Decreased Accommodative Response in the Nondominant Eye of Patients With Intermittent Exotropia




Purpose


To evaluate objectively the accommodative response in patients who have intermittent exotropia with a dominant eye.


Design


Observational cohort study.


Methods


setting: Institutional. patients: One hundred thirty-three patients younger than 15 years, including 33 patients with intermittent exotropia and equal dominance, 54 patients with intermittent exotropia with a dominant eye, and 46 patients with orthotropia or exophoria of less than 10 prism diopters. observation: A Shin-Nippon NVision-K 5001 autorefractor was used to measure the accommodative response under binocular and monocular viewing conditions at 33 cm. Patients wore spectacles to achieve distant refractive errors within 0.50 diopter in both eyes. main outcome measures: Accommodative responses of each eye in binocular and monocular viewing conditions were compared between fellow eyes and groups.


Results


During binocular viewing, 65% of nondominant eyes showed an accommodative lag of more than 0.5 diopter, whereas 40% of dominant eyes showed an accommodative lead. In contrast, 77% of the eyes in the equal dominance group and 59% of the normal group showed an accommodative lag of less than 0.5 diopter. During binocular viewing, patients with dominant eye intermittent exotropia showed significantly more asymmetry in the accommodative response between both eyes than patients with equal dominance intermittent exotropia and normal controls ( P = .001). During monocular viewing, there was no significant difference in asymmetry between the 3 groups ( P = .059).


Conclusions


Patients with intermittent exotropia with a dominant eye tend to have asymmetric accommodative responses between both eyes during binocular viewing, where the nondominant eye showed a decreased accommodative response.


Accommodative response occurs when the eye changes fixation from one point in space to another at different distances from the retina. This response can be estimated clinically by measuring the accommodative lag or lead. Accommodative lag is defined as the dioptric value with which the accommodative stimulus exceeds the accommodative response, whereas accommodative lead occurs when the response exceeds the stimulus.


The accommodative response in patients with exotropia has been defined poorly. In a previous study of exotropia, asymmetric accommodative responses between both eyes under binocular conditions were documented using dynamic retinoscopy. However, dynamic retinoscopy is a subjective method that relies on the examiner’s ability. There is no objective data on whether the accommodative response differs between exotropes with a dominant eye and those with equal dominance or normal controls. In addition, because intermittent exotropia manifests promptly after monocular occlusion, the accommodative response may differ under binocular and monocular viewing conditions, although this feature has not been demonstrated clearly.


Therefore, we performed this study to evaluate objectively the state and symmetry of accommodative responses in both the eyes of exotropes with a dominant eye and to compare the results with that of those with equal dominance and of normal controls. In this study, we measured the accommodative responses by using a Shin-Nippon NVision-K 5001 (Grand Seiko WR-5100K, Fukuyama, Japan) autorefractor, which is well suited for clinical and objective measurement of accommodation. We directly measured the accommodative response of each eye to an accommodative near target, both during binocular fusional status and under monocular viewing conditions. We compared the results between fellow eyes under monocular and binocular viewing conditions. We also compared the asymmetry in accommodative responses between groups.


Methods


Patients


The subjects of our observational study were consecutive patients younger than 15 years who visited our clinic between September 2009 and January 2010. Patients with basic intermittent exotropia according to the Burian classification and normal controls with orthotropia or exophoria of less than 10 prism diopters (Δ) were included. Strabismus was evaluated by the same pediatric ophthalmologist (J.-M.H.). We noted patient characteristics, including age, gender, best-corrected visual acuity (BCVA), refractive error, deviation at distance and near, type of exotropia according to the Burian classification, constancy of deviation (intermittent or constant), fixation dominance, and stereoacuity.


The patients were divided into 3 groups: (1) basic intermittent exotropia with equal dominance, (2) basic intermittent exotropia with a dominant eye, and (3) orthotropia or exophoria of less than 10 Δ. Patients were characterized as having basic intermittent exotropia if they met the following criteria : (1) normal accommodative convergence or accommodation ratio determined by the gradient method, (2) difference between distance and near exotropia of 10 Δ or less measured before monocular occlusion, and (3) lack of tenacious proximal fusion or strong proximal convergence after monocular occlusion for 1 hour. Patients were characterized as having intermittent exotropia if deviation was manifest intermittently at either distance or near; consequently, patients with constant exotropia at distance but intermittent exotropia at near were included. Eye dominance was determined on the basis of the results of a repeated cover–uncover test alternatively on each eye more than 3 times, which invariably revealed a fixation shift to a dominant fixating eye after uncovering the occluder during the tropic phase of exotropia. Patients were excluded if they had amblyopia, anisometropia, refractive errors exceeding −6.00 diopters (D; myopia) or +3.00 D (hyperopia), astigmatism of more than 1.50 D, constant exotropia at near, A- or V-pattern strabismus, dissociated vertical deviation, vertical deviation of more than 5 Δ, a history of strabismus surgery, paralytic or restrictive exotropia, ocular disease other than strabismus, chromosomal anomalies, or systemic disorders such as congenital anomalies or neurologic disorders. Patients with BCVA worse than 20/20 in either eye also were excluded. Anisometropia was defined as a spherical or cylindrical difference of more than 1.50 D between the eyes. Amblyopia was defined as a difference of 2 lines or more between monocular BCVA. An A pattern was defined as an increase of 10 Δ or more in exodeviation at downgaze compared with upgaze, and V pattern was defined as an increase of 15 Δ or more of exodeviation at upgaze compared with downgaze.


Ophthalmologic Examination


All patients underwent a complete ophthalmologic examination. Prism and alternate cover testing were performed using accommodative targets for fixation at 1/3 and 6 m. An additional near measurement was obtained after 1 hour of monocular occlusion of the habitually deviating eye, and another postocclusion near measurement was obtained using an additional +3.00-D sphere over each eye before allowing the patient to regain binocular fusion. Constant deviation was defined as divergence for 100% of waking hours; the constancy of deviation was assessed by the same ophthalmologist (J.-M.H.). Patients with hyperopia were given spectacles with lenses of approximately +1.00 to +1.50 D less than the full cycloplegic hyperopic refraction. Refractive errors were determined using cycloplegic refraction with 1% cyclopentolate hydrochloride and were reported as spherical equivalent values. Sensory status was evaluated using the Randot stereoacuity test (Stereo Optical Co, Inc, Chicago, Illinois, USA). A stereoacuity of 100 arc seconds or better, measured with the Randot stereoacuity test, was defined as good.


Correction of Distant Refractive Errors


The patients wore full or partial correction spectacles to achieve BCVA that was 20/20 or better in both eyes. A distant autorefractor measurement after correction was obtained with the Shin-Nippon NVision-K 5001 autorefractor. The patients were positioned such that the tested eye viewed a distant target directly aligned along the visual axis of the eye. The patients were asked to observe a distant spotlight monocularly. Five consecutive autorefractor readings were obtained for each eye, and the final autorefractor prescription was the average of these readings (power in increments of 0.12 D). The patients proceeded to the next examination if their corrected spherical and cylindrical refractive errors were within 0.50 D (−0.50 to +0.50 D). If either spherical of cylindrical refractive errors were more than 0.50 D, spectacles were prescribed according to their cycloplegic refractive errors. These patients came back 1 month later to continue with the examination wearing their newly prescribed spectacles, of which the corrected distant refractive errors were within 0.50 D.


Measurement of the Accommodative Response


Accommodative response was measured while the patient was wearing distance correction spectacles. The patient was asked to fix his or her gaze on a detailed near target (a high-contrast Maltese cross) located 33 cm away; this induced a 3.00-D demand of accommodation. The patients were instructed to look at the center of the cross and to keep the image clear. The accommodative response of each eye was measured using a Shin-Nippon NVision-K 5001 autorefractor during binocular and monocular accommodation. Binocular viewing was assessed first to maintain fusion during measurements, and the left and right eyes were examined in random order. The spherical equivalent of the accommodative response was subtracted from the 3.00-D demand, yielding an accommodative lag if positive or an accommodative lead if negative.


Main Outcome Measures


Primary outcome measures included the accommodative lag or lead of each eye in the binocular fusional state and during monocular occlusion. Accommodative responses were compared between fellow eyes within groups. Secondary outcome measures were evaluated on the basis of the asymmetry of the accommodative response between both eyes, which was defined as the difference in the amount of accommodative response between fellow eyes; the accommodative responses of the right eye or the dominant eye were subtracted from those of the left eye or the nondominant eye.


Statistical Analysis


Statistical analyses were performed using SPSS software for Windows version 15.0 (SPSS, Inc, Chicago, Illinois, USA). The paired-samples t test was used to compare characteristics between fellow eyes within the groups. The Pearson chi-square test, Fisher exact test, and one-way analysis of variance were used to compare the accommodative response and asymmetry of fellow eyes between groups. P values of < .05 were considered statistically significant.




Results


Of the 150 consecutive patients who visited our clinic between September 2009 and January 2010 and satisfied the inclusion criteria, 17 were excluded because of poor cooperation or because they were lost to follow-up after correction. Finally, 133 patients (266 eyes; mean age ± standard deviation, 7.1 ± 5.4 years) were included; among them, 33 had basic intermittent exotropia with equal dominance, 54 had basic intermittent exotropia with a dominant eye, and 46 were normal controls with orthotropia or exophoria of less than 10 prism diopters. There was no significant difference with regard to patient characteristics ( Table 1 ) between the 3 groups. Near and distant exodeviation were not significantly different between the groups of patients with exotropia with and without a dominant eye ( P = .081 and P = .311, independent t test). Good stereoacuity of 100 arc seconds or better was present in 79.7% patients, and there was no significant difference between the 3 groups ( P = .178, Pearson chi-square test).



TABLE 1

Characteristics of the Patients in the 3 Groups: Intermittent Exotropia with or without a Dominant Eye and Normal Controls




































































Group
Intermittent Exotropia with Equal Dominance (n = 33) Intermittent Exotropia with a Dominant Eye (n = 54) Normal (n = 46) P Value
Mean age ± SD (range), (yrs) 9.3 ± 2.9 (5 to 15) 8.7 ± 3.0 (4 to 15) 9.1 ± 2.6 (5 to 15) .630 a
Male gender, no. (%) 19 (57.6) 22 (40.7) 16 (71.7) .120 b
Mean exodeviation at distance ± SD (range), (Δ) 19.0 ± 6.9 (8 to 45) 22.1 ± 9.6 (6 to 45) .081 c
Mean exodeviation at near ± SD (range), (Δ) 20.1 ± 9.3 (8 to 45) 22.4 ± 11.4 (6 to 45) .311 c
Stereopsis, no. (%)
Good (≤ 100 arc seconds) 27 (81.8) 39 (72.2) 40 (87.0) .178 b
Dominance of fixation, no. (%)
Right 22 (40.7)
Left 32 (59.3)

Δ = prism diopters; SD = standard deviation; yrs = years.

a One-way analysis of variance.


b Pearson chi-square test.


c Independent t test.



Accommodative responses to a 3.00-D demand target are shown in Table 2 . During binocular viewing, 77% of eyes in the group comprising patients who had intermittent exotropia with equal dominance and 59% of eyes in the normal group had an accommodative lag of .50 D or less. In the intermittent exotropia with a dominant eye group, however, 65% of nondominant eyes showed an accommodative lag of more than .50 D and 5.6% showed an accommodative lag of more than 1.00 D. An accommodative lag of more than 1.00 D was found only in the group with nondominant eyes. In contrast, 40% of dominant eyes showed an accommodative lead, whereas only 6% of eyes in the intermittent exotropia with equal dominance group and 14% of eyes in the normal group showed an accommodative lead. During monocular viewing, 7.6% of eyes in the intermittent exotropia with equal dominance group and 1.9% of eyes in the dominant eye group showed an accommodative lag of more than 1.00 D.



TABLE 2

Accommodative Response of Both Eyes to a 3.00-Diopter Demand Target in Patients of the 3 Groups: Intermittent Exotropia with or without a Dominant Eye and Normal Controls





















































































Intermittent Exotropia with a Dominant Eye
Accommodative Response Intermittent Exotropia with Equal Dominance (n = 66) Dominant Eye (n = 54) Nondominant Eye (n = 54) Normal (n = 92)
Binocular viewing, no. (%)
Lag ≤ 0.50 D 51 (77.3) 28 (51.9) 18 (33.3) 54 (58.7)
0.50 D < lag ≤ 1.00 D 11 (16.7) 4 (7.4) 32 (59.3) 25 (27.2)
Lag > 1.00 D 0 (0) 0 (0) 3 (5.6) 0 (0)
Lead > 0.00 D 4 (6.1) 22 (40.7) 1 (1.8) 13 (14.1)
P value .861 a <.001 b (.245 a ) .769 a
Monocular viewing, no. (%)
Lag ≤ 0.50 D 40 (60.6) 36 (66.7) 30 (55.6) 52 (56.5)
0.50 D < lag ≤ 1.00 D 6 (9.1) 12 (22.2) 20 (37.0) 20 (21.7)
Lag > 1.00 D 5 (7.6) 0 (0) 1 (1.9) 0 (0)
Lead > 0.00 D 15 (22.7) 6 (11.1) 3 (5.5) 20 (21.7)
P value .716 a <.020 b (.250 a ) .540 a

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Jan 16, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Decreased Accommodative Response in the Nondominant Eye of Patients With Intermittent Exotropia

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