Extended Abstract
Introduction
Intermittent exotropia is the most common form of exotropia in children. The condition is characterized by alternating periods of fusion failure, followed by periods of maintained ocular alignment and sensory fusion. Both surgical and non-surgical treatments are common for this disease; however, there is a disagreement regarding the timing and type of treatment.
Non-surgical treatments can control deviation, maintain stereopsis, and ultimately improve visual function in these patients. In some patients, non-surgical treatments may delay or eliminate the need for surgery. One of the treatments used in this condition is wearing overminus spectacles. Overminus spectacles work by stimulating accommodation to control deviation and improve visual function. Various studies have investigated the effect of non-surgical treatments, including patching, wearing negative glasses, convergence therapy, or even botulinum toxin injection, with each having different results.
Given the problems of other non-surgical treatment methods, such as intolerance in patch therapy or orthoptic exercises, and the limitations of using high-power prisms, this study was conducted to compare the effects of wearing overminus spectacles versus patch therapy in 3- to 8-year-old children with intermittent exotropia.
Methods
This clinical trial was conducted on 30 children (9 boys and 21 girls) with intermittent exotropia aged 3 to 8 years (mean age: 4.53±1.4) with no previous treatment history, who referred to the strabismus clinic of Khatam-al-Anbia Hospital in Mashhad between 2018 and 2019.
Inclusion included an age range of 3 to 8 years, the presence of intermittent exotropia in distance or near, a deviation of more than 10 prism diopters in distance or near based on the alternative prism and cover test, and patient cooperation for examinations and measurements.
Ophthalmological examinations included visual acuity assessment (Snellen chart) and a complete assessment of eye movements, including the alternative prism and cover test in distance and near. In all patients, after measuring the deviation in distance and near, the eye was patched for 45 minutes and the measurement was repeated. If the difference between the deviation in distance and near was less than 10 prism diopters, the patient was classified as having a basic type. If there was a difference of more than 10 prism diopters (less deviation in near) after closing the eye, the eye deviation was rechecked with +3 glasses in near. If the deviation in near changed by more than 10 prism diopters, the patient was placed in the group with a high ratio of convergence to accommodation and was excluded from the study. Only patients with a difference of less than 10 prism diopters between the deviation in distance and near were included in the study.
In the patch therapy group, the healthy eye of the patient was patched for 6 months, 2 to 4 hours per day. Patching was performed alternately or on the dominant eye. The deviation control status was measured and recorded using the Newcastle Scale Score (NSS) in all patients. If the patient cooperated, near stereopsis was checked using the Titmus test.
Overminus spectacles were prescribed based on cycloplegic refraction between 2 and 4 diopters, with full astigmatism correction.
Patients were advised to wear the spectacles full-time. Follow-up appointments were scheduled at 3 and 6 months. Primary treatment success was defined as the presence of exotropia less than 10 prism diopters for both near and distance vision, or improvement in deviation control based on the NSS criterion to less than 3. Secondary success was defined as improvement in stereopsis to less than 100 arcseconds.
Results
Before the intervention, the mean spherical error of patients in the overminus group was +1 diopters in the right eye and +0.75 diopters in the left eye. In the patch therapy group, the mean spherical error was +0.75 diopters in both the right and left eyes. Six months after the intervention, the mean spherical error in the overminus group was +0.62 diopters in both the right and left eyes, and in the patch therapy group, it was +0.75 diopters in the right eye and +0.62 diopters in the left eye. No statistically significant difference was found between the groups.
The median deviation size of patients in the overminus group before intervention was determined to be 25.00 prism for both distance and near vision. Three months post-intervention, it was 25.00 prism for distance and 22.50 prism for near vision. Six months post-intervention, it was determined to be 22.50 prism for distance vision and 20.00 prism for near vision. Similarly, the median deviation size of patients in the patch therapy group was determined to be 25.00 prism for both distance and near vision before intervention. Three months post-intervention, it was determined to be 22.50 prism for distance vision and 25.00 prism for near vision. Six months post-intervention, it was determined to be 22.50 for both distant and near vision. No statistically significant difference was found between the groups. Additionally, the success rate in improving the deviation angle (less than 10 prism) was 20% (2 out of 10 patients) in the overminus group and 15% (3 out of 20 patients) in the patch therapy group.
The median NSS of patients was determined to be 3.50 in the overminus group and 4.00 in the patch therapy group before intervention. Three months post-intervention, it was determined to be 3.00 in both groups. Six months post-intervention, it was found to be 1.50 in the overminus group and 3.00 in the patch therapy group. There was no statistically significant difference between the groups.
Near stereo acuity was assessed in 10 patients, and no change was observed in near stereo acuity (range 40-400) in any of them. Other patients did not cooperate for near stereo acuity assessment.
Conclusion
According to the results of this study, both the overminus spectacles and patch therapy methods were found to be influential in treating patients with intermittent exotropia; however, patients in the overminus group exhibitd a non-significantly greater improvement compared to the patch therapy group.
Ethical Statement
This study has been approved by the Ethics Committee of Mashhad University of Medical Sciences (IR.MUMS.FM.REC.1396.14) and registered in the Iranian Registry of Clinical Trials (IRCT20190307042953N1).
Funding
This article has been extracted from the doctoral dissertation of Ms. Negar Shahsavar for the specialty degree in General Medicine at Mashhad University of Medical Sciences.
Conflicts of Interest
No conflict of interest.
Key message: Both the overminus spectacles and patch therapy methods are applied in the treatment of patients with intermittent exotropia. Patients using the overminus method demonstrated greater deviation control compared to those using patch therapy.