Ing's clinical study revealed an intriguing finding: patients who were aligned after 24 months showed notably less evidence of binocularity, despite achieving satisfactory motor alignment (1). This finding aligns with the findings of an experimental animal study suggesting that early surgical intervention contributes to a more advanced neurophysiological framework for binocular outcomes (3). However, precise examinations of infants between 6 and 12 months of age are likely to be challenging. Consequently, performing surgery based on insufficient information could lead to a greater frequency of overcorrections and undercorrections. As a result, such outcomes may deter surgery from its original purpose (4), causing monofixation syndrome (5) and resulting in latent nystagmus (6). To improve vision in the fixing eye in latent nystagmus, asymmetric convergence occurs but also results in an unavoidable and undesirable elevation of the fellow eye, which we recognize as DVD (6). In this series, neither latent nystagmus nor DVD developed. This may be because the intervention was performed during the critical period of visual cortex development. Tychsen suggested that ophthalmic surgeons realign the eyes to within an envelope of 2.5 to 5.0 degrees within 60 days after the onset of strabismus. Accordingly, interventions should be tailored to the age of onset and not chronological age (5). The age of strabismus onset reported in this series is not very reliable, but approximate ages were reported by parents. In Patient 5, the parents reported that their baby had experienced strabismus since birth. This confusion arises from the uninterrupted period between the baby's settlement of Hering’s reflex and the onset of strabismus. Some parents have recently noticed strabismus but cannot provide a precise onset age. Therefore, the age of strabismus onset was approximate. However, the intervention was performed in three patients within two months of strabismus onset (patients 1, 3, and 4). Two of these patients achieved orthophoria, whereas the third exhibited suppression in the right eye due to insufficient parental compliance. Patient 2 had an accommodative component as well, and ultimately, this patient developed orthophoria through hypermetropia correction and achieved binocularity. Patient 5 required the most intensive patching of the dominant eye. However, the parents were most likely not up to this difficult task, so the right eye remained dominant, and the left eye remained suppressed.
The author does not recommend the management of infantile esotropia solely through botulinum toxin injection. Instead, the author proposed botulinum toxin injection if the patient experienced strabismus within 60 days of onset. This is because the change in alignment after the injection of botulinum toxin brings the eyes within an acceptable anatomical range. Subsequently, the binocular visual system is established and begins functioning. As the direct effects of botulinum toxin gradually dissipate, the binocular system starts receiving feedback from disparities in motor alignment. This reboot of the binocular visual system sustains motor fusion and maintains alignment (7).
Additionally, if the rectus muscles, which are in a phase of maturation during infancy, are not disturbed by invasive surgical corrections, infants around the age of 6.5 months respond best to this mechanism (8) because contracture in the medial rectus muscles increases over time (9) and surgical correction disrupts the structure. This approach could provide more accurate surgical correction over time and prevent patients from being affected by monofixation syndrome, latent nystagmus, and DVD.
In contrast to the absence of latent nystagmus and DVD, IOHF developed in all the patients. The highest IOHF reports in the literature are by Hiles et al. and Wilson and Parks (10, 11). Both reports could detect the range of time but could not explain its main cause. Wilson says that IOHF is a true mystery in strabismus (11). Hiles et al. reported that the incidence of IOHF was 78% in their study and noted that the greatest occurrence was during years 3 and 7 (10). Wilson and Parks reported that the incidence of IOHF was 71%, and IOHF was most commonly detected in individuals aged 1 to 3 years (11). Lee et al. also reported that the median age at the development of IOHF was 3 years (12). The time of occurrence of IOHF in this series is consistent with others. However, as a different finding, patients with better visual acuity displayed the development of IOHF at a later stage, suggesting an inverse relationship between the age of onset of IOHF and the observed visual acuity. Although any explanation about the cause of IOHF development will be solely a comment, the author’s perspective is that since all the reported literature about the time of the occurrence of IOHF is coherent, it raises a thought. In infantile esotropia, IOHF may not be an isolated disorder; instead, it may be a component of rectus discordance that affects the horizontal rectus muscle at one age and the inferior oblique muscle at another age.
The sensorial evolution of the patients in this series resulted in binocular vision or suppression of one eye. Monofixation syndrome and its consequences, such as latent nystagmus and DVD, did not occur in any patient. Although the author cannot prove that these patients did not have any deficits in sensory adaptation, the fact that all the patients eventually showed signs of visual maturation supports the idea that visual faults secondary to infantile esotropia are most likely not due to a congenital defect. Rather, they are secondary adaptations to poor fusion and motor misalignment.
This series is the work of one surgeon. Some patients in this series missed their follow-up appointments at times; otherwise, they would never have been left without further intervention. Some parents missed follow-up appointments for more than three years; however, the surgeon was eventually able to reach them and bring them back under control. In this respect, this study consists of long-term findings of a single botulinum injection for infantile esotropia, similar to a consequential fate report. Some patients most likely missed adequate vision therapy and developed suppression in one eye. On the other hand, if they had not missed adequate vision therapy, the results of a single botulinum toxin injection could have been better. In addition, the absence of control groups, including patients with esotropia who were injected after two years of age or those treated with standard muscle surgery, is the main limitation of this study.