What Are Strabismus and Amblyopia?
Strabismus (squint, turned eye) and amblyopia (lazy eye) affect about 3% of the population, and the majority of squints and lazy eyes begin in early childhood.
A convergent squint (esotropia) is when one eye turns in compared to the other. A divergent squint (exotropia) is when one eye turns out compared to the other. A squint can be in one eye or the other, or may be alternating between the two eyes.
An amblyopic (lazy) eye is an eye that has a poor visual acuity which doesn’t improve despite any glasses prescription, and in the absence of any eye disease.
Divergent Squint(Exotropia)
Divergent squints are often the result of head trauma and accident, and can be secondary to surgery for a convergent squint.
Intermittent Divergent squints are generally the result of Near Point Stress.
Convergent Squint (Esotropia)
Early convergent squints can be from six months old and tend to be large angle, often 60 degrees, and the child is likely to have a lazy eye and a longsighted glasses prescription.
The more common age of onset for convergent squints is 2 to 2.5 years old. If a child aged 2yrs has a poor general motor system, they will have poor eye movements. When they want to look at near they may not have the ability to converge, maintain convergence and focus accurately, to bring the two images together and fuse them to see singly. This results in visual confusion, but if one eye is turned in further (over-converged) then it’s image falls on the blind spot of the other eye, the visual confusion is removed and the child sees singly.
By practising, strabismus and amblyopia become adaptations to avoid visual confusion. The angle of strabismus may be micro (10 degrees or less), 25 degrees or 45 degrees depending on the development of the child, and the age of onset. Also the angle of squint may vary depending on where the child is looking.
The underlying factor in strabismic adaptations is an immature general motor system leading to visual confusion and/or Near Point Stress.
Optometric Vision Therapy (OVT) for Strabismus and Amblyopia
OVT can be of benefit for both strabismus and amblyopia by improving the general motor system, and the patient’s eye movement skill, to be able to point both eyes at the same place and gain fusion of the images.
For many years, it was thought that amblyopia and strabismus were only amenable to treatment during the "critical period". This is the period up to age seven or eight years. Current research has conclusively demonstrated that effective treatment can take place at any age, but the length of the treatment period increases the longer the condition has existed prior to treatment.
