Pseudostrabismus

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http://www.pediatriceyemd.com/service/child/pseudostrabismus

 

Introduction

Pseudostrabismus or pseudoesotropia remains a common reason for referral from pediatricians and other primary care providers to ophthalmologists. Concern originates from the possibility of failing to recognize true esotropia, which may be difficult to distinguish from pseudoesotropia, and that may be in need of prompt treatment.

Below are some thoughts relating to the nature and significance of several specific possibly confounding conditions, and to ways in which the primary care doctor can more readily and reliably differentiate them from pseudoesotropia, with implications regarding the urgency of referral.

 

Constant Strabismus

Occasionally a child with pseudoesotropia is thought to have constant strabismus—that is, the eyes appear to the family (or, less commonly, the pediatrician) to be crossed at all times.

Constant eye misalignment in infancy, regardless of origin or associations, poses a significant threat to visual development, and should generally be treated (usually with surgery) within a few months of onset, or at latest before age 1 year.

For the ophthalmologist (and often for the pediatrician), differentiating the two conditions in this instance is relatively easy and straightforward, with diagnosis of pseudoesotropia reliably accomplished simply by establishing that the examination is normal, and pointing out to the family the cause (epicanthal skin folds) of their confusion. If the family indicates agreement once this is explained (the aha! moment), their concerns will be ended.

 

Intermittent Strabismus 

More often, though, the issue is intermittent appearance of eye crossing. Here the situation is more complex. Cases with real strabismus creating such concern can be divided between those in which esotropia is truly intermittent—that is, the eyes are in fact straight some (usually most) of the time, and presumably supporting normal binocular vision during those periods of alignment—and those with constant but variable eye deviation, who give a false impression of having straight eyes at times when the angle of misalignment is small.

Both of these situations are commonly encountered in pediatric practice. Patients in the latter group are at risk for the same consequences as those with consistently larger angle deviation; in addition, patients with strabismus secondary to ocular pathology (including cataract and retinoblastoma) tend to fall into this category, so the importance of timely diagnosis and management is heightened.

Truly intermittent strabismus, on the other hand, does not represent an immediate threat to vision, rarely if ever causing amblyopia or damage to binocular vision potential.

Intermittent esotropia does, however, often evolve (typically over a period of weeks to months) into slight-threatening constant strabismus, and this category also includes most infants with accommodative esotropia, who can and should be promptly treated with glasses to correct hyperopic refraction.

 

Difficulties in Diagnosis

A real issue with these often straight-looking infants is the possibility that the physician (ophthalmologist or pediatrician) will be inappropriately reassured by the lack of objective abnormal findings, if strabismus happens not to be evident at the time of examination.

For the eye specialist it is at least straightforward to identify or rule out significant associated abnormalities (media opacity, fundus abnormality, refractory errors), though their significance can be difficult to determine in milder cases.

For the primary care doctor, lack of objective findings may create a quandary regarding whether and how quickly to refer.

 

Differentiation Normal from Abnormal

The key to differentiating pseudoesotropia from true esotropia that is intermittent and infrequently manifest  (or variable and undetectable much of the time) lies in careful history taking, which can and should be done effectively by both primary care and eye specialists when such concern is present.

 

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http://www.pediatriceyemd.com/service/child/pseudostrabismus

The Hirschberg test done by holding a point light source about 30 cm in front of the eyes alows the examiner to judge the eye alignment according to the position of the light reflex on the corneas.  This test helps differentiate a pseudostrabismus (above) from a real strabismus (below).

 

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http://www.aapos.org/terms/conditions/48

 

There are 4 important questions to ask the family:

  1. Is the appearance of eye crossing more evident when the infant is tired?
  • If YES (and if the history is reliable—some working parents who only see their kids near bedtime may give misleading information), suspicion of true intermittent esotropia, almost always worse in association with fatigue, should increase.
  1. Do you ever see one eye actually move toward the nose (“pull in”) while the other eye remains stationary, even if alignment is recovered after just a few seconds?
  • Such convergence movement is typically seen with true intermittent esotropia, never with pseudoesotropia. If the parent quickly gives a YES answer in response to this query, you’re dealing with real strabismus.
                             
  • With pseudoesotropia, the impression of eye crossing is either present or absent; transition is never observed.
                             
  • Of note, this movement of the eye to the nose may be normal in infants up to four months of age before the development of binocular vision.
  1. Are you seeing more appearance of eye crossing (greater frequency or magnitude or both) as time goes by?
  • Pseudoesotropia never gets worse. Appearance gradually normalizes with growth and maturation of the face over a period of months to years, and as parents adapt to the everyday appearance of their infant they tend to notice it less over time.
                                     
  • If you get a YES answer to this question (even after previous negative evaluation by an ophthalmologist), further investigation is required.
  1. Do you notice the appearance frequently/especially in photographs?
  • This is key. Pseudoesotropia appearance is exaggerated in photos taken with the eyes directed slightly to one side, a very common occurrence.
                   
    • This results in the eye that is abducting (turned away from the nose) appearing to be centered (because equal amounts of white are seen on each side of the iris/cornea), while the other eye, which is adducting (turned toward the nose) by the exact same amount appears to be way close to the inner corner (because the nasal white is mostly covered by the epicanthal fold).
                                
    • Look at the ears in the photo—you’ll often see more of one than the other indicating that the face is turned—causing the eyes to look askance toward the camera.

 

A Word About Photographs...

With pseudoesotropia parents not infrequently volunteer that their concern about cross-eyed appearance comes largely from repeated observation in photos.

A typical image on a parental phone can be used to provide that aha! moment. On the other hand, true intermittent esotropia that is infrequently present is MUCH less likely to show up in multiple photos. For some reason, relatively few parents report noticing this lateral gaze effect in live situations.

 

Making the Diagnosis

What to do with this information? If you see an infant for concern about esotropia with normal findings on examination and epicanthal folds, I will make the diagnosis of pseudoesotropia if and only if answers to questions 1-3 are NO, and with greater confidence if the answer to question 4 is YES.

In such cases I do not plan a follow-up visit, but my parting words to the family are “You MUST bring the child back if you think you see more crossing with the passage of time” (question 3 again).

 

If I get a YES answer to one or more of questions 1-3 (especially 2), I make the tentative diagnosis of intermittent esotropia, and schedule a visit to ophthalmologist.

 

For the pediatrician, evaluation in all such cases should include simultaneous inspection of the fundus red reflexes from both eyes with a direct ophthalmoscope in standard fashion. If any asymmetry or other definite reflex abnormality is detected, the patient should be referred for prompt ophthalmologic evaluation.  

 

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Inspection for a red reflex (Bruckner test) in this child reveals asymmetry with leukocoria (white pupil) of the right eye secondary to retinoblastoma.  http://retinatoday.com/2015/08/personalized-medicine-in-ocular-oncology

 

If the red reflexes are normal and answers to questions 1-3 are NO, and especially if the answer to question 4 is YES, observation without referral may be appropriate.

If the answer to one or more of questions 1-3 is YES, referral should always be made.  

 

And when it comes to pseudostrabismus versus real strabismus...

When in doubt, REFER.