Prevalence of strabismus ranges from 3-5%,12 esodeviations being more common than exodeviations (prevalence ratio 5:2).34 However, geographical and ethnic variations in this pattern are known.456 Amongst esodeviations, accommodative esotropia is the commonest type followed by congenital or infantile esotropia.7 The prevalence of spontaneous late-onset comitant acute nonaccommodative esotropia (ANAET) (after one year) remains unknown but is certainly considered rare.8 Previous investigators89101112131415 have classified ANAET into five subtypes-Type 1 / Swan type: Esotropia due to the disruption of the fusion (precipitated by monocular occlusion), Type 2 / Burian-Francesschetti type characterized by minimal hypermetropia and diplopia that is often associated with physical or psychological stress, Type 3 / Bielchowsky type: occurs in adults with myopia, Type 4 / Refractive-accommodative type characterized by high hypermetropia that can be adequately controled with the refractive correction alone, Type 5: Associated with intracranial pathology, most commonly a posterior fossa lesion.
We herein report the clinical characteristics of 15 children with ANAET presented within a period of 17 months with the history of sudden onset of deviation after age of one year not associated with occlusion, intracranial pathology or accommodative component. To our knowledge this is the first report on ANAET in children from India and we believe this variety of strabismus occurs more frequently than reported in the medical literature.
Materials and Methods
This retrospective cohort study included 15 consecutive patients presenting in the department of Pediatric Ophthalmology and Strabismus of a tertiary eye centre in Western India between April 2003 and August 2004. The medical records of the patients diagnosed to have ANAET who fulfilled the following criteria were included in the study.
- Age under 16 years,
- Sudden onset of strabismus (within a few hours to days and photographic evidence of absence of strabismus before the history of onset of esotropia),
- Convergent and comitant strabismus,
- Age of onset after one year,
- No accommodative component.
Following data were abstracted from the medical records:
- Age of the patient,
- Age at the onset of deviation,
- Duration of deviation,
- Prior debilitating illness,
- Association with vaccination or teething,
- Angle of deviation for near and distance fixation,
- Pattern of deviation,
- Cycloplegic refraction and
- Surgical outcome.
A strabismologist examined all the patients. A detailed systemic history and clinical examination was done to rule out neurological lesion.
The data were entered in a Microsoft excel data sheet. Standard deviation and 95% confidence intervals were calculated.
Of 15 patients [Table 1] eight were females. Mean age was 7.15 years (range 2.5-13, SD 3.34). Mean age of the onset of deviation was 3.2 years (range 1.5-9, SD 2.26). Mean duration of strabismus was 36 months (range 3-132, SD 43). History of precipitating event was present in five cases (33.3%). Each of these had febrile illness. One had associated teething and another one had associated febrile seizure with normal CT scan of the brain. Mean cycloplegic refraction was 1.84 diopter sphere (DS) (range -5.75 to +7.25, SD 3.55). Anisometropia of 1.25 DS was present in one. Mean esodeviation for near and distance fixation was 40 prism diopter (PD) (range 15-90, SD 23.9). The majority (80%, 12 patients) had a deviation measuring over 30 PD. None had near/distance disparity of more than 5 PD. Vertical incomitance was present in four cases that was equal to 4 PD. Significant pattern with inferior oblique over action (30 PD of V pattern in patient number 12) was present in one. Amblyopia was present in 13 cases (87%); unilateral (strabismic amblyopia) in eight, with the left eye being more involved (six patients), mixed (anisometropic with strabismic) amblyopia in one and strabismic amblyopia with ametropic amblyopia in four. The density of the amblyopia was mild (vision in amblyopic eye better than 20/60) in all cases. Strabismus surgery was advised for all the patients, eight patients underwent the surgery. One patient with large 30 PD V pattern also underwent simultaneous bilateral 10 mm recession of the inferior oblique muscles (Patient Number 12). Postoperatively five patients had orthophoria and two were aligned within less than 8 PD of esotropia and one had intermittent esotropia less than 8 PD at the last follow-up (mean 8.7 months, range 4-108 weeks). Four patients who underwent strabismus surgery have completed more than 10 months follow-up without developing any neurological lesion. Patient number 12 had presence of binocular single vision for near and distance on Worth 4 dot test, patient Number 3 had fusion response for the near only and patient Number 1 had constant suppression in the squinting eye. Sister of patient Number 1 developed esotropia at four months of age. The parents of both these children were orthophoric and the perinatal history was not significant. She underwent bilateral medial rectus recession after three months of occlusion therapy at the age of 14 months achieving orthophoria.
The ANAET is considered less common than accommodative and congenital esotropia.78 However, we examined 15 patients within a span of 17 months and we have continued to see more number of patients raising the possibility of a higher incidence of this strabismus in this part of the world.
None of the patients in our series had history of monocular occlusion preceding the onset of strabismus. They neither had any intracranial abnormality on presentation nor developed any later. None were myopic adults to be labeled as Bielchowsky's type of ANAET. Our inclusion criteria effectively excluded accommodative esotropia. Hence our patients seem to fall in the subgroup that resembles Type 2 (Burian-Francesschetti type) ANAET. In Burian's paper10 the age group was 11-72 years, patients had low hypermetropic errors, they complained of diplopia, angle of deviation ranged between 20 to 60 PD and had excellent functional outcome after the strabismus surgery. Our study had patients in a younger age group and none of the parents could recall their child complaining of diplopia. This could be a recall bias in some, rapidity of suppression in very young children or inability on the part of very young children to complain diplopia. This could also happen if these patients had decompensation of a preexisting microtropia.16 Only the absence of bifoveal fusion before the onset of esoptropia could have confirmed this notion. A photographic evidence of absence of strabismus could be deceptive in those cases. However, in a previous report by Spierer17 where ten adults with ANAET were surgically aligned, none had decompensated microtropia as all gained normal stereopsis. The duration between the onset of strabismus and realignment may be important.
The incidence of unilateral amblyopia was found to be high in this study. Once amblyopia is established in the patients with ANAET there is always a suppression scotoma. However, this is expected to have taken some time after the onset of esotropia, unless the patients with the ANAET had a preexisting monofixation syndrome. Hence if the clinician diagnoses ANAET a prompt surgical realignment of the eyes could prevent the emergence of suppression and there by amblyopia. The loss of fusion is also instrumental in the development of A or V patterns, hence a timely intervention has the potential to avert the emergence of vertical incomitance in the patients with ANAET.18
The possibility of an underlying lesion or malformation of the central nervous system should be kept in mind in these patients1920 and careful examination to rule out divergence paralysis or bilateral 6th nerve paresis by careful motility examination, fundus examination for papilledema and optic atrophy is essential. Some clinicians may recommend routine neuroimaging in these patients but an exceedingly lower incidence of patients with underlying intracranial pathology makes a case against routine neuroimaging. We order neuroimaging only when there is an associated neurological deficit or a history of convulsion. Absence of neurological signs and presence of good fusion response with prism correction seem to be good predictors of absence of intracranial pathology.1321 Nevertheless, there are now two well-documented cases of brain tumors in which good motor and sensory fusion could be shown before and after intracranial surgery. Hence presence of fusion does not rule out an intracranial pathology and the importance of a careful long-term observation should be emphasized to the parents.212223
There is no definition in the literature on how late the onset for late-onset esotropia should be. We defined onset later than one year as ‘late’ as most of the infantile esotropes present within first six months and certainly within one year.
In our study the refractive error ranged from high myopia to high hypermetropia, there was no patient with significant anisometropia (> 1.5 diopter). Ametropia or anisometropia probably does not play any significant role in the pathogenesis of ANAET. Ahmed and Young24 have reported ANAET in two pairs of monozygous twins and in our study one patient had the younger sister affected with congenital esotropia suggesting the hereditary basis.
The mechanism proposed by von Noorden for the pathogenesis of the Burian-Francesschetti syndrome is the loss of borderline fusion (poor fusional divergence) and the precipitation of the nonaccommodative comitant esodeviation.13 Strabismic amblyopia associated with late-onset esotropia is perhaps the most common form of amblyopia.25
In our experience all the patients require surgical intervention. An early surgery could prevent the onset of amblyopia and prevent a permanent reduction in binocular vision and stereoacuity. The angle of the deviation generally remains stable. However, prism adaptation has been suggested preoperatively to bring out the full deviation and to estimate the fusional potential.25 Use of Botulinum toxin injection in this group of patients is reported.27 However, limitations to its use are the need of more than one injection, lack of predictability and unknown dose-response relationship.
In summary ANAET is more common than reported in the previous literature, has a variable time of onset and is associated with a high incidence of amblyopia. Timely management would avert the emergence of amblyopia and a vertical incomitance thereby promising better binocular outcome.
Dr. Kulin Kothari
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