To evaluate factors associated with the direction of horizontal deviation in the sensory strabismus of patients with unilateral organic amblyopia.
The medical charts of 53 patients who had been diagnosed with sensory strabismus between 2000 and 2009 were reviewed retrospectively. The underlying ocular disease, time of onset and the duration of vision impairment, refractive error and axial length of the fixing eye, and the direction and angle of deviation were analyzed to determine the distribution of underlying diseases and any factors relevant to determining the direction of the horizontal deviation.
Congenital cataracts were the most common underlying disease, found in 33 patients, followed by acquired cataracts, optic nerve disorders, retinal detachment, glaucoma and lens subluxation. Among the 50 patients with horizontal strabismus, 11 had esotropia and 39 had exotropia. The incidence of esotropia was significantly higher when the fixing eye had hyperopia or emmetropia, than when the eye was myopic. Age of onset of vision deterioration and at diagnosis of sensory strabismus, and the axial length of the fixing eye had no relationship to the direction of horizontal deviation. In addition, the duration of visual impairment had no significant relationship with the direction or extent of horizontal deviation.
The most common cause of sensory strabismus was congenital cataracts and the most frequent type of strabismus was exotropia. With respect to the direction of horizontal strabismus, esotropia occurred significantly more often when the refractive error of the fixing eye was hyperopia or emmetropia than when the fixing eye was myopic.
Sensory strabismus is diagnosed when unilateral or bilateral asymmetrical visual impairment, caused by anisometropic amblyopia or an organic disease, destroys fusion, and thus disrupts the eyeball array [
Factors relevant to the direction of deviation in sensory strabismus have been explored in many studies [
We conducted a retrospective review of the medical charts of patients with sensory strabismus caused by unilateral organic amblyopia in which the angle of deviation had been measured between March 2000 and November 2009. Sensory strabismus was classified as either esotropia or exotropia, and we investigated any underlying diseases, the time of onset and the duration of vision impairment, the refractive power and axial length of the fixing eye, as well as the angle of deviation. Patients with vision impairment caused by strabismic amblyopia or anisometropic amblyopia were excluded; thus, only those with sensory strabismus of organic origin were included in this study. When two or more underlying diseases were present, the condition most related to the vision impairment was selected for analysis.
With respect to the refractive error, emmetropia was considered present when the spherical equivalent after cycloplegic refraction using 1% atropine or 1% cyclopentolate hydrochloride was not more than ±0.5 diopter. Thirty-seven patients were diagnosed with myopia or hyperopia. The angle of deviation was measured using the alternate prism cover test, the Hirshberg test or the Krimsky prism test, depending on the level of vision and the extent of patient cooperation.
Statistical analysis was performed using SPSS ver. 12.0 (SPSS Inc., Chicago, Il, USA). Results were analyzed with the Mann-Whitney test, the chi-squared test or Pearson's correlation. The
A total of 53 patients, 25 females (47.2%) and 28 males (52.8%), were diagnosed with sensory strabismus, and the age at which vision impairment initially occurred ranged from birth to 44 years (mean, 6.1 years). Among the 50 patients with horizontal strabismus, 11 (22.0%) had esotropia and 39 (78.0%) had exotropia. Of the remaining three patients, one had dissociated vertical deviation (DVD) only and two had both DVD and dissociated horizontal deviation. Inferior oblique overaction (IOOA) was observed in 6 patients (11.3%), among whom one had unilateral IOOA and five had bilateral IOOA.
With respect to the disease underlying vision impairment, congenital cataracts were the most common, being found in 33 (62.3%) patients. Five (9.4%) patients had acquired cataracts, 4 (7.5%) an optic nerve disorder, 3 (5.7%) experienced retinal detachment, 2 (3.8%) had glaucoma and 2 (3.8%) other patients had lens subluxation (
The age at which vision deterioration occurred was 8.3 ± 14.3 years (range, 0 to 44 years) in the esotropia group and 6.0 ± 10.5 years (range, 0 to 43 years) in the exotropia group (
A refractive error in the fixing eye was observed in 48 patients. When the fixing eye had hyperopia or emmetropia, 9 patients had esotropia and 18 had exotropia. When the fixing eye was myopic, 1 patient had esotropia and 20 exotropia. The frequency of esotropia was significantly higher when the fixing eye had hyperopia or emmetropia than when myopia was present (
With respect to the relationship between the duration of vision impairment (≤5 years vs. >5 years) and horizontal strabismus, 8 of the patients with a shorter disease duration had esotropia and 34 exotropia (esotropia : exotropia ratio = 0.24). Of patients who had a longer duration of disease, 2 had esotropia and 6 exotropia (esotropia : exotropia ratio = 0.33). The ratios were not significantly different (
When the relationship between the duration of vision impairment and the degree of eyeball deviation was examined, esotropia and exotropia were 34.6 ± 20.7 prism diopters (PD) and 27.0 ± 13.9 PD, respectively, in patients with a disease duration of less than 5 years, and 50.0 ± 42.4 PD and 31.1 ± 16.8 PD, respectively, in those who had experienced disease for more than 5 years. Thus, no significant relationship was apparent between the duration of vision impairment and the degree of eyeball deviation in patients with either esotropia or exotropia (
When the extent of vision in the deviated eye was measurable, there was no statistically significant difference in the direction of deviation with respect to deviated eye vision between patients with a visual acuity of 20 / 200 or below and those with a visual acuity above 20 / 200 (
Sensory strabismus occurs when loss or deterioration of vision, arising in various ways, destroys fusion and thus, disrupts the eyeball array. Horizontal strabismus is the most common form of the condition and, in Korea, exotropia is reported to account for 75% to 85% of strabismus cases [
With respect to the cause of sensory strabismus, we found that cataracts were often to blame, being present in 71.7% of all patients, followed (in frequency) by optic nerve disorder, retinal detachment, glaucoma and lens subluxation. Sidikaro and von Noorden [
Sidikaro and von Noorden [
Many studies have explored the relationship between the refractive error of the normal eye and the direction of horizontal deviation in sensory strabismus. Von Noorden [
A possible association between the duration of vision impairment and the extent of eyeball deviation has been studied. Yoon et al. [
Jampolsky [
In conclusion, the most common cause of sensory strabismus in the present study was congenital cataracts and the most frequent type of strabismus was exotropia. With respect to the direction of horizontal strabismus, esotropia occurred significantly more often when the refractive error of the fixing eye was hyperopic or emmetropic, compared to when the fixing eye was myopic.
This paper was presented as a poster at the 103rd annual meeting of the Korean Ophthalmological Society, April 3, 2010, Busan, Korea.
No potential conflict of interest relevant to this article was reported.
Etiology of vision loss based on the type of deviation in patients with sensory strabismus
DVD = dissociated vertical deviation.
Relationship between the refractive error in the fixing eye and the direction of horizontal deviation
*Spherical equivalent of ≤±0.5.
Relationship between visual acuity of the deviated eye and the direction of the horizontal deviation
HM = hand motion; FC = finger counting; LP = light perception.