Many patients complain of blurred vision, which is usually worse when viewing distant objects. If the patient is unable to read small print, the surgeon might suspect that other pathology, such as macular degeneration, could be present. One must bear in mind that some elderly patients say that they cannot read when it is found that they can read small print if carefully tested. It is a curious fact that when the cataract is unilateral, the patient can claim that the loss of vision has been quite sudden. Elucidation of the history in these cases sometimes reveals that the visual loss was noted when washing and observing the face in the mirror. When one hand is lowered before the other, the unilateral visual loss is noticed for the first time and interpreted as a sudden event. The history in cataract cases might be further confused by a natural tendency for patients to project their symptoms into the spectacles, and several pairs might be obtained before the true cause of the problem is found. In order to understand the symptoms of cataract, it is essential to understand what is meant by index myopia. This simply refers to the change in refractive power of the lens, which occurs as a preliminary to cataract formation. Index myopia can also result from uncontrolled diabetes. If we imagine an elderly patient who requires reading glasses (for presbyopia) in the normal way but no glasses for viewing distant objects, the onset of index myopia will produce blurring of distance vision, but also the patient will discover to his or her surprise that it is possible to read again without glasses. In the same way, the hyper-metropic patient will become less hyper-metropic and find that it is possible to see again in the distance without glasses. The ageing fibres in the precataractous lens become more effective at converging light rays so that parallel rays of light are brought to a focus more anteriorly in the eye.

Apart from blurring of vision, the cataract patient often complains of monocular diplopia. Sometimes even a slight and subtle opacity in the posterior part of the lens can cause the patient to notice, for example, that car rear lights appear doubled, and this can be reproduced with the ophthalmoscope light. Monocular diplopia is sometimes regarded as a rather suspect symptom, the suggestion being that if a patient continues to see double, even when one eye is closed, then he or she might not be giving an accurate history. In actual practice nothing could be further from the truth and this is quite a common presenting feature of cataract.

Glare is another common presenting symptom. The patient complains that he or she cannot see so well in bright light and might even be wearing a pair of dark glasses. Glare is a photographic term but here it refers to a significant reduction in visual acuity when an extraneous light source is introduced. Light shining from the side is scattered in the catarac-tous lens and reduces the quality of the image on the retina. Glare becomes an important consideration when advising an elderly cataractous patient on fitness to drive. The visual acuity might be within the requirements laid down by law (seeing a number plate at 20.5 m) but only when the patient is tested in the absence of glare.

A consideration of all these factors makes it relatively easy to diagnose cataract even before examining the patient. To summarise, a typical patient might complain that the glasses have been inaccurately prescribed, that the vision is much worse in bright sunlight, that sometimes things look double and that there is difficulty in recognising people's faces in the street rather than difficulty in reading. Patients with cataracts alone do not usually complain that things look distorted or that straight lines look bent, nor do they experience pain in the eye.

Rarely, cataracts become hypermature; that is to say, the lens enlarges in the eye and this in turn can lead to secondary glaucoma and pain in the eye. Urgent surgery might be needed under these circumstances. In its late stages, a cataract matures and becomes white, so that exceptionally a patient might complain of a white spot in the middle of the pupil.

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