Do you know the difference between shrimp and prawns? Or Great Britain and the United Kingdom? What about being able to tell a mule and a donkey apart when you’re not afflicted with double vision?
Well, when it comes to shrimp and prawns, we can tell you that while they’re both decapods with exoskeletons, they are different animals with other forms of gills, claws, pincers and body structure that differ. Meanwhile, Great Britain refers to the island which includes England, Scotland and Wales, and the United Kingdom refers to the unified monarchies of England and Scotland (and we’re leaving Northern Ireland out here because we don’t need that kind of drama). As for our furry horse-like friends, a mule is a hybrid, sterile animal, whereas a donkey comes from its own species, but both bless with smart a stubborn brain.
If you’re following, our point is that there are a lot of things that are confused with others — whether they be food, political entities or animals. The same applies in ophthalmology too, especially among the lay community, which no doubt has led to considerable exasperation among ophthalmologists over the years. One of the best examples of this is the difference between strabismus and amblyopia, two of the most commonly encountered medical conditions in the field.
Squint Eye is so 1990s
We recently covered the link between strabismus and retinal detachment surgery — and the feedback we received got us thinking about how often strabismus and amblyopia are confused as vision problems. Strabismus occurs when one’s eyes are not lined up properly and they point in a different direction, leading to the commonly used and cruel pejorative “squint eyes.” It is most commonly encountered in children and it is usually treatable by either wearing special glasses or surgery in more severe cases.1
Amblyopia on the other hand, is often described as “lazy eye.” Unlike strabismus — which does not usually have a significant impact on visual acuity — amblyopia can seriously affect vision. Amblyopia usually begins as strabismus, but if the eye does not achieve normal visual acuity, cannot be fixed with glasses or contact lenses, and if the angle of the strabismus or eye turn is particularly large (and especially if it’s a case of constant strabismus), the brain forgets to use the affected eye to see, relying on the stronger eye instead. This causes the misaligned eye to become extremely weak, with all visual signals ignored, leading to atrophy and the potential for loss of binocular vision.2
The confusion about the two conditions being the same primarily stems from their similar symptoms, causes vision problems, and that amblyopia often develops from strabismus. Think champagne and sparkling wine: While all champagne is sparkling wine, the reverse is not true and that analogy applies here. The key to successfully treating both conditions, and especially the case with amblyopia, is early diagnosis and aggressive intervention to arrest the development of ocular atrophy.
So we’ve established that strabismus and amblyopia are two similar yet different eye conditions, with the latter sometimes emerging from the former, but how common are they? What are the prevalence rates of strabismus and amblyopia — and what are the various subtypes? This was the question considered by a group of researchers from China, primarily based in the historical city of Nanjing.
A Solo Study on the Han
Prevalence of Amblyopia and Strabismus in Hani School Children in Rural Southwest China: A Cross-Sectional Study3 offered some fascinating insight into the questions posed above. The researchers decided to focus on Han Chinese children, who are part of the vastly dominant ethnic group in that country, with relatively high rates of poor vision and vision problems. They examined grade 1 and grade 7 children in Mojiang Hani Autonomous County, located in southwest China. Participants were invited to attend comprehensive eye examinations performed by experienced ophthalmologists and optometrists, including visual acuity, ocular alignment and movements, cycloplegic autorefraction, and anterior segment and fundus examinations.
A total of 1,656 young children from grade 1 and another 1,393 students from grade 7 were examined, with amblyopia reported in 25 students (0.82%). Of this number, 17 had unilateral amblyopia and 8 had bilateral amblyopia (including 16 anisometropic, 8 binocular refractive and 1 strabismic). Strabismus was found in 59 students (1.93%). Of this number 47 had intermittent exotropia type strabismus, 6 had constant exotropia, 5 had constant esotropia, and 1 was affected by unilateral superior oblique palsy.
The relatively low rates of diagnosis surprised the Nanjing researchers, who concluded that “the prevalence of amblyopia and strabismus in Chinese Hani school children are both lower than that previously reported for Chinese Han children in China.” They stated that refractive error is the major cause for amblyopia and intermittent exotropia for strabismus.
So remember, it’s like sparkling wine and champagne … and to intervene early for the best outcomes. The effect of both amblyopia and strabismus on the eye muscles (and resulting eye movement) can be considerable. Early intervention and treatment is crucial to protecting the weaker eye and minimizing vision loss, so make sure you check.
- Strabismus in Children. The American Academy of Ophthalmology. Available at https://www.aao.org/eye-health/diseases/strabismus-in-children. Accessed on Friday, Jul 13, 2021.
- Crossed Eyes or Lazy Eyes? The Difference Between Strabismus and Amblyopia. Optimax Eye Surgery. Available at https://www.optimax.co.uk/blog/difference-between-strabismus-amblyopia/. Accessed on Friday, Jul 13, 2021.
- Zhu H, Pan C, Sun Q et al. Prevalence of Amblyopia and Strabismus in Hani School Children in Rural Southwest China: A Cross-Sectional Study. BMJ Open. 2019 Feb 19;9(2):e025441.