Diagnosing Keratoconus Without a Topographer
You can achieve it by following these five steps.
SUSAN J. GROMACKI, O.D., M.S., F.A.A.O., SILVER SPRING, MD. AND VALERIE SELIGSON, O.D., F.A.A.O., COLUMBIA, MD.
Imagine not being able to see clearly and, after having visited multiple eye doctors through several years, still not having a solution — or even a proper diagnosis. This is what life is like for undiagnosed keratoconus (KC) patients.
The condition, which affects 1 in 1,500 to 2,000 individuals, is often underdiagnosed or misdiagnosed as “normal” astigmatism, according to the National Keratoconus Foundation, negatively affecting these patients’ quality of life.
Some of these patients go through life with non-progressive keratoconus — still a burden if not identified — while in others the condition advances significantly, prompting the eventual correct diagnosis and, often, subsequent corneal transplantation. Advanced keratoconus does not discriminate.
As optometrists, we have an obligation to diagnose keratoconus as early as possible so these patients can achieve optimum vision through spectacles or contact lenses. Also, early diagnosis is in their best interest because corneal collagen crosslinking (CXL) (vitamin B2 drops with UV-A radiation used to increase the biomechanical and biochemical stability of the stromal collagen fibers to improve corneal rigidity) has been proven to arrest keratoconus progression and will soon be FDA-approved. Something else to consider: Corneal transplantation doesn’t guarantee a lifetime free from contact lens wear, and it doesn’t always last forever. If CXL can help delay or prevent corneal transplantation, it’s a procedure worth performing.
We, and other optometrists, utilize corneal topography to facilitate the keratoconus diagnosis. If, however, you don’t own topographer or a wavefront analyzer — both beneficial instruments — you can still diagnose the condition early and improve your patients’ quality of life.
Here, we explain how.
“Three-point-touch” fluorescein pattern with a GP lens on a keratoconic eye.
PHOTO COURTESY OF DONNA WICKER, O.D.
1 Ask about family history/eye-rubbing.
Research has shown a definite genetic predisposition to the condition. Question the patient whether they have a family history of keratoconus. Keep in mind that keratoconus is diagnosed most often between puberty and age 30 (but can also be diagnosed in older patients), according to Survey of Ophthalmology. Also, many hereditary conditions are related to keratoconus, says Contemporary Optometry. (See “Hereditary and Other Conditions Found in Keratoconus Patients,” page 50.)
Further, ask whether the patient rubs their eyes often. Although some debate exists regarding eye-rubbing’s contribution to the origin and progression of the condition, most keratoconus patients rub their eyes vigorously, reveals the British Journal of Ophthalmology. Some may not even realize they do it, until asked.
2 Listen for visual complaints.
Listen for complaints of blurred vision and/or distortion of images, which are common symptoms of keratoconus. Here are telling patient complaints:
▸ “I have never been able to see correctly out of my glasses.”
▸ “Lately, I haven’t been able to see the 20/20 row at my doctor’s office, even with my soft toric contact lenses on.”
▸ “My doctor has changed my soft toric lenses several times, and I still can’t see clearly.”
▸ “I have seen several eye doctors, and no one can get my vision clear.”
▸ “I see ghosted double or multiple images.”
▸ “I always have a headache in or around my eyes.”
Even just one of these statements should raise your suspicion for keratoconus.
3 Be aware of testing oddities.
The patient who has keratoconus may tell you they prefer to read the chart from right to left, based on our personal experiences. In addition, they may be able to read the letters, but state, “nothing is sharp.”
For example, if the patient achieves 20/50 visual acuity in either eye, they may report that even the 20/100 row is blurry. Also, they may achieve better acuity if a line or letter is isolated.
4 Look for refraction anomalies.
Regarding autorefraction, keratoconus patients frequently demonstrate a distortion of the mires while the device acquires the reading. In addition, the autorefractor may show either an error message or a low-confidence score. If it does give you a reading, it will likely reveal a high amount of astigmatism, possibly at an oblique axis.
Refraction itself is difficult in these patients. First, the autorefraction result may not be accurate due to the shape and histological composition of the cornea.
In addition, because KC patients’ vision is so poor, 0.25D changes in power during the refraction may not be enough for them to notice a difference.
We recommend using at least 0.50D variations in power when refracting. Then, your final refraction may be quite different from the patient’s current glasses or soft toric contact lens prescription.
Through time, keratoconus patients may demonstrate frequent changes in their spectacle prescription, with alterations in sphere, cylinder and/or axis.
Most keratoconus patients do not correct to 20/20 with a spectacle refraction.
5 Assess four more diagnostic tests.
To determine whether the patient has keratoconus, evaluate the results of four additional diagnostic tests:
1. Manual keratometry. This is quite diagnostic, in that it shows distorted mires in keratoconus patients and, in advanced cases, corneal steepening that often exceeds the upper limit of the instrument.
2. Retinoscopy. This will show a scissors reflex.
3. Direct ophthalmoscopy. This often reveals a circular dark red-brown shadow surrounded by the red fundus reflex typical of all patients.
4. Slit-lamp biomicroscopy. In keratoconus patients, this shows one or more of the following characteristics:
▸ Cone-shaped protrusion.
▸ Stromal thinning at the cone apex.
▸ Fleischer ring (epithelial iron ring at the base of the cone).
▸ Sub-epithelial fibrillary lines.
▸ Prominent corneal nerves.
▸ “Three-point-touch” fluorescein pattern with a standard GP lens.
▸ Vogt striae (vertical stress lines in the deep stroma or Descemet membrane).
▸ Scarring at the level of Bowman membrane or anterior stroma.
The latter is indicative of advancing keratoconus, as is a Munson sign: the bulging of the lower eyelid with down gaze. Not all keratoconus patients exhibit these signs, particularly early in the disease. The Collaborative Longitudinal Evaluation of Keratoconus study found 86% of its 1,209 subjects with a Fleischer ring, 65% with Vogt striae and 53% with corneal scarring, according to Contact Lens & Anterior Eye.
Providing an answer
Many undiagnosed keratoconus patients may seek care less frequently than routine patients because they think, “no one can help me.” By following the five outlined tips, you can intervene early and offer them the best vision with spectacles or specialty contact lenses so they do not suffer decreased productivity at work or school. Also, you can recommend procedures such as CXL. Ultimately, our actions make a positive impact on our patients’ quality of life. OM
Hereditary and Other Conditions Found in Keratoconus Patients
▸ Addison disease
▸ Atopic disease
▸ Blue sclera
▸ Down syndrome
▸ Ehlers-Danlos syndrome
▸ Marfan syndrome
▸ Osteogenesis imperfecta
Dr. Gromacki is a diplomate in the Cornea, Contact Lens, and Refractive Technologies section of the American Academy of Optometry. She lectures internationally on the topics of cornea and contact lenses. E-mail her at Sgromacki3@hotmail.com, or send comments to firstname.lastname@example.org.
Dr. Seligson practices at the Wilmer Eye Institute, where she has a particular interest in fitting complex contact lenses and performing consultations for LASIK patients.