Written by Khalil Al-Salem M.D FRCS, FICO
Ocular miss alignment is a problem seen in 5% of the eye clinic patients. Because of the high frequency, careful assessment and good knowledge of the care giver is mandatory.
- Comitant squint: a squint with equal amount of deviation while doing cover uncover test. ex. when covering the right eye, you discover a 20 prism diopter of esodeviation. if you repeat the test while covering the left eye. both angles will be equal.
- non-comitant squint: a squint with unequal amount of deviation when measuring the deviation using cover uncover test. ex. covering the right eye (20 PD ) and covering the left eye 40 PD.
- tropia: manifest squint
- phoria: hidden squint
- esotropia /esophoria: towards the nose. the eyes are going inside.
- exodeviation: a way from the nose
- hypertropia: eye is deviating upwards
- hypotropia: is deviating downwards.
how to examine the patient:
examples of common types if squint:
- intermittent exotropia: This type of squint usually starts late in life after the age of 4 or 6 years. both eyes have normal vision or slightly myopic. Most of the time the patient is not complaining of any problem. The parents usually are not happy about a momentary eye movement to the out side. That is frequently corrected when the patient is asked to.
- the patient can be classified as having
- good control: rarely the patient has exo-deviation (seen in visual inattention periods or when the patient is tried or sick
- fair control: when the patient has the problem being manifested 2-5 times a day.
- poor control: when the eyes are seen outwards most of the day.
When to treat:
- Usually patients with good control are given corrective glasses or slightly hypopic correction like an extra -1.0 D on glasses to give more control over the exotropia.
- patients with fair and poor control, are best managed by recess or resect (strabismus surgery)
There are two types that are very important to recognize in comitant esotropia:
- Congenital esotropia: this type is characterized by :
- Large angle esodeviation, the patient is born with a 40-50 PD or even larger angle.
- The patient has esodeviation before the age of 6 months.
- Usually the patient has very mild hypermetropia +1 to +3 D not more, or the patient might be emetropic or myopic.
- The patient has full ductions and he does not have any motility restriction, it is important to R/o congenital 6th nerve palsy which is very rare.
- Treatment of the condition is surgical. It is advised to perform surgery as early as possible to prevent amblyopia and muscle contracture which can happen as time goes by.
2. accommodative esotropia: this type is cause by high refractive error in the patient’s early life (2- 3 years); like high hypermetropia +6.0 and above or high astigmatism. The high refractive error will force the child to accommodate to clear up the image. In turn, this will activate both convergence and myosis along with the cilliary body contraction. From our prospect, what we see is he squint.
- Treatment: to relax the natural synchinatic relation ship already built in. We simply need to correct the refractive error of the child, either making him emetrope or slightly myope.
- This type is more likely to get amblyopia than any other type, because most of the time there will be ocular preference very early in life ( the child will prefer one eye, neglecting the other one). That is why prompt correction of refraction with or without monocular occlusion therapy, is needed to regain normal vision in these children.
Cover/ uncover test for patients with vertical strabismus
Amblyopia a quick definition and review:
Non- comitant squint :
- third nerve palsy
- fourth nerve palsy
- sixth nerve palsy