Amblyopia (lazy eye) is a condition where defects in neural connectivity between the brain and the eye of a developing child can cause steady degradation of visual acuity in one or both eyes. The eyes may also drift out of alignment. Amblyopia carries a small risk of getting misdiagnosed. In such cases, typical treatment includes using corrective eyewear, occlusion therapy (eye patch), and surgery. This is successful in about 80% of the children with amblyopia. If the visual acuity in the affected eye(s) does not improve, or improves partly and then stops, a co-existing disease may be the underlying cause of vision impairment. If the underlying etiology is not identified and treated in time, it may be too late to save the child’s eye. But what are some hidden pathologies that could co-exist with amblyopia?
Dr. Virender Sachdeva, Head of LVPEI’s GMR Varalakshmi Campus, Visakhapatnam, and a pediatric ophthalmologist, explores this question in his new research paper. The paper describes various alternate etiologies and their prevalence in patients with amblyopia whose visual acuity did not improve after treatment. This discussion is about that paper and its topic.
What are your areas of medical practice and research interests?
I specialize in pediatric ophthalmology, strabismus (squint) in children and in adults, amblyopia, and neuro-ophthalmology; all diseases that involve the brain-eye connection. Pediatric ophthalmology is a challenging area within ophthalmology because we are dealing with children and their sensitive physiology. But I have felt a calling to meet that challenge since my days as a post-graduate fellow at LVPEI.
As a pediatric ophthalmologist, it is essential to understand and know how to treat amblyopia, because it is one of the more common ocular conditions in children. As I treated more amblyopia cases, I noticed that the visual acuity in some patients did not improve. In those cases, I began to try newer modalities. That is how I became so engaged with research in amblyopia.
What is amblyopia and why does it happen?
Amblyopia, commonly known as lazy eye, is a condition where, even in the absence of any ocular pathology, the difference in best corrected visual acuity (BCVA)—visual acuity with corrective spectacles or contact lenses—between the two eyes is significantly uneven (difference of two or more lines on a Snellen chart), or if the BCVA of both eyes is less than 20/40 on the visual acuity chart.
Amblyopia is a common eye condition among children. It can happen due to several reasons that prevent the maturation of the visual pathway connecting an eye to the brain during early childhood. Amblyopia can happen due to uncorrected refractive error, uncorrected squint, or a difference in the refractive error between both eyes (anisometropia). A rarer type of lazy eye called deprivational amblyopia can happen if light cannot enter the eyes properly, such as in patients with severely drooping eyelids (ptosis) or those with pediatric cataracts.
How did this project begin? What were some of the questions that led to it?
Treatment for amblyopia, such as corrective spectacles, eye drops, an eye patch on the healthy eye, or therapeutic video games, should work in 80-90% of patients if the child is compliant. Yet, we had amblyopia cases at LVPEI where the child’s BCVA was not improving despite treatment compliance.
We realized that there may be co-existing pathologies that is the underlying cause for the lack of improvement. This phenomenon needed to be documented, published, and shared. Over time, we pooled similar cases at LVPEI so that we had enough patients to analyze these alternate etiologies.
What are some of these alternate etiologies that may get overlooked in some amblyopia patients? What makes them so hard to detect?
Optic neuropathy, a disease that affects the optic nerve, can be one of the causes. Mild optic neuropathy is difficult to diagnose, especially in children as they might be uncooperative and give us little time to focus on their eyes. That makes it difficult to spot the presence of an optic disc pallor, a small white spot that is a sign of optic neuropathy.
Another such pathology could be a mild maculopathy–a disease affecting the macula, a photoreceptor-rich zone in the central retina. One such maculopathy is called occult macular dystrophy (OMD). Patients with OMD have a normal looking retina, but they also have poor visual acuity. Such subtle abnormalities in the retina can only be detected using high-resolution optical coherence tomography (OCT). Most doctors will not opt for such a thorough and expensive examination if all they suspect is amblyopia.
These two were the most common co-existing pathologies in our paper. A few patients had retinoschisis, a condition where the retina peels away into multiple layers. Again, an OCT is required to diagnose retinoschisis. We also encountered some patients with keratoconus, a disease that causes the cornea to bulge outward.
What are some diagnostic tools that can be used to detect alternate etiologies in amblyopia?
The ideal diagnostic tool will depend on the suspected disease. OCT is the most valuable tool, as it can be used to detect both optic neuropathy and maculopathy. Changes in the visual field can be detected using perimetry which can help us detect optic neuropathy. The patient is given a light stimulus, and the patient is asked to react to it. That way we can chart out their peripheral vision. Defects in peripheral vision can also be due to optic neuropathy. Finally, color vision can be tested to see if there are any problems with the optic nerve or macula.
However, the challenge is access to all these diagnostic tools, especially OCT. Most clinics, especially in rural areas, will not have such advanced machinery. Thus, doctors need to be vigilant and refer them to major urban eye hospitals if they suspect that a child has more than just amblyopia.
Do patients with co-existing pathologies have amblyopia, or are these alternate etiologies making the outward symptoms look like amblyopia?
It can be either scenario. Usually, such patients have amblyopia and another underlying condition that is preventing their visual acuity from improving. For example, amblyopic patients with anisometropia are likely to have anisometropic amblyopia along with another etiology for their poor visual acuity, such as optic neuropathy.
In such patients, treatment of amblyopia partially improves their visual acuity. But the improvement in visual acuity is not sufficient. For instance, visual acuity improves from 20/100 to 20/60 and then stops. This means the patient’s amblyopia is corrected, but something else does not allow visual acuity to improve to the expected level.
I have also seen cases where the patient’s eye with a higher refractive error has better vision than the eye with lower refractive error. An unusual scenario that happens because the eye with the lower refractive error has a co-existing pathology, such as optic neuritis, rather than amblyopia.
How can the findings of this study be used to improve diagnosis and treatment of lazy eye?
Doctors need to bear in mind that one out of twenty children with amblyopia may have a co-existing pathology. That is why a careful eye examination, especially that of the retina, is important for patients with amblyopia. Doctors also need to ask the patient’s parents if the child has a history of rhinitis, parental consanguinity, difficulty seeing in bright light, or poor night vision. A slit lamp examination to check for corneal defects and gauging the color vision of the patients are other crucial steps a doctor can take during the diagnosis of an amblyopic child.
Once the patient has begun treatment for amblyopia, if their vision has not improved after 12-24 weeks, it is likely that there is a co-existing pathology. In that case, the doctor needs to recommend a thorough examination, including an OCT test. So, following up with the patient is critically important.
Doctors also need to set aside any bias towards amblyopia based on clear symptoms like squint or sub-normal vision in one eye in absence of any other ocular pathology. We need to objectively evaluate and keep our minds open for alternate possibilities to avoid over diagnosis.
What is the next step for this project? What other projects are you working on?
We are planning on a prospective study to assess if we can diagnose amblyopic patients with co-existing pathologies at an early stage, based on the findings of this paper.
Secondly, me and my team want to inform ophthalmologists about the findings of this study and see if their practice patterns change and if they manage to diagnose more cases of amblyopia with alternate etiologies.
Finally, we are also looking to study some novel therapies for amblyopia.
Dr. Virender Sachdeva spoke to Sayantan Mitra, Science Writer, LVPEI. Read more about his research here.
Citation
Sachdeva, V., Bhattacharya, B., Ganatra, S., & Kekunnaya, R. (2024). Subnormal visual acuity after compliant amblyopia therapy: residual/refractory amblyopia or co-existing pathology? - a retrospective analysis. Strabismus, 1–12. Advance online publication. https://doi.org/10.1080/09273972.2023.2294997
