The best way of picking up a cataract in its early stages is to view the pupil through the ophthalmoscope from a distance of about 50 cm. In this way, the red reflex is clearly seen. The red reflex is simply the reflection of light from the fundus and it is viewed in exactly the same manner that one might view a cat's eyes in the headlamps of one's car or the eyes of one's friends in an ill-judged flash photograph. In fact, such a flash photo could well show up an early cataract if an elderly relative were included in the photograph. When using the ophthalmoscope, the opacities in the lens are often seen as black spokes against the red reflex (Figure 11.2). It is important to focus one's eyes onto the plane of the patient's pupil if the cataract is to be well seen, and it is preferable to dilate the pupil beforehand or at least examine in a darkened room. Typical age-related lens opacities are wedge shaped, pointing towards the centre of the pupil. At the same time, the central nucleus of the lens can take on a yellowish-brown colour, the appearance being termed "lens sclerosis", and ultimately, the lens can become nearly black in some instances.
After inspecting a cataract with the ophthalmoscope held at a distance from the eye, one must then approach closer and attempt to examine the fundus. Further useful information about the density of the cataract can be obtained in this way. It is generally true that if
the observer can see in, the patient can see out. If there is an obvious discrepancy between the clarity of the fundus and the visual acuity of the patient, some other pathology might be suspected. Sometimes the patient might not have performed too well on subjective testing and such an error should be apparent when the fundus is viewed. Some types of cataract can be misleading in this respect and this applies particularly to those seen in highly myopic patients. Here, there is sometimes a preponderance of nuclear sclerosis, which simply causes distortion of the fundus while the disc and macula can be seen quite clearly.
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