Strabismus - Fundamentals of Clinical Ophthalmology.pdf

ADULT STRABISMUS
Case example
An adult patient presents with double vision
and divergent eyes. History may reveal the
patient had a convergent squint during visual
immaturity. Subsequent divergence following
convergence of the eyes when the visual system
is mature implies that as an adult, the position of
the optic axis has taken the eye out of the
suppression area present when convergent. A
helpful confirmatory test is to overcorrect the
deviation with prisms and see if this eliminates
the diplopia.
The diplopia may occur even if the patient
is amblyopic. Surgical treatment involves
adjustable suture surgery to realign the eye so
that there is suppression of the diplopia. In our
experience, suppression can occur but may take
months or even 1–2 years to occur. Patients are
encouraged to use one eye, and reassured that
amblyopia is a childhood condition not an adult
one. Patients should be encouraged to use
the dominant eye, particularly for distance,
and to ignore the second image to stimulate
suppression. The patient may prefer the nondominant
eye for near tasks and reading.
Loss of fusion with head trauma or
cerebral (brainstem) lesion
Diplopia after severe head trauma requires
the exclusion of bilateral superior oblique palsy.
These patients may have little evidence of palsy
except esotropia in downgaze; the bilateral
excyclotorsion can be missed unless carefully
looked for. The excyclotorsion can be
demonstrated with the Maddox Rod test. It can
also be confirmed by careful fundus examination
and recorded by fundus photography showing in
the rotated retina the macula below its normal
position. The mature visual system in the adult
is unable to develop suppression in a short
period of time. Treatment consists of the
surgical technique of Harada–Ito, tightening the
anterior fibres of the superior oblique muscle.
Severe head trauma may also cause central
fusion disruption, as can a cerebral tumour. 4,5
The sudden onset of palsies of more than one
oculomotor nerve (third, fourth, sixth) may
create diplopia especially if the patient looks into
the direction of the weakened muscle(s). In
these adult patients with a mature visual system,
diplopia occurs in the context of one image
falling on the macula in one eye and the second
image falling on an extrafoveal area of the retina
of the other eye, resulting in diplopia.
Confusion
This results when there is recent onset of
strabismus in adults and each fovea sees a
different object that cannot be fused. Retinal
rivalry ensues and later the eye looking at the
object (the dominant eye) may prevail and the
confusing image from the other eye be
suppressed.
Significance of Hering’s Law
Hering’s Law of equal innervation of agonist
pairs indicates that paired muscles in either eye
receive equal stimulus for movement. If one
muscle is paretic fixing with the paretic eye in
preference to the non-paretic eye, this will cause
a greater deviation of the other eye.
The Parks 3-step test
This test can be helpful in identifying paretic
vertical muscle in a strabismus by a process of
elimination. Red and green filter glasses are
worn to break fusion.
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●
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Step 1. Which eye is higher (hypertropic)?
Step 2. Is the hypertropia worse in left or right
gaze?
Step 3. Is the hypertropia worse in left or right
tilt? (Bielschowsky head tilt test) 6
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