Clinical features and biometric profile of patients presenting with unilateral high myopia

Abstract

Background

Unilateral myopia, though less common than bilateral myopia, presents unique clinical challenges. This study aimed to explore the prevalence and clinical characteristics of children presenting with unilateral myopia.

Methods

Children presenting with unilateral high myopia at a tertiary care center, with a cycloplegic spherical equivalent (SE) ≤ -5D in one eye and ≥ -3D in the other, between January 2022 and January 2023, were recruited. A comprehensive review of their birth records and ocular examination was undertaken. Ocular biometric parameters, including axial length (AL), keratometry (K), and lens thickness (LT), were measured by IOLMaster 700, and the progress of refractive error since diagnosis was noted.

Results

The study analyzed 25 patients with a mean age of 11.9 years (1–12 years) and a mean follow-up of 24.45 ± 2.4 months. Axial myopia was found in 84% of patients, and optic nerve abnormalities were present in 40%. There was associated amblyopia in 32%. The difference in the inter-eye AL, K, and LT was 0.85 ± 0.45 mm, 0.35 ± 0.20 D, and 0.12 ± 0.05 mm. Mean annual myopic progression in these eyes was 0.74 D (0.2–1.5 D).

Conclusions

Unilateral myopia in a samples Indian population presents unique clinical characteristics. Unilateral axial myopia in a patient should prompt us to take a detailed birth history and look for optic nerve abnormalities. Amblyopia is seen in a significant proportion of unilateral myopes, and their myopic progression was 0.74D/year in our cohort.

Introduction

Unilateral high myopia though less common than myopia, it presents unique clinical challenges and complexities. Myopia, characterized by an eye that is too long for its optical power, typically results in symmetric growth in both eyes. However, an asymmetry suggests differences in axial growth or the combined refractive power of the cornea and lens between the eyes [1]. There is no clear definition of unilateral high myopia, and for practical purposes, anisometropia more than 2 D is used as a surrogate. Unilateral myopes have different aetiologies, pathogenesis, and clinical features as compared to usual bilateral myopes. Unilateral myopia deserves independent study because it behaves differently from bilateral myopia, carries a distinct amblyopia risk profile, and may reveal unique mechanisms of emmetropization and ocular growth that are masked when both eyes are similarly myopic [2–16]. Hence, most literature has focused on the treatment and visual outcomes of anisometropic myopia, highlighting the complexities of managing this condition [4–12].

There is a lack of literature on the global incidence of unilateral myopia in children, but it has been reportedly seen in 30% of adults [17]. This study aims to explore unilateral myopia in children, focusing on visual acuity, biometric profiles, and myopia progression in these patients. We aim to enhance our knowledge and suggest better management strategies for unilateral myopia and its progression.

Materials and methods

This study was conducted at the Advanced Eye Center, Department of Ophthalmology, Post Graduate Institute of Medical Education and Research, Chandigarh, India, adhering to the principles outlined in the Declaration of Helsinki, with ethical waiver obtained from the institute. It was a consecutive case series. We reviewed the medical records of all children who visited the pediatric ophthalmology clinic between January 2022 and January 2023. This retrospective consecutive case series included all patients(< 18 years) meeting predefined inclusion criteria identified from electronic medical records over a one-year period.

Unilateral myopia was characterized by a cycloplegic spherical equivalent (SE) ≤ --5D in one eye and ≥ -3D in the other eye (difference of at least 2D between the two eyes) [11]. Patients with a history of trauma, any anterior segment pathology (ptosis, corneal scars/opacities, keratoconus, cataracts), glaucoma, and prior scleral buckling, or any other pathology that could account for the anisomteropia were excluded. Children who fulfilled the inclusion criteria were telephonically called for follow-up. On this visit, after informed consent, parents were interviewed for any history of ocular abnormalities or treatments taken during the first six months of life. Parental interviews were conducted using a structured data collection form capturing family history, and perinatal factors, adapted from studies on risk factors for unilateral myopes The questionnaire specified information including prematurity, history of cranial and/or ocular trauma, records or history suggesting vitreous haemorrhage, any orbital swelling, ptosis, treatment for haemangiomas, or corneal ulcers from birth till diagnosis. Each patient underwent a comprehensive ocular examination. The records were reviewed for visual acuity, strabismus, and amblyopia. The refractive error was assessed by a certified optometrist using streak retinoscopy after dilation with cyclopentolate 1% (administered three times at 10-minute intervals, with the reading taken 30 min after the last instillation). Visual acuity was measured at a distance of 6 m using the Snellen chart for children who could cooperate and using LEA SYMBOLS/Cardiff and Tellers Acuity Charts for younger children. These measurements were then converted into the logarithm of the minimum angle of resolution (LogMAR) for statistical analysis.

The biometric profile included measurements of axial length (AL), keratometry (K), and lens thickness (LT) using the intraocular lens master (Carl Zeiss Jena, Germany). All measurements were performed on awake children in the outpatient clinic. The posterior segment of the eye was examined using indirect ophthalmoscopy and a 20D lens to detect any structural abnormalities.

We collected data from all previous examinations and treatments administered till the presentation during the study period. As a retrospective case series, follow-up visits were not prospectively standardized but followed routine clinical protocols based on patient needs and the presence of amblyopia (3–6 monthly for amblyopia treatment monitoring; 6–12 monthly for stable cases), with all available record data extracted and follow-up duration reported descriptively per patient. Patients were prescribed patching if associated with amblyopia according to guidelines by the Pediatric Eye Disease Investigator Group [12, 18, 19]. Axial myopia was defined as myopia resulting from interocular differences in AL, while refractive myopia was defined as myopia due to increased refractive power of the cornea, lens, or both. Axial anisometropic myopia was considered absolute when the AL of the more myopic eye exceeded the normal range (for that age [20, 21]), and relative when the AL was within or below the normal range. Fundus photographs, OCT, MRI, and visual field data were reviewed wherever available. Optic nerve hypoplasia was defined as a congenitally small optic disc with reduced disc size relative to the disc–macula distance (DD/DM ratio < 0.35 or D–M/DD ≥ 3), often with a peripapillary double-ring sign, Segmental hypoplasia of the optic nerve was defined clinically as a non-progressive, localized thinning or pallor of one optic disc sector with a corresponding sectoral retinal nerve fiber layer (RNFL) defect on OCT and matching localized visual field loss where age appropriate perimetry was possible.

For statistical analyses, all data were fed into a Microsoft Excel sheet. Continuous data were presented as mean ± standard deviation, while categorical variables were presented as numbers and percentages. Descriptive statistics and frequencies were calculated. The regression slope was calculated to identify the average change in the spherical equivalent (y) for a one-unit increase in the axial length (x). The r-value was used to indicate the strength and magnitude of the relationship.

Results

A total of 25 patients were analyzed, including 14 males (56%) and 11 females (44%). The age of the patients ranged from 1 to 12 years, with a mean age of 11.9 years. Given the presence of potential outliers, the median age was 6.0 years, with an interquartile range (IQR) of 3.75–9.0 years. In 10 patients (40%), the more myopic eye was the right eye.

Optic nerve abnormalities were present in 10 eyes (40%), including hypoplasia in 8 (32%) and myelinated nerve fibres in 2 (8%). Optic nerve hypoplasia was segmental in 6 eyes (24%) and diffuse in 4 eyes (16%). A family history of moderate to high myopia was noted in 10 patients (40%). One patient (4%) had genetically confirmed Ehlers-Danlos syndrome.

Eight patients (32%) had no identifiable congenital or acquired ophthalmic history that could account for significant interocular asymmetry. Strabismus was observed in 6 patients (24%), and all cases were exotropia. Amblyopia was present in 8 patients (32%), all of whom were treated with patching.

Table 1 illustrates the demographic data along with clinical characteristics.

Table 1.

Patient demographics and clinical data

Parameter	Value (mean ± SD)
Gender(M/F)	14/11
Mean age at diagnosis (years)	11.9 ± 8.1 (1 year-12 years)
Median	6 years
Unaided vision at presentation	6/36 (0.8 Log Mar)
Etiology	Disc abnormalities (10); Systemic Collagen abnormalities (2); Severe laser-treated ROP (3); Straatsma (2)
Amblyopia	8 (32%)
Strabismus	6 (24%)
Best corrected visual acuity (Amblyopic eye)	0.4 ± 0.3

Myopia was axial in 84% of patients (21). The fellow eye was myopic in 8, emmetropic in 8, and hyperopic by one dioptre or more in 9 patients. The biometry parameters are outlined in Table 2.

Table 2.

Visual acuity and biometric profile of all patients

Parameter	Study Eye (Mean ± SD)	Normal Eye (Mean ± SD)
Spherical equivalent (D)	-9.2 ± 6.1	-0.25 ± 0.50
Axial length (mm)	24.3 ± 2.1	22.3 ± 0.5
Keratometry (D)	44.5 ± 1.6 (40.0 to 49.4)	43.0 ± 1.5
Lens thickness (mm)	3.5 ± 0.5	4.0 ± 0.2
Mean follow-up	24.45 ± 2.4

The average difference in refractive power between the eyes was 9.4 diopters, with a standard deviation of 3.6 diopters, ranging from 4.5 to 18.2 diopters. On average, the more myopic eye was 3.3 mm longer than the less myopic eye, with a standard deviation of 1.8 mm and a range of 0.8 to 8.9 mm. The difference in the inter-eye axial length, keratometry, and lens thickness was 0.85 ± 0.45 mm, 0.35 ± 0.20 D, and 0.12 ± 0.05 mm.

The regression analysis revealed a slope of 0.35, indicating that for every 1 mm difference in axial length, there was an associated refractive difference of 2.9 diopters (1/0.35 = 2.9) (Fig. 1). This relationship was statistically significant, with an r^2 value of 0.62 and a p-value of less than 0.001, suggesting that the interocular refractive discrepancy was primarily attributed to differences in axial length between the eyes. When stratified by fellow eye refractive status (myopic n = 8, emmetropic and hyperopic n = 17), anisometropia magnitude did not differ significantly across groups, though emmetropic/hyperopic fellow eyes showed marginally greater anisometropia (10.04 ± 3.78 D vs. 9.4 ± 3.6 D).

Fig. 1.

Represents the regression plot comparing the difference in dioptres (refractive error) with the corresponding difference in total axial length (TAL) in millimeters. The data points represent individual comparisons between the more myopic eye and the less myopic eye. A linear regression line (blue) is fitted to the data, with the equation y = 0.2441x + 0.4916y = 0.2441x + 0.4916y = 0.2441x + 0.4916 and an R2R^2R2 value of 0.35, indicating the strength of the correlation between these two variables

Five patients in the study were born prematurely, with a mean gestational age of 26.6 weeks. Three patients also had a history of Retinopathy of Prematurity (ROP), which was lasered. In these cases, the AL of the more myopic eye was within the normal range for that age in two patients, whereas it was below normal in the other three. On average, the more myopic eye was 2.8 mm longer than the less myopic eye, with a range of 1.4 to 5.3 mm. Each of these patients exhibited ROP residual effects in the posterior pole.

Figure 2 illustrates the mean myopic shift of each patient every year. The average myopic shift was 0.74 D/year (0.2–1.5 D). Low-dose atropine 0.01% was started for seven patients (28%) for myopic progression.

Fig. 2.

Bar chart plotting the mean myopic shift per year in all patients

Discussion

The present study seeks to identify the characteristics of unilateral myopia. These patients have unique characteristics, and only genetic and environmental factors do not govern the amount of myopia. The literature on this subset of patients is scarce, so the trends in myopia progression in these patients are unclear.

The prevalence of unilateral myopia is not apparent. There are a few reports on unilateral myopia with or without amblyopia [8–12]. “While overall myopia prevalence in Indian schoolchildren is approximately 7–8% (higher in urban areas at 8.5% vs. rural 6.1%), unilateral myopia specifically comprises 5–8% of myopic cases in regional studies, highlighting its understudied but clinically relevant burden in Indian populations [22] All these are cross-sectional studies with different durations of follow-up. Our study also identified these patients consecutively, so the exact prevalence of unilateral myopia remains understudied. However, our numbers are relatively large compared to the most extensive series of 79 patients collected over ten years [23].

The etiology of unilateral myopia is supported by the theory that unilateral image degradation leads to axial elongation and, consequently, myopia. The causes include blepharoptosis, media opacities such as corneal scars, cataracts, or vitreous hemorrhage [2, 10, 15, 16]. Environmental influences may cause monocular visual deprivation, axial elongation, and myopia [4, 7, 13, 24]. Other conditions linked with high incidence of unilateral myopia include myelinated nerve fibers and optic nerve hypoplasia [3, 4]. Limited literature supports other hypotheses, including interocular differences in the cornea, intraocular pressure, convergence and accommodation, higher-order aberrations, brain abnormalities, defects in emmetropization, and ocular dominance [8, 11]. There is also a theory about genetic predisposition, including skewed lyonization coupled with environmental factors like hemifacial microsomy, causing unilateral myopia [11].

The association between optic nerve abnormalities and axial myopia observed in our study aligns with the findings of others [3, 15]. Optic nerve hypoplasia, segmental or diffuse, was prevalent in our cohort (48%), suggesting a potential link between optic nerve development and the occurrence of axial myopia. These abnormalities raise the possibility that congenital optic nerve or peripapillary structural changes may be associated with abnormal ocular growth in some unilateral myopia phenotypes, which could contribute to the asymmetric growth observed in unilateral myopia. Sometimes these abnormalities may be subtle, highlighting the need for comprehensive ocular examinations in affected patients. However, a significant proportion (32%) had no significant contributing factor to cause anisometropia. Some undiscovered aetiologies might have contributed to the unilateral axial elongation. Although with the small sample size and retrospective design, the optic nerve abnormalities could not have been causative. Larger, prospective studies with standardized imaging and controls are needed to confirm whether optic nerve hypoplasia is truly linked to axial elongation in unilateral myopia.

There have been other papers studying the biometric profile in these patients. A Chinese study examined the biometric variables via Anterior Segment Optical Coherence Tomography in 91 participants with unilateral myopia [23]. Compared to the contralateral eye, patients with unilateral myopia exhibited lower lens power with no significant difference in lens thickness. They hypothesized peripheral lens compression as an underlying mechanism.

Interestingly, our study also noted a subset of patients with a history of ROP. These patients exhibited characteristics distinct from the general population, with relative differences in AL between the two eyes. Children with ROP may have myopia that is not axial [25–28]. However, anisometropia in these children is only due to a difference in axial lengths.

The prevalence of amblyopia in our subset of patients is very high (32%). The challenges in managing amblyopia in patients with unilateral myopia have been well-documented in previous studies [10, 13]. These patients are detected late as the amblyopia is unilateral, which may affect the visual outcome in these patients. However, we couldn’t establish this due to the nature of our study. Neonatal and preschool screening of children may help detect these refractive errors early and treat amblyopia promptly.

One of the most important findings of our study was the mean myopic progression in our cohort (0.74 D), which is more than the mean myopic shift in urban children with high myopia (estimated to be 0.5 D) [29, 30]. Unilaterality may predispose the patients towards more myopic progression. There might be regional variations in the amount of progression, which may be affected by age, degree of myopia, and amblyopia.

Our series, therefore, represents unilateral myopia presumed to arise from congenital or idiopathic mechanisms. Ocular dominance, near work, and broader environmental influences are well-recognized contributors to typical bilateral school-age myopia, but they are less clearly implicated in congenital or idiopathic unilateral high myopia, where structural or developmental factors (e.g., optic nerve or posterior segment anomalies) are thought to play a more significant role.

Being retrospective in nature, this study has the related limitations further compounded by selection bias due to its hospital-based setting. There was a varied range of patients in the cohort, causing individual differences so that an age response couldn’t be elicited. The sample size is small with a smaller proportion of patients in different aetiologies.

The findings of our study describe the profile of patients with unilateral myopia. Unilateral axial myopia in a patient should prompt us to take a detailed birth history and look for optic nerve abnormalities. Amblyopia is seen in a significant proportion of unilateral myopes, and their myopic progression was 0.74D/year in our cohort. In clinical practice, unilateral myopia requires simultaneous management of amblyopia risk and long-term myopia control in the affected eye, while protecting the fellow eye. Full optical correction of the myopic eye (preferably with early spectacle or contact lens wear) and timely initiation of amblyopia therapy remain the cornerstone in younger children. Future research should continue to explore the long-term outcomes of unilateral myopia and the progression compared to their bilateral counterparts, focusing on optimizing anti-myopia strategies for these individuals.

Author contributions

All authors contributed to the study conception, data collection, analysis, and manuscript preparation. SK conceptualized the study, recruited patients and was involved in Manuscript writing, KA & HM: Involved in data collection, JS: Senior author and supervision, contributed patients to the data set.

Funding

None.

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethical approval

The study adhered to the principles of the Declaration of Helsinki. The study was submitted to and approved by the Institute Ethics Committee, PGIMER, Chandigarh. The approval reference number is [IEC-INT/2026/Study-3623].

Consent to participate

Written informed consent was obtained from parents or guardians, and verbal consent/assent was obtained from the participants.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.