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]).
(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. |
In emmetropia, if the lens be removed, a glass of + 11 D. has to be placed before the eye for distance vision and + 14 D. for near vision. It is impossible to predict the exact amount of correction of myopia which will be produced by the removal of the lens, owing to the surgeon’s inability to estimate the refractive power of the lens associated with the distortion of the posterior pole of the globe. Usually a patient with about 22 D. of myopia is rendered emmetropic by the operation.