Introduction

Congenital ptosis represents an eyelid malposition that can result in cosmetic, functional and psychosocial problems in children. It is commonly accompanied by significant ocular abnormalities or consequences [1]. Amblyopia, strabismus, and refractive errors are substantially more common in congenital ptosis patients than in the general population [1-5]. Strabismus has an estimated prevalence of 1% to 5% in the general population [6,7]. It has been reported that the prevalence of strabismus is 10.3% to 32% in patients with congenital ptosis, which is at least four times higher than the prevalence in the general population [2,3,8].

When strabismus and ptosis coexist, ptosis can negatively affect stereopsis and vision in patients with strabismus. Our previous study has revealed that the presence of coexisting ptosis can have a further deleterious impact on binocular function in patients with intermittent exotropia (IXT) [9]. The ptotic eyelid can occlude visual input and disrupt control or fusion. The IXT-ptosis group had worse distance stereoacuity and a larger proportion of patients had suppression on the Bagolini test than the IXT-only group. Therefore, patients with IXT accompanied by ptosis had worse binocular function than IXT-only patients [9]. However, stereopsis and other clinical characteristics of esotropia (ET) accompanied by congenital ptosis compared to ET without ptosis have not been reported yet. Thus, the purpose of this study was to compare binocular function and clinical features in ET patients with congenital ptosis to those without ptosis.

Methods

Ethical statements: This study was approved by the IRB of Pusan National University Yangsan Hospital (IRB No. 63804). Patient consent was waived due to a retrospective study.

1. Study design and subjects

Medical records of 44 patients aged 4 to <10 years who had been diagnosed with ET accompanied by congenital ptosis (ET-ptosis group) were reviewed retrospectively. The control group included 71 age-matched patients who were diagnosed with ET, but without congenital ptosis (ET only group)

Consecutive children aged 4 to <10 years (at the first visit) with previously untreated ET (other than refractive correction) and congenital ptosis who met the following criteria were eligible for this study: (1) any type of ET or esophoria at distance and near, (2) esodeviation with magnitude of deviation measuring 10 prism diopters or greater at distance or near based on measurements by the prism and alternate cover test (PACT). Exclusion criteria were as follows: (1) presence of ocular abnormalities (including glaucoma and congenital cataract) or optic nerve abnormalities, (2) prior strabismus surgery, intraocular or refractive surgery, and (3) significant neurologic diseases such as cerebral palsy.

2. Clinical evaluations

Records of patients were reviewed if they had undergone assessments of best-corrected visual acuity (BCVA), stereoacuity, ocular alignment, marginal reflex distance 1 (MRD1), and cycloplegic refraction at the first visit. Charts of all ET cases with congenital ptosis during the time interval at one hospital were reviewed. Cases with missing information were excluded. BCVA was measured monocularly and followed the age-based testing protocol using the Early Treatment Diabetic Retinopathy Study chart. MRD1 is a measurement in millimeters from light reflex on the patient’s cornea to the level of the center of the upper-eyelid margin with the patient gazing monocularly in the primary position [10]. Patients with mild congenital ptosis (0<MRD1≤2) were included. MRD1 was measured when patients looked at the target monocularly because MRD1 could be affected by eyeball deviation.

Near stereoacuity was assessed using the Titmus stereoacuity test (circles, animals, and fly) and the Randot Preschool stereo test at 40 cm. The eyelid was lifted up during stereoacuity testing when needed. In addition, ocular alignment was assessed using the cover/uncover test and the PACT at distance (4 m) and near (33 cm). Coexisting vertical deviation was defined as a constant deviation in all directions with a primary gaze angle of deviation of 4 prism diopters or greater [11]. During the assessment of stereoacuity and PACT, patients were corrected for BCVA. Amblyopia was defined as a visual acuity of 20/40 or worse and a difference in vision between eyes of two or more lines on a vision chart. Severe amblyopia was defined as a visual acuity of 20/100 or worse and moderate amblyopia was defined as a visual acuity of 20/100 to 20/50.

3. Outcome measures

Primary outcome measures were comparisons of stereopsis and clinical features between ET-ptosis and ET-only groups. The secondary outcome measures were comparison of stereopsis and office-based control scores between the patients in the 0<MRD1≤1 and 1<MRD1≤2 groups.

4. Statistical analysis

Descriptive statistics was used for age, sex, BCVA, refractive errors, magnitude of deviation and stereoacuity. Pearson’s chi-square test was used for categorical variables and independent samples t-test was employed to compare continuous numerical variables. Before performing the t-test, normality of data was assessed. All p-values provided were obtained using a two-tailed test. IBM SPSS ver. 23.0 (IBM Corp.) was used for all statistical analyses. Stereoacuity was converted into a log scale for analysis. For the purpose of statistical analysis, no measurable stereopsis was coded as 3.2 log seconds of arc [12]. Statistical significance was defined as a p-value less than 0.05.

Results

The mean and standard deviation age of patients (n=115) was 5.7±1.9 years. There were 55 males and 58 females in the cohort. Of these 115 patients, 44 had ET with congenital ptosis and 71 did not have congenital ptosis. The MRD1 of patients with ptosis was greater than 0 but less than or equal to 2, indicating that mild ptosis was included. There was no statistically significant difference in age, sex, refractive errors or BCVA between the two groups (Table 1). Magnitude of esodeviation at distance and near did not differ significantly between the two groups (at distance, 17.9±6.6 vs. 20.0±12.6, p=0.44; at near, 18.6±7.9 vs. 23.7±11.4, p=0.06). Numbers of patients with inferior oblique overaction, dissociated vertical deviation, latent nystagmus and coexisting vertical strabismus were not significantly different between the two groups either (inferior oblique muscle overaction, 1 [2.3%] vs. 8 [11.3%], p=0.10; dissociated vertical deviation, 3 [6.8%] vs. 5 [7.0%], p=0.97; coexisting vertical strabismus, 10 [22.7%] vs. 8 [11.3%], p=0.16; latent nystagmus, 4 [9.1%] vs. 9 [12.7%], p=0.28). The number of patients with amblyopia did not differ significantly between the two groups either (n=16 [36.4%] in the ET-ptosis group vs. n=35 [49.3%] in the ET-only group, p=0.39). Near stereoacuity, which was measured using the Randot stereo test and the Titmus test, did not differ significantly between the two groups either (Titmus test, 2.86±0.45 vs. 2.93±0.32, p=0.73; Randot stereo test, 2.95±0.31 vs. 2.89±0.39, p=0.49) (Table 1).

The magnitudes of esodeviation, near stereopsis and BCVA did not differ significantly between the 0<MRD1≤1 group and the 1<MRD1≤2 group. Although the number of patients with severe amblyopia tended to be greater in the 0<MRD1≤1 group than in the 1<MRD1≤2 group, the difference between the two groups was not significant (p=0.14) (Table 2).

Discussion

In this retrospective study, we compared stereopsis and other clinical features between the ET-ptosis group and the ET-only group. The mean stereopsis at near and the number of patients with amblyopia did not differ significantly between the two groups. Mild ptosis had no additional negative effect on stereopsis and amblyopia in patients with ET.

Binocular perception of depth is the highest form of binocular vision and important for some professions such as pilots and ophthalmic surgeons who need high degree of hand-eye coordination [13]. Maturation of stereopsis rapidly develops at 8 to 18 months of age [14]. Many studies have shown that patients with IXT have different degrees of damage to their binocular function [11,15,16]. Generally, near stereoacuity is normal in patients with IXT, while distance stereopsis is often worse than in normal controls [15]. Other studies have suggested that some patients with IXT have a decline in near stereopsis [16]. In our previous study, distance stereoacuity was significantly impaired when ptosis coexisted with IXT. However, near stereoacuity of the patients was not affected by ptosis [9]. A larger proportion of patients had suppression on the Bagolini test in the IXT-ptosis group than in the IXT-only group. Also, a higher proportion of patients in 0<MRD1≤1 group had suppression on Baolini test compared to the 1<MRD1≤2 group. Furthermore, office-based control scores at distance tended to be slightly worse in the IXT-ptosis group than in the IXT-only group. In IXT patients, the presence of coexisting ptosis can have a further deleterious impact on binocular function [9].

Infantile ET is related to a higher incidence of amblyopia and impaired binocular sensory function. In a recent prospective study, 129 children who were diagnosed with infantile ET by 6 months of age and followed up for at least 5 years were found that, even though more than 90% of these children were treated for amblyopia during follow-up, less than 10% exhibited persistent amblyopia at the final visit, with majority of persistent cases of amblyopia being mild [17]. In contrast, treatment for binocular sensory impairment is rarely successful. Even with optical correction and early surgery, less than 0.5% of this prospective cohort had normal stereoacuity by the age of five, and over 60% had no stereoacuity at all [17]. This study excluded patients who had strabismus surgery, hence infantile ET was not included.

The onset of an initially intermittent nasalward misalignment in patients with accommodative ET typically starts between the ages of 18 and 48 months. Accommodative ET often leads to impaired binocular sensory function, despite its late development. Even when accommodative ET in children was diagnosed in its earliest stage, more than 40% showed impaired stereoacuity [18]. In this study, ptosis had no further deleterious impact on stereoacuity in ET patients. This was due to the inclusion of mild ptosis in this study. Therefore, mild ptosis had no effect on stereoacuity in ET patients who already had poor stereoacuity.

Amblyopia has been found to be more common in patients with congenital ptosis caused by astigmatism or other refractive errors and/or the visual axis obstruction [8]. In the study of Hornblass et al. [19], they found a significant relationship between the severity of ptosis and the development of amblyopia. Preoperative MRD1 ≤−1 mm, preoperative lid fissure ≤4.5 mm, preoperative anisometropia, and postoperative astigmatism were associated with amblyopia in congenital ptosis after frontalis sling surgery [20]. Amblyopia is uncommon in IXT patients unless there is severe anisometropia [21]. The reported incidence of amblyopia in patients with infantile ET ranges between 30% and 75% [22-27]. The high prevalence of amblyopia in ET is due to asymmetry between the nasal and temporal hemiretina. In ET, the fovea in the deviating eye competes with the more powerful temporal hemiretina in the non-deviating eye, resulting in amblyopia [11,28]. In this study, the number of patients with amblyopia did not differ between the ET-ptosis group and the ET-only group. Amblyopia already occurs frequently in patient with ET, and coexisting mild ptosis did not have a further negative impact on their vision.

This study has some limitations. First, this was a retrospective review of medical records, which could inherently limit the quality of data. Second, the sample size was also relatively small. Third, this study does not disclose whether binocular function would improve after ptosis surgery. Fourth, this study did not analyze the lateralization of ptosis, so it was not possible to compare the vision of the eye with and without ptosis. Finally, this study did not analyze the type of ET, so the effect on visual acuity and stereoacuity according to the type of ET was not analyzed. However, the strength of this study was its quantitative evaluation of binocular function in ET patients with congenital ptosis compared to ET-only patients.

In conclusion, stereoacuity and visual acuity did not differ between the ET-ptosis group and the ET-only group. The presence of coexisting mild ptosis might not have a further deleterious impact on stereopsis or visual acuity in patients with ET.

Article information

Conflicts of interest

No potential conflict of interest relevant to this article was reported.

Funding

None.

Author contributions

Conceptualization: SJK. Data curation: SAY, KEH, Formal analysis: SAY, KEH. Investigation: KEH. Methodology: SJK. Project administration: SJK. Resources: SJK, HC. Supervision: HC. Writing - original draft: SJK, SAY, KEH. Writing - review & editing: SJK, HC. All authors read and approved the final manuscript.

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Figure & Data

References

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