Anisometropia is defined as an interocular difference in refractive error originating from discrepancies in either axial length or refractive power.1 In clinical settings, an interocular difference in spherical equivalent refraction (SER) of ≥1.00 diopter (D) serves as the standard diagnostic criterion.2–4 This condition frequently co-occurs with myopia.5 Consequently, myopic anisometropia has become a highly prevalent clinical presentation, affecting up to 10% of the young adult population.1 The unequal refractive status inherent in anisometropia is a primary etiology of amblyopia.6 It causes continuous unilateral retinal blur, prompting the visual cortex to preferentially process the clearer image while suppressing the blurred one.7 Furthermore, even in the absence of amblyopia, myopic anisometropia severely compromises binocular vision due to aniseikonia—a clinically significant inequality in retinal image sizes. This disparity degrades fusional ability, leading to diplopia, visual suppression, and diminished stereopsis.8–10 Consequently, affected individuals frequently experience asthenopia, headaches, and impaired depth perception during demanding visual tasks, which substantially deteriorates their daily visual quality.11 Currently, spectacles (ophthalmic lens) and contact lenses remain the primary modalities for refractive correction.12 However, these approaches exert distinct physiological effects on binocular interaction. Ophthalmic lenses sit at a vertex distance of 12 to 14 millimeters13 which exacerbates aniseikonia by inducing inherent optical magnification differences.14 Additionally, during near-vision tasks, minus ophthalmic lenses induce a base-in prismatic effect. Conversely, contact lenses eliminate the vertex distance and this associated prismatic effect.15 Selecting the optimal corrective modality is therefore critical to restoring binocular harmony. However, current literature reveals a paucity of robust evidence comparing the specific accommodative and vergence effects of ophthalmic versus contact lenses in young adults with myopic anisometropia. To address this clinical gap, this study investigated the optimal refractive management strategy by comprehensively comparing binocular and accommodative functions under ophthalmic versus contact lens wear in young adults with myopic anisometropia and myopic isometropia.

The primary objective of this study was to compare binocular visual efficiency and accommodative dynamics under ophthalmic versus contact lens wear in young adults with myopic anisometropia and isometropic myopia. Our principal findings demonstrate a distinct clinical trade-off between the two correction modalities: while contact lenses induce specific near-point accommodative and vergence shifts, they afford significantly superior stereoscopic performance compared to ophthalmic lenses, particularly in individuals with moderate anisometropia (difference SER ≥ 1.50 D).

Stereoacuity represents the highest level of binocular visual processing, requiring precise cortical integration of disparate monocular inputs.18 In the uncorrected state, baseline stereopsis was profoundly degraded in the anisometropic cohort compared to the isometropic group (p < 0.001) (Table 2). This finding aligns with Khan et al., who demonstrated that anisometropic individuals exhibited significantly reduced stereopsis compared to isometropic and emmetropic subjects, with myopic anisometropia yielding the poorest stereoacuity.19 Furthermore, Oguz and Oguz reported that stereopsis degrades as the magnitude of anisometropia increases, noting that an interocular difference of 1.00 D or greater reduces stereoacuity by an average of 57 to 59 sec of arc. Thus, even low levels of anisometropia can significantly compromise binocular vision.20 The poorer uncorrected stereopsis observed in the anisometropic group may be explained by abnormal binocular visual development, in which unequal retinal input disrupts cortical binocular integration and leads to reduced stereopsis,21 confirming that even relatively low levels of interocular refractive differences severely disrupt binocular cortical pathways.19–21

Although ophthalmic lens correction restored stereoacuity to functional clinical ranges, the anisometropic group still exhibited lower performance than their isometropic peers. Crucially, as detailed in Fig. 1 and Table 3, contact lens correction yielded a statistically significant enhancement in stereoacuity over spectacles within the anisometropic group (p = 0.032). This clinical superiority is hypothesized to be primarily driven by the mitigation of aniseikonia; theoretically, contact lenses minimize the interocular retinal image size disparities inherently induced by the differential magnification of minus spectacle lenses, thereby facilitating robust binocular bifoveal fusion.21–23 Notably, our subgroup analysis revealed that for patients with an interocular SER difference of ≥1.50 D (Groups B and D), contact lenses showed a suggestive functional advantage, demonstrating marginal improvements in stereopsis than both the uncorrected and spectacle-corrected conditions (p = 0.048 and p = 0.028, respectively). This suggests that an interocular SER difference of ≥1.50 D may represent a hypothetical clinical point for supporting stereoscopic depth perception, which requires further longitudinal investigation. Clinically, this enhancement from gross to finer stereopsis translates to more precise binocular depth perception, which is crucial for fine motor tasks, hand-eye coordination, and navigating complex visual environments in daily life. In contrast to the distance parameters (Table 4) and vertical vergence profiles which remained highly stable across both refractive groups and correction methods, near-point binocular and vergence dynamics exhibited significant alterations under contact lens wear (Table 5). The anisometropic cohort experienced a distinct near esophoric shift when transitioning from spectacles to contact lenses. This phenomenon is theoretically rooted in the loss of the induced base-in (BI) prismatic effect that minus spectacle lenses naturally provide during convergence at near.15,24 By eliminating this spectacle-induced BI prism, contact lenses are thought to increase the active accommodative convergence demand. Consequently, this increased esophoric posture amplifies the compensatory fusional divergence demand, directly culminating in the observed significant reduction in the near negative fusional vergence break reserves (p = 0.012). Despite these near vergence stresses, positive fusional vergence and vergence facility remained intact, indicating that the overall fusional reserve capacity was compromised but not entirely destabilized.25

This optical-mechanical shift also directly modulated the accommodative profiles (Table 6). When wearing contact lenses, the anisometropic group demonstrated a significantly greater lag of accommodation (p < 0.001) and a concomitant elevation in NRA values (p = 0.007) compared to spectacle correction. The elimination of the spectacles' near BI prismatic effect effectively increases the objective accommodative demand at near, causing the accommodative system to operate with a larger steady-state error (greater lag) to maintain focus without over-expending energy.15 Importantly, because these accommodative lag values remained within acceptable functional norms (< +1.00 D),26 and dynamic accommodative facility was unaffected (p > 0.05), this shift represents a benign physiological adaptation rather than a pathological breakdown of the accommodative apparatus.15,27

Several limitations warrant consideration when interpreting these findings. Methodologically, the fixed, non-randomized testing sequence (ophthalmic lenses followed by contact lenses) introduces potential learning or practice effects, and the 10 min adaptation window restricts observations to acute physiological responses rather than long-term stability as longer adaptation may influence accommodative and binocular vision outcomes. Demographically, the cohort comprised exclusively young adults, limiting generalizability to presbyopic populations, and despite strict washout periods, prior contact lens experience may have influenced initial sensory adaptations compared to complete neophytes. Regarding the outcomes, while changes in accommodative lag and negative relative accommodation were statistically significant, their small absolute magnitudes may not meaningfully impact daily visual performance in asymptomatic individuals, though they remain relevant for patients with high visual demands, prolonged near work, or pre-existing binocular vision anomalies. In contrast, the observed stereoscopic improvements offer clearer functional relevance. Nevertheless, the absence of subjective symptom evaluations (e.g., asthenopia or visual comfort) leaves the real-world impact of these accommodative shifts unquantified, underscoring the need for future studies utilizing patient-reported outcome measures. Finally, the subgroup stratifications (Groups A−F) were strictly exploratory and hypothesis-generating; the small sample sizes in higher anisometropia cohorts (n = 3) restrict statistical power and increase the risk of Type II errors. Consequently, these specific observations should be interpreted with clinical caution and not dictate definitive thresholds until validated by larger, adequately powered longitudinal trials.

Taken together, these findings provide valuable clinical insights for the management of myopic anisometropia. While spectacles offer a conventional correction that preserves near vergence and accommodative reserves, they may limit stereoscopic performance in patients with interocular SER differences ≥1.50 D. For these patients, contact lenses may offer functional advantages in supporting binocular integration and stereopsis, provided that clinicians monitor and manage the potential increase in near esophoria and reduced negative fusional vergence reserves. If visual symptoms arise, these accommodative and vergence shifts can be managed appropriately through targeted visual hygiene or vision therapy.

The modality of refractive correction fundamentally alters binocular and accommodative dynamics in myopic anisometropia. While ophthalmic lenses uniformly preserve baseline binocular functions across myopic profiles, contact lenses elicit distinct physiological shifts. Specifically, the optical removal of the near base-in prismatic effect with contact lenses is proposed to increases accommodative demand, manifesting clinically as a greater accommodative lag and higher NRA. Furthermore, contact lenses induce a near esophoric shift, amplifying the fusional divergence demand and consequently diminishing the negative fusional vergence reserve.

Despite these accommodative and vergence alterations, contact lens wear was associated with better stereoacuity compared to ophthalmic lenses, theoretically driven by the hypothesized mitigation of aniseikonia. Therefore, while both modalities are clinically viable, contact lens correction suggests potential functional advantages in stereoscopic performance for higher degrees of myopic anisometropia (e.g., ≥1.50 D), though this exploratory finding warrants further investigation. Ultimately, these findings elucidate the clinical differences between refractive modalities, providing valuable clinical insights for the assessment, management, and follow-up of myopic anisometropia to support specific binocular functions and stereoscopic integration. However, given the limited sample sizes in certain subgroup analyses, these specific findings should be considered strictly exploratory and hypothesis-generating. Future longitudinal studies utilizing larger clinical cohorts, longer adaptation periods, and patient-reported outcome measures are necessary to comprehensively explore the long-term physiological trends and conclusively validate these observations.

This work was partially supported by Frontier Research and Innovation Cluster Fund, Naresuan University [Grant number R2569C006]. The sponsor provided financial support for the conduct of the research in the writing of the manuscript.

Conceptualization and design of the study, acquisition of data, analysis and interpretation of data and drafting the article, A.D., B.S., C.K., M.S., W.K., and S.W.; writing—review and editing, A.D., and S.W.; visualization and funding acquisition, S.W.; supervision and project administration, A.D., and S.W. All authors have read and agreed to the published version of the manuscript.

During the preparation of this work the authors used Gemini 3.1 Pro in order to improve readability and especially improve language in drafting this paper in English. After using this tool/service, the authors reviewed and edited the content as needed and take full responsibility for the content of the published article.