Have fun with strabismus!

What the congenital esotropia syndrome has to do with DVD's

In the literature you'll see the both the terms "congential esotropia syndrome" and "essential infantile esotropia syndrome" used for the same thing. I'll use "congenital esotropia symdrome" because I personally just happen to not like the alternative - 'Hey dude, what's your problem?' 'Well, it seems I have essential infantile esotropia syndrome.' - it just sounds too much like a pediatric problem, like measles and diaper rash.

Congenital esotropia syndrome is the most common strabismus variety known to man. It is estimated to affect between 0.1 and 1% of the population. Babies enter the world with their visual systems still very much under construction, and newborns don't have well developed eye movements yet, so it is common for a baby younger than 3 months, to have his/her eyes not aligned all the time. Perhaps this is where the myth comes from that children will 'outgrow' strabismus - but if a baby still has crossed eyes after three months you'd better take it to a doctor. Because by then, chances are pretty good you're having a squinter in the house. And the sooner it's treated, the better the changes for the little one to develop good binocular vision and stereoscopic depth perception.

The Mysterious Syndrome

The "syndrome" extension to "congenital esotropia" means it's a collection of symptoms that often occur together.

Signs that are always present are the following:

• It first occurs before a baby is 6 months old
  
• The deviation is stable and large (30 degrees or more) (hard to not notice it)
  
• Initially, there will be alternation with crossed fixation (baby will switch back and forth between using one eye and the other).
  
• The central nervous centre is normal (that's good to know!)
  
• Asymmetric optokinetic nystagmus (see the special effects page).
  

• Amblyopia (see the amblyopia page).
  
• Apparently defective abduction (ability to turn the eye inwards, towards the nose)
  
• Excessive adduction (ability to turn the eye outwards)
  
• Dynsfunction of oblique muscles
  
• A- or V- pattern (for example, an extreme A pattern would be when the eyes both turn inward when you look up and outward when you look down)
  
• Dissociated vertical or horizontal deviations (We'll get to those)
  
• Manifest-latent nystagmus (see the nystagmus page).
  
• Anomalous head posture (torticollis; tilting and/or turning the head)
  
• Heredity (often strabismus runs in the family)
  

Vertical deviations that can accompany congentical esotropia

"Primary inferior oblique overaction" is one condition mentioned in the books, and it is likely to cause a V-pattern (eyes turning in when you look down). Von Noorden mentions a 68% percent incidence of inferior oblique overaction in congenital esotropia cases. "Dissociated horizontal deviations" (meaning that if you cover one eye and view with the other, the covered eye will drift in- or outwards) are also a common finding.

The 68% statistic may be somewhat inaccurate as it is hard to get an infant to cooperate with eye motility analysis ("If you sit still and watch the little light for another half hour, you get an icecream.." "WHAAAHH!!"), so it may be overlooked in some cases.

However, the inferior oblique itself mostly doens't seem to be the source of the problem; as the 'overaction' often disappears after surgical correction of the esotropia by operating on the horizontal rectus muscles alone. And inferior oblique overaction can also come up years after successful alignment of the eyes. Nobody knows why.

Once upon a time there was a popular (well, its use was not very widespread) surgical method for the correction of esotropia, that routinely included displacing, recessing or cutting the inferior obliques alltogether, combined with standard horizontal surgery. Results indicated it was not worth the trouble.

There's another type of frequently occurring vertical deviation - the "dissociated vertical deviation" or DVD for short (don't put that in a search engine - it will present you with thousands of hits pertaining to Digital Video Discs or Digital Versatile Discs) - unless you're interested in those as well, of course. It is difficult to distinguish between "inferior oblique overaction" and DVD. About half of those with congenital esotropia syndrome, also have a DVD. Some sources report it's even more - up to 90%.

You can easily diagnose a DVD yourself using the "translucent occluder of Spielmann" and a mirror. For a translucent occluder, use any sort of plastic that will blur vision enough for you to see nothing much through it, but still allowing you to observe the position of the eye through it.

Those matte see-thru plastic folders used for storing papers work great. Occlude your one eye and if you have a DVD you'll see it drift upwards slowly, behind the cover. Repeat procedure for the other eye. (Never mind the artwork here.)

It is also interesting to see what the eyes do when they're both behind the occluder, but that's not for you to see, you'll need to ask someone else to have a look or take a picture of yourself. It goes without saying that this is by no means an accurate diagnosis unless verified by an ophthalmologist. Usually DVDs are not problematic as the eyes are straight when you use them together. There are however DVD's that present a cosmetic challenge because one eye stays up there forever even if you do use both eyes. Sometimes a DVD will progress up to a point where mechanisms as ARC (see amblyopia page) and suppression don't quite cut it anymore, resulting in diplopia and/or confusion.

Especially for parents of a kid whose squint appeared to have been successfully cured, they'd forgotten all about it, and then, years later, Junior presents with a DVD, it can be distressing. But it just happens sometimes, and most often matters can be put straight again.

As happens so often when you research these things, a lot of data has been gathered, but the interpretation can differ. Data by itself is just a load of numbers, and doesn't make sense unless it can be explained. Quite often research data is explained, but mentioning on the side that someone else explained it differently, or that it is simply "puzzling". The relationship between congenital esotropia, DVD, asymmetric OKN and latent nystagmus is intriguing, has fueled many a hypothesis, but there still is no proof there is one underlying responsible mechanism for these things to occur together in such a statistically significant way. The numbers suggest these things could be related, but again, nobody really knows why. Mysterious!