common problem).

WHAT TO DO

• Turn off the lights or draw the curtains.

• Sit opposite the patient.

• Check the focus is set at zero, and that the light works and is on the correct beam.

• Ask the patient to look at a particular point in the distance at his eye level (e.g. a light switch, a spot on the wall).

To examine the right eye (Fig. 8.2):

• Take the ophthalmoscope in your right hand.

• Approach the patient’s right side.

• Look at his right eye from about 30 cm away with the ophthalmoscope in the same horizontal plane as his eye, about 15 degrees from the line of fixation. Aim at the centre of the back of his head. Keep out of the line of sight of the other eye.

• The pupil should appear pink, as in bad flash photographs. This is the red reflex.

• Opacities in the eye, notably cataracts and floaters, appear as silhouettes. Cataracts usually have a fine web-like appearance.

• Gradually move in towards the eye.

• Stay in the same horizontal plane, aiming at the back of the patient’s head. This should bring you in at about 15 degrees to his line of fixation.

• Encourage the patient to keep looking at the distant point and not at the light.

• Bring the ophthalmoscope to within 1–2 cm of the eye.

• Keep the ophthalmoscope at the same level as the patient’s eye and the fixation point.

• Focus the ophthalmoscope as described above.

If the eye is approached as described, the optic disc should be in view. If it is not, focus on a blood vessel and follow it. The acute angles of the branches and convergence of artery and vein indicate the direction to follow. Alternatively, start again.

TIP