Strabismus - squint or crossed eyes
Strabismus, or squint, describes the eyes being out of alignment.
Strabismus may affect a child from birth, or it can develop later in life.
The brain can usually compensate for the misalignment in younger children, but from around eight years old, strabismus can cause double vision or diplopia.
What causes strabismus?
Some people are born with eyes that do not align in the usual way. This is called congenital strabismus (congenital squint). In many children, there is no clear cause of strabismus. In some cases, it is a result of a problem with the nervous system, especially the part that controls the muscles of the eyes. If it is not corrected, strabismus can continue into the adult years. Most adults who have strabismus were born with it.
If strabismus does not appear until later in life, it will cause double vision. If the eyes become misaligned in an adult who did not have strabismus as a child, it could be a sign of a serious condition such as a stroke. A sudden misalignment of the eyes, or double vision, is an important reason to seek medical advice immediately.
Someone who is born with strabismus will see without having double vision, but there might be other effects on vision. Because the two eyes are not working well together, depth perception and peripheral vision (vision off to the side) will not be very good. Eyestrain and headaches can occur frequently. It might also be necessary to turn the head in unusual ways in order to see in certain directions.
How is strabismus diagnosed?
Checking the position of each eye and its movements will reveal crossed eyes or other forms of strabismus. The examination may include these parts:
- An eye chart uses letters of decreasing size to determine the sharpness of your vision at distance.
- The retinoscope projects a thin beam of light into the eye. When used with the rotating lens dial (called the phoropter) the optician measures any refractive error like short-sightedness, long-sightedness or astigmatism.
- A slit-lamp scope examination of the surface of each eye. The same device is used to inspect internal eye structures located in the front portion of the eye. This is how changes in the clear cornea and lens are identified.
- Pressure inside the eye is measured using one of several devices.
- Examination with hand-held ophthalmoscope can reveal abnormalities of the retina, the macula and the optic nerve.
- Dilating eye drops may be given to enable a fuller examination.
How is strabismus treated?
A doctor may recommend that patients go through physiotherapy to help strengthen their eye muscles. Vision therapy is also used to help a person correct their vision when suffering with strabismus. This therapy helps train a patient's brain to be able to align their eyes and focus and visually process images. Vision therapy uses computerised optical devises, including lenses and filters, to develop the eye muscles. Glasses, an eye patch, and a botulinum toxin injection, might also be used as treatment.