A Brief Overview of Keratoconus and its Topographical Findings
Title: A Brief Overview of Keratoconus and its Topographical Findings
Author: Zachary Mortensen, MS4, MBA
Photographer: James Gilman, CRA, FOPS
Date: August 24, 2018
Keywords/Main Subjects: keratoconus, cornea, corneal ectasia, corneal topography, collagen cross-linking
Summary of the Case: Progressive keratoconus in a young patient that is marked by progressive astigmatism, thinning and steepening of the cornea. The patient is monitored with corneal topography. He is an excellent candidate for corneal collagen cross-linking.
A 14-year-old boy with seasonal allergic rhinitis presents with a four-year history of keratoconus in both eyes that continues to progress. He has asymmetric astigmatism and has used prescription glasses in the past, but he now uses rigid gas permeable contact lenses. He has some optic nerve atrophy in the left eye due to a sledding accident trauma seven months ago that is now likely stable. He has no known family history of keratoconus or other eye diseases. He uses preservative free artificial tears as needed for eye dryness and oral antihistamines as needed for allergies.
Upon presentation to our clinic, his best corrected visual acuity with gas permeable contacts was 20/30-2 and 20/60-1 in the right and left eyes respectively. Slit Lamp examination of the anterior segment examination reveals the following image (Figure 1):
Central thinning, Vogt’s striae, and iron rings were appreciated on corneal examination in both eyes, and an apical scar seen in the left eye. The rest of the exam was unremarkable besides temporal sloping and some pallor of the left optic disc, likely due to the history of trauma.
Atlas Corneal Topography
Corneal topography is the gold standard for screening patients for keratoconus. Early screening for keratoconus is helpful because patients often look normal on slit lamp examination. It is also important for monitoring progression.1 Below is a Zeiss Atlas report (Figure 2) of the patient that has both an axial curvature map and a “Rings Image” which is a Placido disc-based topography. The warmer (redder) areas mark the areas of greater steepening.
Calculating an inferior/superior (I-S) value can also be helpful when looking for keratoconus. The ratio of the average power differences between the inferior hemisphere and superior hemisphere on the cornea is the I-S value. A positive value indicates that the inferior cornea is steeper. An I-S value higher than 1.8 has been used by some as the cut-off point for clinical keratoconus.3 If the I-S value is calculated between 1.4 to 1.8, keratoconus can be suspected.3
Scheimpflug tomography (Pentacam)
The patient’s first Scheimpflug tomographic images (Oculus Pentacam) were taken at age 14 (Figure 3). The Pentacam shows several elevation maps. One of the significant advantages of the Pentacam is in its ability to show the posterior elevation changes.4 The elevation maps show an anterior and posterior elevation of the cornea relative to the best fit sphere (BFS). On average, normal anterior elevation change values are between 1 and 2μm, while keratoconic anterior elevation change values are can be 20 μm or greater.4 On average, normal posterior elevation change values are between 2 and 3 μm, while keratoconic posterior elevation change values can be 39-45 μm or greater.4
This patient has keratoconus in both eyes with characteristic progression. The patient has continued to progress when compared to old Atlas and Pentacam images, though manifest refraction has not largely changed. This patient’s keratoconus will likely continue to progress through pubescence and young adulthood.
This patient is encouraged to avoid eye rubbing, which is an associated risk factor.5 It is important to help patients manage anything that can cause them to continue rubbing their eyes, such as prescribing steroids for those with atopic diseases.
When the patient was first seen at 10 years of age, he was managed by correcting visual acuity with spectacles. As he aged, the ectasia progressed, so he then started using rigid gas-permeable contact lenses.
There are also surgical management options that have been discussed with the patient. Intrastromal corneal ring segments are plastic inserts that are implanted into the cornea to flatten it. This can help with the visual acuity but does not stop progression.1 Corneal transplant (keratoplasty) is often used after contact lenses are no longer helpful.1 After discussion, we decided to delay keratoplasty until college-age years in an effort to achieve his best outcome since a higher rate of graft failure has been noted in pediatric penetrating keratoplasties.6
Collagen cross-linking is an intervention approved by the FDA in 2016 that slows the progression of keratoconus by strengthening bonds in the cornea. The procedure involves applying riboflavin (Vitamin B2) drops, then exposing it to ultraviolet light, and a photosensitizer. As it is relatively new in the United States, this procedure may be difficult for patients to acquire health insurance coverage. This patient is a good candidate for collagen cross-linking, so we have worked with him and his insurance company so that he can receive treatment.
Keratoconus, the most common ectatic disease of the cornea, is characterized by progressive central or paracentral thinning and steepening of the cornea such that the cornea takes on the shape of a “cone” (Figure 3). Early-stage keratoconus may look normal on slit lamp examination. Because of this, topography has become the gold standard for screening patients for keratoconus and other corneal ectasias. Topography and tomography are also useful for monitoring disease progression. Regular monitoring can permit early treatments such as corneal collagen cross-linking or corneal transplantation. While each patient should be evaluated individually, collagen cross-linking may be chosen in young patients with progressive keratoconus.
- Wayman, L. L., Trobe, J., Wilterdink, J. L., (2018). Keratoconus. UpToDate. Waltham, MA: UpToDate Inc. http://www.uptodate.com (Accessed on August 23, 2018)
- Anderson, D. Understanding Corneal Topography (unknown date). Paraoptometric Resource Center. Retrieved from https://www.aoa.org/Documents/optometric-staff/Articles/Understanding-Corneal-Topography.pdf
- Cavas-Martínez, F., De la Cruz Sánchez, E., Martínez, J. N., Cañavate, F. F., & Fernández-Pacheco, D. G. (2016). Corneal topography in keratoconus: state of the art. Eye and Vision, 3(1), 5.
- Belin, M.W., Khachikian, S. S., Holladay, J. T., Tehrani, M. New Advances and Technology with Pentacam (2008). Highlights of Ophthalmology. Retrieved from https://www.oculus.de/uploads/media/oculus_low_res.pdf
- Sugar, J., & Macsai, M. S. (2012). What causes keratoconus?. Cornea, 31(6), 716-719.
- Bernfeld, E., Epley, K. D., Woodward, M. A. (2017). Pediatric penetrating keratoplasty. EyeWiki. Retrieved from http://eyewiki.aao.org/Pediatric_penetrating_keratoplasty
Faculty Approval by: Mark Mifflin, MD; Griffin Jardine, MD
Copyright statement: Copyright Author Name, ©2018. For further information regarding the rights to this collection, please visit: http://morancore.utah.edu/terms-of-use/