Constant Exotropia
Congenital Exotropia
Age of onset at birth.
Large and constant deviation
Dissociated vertical deviation (DVD) may
be present.
Neurological anomalies my present.
Sensory Exotropia
Sensory exotropia occurs as a result of
unilateral or bilateral serve visual
impairment.Consecutive Exotropia
Exotropia following surgical overcorrection
of esotropia called consecutive exotropia.
Treatment
1.Wait atleast for six month if deviation is
not much.
2. Surgical treatment according according to
deviation if it is significant
Intermittent Exotropia
Age of onset around 2 years.
Starts with Exophoria
Exophoria break down to exotropia under
fatigue, bright light or visual in attention
or ill health.
Phases of
exodeviation and clinical
presentation (Calhounz et al )
-
Exophoria at
distance,
orthophoria at
near.
Asymptomatic
-
Intermittent
exotropia for
distance,
orthophoria/
exophoria at
near.
Symptomatic for
distance.
-
Exotropia
for distance,
exophoria or
intermittent
exotropia at
near. Binocular
vision for near,
suppression
scotoma develops
for distance.
-
Exotropia at
distance as well
as near. Lack of
binocularity
|
|
Symptoms Intermittent
Exotropia
1.Transient Diplopia
2.Asthenopic symptoms like eyestrain,
blurring, headache and difficulty with
prolonged periods of reading.
3.Micropsia
4.Diplophotophobia :closure of one eye
in bright sunlight. Bright sunlight
dazzles the retina so that fusion is
somehow disrupted, causing the deviation
to become manifest. Thus one eye is
closed in order to avoid diplopia and
confusion
Signs of
Progression of Intermittent
Exotropia
-
Gradual loss of fusional
control evidenced by the
increasing frequency of the
manifest phase of squint
-
Development of Secondary
convergence insufficiency
Increase in size of the
basic deviation
-
Development of suppression
as indicated by absence of
diplopia during manifest
phase
-
Decrease of Stereoacuity
|
|
Basic intermittent
exotropia: In which angle
of deviation is nearly same for
distance and near fixation
Divergence excess type of
intermittent Exotropia:
The angle of deviation for distance
is more than >15 Δ then near. This
type of exotropia may be two type.
True Divergence Excess Type of
intermittent Exotropia
Or Simulated Type of Divergence
Excess intermittent.
When patient is examined after
a uniocular patient for more than 60
min. or looking through +3.00D lens,
if near deviation is constantly less
than distance deviation. Then it is
called as true Divergence excess
type of exotropia. If near deviation
and distance deviation are same then
is called as Simulated type of
Divergence excess.
Tenacious Proximal Fusion:
Distance measurement initially
exceeds near, but the near
measurement increases after 60min.
of occlusion
Proximal Convergence :
Distance measurement exceeds near
measurement,even after 60min. of
occlusion. AC/A ratio is normal
Convergence
Insufficiency Type Of Exotropia
The angle of deviation for near is more
than >15 Δ then Distance.
|
Patch Test -
The patch test is used to
control the tonic fusional
convergence to differentiate
pseudo-divergence excess from true
divergence excess and to reduce the
angle variability. Contrary to the
earlier practice of patching one eye
for 24 hrs it is now found that
patching the eye for 30 min. is
sufficient to suspend the tonic
fusional convergence and thus reveal
the actual amount of deviation (1).
+3.0 D near add
test (lens gradient method)
- This test has been devised to
diagnose the patients of divergence
excess type who have true divergence
excess due to high AC/A ratio. This
test uses the lens gradient method
to measure the AC/A ratio. These
patients are the ones who will
continue to have a distance-near
disparity post-operatively, and may
require bifocal spectacles after
surgery for a consecutive esotropia
at near. This test should be
resorted to in patients who have a
distance deviation greater than near
deviation of 10 prism diopters or
more after the patch test. After the
patch test while still dissociated,
re-measure the deviation at near
with a +3.0 add. If the exodeviation
at near increases by 20 prism
diopters or more the diagnosis of
high AC/A ratio true divergence
excess intermittent exotropia is
made.
Far distance
measurement - Measuring the
deviation by fixating a far object
reduces measurement variability and
helps uncover the full deviation by
reducing near convergence. Combining
the patch test and far distance
measurement can greatly reduce
under-corrections and has improved
the overall result. In a prospective
randomized trial, 86% of patients
who underwent surgery for the
largest angle had a satisfactory
outcome, compared with 62% who were
operated on for the standard 6 meter
distance deviation (2).
|
Management
Non-surgical Treatment
Indication
In patients with small
(<20pd) deviations
Very young patients in
whom surgical overcorrection
could lead to amblyopia or
loss of bifixation
In patients who otherwise
cannot be taken up for
surgery
Patients with a high AC/A
ratio may be responsive to
non-surgical methods.
Non-Surgical Management
Options Of Intermittent
Exotropia
1.Spectacle Correction of
Refractive Errors:
Refractive errors
myopia, hyperopia.
,anisometropia and
astigmatism can impair
fusion and promote a
manifest deviation. A
trial of corrective
glasses based on
cycloplegic refraction
is often warranted (16).
2.Overcorrecting
minus lens therapy:
This is particularly
useful in patients who
have a high AC/A ratio.
This therapy is based on
the principle that
stimulating
accommodative
convergence can reduce
an exodeviation (17).
3.Part time occlusion:
It is a passive
anti-suppression
technique as opposed to
the active techniques
involving diplopia
awareness This technique
has found some use in
very young children.
Part time patching of
the non-deviating eye
for four to six hours
daily may convert an
intermittent exotropia
to a phoria. Although
the benefit is usually
temporary, occlusion can
be used to postpone
surgical intervention in
responsive patients
(18). Alternate
occlusion may be used in
patients with equal
fixation preferences.
Initially the results
are evaluated after 4
months of occlusion. If
the angle of deviation
is decreased the
occlusion should be
continued and assessment
made every 4 months
until no further change
occurs. In case there is
no improvement for 4
months, it is
discontinued.
4.Prismotherapy:
can be used to improve
fusional control, or as
a temporizing measure,
either pre or
postoperatively Prisms
are rarely a long-term
solution in patients
with intermittent
exotropia.
5.Orthoptics:
according to Knapp
orthoptics should not be
used as a substitute for
surgery but rather as a
supplement. The aim is
to make the patient
aware of manifest
deviation and to improve
the patient's control
over it (19). Active
anti-suppression and
diplopia awareness
techniques can be used
in cases with
suppression
|
|
|
Timing for Surgery
- There is a controversy
about the management of children
less than 4 years of age because in
contrast to infantile esotropia
these children have intermittent
fusion and excellent stereopsis.
Knapp and many other workers
advocated early surgical
intervention to prevent development
of sensory changes that may prove
intractable later (3-7). However
they do caution that in visually
immature children a slight
undercorrection should be attempted
to prevent occurrence of
monofixation syndrome from
consecutive esotropia (8). Jampolsky
advocates delayed surgery, citing
advantages like accurate diagnosis
and quantification of the amount of
deviation and to avoid consecutive
esotropia and development of
amblyopia. Although one study
reported better outcomes in children
who were under the age of 4 years
(7), most studies have failed to
show that age at time of surgery
makes any difference in outcome
(9-11). Thus it is now believed that
the surgery in this age group is
reserved for patients in whom rapid
loss of control is documented. In
the interim, minus lenses or part
time patching may be used as non
surgical methods and these patients
followed closely for signs of
progression (12,13). |
|
Type
of Surgery
Basic Types:
should be treated with recession
lateral rectus- recession
lateral rectus in both eyes or
unilateral lateral rectus muscle
recession/medial rectus muscle
resection
Simulated Divergence Excess :
should be treated with recession
lateral rectus- recession
lateral rectus in both eyes or
unilateral lateral rectus muscle
recession/medial rectus muscle
resection
Divergence excess type
should be treated with bilateral
lateral rectus muscle
recessions.
Convergence insufficiency type:
should be treated with bilateral
medial rectus muscle resections
Exo-deviation with one eye is
amblyopic:
unilateral lateral rectus muscle
recession/medial rectus muscle
resection
Symmetric(Recession
lateral rectus- Recession
lateral rectus in both eyes) Vs
Asymmetric((Recession lateral
rectus Resection medial
rectus in one eye):Symmetric
surgery is usually preferred
over monocular
recession/resection procedures,
since a recession/resection
procedure may produce lateral
incomitance with a significant
esotropia to the side of the
operated eye. In adults, this
incomitance can produce diplopia
in side gaze.
|
References
1.Kushner BJ: The distance angle to target
in surgery for intermittent exotropia. Arch
Ophthalmol 1998:116:189-194.
2.Hutchinson AK. Intermittent Exotropia.
Ophthalmol Clinics Of North Am.
2001;14:3:399-406.
3.Asbury T. The role of orthoptics in the
evaluation and treatment of intermittent
exotropia. In: Arruga A. ed.: International
strabismus symposium, Basel 1968, S. Karger
AG 331.
4.Dunlap EA. Over correction in esotropia
surgery. In: Arruga A. ed.: International
strabismus symposium, Basel 1968, S. Karger
AG 319.
5.Parks MM. Metchell P. Concomitant
exodeviation. In: Duane TD ed. Clinical
Ophthalmology, Vol. 1.Philadelphia 1988, JB
lippin cott Co. p 1.
6.Pratt Johnson JA, Barlow JM & Tilson G.
Early surgery for Intermittent exotropia. Am
J Ophthalmol. 1977;84:689.
7.Raab EC. Management of Intermittent
exotropia : for surgery. Am Orthopt J.
1998;48:25-29.
8.Ing MR, Nishimura J, Okino L: Outcome
study of bilateral lateral rectus recession
for intermittent exotropia in children.
Trans Am Ophthalmol Soc (XCV): 1997:433-452.
9.Richard JM, Parks MM: Intermittent
exotropia: Surgical results in different age
groups. Ophthalmology. 1983;90:1172-1177.
10.Stoller SH, Simon JW, Liniger LL:
Bilateral lateral rectus muscle recession
for exotropia: A survival analysis. J
Pediatr Ophthalmol Strabismus 1994;
31:89-92.
11.Rosenbaum AL: Exodeviations. In Current
Concepts in Pediatric Ophthalmologya and
Strabismus, p 41, Ann Arbor MI, University
of Michigan 1993.
12.Santiago AR, Ing MR, Kushner BJ,
Rosenbaum AL: In Rosenbaum AL, Santiago AP
(ed) Clinical Strabismus Management:
Principles and Surgical Techniques. W.B.
Saunders company, Philadelphia 1999.
14.Wilson ME: Exotropia. Focal Points
Clinical Modules for Ophthalmologists
XIII:1999:1-14
15Moore S: The prognostic value of lateral
gaze measurements in intermittent exotropia.
Am Orthop J. 1969;19:69-71.
16.Iacobucci IL, Archer SM, Giles CL:
Children with exotropia responsive to
spectacle correction of hyperopia. Am J
Ophthalmol. 1993;116:79-83.
17.Caltreider M, Jampolsky A: Overcorrecting
minus lens therapy for treatment of
intermittent exotropia. Ophthalmology
1983;90:1160-1165.
18.Freeman RS, Isenberg SJ: The use of part
time occlusion for early onset unilateral
exotropia. J Pediatr Ophthalmol Strabismus
1989;26:94-96
19.Knapp P. Divergent deviations. In: Allen
JH ed. Strabismic ophthalmic symposium II.
St. Louis 1958, Mosby-Year Book 354
|
