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Could it be KC (KERATOCONUS)?

KC File #2: Autorefractor Clues That Were Ignored

Susan “Super Sleuth” Gromacki, OD, MS, FAAO, FSLS, First Sight Vision Care

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A young woman who had relocated to my area for her first job after college was referred to me by the hometown optometrist who had seen her regularly since childhood. She was a high myope, wearing a spectacle prescription of -4.75 sphere OD and -9.25 -1.25 x003 OS.

The optometrist’s records showed a slow but steady decline in best-corrected visual acuity (BCVA). This went unremarked until 2022, when the patient’s OS could not be corrected even to 20/30. At that point, she was referred to a retina specialist, who ruled out a suspected epiretinal membrane and reported other findings all within normal limits.

In retrospect, there were three clues that could have alerted the practitioner to the possibility of keratoconus. First, when a young person can’t be corrected to 20/20, the cornea is a more likely culprit than the retina. The patient’s vision in the left eye hadn’t been a sharp 20/20 for several years. Secondly, an increase of 0.5 D of astigmatism between annual visits is a significant red flag. And finally, another clue came from the simplest diagnostic tool in the office-the autorefractor. The autorefraction in 2022 showed 2.75 D of astigmatism-a full diopter more than the spectacle prescription-and the quality score was only 8 out of 10. I would expect it to be 10/10 in a healthy young person.

A history of “lazy eye” as a child may be why the declining BCVA in her left eye was not taken very seriously at first. This was noted in her chart, although there was no evidence of binocular vision testing, no mention of exophoria or esophoria, and she didn’t have the typical hyperopic refraction we usually see in a lazy eye. Sometimes practitioners label a worse-seeing eye as a “lazy eye.” While this certainly may be the case, that label threw off her long-time optometrist. The clues could have led the optometrist to a KC diagnosis.

In 2023, when I first saw this patient, corneal topography showed 2.80 D of astigmatism OS with a classic pattern of inferior steepening that is pathognomonic for progressive KC. She was treated with iLink® corneal cross-linking in the left eye and we continue to follow her right eye closely because KC is a bilateral, asymmetric, disease. Recently the patient shared with me that her uncle has KC, something she didn’t know when I asked her initially.

By following the KC clues that are hiding in plain sight, you can help patients like this one avoid years of declining vision-and sleuth out the right specialists to treat the underlying progressive condition that is stealing her sight. Visit iDetectives.com to learn more.

Changing refractive astigmatism and vision:

YEARDCBCVA
20141.0020/20
20151.2520/20
20171.2520/20-1
20181.2520/20
20191.2520/25
20211.2520/20-2
20221.7520/30-1
20232.2520/30

Could it be KC (KERATOCONUS)?

KC File #1: The Patient
Who Corrects to 20/20

Mitch “Private Eye” Ibach OD, FAAO, Vance Thompson Vision

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A 29-year-old patient came to our office for a LASIK consult because she was unhappy with fluctuating vision in her contact lenses. The patient had ocular allergies but had no other ocular diagnoses.

Her entering glasses prescription was a modest one and we were able to refract her to 20/20. However, the refraction in the right eye was our first clue that something was not quite right.

Not only is >2.00 D of refractive cylinder a warning signal for keratoconus, but the oblique axis is also unusual. About 90% of young corneas have with-the-rule (WTR) astigmatism.1 The change in myopic spherical equivalent (SE) from baseline (the glasses prescription) was not what we would expect to see in an adult patient, either.

Refraction and exam findings

Right Eye BCVA Left Eye BCVA
Lensometry -0.50 -1.50 x31 20/30 -1.50 -0.50 x172 20/20-
Refraction at Phoropter -0.75 -2.25 x34 20/20 -1.75 -0.75 x160 20/20+
Pachymetry 478 μm 483 μm
Autokeratometry 45.5 / 47.50 x 112 44.9 / 46.75 x 80

scroll to see the full table

Autokeratometry from her referring optometrist was on the steeper side of normal, and our pachymetry measurements showed that both eyes had borderline thin corneas. Upon further questioning, the patient recalled that her sister had keratoconus. Having a first-degree relative (a parent, sibling, or child) with keratoconus increases the risk of developing the disease by 15- to 67-fold.2

At this point, we have some risk factors, but not a clear diagnosis. A closer
look at topography, tomography, and anterior segment OCT epithelial
mapping provided further information to make a decisive diagnosis of
progressive keratoconus in the right eye.

This case illustrates that patients who see 20/20 at the phoropter can still
have keratoconus. At 29, our patient was at an age where there is greater
risk of progression,3 and her ocular allergies and family history elevate that
risk. She was fortunate to be diagnosed and treated early in the course of
her disease, while she was still correctible to 20/20.

Simply by following the KC clues that are hiding in plain sight, you can help
patients like this one preserve their vision by referring them to a corneal
specialist. If further testing confirms the patient has progressive KC, iLink®
cross-linking could slow or halt its progression.

REFERENCES

  1. Kojima T, et al. Am J Ophthalmol 2020;215:127-34,
  2. Wang Y, et al. Am J Med Genet 2000;93(5):403-9.
  3. Ferdi AC, et al. Ophthalmology 2019;126(7):935-45.

Indications

Photrexa® Viscous (riboflavin 5’-phosphate in 20% dextran ophthalmic solution) and Photrexa® (riboflavin 5’-phosphate ophthalmic solution) are indicated for use with the KXL System in corneal collagen cross-linking for the treatment of progressive keratoconus and corneal ectasia following refractive surgery.*1

Important Safety Information

Corneal collagen cross-linking should not be performed on pregnant women.

Ulcerative keratitis can occur. Patients should be monitored for resolution of epithelial defects. The most common ocular adverse reaction was corneal opacity (haze). Other ocular side effects include punctate keratitis, corneal striae, dry eye, corneal epithelium defect, eye pain, light sensitivity, reduced visual acuity, and blurred vision.

These are not all the side effects of the corneal collagen cross-linking treatment. For more information, click View Prescribing Information button below to obtain the FDA-approved product labeling.

You are encouraged to report all side effects to the FDA. Visit www.fda.gov/medwatch, or call 1-800-FDA-1088.

*Photrexa® Viscous and Photrexa® are manufactured for Avedro. The KXL® System is manufactured by Avedro. Avedro is a wholly owned subsidiary of Glaukos Corporation.

Reference

1. Photrexa Prescribing Information. Burlington, MA: Avedro, a Glaukos company 2022.

View Prescribing Information