(_a_) _Vision._ It must be remembered that in children a defective eye retaining the power of accommodation is often more useful than an eye which sees better but has to wear different glasses for different distances. Vision must be reduced to less than 6/18 in both eyes after correction with glasses before the operation should be undertaken. In rare cases, in children, and in traumatic cataract where the cataract is very dense and confined to one eye, it may be removed partly to improve the personal appearance and partly to enable the patient to see large objects. An eye without a lens (aphakia) will not work with an eye with a lens even if the former be corrected with glasses. If the patient be unable to see letters, he should have a ready and quick perception of light, no cataract, however dense, being sufficient to prevent this. (_b_) A patient should have a good _projection of light_; that is to say, he should be able to locate the light when thrown into the eye with a mirror whatever direction it comes from. Children generally turn the head towards the light, provided that they can see it and that the eye is not defective from other causes. (_c_) Note whether _the pupils_ are equal and active. In children most useful information can often be obtained as to the condition of the fundus by means of the pupil, which often will not react when the patient is unable to appreciate light. (_d_) _The condition of the fundus of the other eye_, if observable, should be taken into account, as many diseases of the fundus, such as choroiditis and myopia, are bilateral, and would influence the prognosis considerably. (_e_) _The lachrymal sac_ and conjunctiva should be free from all signs of inflammation (see p. 181). [Illustration: FIG. 85. EYE SPECULUM.] [Illustration: FIG. 86. FIXATION FORCEPS.] (ii) =For the removal of a lens for high myopia.= In selected cases operation gives very satisfactory results with great improvement of vision; indeed full normal distance vision has been obtained without glasses. The operation, however, is only justifiable under certain circumstances, the chief of which are:-- (_a_) The amount of myopia should exceed 18 D. (_b_) Distance vision should be defective--less than 6/18 with glasses. (_c_) Ophthalmoscopically the macular region should be sound. (_d_) Binocular vision should be absent. (_e_) The patients should be children or young adults. (_f_) If there is some serious reason why the patient is unable to wear glasses.