BLOG: Is it amblyopia or keratoconus?
Click Here to Manage Email Alerts
When a young patient presents with atypical refractive findings and an inability to see 20/20 in one eye, that eye is often labeled “amblyopic.”
Amblyopia occurs when something happens during the first 8 years of life that prevents development of normal vision. It may be due to strabismus, refractive error or deprivation of sight from something like cataract or severe ptosis. Regardless of the cause, if vision is limited during that critical 8-year visual development period, it will always be limited.
Just knowing that the patient in your chair isn’t seeing 20/20 is not enough information to diagnose amblyopia. It is important to understand whether some other underlying condition, such as keratoconus, could be affecting the vision.
Most people are pretty symmetrical, with a similar refraction in both eyes. Significant anisometropia, or a difference of at least 3.00 D between the two eyes, is a red flag because keratoconus often presents asymmetrically, even though it is a bilateral disease. High cylinder in one or both eyes also increases the risk for keratoconus and warrants further investigation. But ferreting out the difference between amblyopia and keratoconus in the primary care setting can be a little challenging.
Challenges in pediatric population
Let’s say a 6- or 7-year-old child fails a vision screening at school and upon presentation at the office, one eye has significantly worse vision. You first have the challenge of refracting a pediatric patient. Not everybody enjoys working with this age group, and it can be hard to tell if the child really can’t see or is just being uncooperative.
The next challenge is figuring out if this child, who is nearing the end of the visual development period, is amblyopic due to long-term anisometropia — or are they anisometropic because there is something structurally wrong with one eye, like keratoconus? I have recently had a rash of children diagnosed with keratoconus at age 9 years, so it is not impossible for children this young to already have signs of keratoconic progression.
Retinoscopy: An ‘underutilized’ tool
You can face the same dilemma with an anisometropic 12-year-old patient who has never worn glasses, or an older teen or young adult who claims they “never saw well” out of one eye. In all of these cases, I strongly recommend performing retinoscopy, an underutilized tool that all optometrists should be familiar with.
Retinoscopy is actually quite a sensitive and reliable test for detecting keratoconus (Al-Mahrouqi H, et al.). Here are some clues on retinoscopy that point to keratoconus and should prompt further topography/tomography imaging or a referral to a cornea specialist:
- Retinoscopy reflex is not clear or crisply in focus
- Asymmetry in the reflex between the two eyes
- An “oil droplet” appearance in the center of the reflex
- The axis won’t line up with the reflex
There are several reasons to discern whether a suspected amblyope might have keratoconus. The first and most obvious is that if the patient has progressive keratoconus, you want to be able to refer them for an iLink corneal cross-linking consultation as early as possible in the course of the disease. Second, a keratoconus diagnosis could affect other planned treatments. I recently saw a young patient whose parents wanted a second opinion on proposed myopia control therapy. She actually had keratoconus, and one clue was significant asymmetry between the two eyes.
Finally, the right diagnosis tells us more about the patient’s visual potential. If that anisometropic 12-year-old patient is refractively an amblyope, my expectation when prescribing vision correction is that he won’t be able to see 20/20 because he never developed the ability to see 20/20. But a 12-year-old patient with early-stage keratoconus is a different story: He should be able to see 20/20 with appropriate specialty lenses, such as gas permeable or scleral lenses.
When in doubt, try retinoscopy, look at the topography if available or refer to a cornea specialist.
Reference:
For more information:
Christina Twardowski, OD, FAAO, is a pediatric optometrist and director of the pediatric optometry residency program at Children’s Mercy Hospital in Kansas City, Missouri. She can be reached at ctwardowski@cmh.edu.
Collapse