COMITANT ESOTROPIA:

THERAPY AND OPTIONS

I. Introduction: Esotropias are, by far, the most challenging binocular case to successfully treat. Esotropias may be intermittent or constant and usually categorized (unfortunately) into one of three broad areas:

1. Basic Esotropia (congenital or acquired)

2. Divergence Insufficiency Esotropia

3. Convergence Excess Esotropia

Regimens for remediation of an esotrope will vary extensively depending on the child's age and sensory and motor fusion abilities. Unfortunately, the three categories listed above do not offer a single clue as to the prognosis of the patient. Clinicians have found it much more beneficial to classify esotropias by many factors including:

1. Age of Onset

2. Age of Patient

3. Constancy of Esotropia

4. Presence of Accommodative Component

5. Sensory Fusion (at objective angle or centration point)

6. Motoric Fusion (from objective angle or centration point)

7. Prism Adaptation

For this lecture, we will limit ourselves to the discussion of acquired esotropia. Even with this limitation, therapy regimens must be individually developed for each case. As with exotropes, the characteristics (and diagnosis) may change as the patient gains accommodative and fusional skills.

II. Binocular Evaluation of an Acquired Esotrope:

A. Many published reports state a low success rate with constant esotropes. It is true, however, that acquired esotropes (especially those with a significant accommodative component) have a much higher prognosis (60%-92% success rate). Exact data on the efficacy of vision therapy versus surgical intervention of esotropes is rendered difficult, because there are no established guidelines for "success" in the ophthalmologic (surgical) literature. Prognosis is generally lower than an exotropia, but many of the positive signs are similar. For instance:

1. Later onset may allow for some normal binocular development to occur.

2. Intermittency may allow for some normal binocular development to occur.

3. Accommodative component may allow reduction or elimination of deviation with lenses.

4. Normal sensory fusion (NRC) is a positive sign.

5. Presence of motoric fusional ability is a positive sign.

6. Lack of prism adaptation may allow reduction or elimination of deviation with prisms.

B. Binocular Vision Work-up: It is important to establish a good idea of the strabismic "monster" you're dealing with before initiating therapy.

1. Assess fusional (both sensory and motor) abilities of the patient

a. for an esotrope, you should find a point at near where there is no movement of either eye on alternate cover test. This is the pt's. centration point. It is usually very close to the pt. (1-4 inches)

i. objective centration point: no movement of either eye on alternate cover test

ii. subjective centration point: fusion reported (ie. r/g luster of a light target when wearing r/g glasses)

iii. lack of a centration point is a very negative sign; indicative of embedded horror fusionis or lack of correspondence

iv. a different location for a subjective and objective centration points indicate possible embedded ARC

b. sensory fusion should be assessed by a variety of tests already introduced:

i. Bagolini striated lenses

ii. synoptophore

iii. color field/Worth 4 dot

iv. afterimage testing

c. if ARC is present in all tests, it is a negative sign and will require special ARC therapy to be completed during monocular phase of therapy

2. Obtain a detailed analysis of the strabismus.

a. constant vs. intermittent

b. comitant vs. non-comitant

c. does over-plusing the pt. have any beneficial effect on fusional ability

d. does BO prism neutralize the angle completely, or is there prism adaptation (ie. after a period of time, does the angle of deviation increase while wearing the "neutralizing" prism)

e. magnitude of the deviation (>30 Æ is a negative sign)

3. Obtain detailed information regarding the pts. monocular skills.

a. motility skills will be reduced with constant esotropes

i. look for pursuit and saccade dysfunction

ii. look for some limitations of pursuit ranges: for an esotrope, abduction deficits will be noted and may be severe

iii. this is secondary to co-contracture of the ipsilateral (to the non-fixating eye's) medial rectus

iv. gaze evoked nystagmus is not common in acquired ET

v. DVD is not common in acquired ET

b. accommodation may be reduced and there may be a difference in skills between the two eyes

4. CYCLOPLEGE ALL ESOTROPES. It will provide valuable refractive information.

C. In general, you have four choices when you encounter an esotropic patient:

-You may do nothing.

- You may refer for surgery

- You may continue with non-surgical therapy

-You may conduct vision therapy both before and after surgical intervention.

1. Surgery must be mentioned as an option, but you are also obligated to express your expert opinion as to the feasibility of surgery vs. vision therapy.

a. prism adaptation is a very negative sign when considering surgery.

b. anomalous retinal correspondence is a very negative sign when considering surgery.

2. Both prism adaptation and ARC must be remediated before binocular vision therapy can be considered. Therefore, a patient with these sensory adaptations must be prepared for a long (>1 year) of vision therapy.

3. If the patient is congenital esotrope under 2 years of age, and does not respond to plus or prism correction, surgical intervention may be preferable.

III. Passive Modes Of Therapy (those that do not involve active therapy procedures)

A. Occlusion:

1. Complete opaque: patch covers entire field of view

a. may be full time (constant ET) or minimal occlusion (for intermittent ET/amblyopia)

b. may be alternated to the fellow eye at regular intervals

c. will force non-occluded eye to move into all positions of gaze (ie. forces the non-dominant eye to abduct)

d. it has been used to prevent/remediate ARC

2. Complete translucent: transparent tape or nail polish applied to back surface of the lens (acuity through lens should be worse than 20/400). Usually done after opaque patching regimen has been successful.

a. usually used as a full time occlusion technique (for constant ETs only)

b. may be alternated to the fellow eye at regular intervals (3-4 days)

c. will force non-occluded eye to move into all positions of gaze (ie. forces the eye to abduct)

d. it has been used to prevent/remediate ARC

3. Binasal occlusion: either opaque or translucent partial patch that occludes the lens nasal (0.5-1 mm) to monocular corneal reflex

a. most practitioners allow for convergence by slanting the occlusion nasally 3 mm towards the bottom of the lens

b. used after some sensory and motor fusion has been established around the patient's objective angle

c. in approx. 30% of esotropes, this method will create active divergence activity; a very positive sign

d. it has been used to prevent/remediate ARC

B. Application of full plus or OVER PLUS:

1. Distance Rx: may wish to over plus (depending on child's age):

a. preschool: dist blur to 20/40 OK if near acuities are good and plus reduces or eliminates the deviation at distance

b. grade school: dist. blur 20/30 OK if near acuities are good and plus reduces or eliminates the deviation at distance

2. add: DO NOT LIMIT YOURSELF TO +2.50!...If it reduces or eliminates the deviation; go for it!

C. Application of BO prism for full time wear: rarely used initially in the case of an esotropia (especially a constant esotropia), but should be tried (in the office) on all patients. Who knows, maybe you will be lucky!

1. There are problems with prism adaptation (almost all congenital ET's over the age of 8 that I see have prism adaptation to one extent or another).

2. There have been many reported cases, however, of infants (> 1 year old) responding very well to initial prescription of neutralizing prism. This is the only time I attempt prism application before active therapy begins.

3. Older patients (ie. school aged) will usually have a heavy suppression zone which will not respond to optical correction for the deviation.

4. It may enhance the tendency for ARC in school aged children.

5. Before prescribing BO prism, it will be necessary to eliminate ARC and establish adequate sensory fusion skills.

6. BO prism should be used as a "relieving prism" to allow sensory fusion to occur while reducing excessive divergence demand on the patient.

IV. The Monocular Phase : esotropia therapy is quite important and is usually worked 3-4 sessions before the other phases begin. It may continue throughout therapy (depending on patient’s monocular skills). ARC therapy is administered concurrent with this phase.

A. Full time patching regimens for constant esotropes are usually necessary to break down long established (and inappropriate) sensory anomalies. Part time patching regimens should be considered in all cases of intermittent esotropias. In most cases, some occlusion regimen is necessary until normal fusion is obtained in free space settings.

B. Accommodative skills should be equal and sufficient in both eyes.

C. Oculomotility should be equal and sufficient in both eyes.

1. Both gross and fine pursuits should be established

a. small pursuits in the opposite direction of the eye turn (abduction for an esotrope) is important

b. extension of any limitations of pursuits should be worked on

2. Both gross and fine saccades should be refined

3. In many cases of esotropia, in particular acquired cases, significant reduction of the angle of deviation (15-20%) may be obtained with monocular oculomotility therapy.

V. ARC Therapy: The earliest documented age of onset of ARC that required special therapy is 3 years old. This does NOT imply that ARC develops only after that age. It is just not detectable to our standard battery of ARC tests. In general, any congenital esotrope above the age of six is suspect of having significant and embedded ARC. ARC therapy is a significant challenge, especially with preschoolers and is only necessary if anomalous correspondence is reported in several of the common tests for ARC. Success is limited, because after therapy, the patient is once again exposed the underlying strabismic percept that causes ARC in the first place! Both active and passive techniques have been developed to combat ARC. It must be stressed, however, that ARC must be continually monitored throughout all phases of therapy. It often reappears and may slow down progress in other areas of binocular therapy.

A. Passive modes of anti-ARC therapy: The "two P's". Patching and/or prism therapy should be conducted for at least a 6-8 week period and probably much longer. It may be discontinued when NRC is restored with most tests out to a 6 foot viewing distance OR no progress is noted for several weeks. It is assumed here that:

-esotropia is constant

-ARC is embedded

-monocular skills have been improved

- amblyopes have greatly improved acuities with the non-dominant eye

1. Full field patching: it should be understood that all patching regimens for anti- ARC therapy should be CONSTANT OCCLUSION.

a. as stated earlier, constant, opaque patching is the "standard" for ARC patients

i. should be alternated on a daily basis

ii. adhesive ophthalmic patches should be used for pre-schoolers

iii. typical pirate patch suitable for school aged child

b. translucent patching: a constant patching technique used more in recent years. It is particularly useful with school aged children

i. best results when clear nail polish is "dabbed" heavily on the back surface of the lens (acuities should be worse than 20/400 through stippled lens)

ii. should be alternated every 3-4 days

2. Partial field patching: for esotropes, binasal occlusion is appropriate: this is attempted only after full field occlusion is successful.

a. the fovea of the deviated eye is behind the patch, allowing passive ARC therapy to occur

b. may be opaque (black electrical tape) or translucent (nail polish)

c. application of patching should follow the directions presented earlier in this lecture

3. Application of prism (the second "p"): designed not to neutralize the angle of deviation, but to keep the patient's binocular system in a tizzy. Thus, it is hoped that ARC no longer is a advantageous adaptation

a. overcorrecting prism: application of prism beyond the patient's objective angle will create a situation where there is sensory EXotropia; certainly a jolt to the esotrope's binocular system! Usually 5-25Æ over correction (depending on the amount of prism adaptation) is necessary

b. Ludlam suggests a randomized approach to prism applications in ARC cases. The prismatic amount is changed in amount and direction on a daily basis (ie one day BO; the next day BI; the next day BD etc.)

B. Active modes of anti-ARC therapy: These in office procedures are designed to augment the passive therapy conducted at home. Here, activities are geared to enhance NORMAL binocular patterns and introduce the patient to true sensory fusion (i.e. at the patients objective angle or objective point of centration. It is assumed here that:

-esotropia is constant

-ARC is embedded

-monocular skills have been improved

- amblyopes have greatly improved acuities with the non-dominant eye

1. Synoptophore therapy: as in most cases, the reduced environment of the synoptophore is an ideal place to begin active ARC therapy. One must be reminded however, that skills obtained in the reduced environment of the synoptophore are often difficult to apply to more natural viewing conditions.

a. begin with no slides (ie a contourless light pattern) and work your way to:

- large superimposition targets

- small superimposition targets

- large flat fusion targets

- small flat fusion targets

- stereo targets (if possible)

b. techniques to achieve normal, bifoveal fusion: for all of these procedures, it is best to have the non-dominant eye fixating the target (ie. dominant eye is eso.)

i. overcorrect the patient by 5 -15pd initially, then move the target back (ie in a less eso direction) to the objective angle

ii. monocular massage: keep the target presented to the eso eye moving between the pts. subjective angle + pd eso (never allow the pt. to view the targets at their subjective angle) to 20 -3pd overcorrecting position

- gradually reduce the range until the patient reports fusion at obj.

iii. versions at objective angle: lock the arms of the synoptophore at the patients objective angle and move both targets so the patient must abduct and adduct while maintaining normal sensory fusion

c. with all synoptophore testing, it may be necessary to use flashing techniques to achieve normal (bifoveal) sensory fusion

i. start with rapid flashing * slow flashing * constant illumination

ii. start with alternate flashing * synchronous flashing * constant illumination

d. the patient is successful at a particular phase of any of the above listed synoptophore therapy regimens when NRC is held for over a minute

2. Free-space techniques: these are, in general, more difficult than the synoptophore therapy. All free-space techniques start at the patients objective centration point.

a. red/green luster: indicative of NRC

i. start with contourless field at the pt's. centration point (while maintaining luster response)

ii. add large peripheral targets as skills improve (while maintaining luster response)

iii. add central targets as skills improve more (while maintaining luster response)

iv. repeat at a larger working distance (while maintaining luster response)

b. after-images: perfect cross indicative of NRC. Utilizes the same game plan as luster techniques. Must not use if eccentric fixation is suspected

c. it may be useful to combine luster and afterimages in one fun packed therapy technique

d. it may be necessary to introduce significantly high over-corrections of plus to achieve NRC at the centration point. Therefore, in each of the above techniques it may be necessary to:

i. significantly overplus patient during therapy (+15 D - +20 D)

ii. gradually reduce the plus as skills improve

e. photic stimulation: a Translid Binocular Interaction Trainer (TBI) is used to present a rapidly alternating light pulse to each eye

i. photic illumination faster than 15 flashes/second eliminate most suppressions and may also not allow ARC to take place

ii. may be used in conjunction with other free-space techniques when the pt. suppresses extensively or has a very stubborn ARC

f. the patient is successful at a particular phase of any of the above listed free- space therapy regimens when NRC is held for over a minute

C. After monocular therapy has progressed and anti-ARC therapy (if needed) has been successful, it is important to reevaluate the patient's visual skills and decide on a further course of action. Remember your four options discussed previously.

1. It may be appropriate to prescribe neutralizing prisms (BO) to allow for sensory orthophoria beyond the centration point. It CANNOT be used, however, if significant prism adaptation remains.

2. It may be necessary to conduct Rehabilitation of a Binocular Pattern therapy before prisms can be used effectively.

3. Surgery, as always is an option, but not a suitable one until prism adaptation is eliminated and decent sensory and motor fusion abilities are developed around the patient's objective angle.

VI. Rehabilitation of a Binocular Pattern. At this phase, anti-suppression, monocular fixation in a binocular field accommodative rock and biocular accommodative rock are included. It is initiated only after sensory fusion has been evaluated and ARC has been ruled out. 

A. Determine the sensory fusion abilities and work to expand them.

1. Establish a centration point: a point in free space where the exotrope is able to obtain bifoveal fixation of a small target. Sensory fusion at this point should be measured.

a. This is an objective measure

b. Work both convergence and divergence from this point

c. This can be done with a light at near point (ie a reduced environment) with the pt. wearing r/g glasses; look for luster responses for indication of sensory fusion without ARC

d. Eventually, you may work with more structured targets, like superimposition of the ring and spot stimuli for the Hess Lancaster screen at the pt's. centration point

2. Anti-suppression techniques are necessary with esotropes, because their suppression zones are usually quite deep (though not as deep as exotropias).

a. free space techniques include Doell's mazes, Worth 4 dot, Box X-0 (for a review of these techniques, see lab 6). These should be conducted at the patient's centration point or while the patient is wearing correcting prism

b. in instrument techniques include the BU series; cards 1-6 and the AN Star series; cards 1-5 (for a review of theses techniques, see lab 5). These should be conducted at the patient's centration point or while the patient is wearing correcting prism

3. Monocular fixation in a binocular field accommodative rock and biocular accommodative rock are important components to establishing some binocular cooperation (for a review of theses techniques, see lab 2). These should be conducted at the patient's centration point or while the patient is wearing correcting prism

VII. The Binocular Phase includes work on the various stages of sensory fusion and motoric fusion abilities. This phase is usually worked on throughout therapy, but is emphasized after success with the rehabilitation of a binocular pattern phase therapy.

A. As you build normal sensory fusion and motoric fusional ranges under the very reduced visual conditions at the rehabilitation of a binocular pattern phase, it may be useful to begin BINOCULAR PHASE activities in instrument techniques.

1. The synoptophore: remember that the synoptophore is set at optical infinity, and may be difficult for some pt's at first

  • a. start with moderate sized superimposition targets

    b. have the pt. fuse the targets at the objective angle or fuse targets at ortho, if the pt. has that ability (there should be no movement on alternate CT

  • c. slowly decrease the BI demand or increase the BO demand (ie. force the pt. to converge

    d. extend BI and BO ranges

    e. go to a smaller superimposition target

    f. try flat fusion and stereo target

    2. Stereoscopes (mirror and Brewster):

  • a. start with superimposition cards of the BU series (for Brewster stereoscopes) or the superimposition paired stereocards (for the mirror stereoscopes)
  • b. start at objective angle or have the pt. fuse the targets at ortho (if they have that ability)

    c. extend BI and BO ranges

    d. try flat fusion and stereo targets

    B. It is important to eventually work in some free space techniques to the regimen (the artificial visual environment that the instruments create do not establish a strong enough binocular pattern to survive "natural" viewing demands).

    1. Brock string: place near ball at the pt's centration point. Work convergence (smooth) and divergence from this point

    2. Vectograms: it is best to start with fixed vectograms and Tranaglyphs again at or near the pt's centration point

    a. the figure eight fixed vectogram and the Quoits variable vectogram (peripheral fusional target is a rope) is a good starting point

    b. eventually, work the vectogram back to a normal (ie. 40-50 cm.) working distance

    c. progress to other vectograms including variable vectograms

    C. Build sensory and motor fusion with all three types of fusion targets. Usually for the esotrope, progress will be made following the dictates of the British Orthoptic model:

    1. superimposition

    2. flat fusion

    3. stereopsis

    D. It may be appropriate to prescribe relieving prisms (BO) during the binocular phase of therapy to allow for sensory orthophoria beyond the centration point. It CANNOT be used, however, if significant prism adaptation remains.

    E. If prism is accepted, therapy may progress rapidly as the patient is able to have a true binocular experience full time.

    1. Prisms should be in the form of Fresnel Press on Prisms

    2. The prisms are gradually reduced as vergence skills around the "artificial orthophoria position" are improved.

    3. If prismatic prescription is less than 20pd, it can be ground into standard spectacle lenses.

    F. Surgery, as always, is an option, but not a suitable one until prism adaptation is eliminated and decent sensory and motor fusion abilities are developed around the patient's objective angle.

    1. may be necessary in those cases where the correcting prism amount is over 25pd.

    2. It should be emphasized that vision therapy should continue after surgery has been completed