Nếu có một sự chênh lệch rõ ràng giữa sự trong sáng của đáy và sắc sảo về thị giác của bệnh nhân, một số bệnh lý khác có thể nghi ngờ. Đôi khi bệnh nhân có thể không đã thực hiện quá tốt về thử nghiệm chủ quan và một lỗi như vậy nên được rõ ràng khi đáy được xem | 86 Common Eye Diseases and their Management 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. Findings on Slit-lamp Microscopy A detailed view of any cataract can be obtained with the slit-lamp. By adjusting the angle and size of the slit beam various optical sections of the lens can be examined revealing the exact morphology of the cataract. The presence of small vesicles under the anterior lens capsule can be seen as an early sign of senile cataract. Cataracts secondary to uveitis or to drugs might first appear as an opacity in the posterior sub-capsular region. For optical reasons an opacity in this region tends to interfere with reading vision at an early stage. Opacities in the lens can appear in a wide range of curious shapes and sizes and earlier in the last century there was a vogue for classifying them with Latin names which are now largely forgotten. Such a classification is of some help in deciding the cause of the cataract although it can sometimes be misleading. Congenital cataracts are usually quite easily identified by their morphology as are some traumatic cataracts. When a unilateral cataract appears many years after a mild contusion injury it can be difficult to distinguish this from an age-related one. Other Important Signs Certain other important signs need to be carefully elicited in a patient with cataracts. The pupil reaction is a particularly useful index of retinal function .
