The cause of the strabismus should be first ascertained—viz., whether this is due to paralysis or to over-action of an ocular muscle after the surgeon has satisfied himself about which of the eyes is at fault.
Convergent, non-paralytic or concomitant strabismus in young people is usually the result of hypermetropia or hypermetrUpic astigmatism, and in some cases it may be cured, for a time at least, by keeping the eyes under the influence of weak Atropine solution, and so paralysing the ciliary muscle and preventing attempts at accommodation and its accom panying convergence. In all cases, however, the vision should be care fully examined, and correcting glasses ordered. In young children these glasses should correct the total hypermetropia and should be worn con stantly, while a drop of Atropine (I gr. to the ounce) should be instilled every morning in both eyes. In a large number of cases, and specially in those of recent origin, this effects a complete cure. This treatment should be persisted in for several months, and when the atropine is stopped, weaker glasses will be necessary. The squinting eye should be exercised for half an hour daily by covering the good eye. Javal's orthoptic treatment is often successful; it consists in producing diplopia by exercises with a prism whose base is directed downwards, after which fusion of the double images is remedied by assiduous exercises with the stereoscope. This instrument is also very useful to train the patient to fuse the images after operation.
Tenotomy of the internal rectus in one or both eyes must be resorted to where these measures fail. This should not, as a rule, be done till about the eighth year. It may be necessary to operate sooner if there are signs of the vision becoming affected, though by closing the good eye several times daily and exercising the weak one this generally may be prevented and operation put off till the age specified.
As it is often impossible to predict the exact amount of correction resulting from the operation, a second operation may be required, hut it is wiser not to divide both recti at one time. The full effect of the operation is often not seen for several months, and if too much is done divergent strabismus may result. If vision is very poor in the squinting eye an operation is not likely to do permanent good, though for a few months it may seem to be improved. In such cases it is better to try
to improve vision by exercising the squinting eye before operation.
The tendon may be easily divided without giving any pain, after thoroughly rendering the conjunctiva insensible by Cocaine. The first step after the introduction of the speculum is to nip up a portion of the conjunctiva by forceps, and with the scissors produce an opening through which the hook and the blades of a pair of fine scissors may be passed, and as the tendon is caught up by the hook it is divided by the scissors close to the sclerotic.
Convergent strabismus, the result of myopia, is generally remedied by suitable glasses, but where these fail, tenotomy should be performed. Divergent, non-paralytic squint is more difficult to remedy; very mild cases, however, may sometimes be successfully treated by suitable concave glasses, which correct the myopia upon which the strabismus often depends. When the constant wearing of the glasses fails to remove the squint, advancement of one or both internal muscles, with tenotomy of the external, when necessary, should be performed.
It must always be remembered that after operations the squinting eye must be constantly exercised, otherwise sharpness of vision will be lost.
Strabismus the result of paralysis must be treated by remedying the underlying mischief, which may he syphilitic or rheumatic. Mercury and Iodides should be freely administered, and massage and Galvanism tried. It is a good plan to act on the paralysed muscle by seizing the conjunctiva near its corneal insertion so as to move the eyeball in the direction in which the affected muscle should act, hut to a greater extent than the normal. The double vision caused by the strabismus may be remedied by wearing a ground glass over the affected eye, and at several times during the day the affected organ should be exercised with the view of preventing wasting of the weakened muscles.
When the above measures fail after several months' trial, operation will be indicated; this should consist in advancement of the paralysed internal or external rectus with tenotomy of its antagonist when necessary.