Fig. 19.1
Life-table estimates of the cumulative percent of patients developing strabismus over time [15]
19.2 Cataract Morphology
There are conflicting reports on the association between the etiology and morphology of pediatric cataracts and strabismus. Such a relationship may be masked by the myriad of associated ocular, syndromic, and neurologic anomalies that are also risk factors for strabismus the same child. Hiles [9] did not detect an increased risk of strabismus with severity or type of cataract or with other ocular and systemic findings. No difference in strabismus prevalence was found when Weisberg and colleagues [16] looked at different cataract types. However, Gregg and Parks [17] reported a strong correlation between cataract morphology and the rate of strabismus. Strabismus was found in 21 % of lamellar cataracts, 48 % of posterior lentiglobus, 65 % of nuclear cataracts, and 100 % of patients with persistent fetal vasculature. Hosal et al. [6] showed better binocular functioning in patients with traumatic cataract and posterior lenticonus and lower levels in congenital and complicated cataracts. France and Frank [13] reported children with acquired cataracts had less strabismus that those with congenital cataract (61 verses 86 %). The lower rate of strabismus with acquired and traumatic pediatric cataracts is likely linked to the development of normal binocular fusion prior to ocular trauma and a more rapid surgical treatment.
19.3 Types of Strabismus
Although reports vary, esotropia is the most common type of strabismus in children with cataracts. Studies have reported esotropia in 50–76 % of children with cataracts (Lambert [1] 50 %, Spanou et al. [3] 76.5 %, Parks and Hiles [11] 66 %, Cheng et al. [5] 59 %). In both the historic studies by Hiles and Cheng and the recent IATS, the percentage of patients with esotropia outnumbered those with exotropia by a ratio of 2:1. In IATS, esotropia (2–70 prism diopters) was present in 50 % and exotropia (3–50 prism diopters) was present in 27 % of children at age 5. Horizontal deviations were typically constant and present at distance and near. Exotropia may be more common with acquired cataracts or in strabismus with delayed onset after prior treatment of cataract (Hiles). Small, vertical deviations, inferior oblique overaction and pattern deviations have been reported but appear uncommon.
19.3.1 Time Course of the Development of Strabismus
The longitudinal development of strabismus has been documented even after timely and successful cataract surgical intervention. In the studies by Hiles [9], France [13], Wilson [14] and Bothun [15], strabismus developed after the cataract surgery at least half of all cases. Wilson’s literature review showed that the presence of strabismus grew from 33 % of patients preoperatively to 78 % with postoperative follow up. In the prospective study of monocular cataracts in the IATS, strabismus prevalence in this study rose from 24 % preoperatively to 70 % at 12 months postoperative to 81 % through age 5 [18]. Although many factors may contribute to the detection and development of strabismus, this report shows that ocular alignment is not stable even 1 year after cataract surgery.
19.3.2 Spontaneous Resolution Rate of Strabismus
Despite excellent vision outcomes, it is unusual to have strabismus resolve simply by removing the cataract and rehabilitating the vision. Awner et al. [10] reported that two of 21 children in his retrospective series regained orthophoria through cataract surgery only. Five of the 27 with strabismus at baseline in the Infant Aphakia Treatment Study regained and maintained orthotropia to 12 months postoperatively [15]. Similarly 19 of 82 patients in the Hiles [9] series became orthophoric once the cataract was removed. Lastly, the development or course of strabismus in the IATS did not correlate to the occurrence of adverse events or need for additional intraocular surgeries in children after initial removal of infantile cataract.
19.3.3 Relationship Between Binocularity and Strabismus
Suppression from a cataract early in infancy may disrupt both vision and binocular development. Thus timely cataract surgery before the critical window in developing sensory fusion closes may minimize strabismus. In the study of France, surgery in the first 2 weeks of life for congenital cataract was associated with lower rates of strabismus. In the Infant Aphakia Treatment Study, orthotropia was found in 27 % of children who underwent early cataract surgery (between 28 and 48 days of life) compared to 13 % who had surgery at an older age (p = 0.085) [18].
Unfortunately maintaining orthophoria after infantile cataract surgery does not guarantee meaningful stereopsis. Despite rare reports of high grade stereopsis after infantile cataract surgery, most children do not demonstrated stereopsis after rehabilitation for unilateral congenital cataract surgery. In addition to the sensory interruption by the cataract or refractive error, full time patching regimens for amblyopia have been implicated as a potential compounding factor poor stereopsis. The hope for better stereopsis was ignited in the 1990s when retrospective studies of part time patching protocols showed improved motor and sensory fusion [4, 7, 19, 20]. With guarded patching in the first 6 months of life, Wright and colleagues [4] obtained sensory fusion in 3 of 13 patients, one with Randot Stereo Acuity of 250 s of arc. After comparable patching regimen in the IATS, gross stereopsis was measured on one or more of three tests in 25.5 % of children at age 4.5 years [21]. Detectable stereopsis is close to three times more likely (18 verses 46 %) in children with orthotropia vs. those with strabismus (P = 0.005). In Hartmann’s report, the highest levels of measured stereopsis were detected by Frisby Stereotest (2 with 170 s of arc).
19.3.4 Relationship Between the Type of Optical Correction and Strabismus
Some reports have suggested that primary intraocular lens (IOL) placement might lower the frequency of strabismus and improve stereopsis. Lambert and colleagues [1] described rates of strabismus of 75 % using IOLs and 92 % using contact lenses in a small series of infants after unilateral cataract surgery. Autrata et al. [2] reported a similar finding with 55 % developing strabismus after IOL vs 83 % using CL. Greenwald and Glaser [22] reported better stereopsis in patients implanted with an IOL. Yet a consistent limitation to these retrospective, small series was that the decision to place an IOL was not randomized. Eyes with higher risk characteristics, such as younger age and associated structural defects, have been less likely to receive IOL at the time. The recently completed IATS study showed randomized infants undergoing monocular cataract surgery to aphakia treatment with contact lens vs IOL [23–25]. After 5 years of age, the development of strabismus was similar whether the child received contact lens or primary IOL implantation for the correction of unilateral aphakia (86 % verses 77 %, p = 0.33) [18].
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