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

It is essential to keep the patient's eye, the point of fixation and the ophthalmoscope in the same plane.

COMMON MISTAKES

Aphakic eye (no lens): severely hypermetropic—use a high positive lens or examine while the patient has glasses on.

To examine the left eye:

Hold the ophthalmoscope in the left hand and use your left eye. If you use your right eye to look at the patient's left eye, you will end up rubbing noses with the patient. Most people find this part of the examination difficult at first so you must persevere.

Figure 8.2 Approaching the patient with an ophthalmoscope

WHAT YOU FIND

1 Optic disc

See Figures 8.3 and 8.4.

Figure 8.3 Flow chart: optic disc abnormalities

Figure 8.4 Optic disc abnormalities

The optic cup is slightly on the nasal side of the centre of the optic disc. Its diameter is normally less than 50% of the disc (Figs 8.5A and 8.6).

Figure 8.5 A. Normal disc, Blue arrow = artery; yellow arrow = vein; B. Papilloedema; C. Optic atrophy, note pale disc; D. Glaucoma, note wide optic cup.

Figure 8.6 Normal variants

The optic nerve head is swollen (Fig. 8.5B). This can be caused by papilloedema or papillitis. Papilloedema usually produces more swelling, with humping of the disc margins—not usually associated with visual disturbance (may enlarge blind spot). Papillitis is associated with visual loss, especially central scotomas.

A swollen optic disc is often difficult to find, the vessels disappearing without an obvious optic disc.

The difference between papilloedema and papillitis can be remembered as follows:

• You see nothing (cannot find the disc) + patient sees everything (normal vision) = papilloedema.

• You see nothing + patient sees nothing (severe visual loss) = papillitis.

• You see everything (normal-looking disc) + patient sees nothing = retrobulbar neuritis.

The optic nerve head is very pale—optic atrophy (Fig. 8.5C). The optic cup is markedly enlarged, taking up most of the disc - glaucoma (Fig. 8.5D).