When do you diagnose keratoconus?
Keratoconus is a naturally occurring weakening of the cornea, characterized by its progressive asymmetric thinning and steepening. Keratoconus typically begins in the teens or 20s, progresses over a decade, and results in significant visual dysfunction, reduced quality of life, and permanent changes in the patient’s lifestyle.
The majority of patients with keratoconus eventually end up in an optometrist’s office searching for correction for blurred vision. At the onset of the disease, blurry vision is often successfully corrected with spectacles. As the disease progresses, astigmatism increases, and patients are often fit with soft toric contact lenses. Over time, vision progressively worsens due to development of irregular astigmatism. As a result, the patient is often refit into a rigid or hybrid contact lens.
This is the pivot point when some patients receive the diagnosis of keratoconus. The patient has significant loss of best-corrected vision and can no longer wear spectacles for functional vision.
Now is when the optometrist should provide vision rehabilitation to the patient with keratoconus. The optometrist’s job is to maintain an acceptable contact lens fit that enables the patient to have functional vision for as many hours as possible. Meanwhile, the disease continues to worsen-the cornea keeps thinning and irregular astigmatism increases, which reduce the patient’s tolerance of the contact lenses. And the patient continues to lose vision.
While optometrists work to maintain the patient’s functional vision, our overarching goal is to put off surgical intervention for as long as possible. Ultimately, 20% of patients with keratoconus require a corneal transplant to restore visual function, typically due to corneal scarring and contact lens intolerance. When corneal transplantation is performed, we provide a better optical system for the patient. However, the patient still requires a lifetime of visual rehabilitation, typically with complex contact lens fitting. Although corneal transplantation has improved with lamellar and femtosecond technology, patients still face significant visual function with reduced quality of life.
It is important to remember that corneal transplantation does not treat the disease of keratoconus; it treats only the resultant irregular astigmatism. Throughout the disease process, the role of the optometrist is a visual rehabilitator. Early diagnosis of keratoconus has had no effect on the clinical treatment choices because our only goal has been to provide maximal vision function and try to avoid the need for corneal transplantation.
Changing KC treatment
The paradigm is about to change with the advent of the first treatment for keratoconus-collagen cross-linking (CXL). CXL uses a natural photosensitizer riboflavin (vitamin B2) combined with ultraviolet light to reinforce the structural weakness found in the corneal stromal in patients with keratoconus (see Figure 1).
While still under investigation in the United States, CXL has been performed for more than a decade outside the U.S. and has been well studied with more than 300 peer-reviewed studies. Following is a summary of what we know about CXL so far:
- 96% of eyes show topographic stability-no progression
- Average corneal flattening of 1.7D of max K
- Amount of flattening reduced in steep cornea
- No change in corneal clarity or index of refraction
- More effective on younger patients
- Reduced side effects, such as stromal haze, on cornea thicker than 400 mμ
- Improves best corrected visual acuity and uncorrected visual acuity by regularizing corneal shape
The most effective form of CXL may be the original Dresden protocol, which requires epithelial removal. Recent improvements in trans-epithelial (epi-on) CXL may provide similar effect with faster visual recovery, less pain, reduced risk of stromal haze with reduced risk of infection, and slow re-epithelialization. Regardless of the method, CXL stops the progression of keratoconus, working best on young, thick, and flat corneas. The earlier the detection and diagnosis of keratoconus, the more effective and safer the CXL treatment.
Outside the U.S. it is no longer acceptable to watch patients with keratoconus lose best corrected vision. As soon as keratoconus is detected-sometimes as young as 12 years old-CXL is recommended to prevent vision loss. Early detection of keratoconus using topography screening has become the norm, resulting in many countries almost eliminating the need for corneal transplantation due to advanced keratoconus.
It is important to remember that topography can detect keratoconus only once the disease has begun to thin and steepen the cornea. Also, all patients with keratoconus begin with normal corneal topography, gradually progressing from symmetric bowtie (regular astigmatism) to asymmetric inferior steep astigmatism with skewed (irregular astigmatism) radial axis (see Figure 2). Future advances in keratoconus detection will continue to improve early diagnosis. Both biomechanical analysis of the cornea and genetic testing promise to detect keratoconus well before topographic changes occur and vision is lost.
Next-generation improvements in CXL methodology-including selective CXL, topo-guided advanced surface ablation, and CXL combined with Intacs-ensure the future of keratoconus treatment will provide stricken patients with an improved prognosis for normal vision and quality of life.
So, when do you diagnose keratoconus?ODT
Figure 1: Collagen cross-linking (CXL) uses a natural photosensitizer, riboflavin (vitamin B2), combined with ultraviolet light to reinforce the structural weakness found in the corneal stromal in patients with keratoconus.
Figure 2. Topographic progression of keratoconus, top and bottom. All patients with keratoconus begin with normal corneal topography, gradually progressing from symmetric bowtie (regular astigmatism) to asymmetric inferior steep astigmatism with skewed (irregular astigmatism) radial axis. (Photos courtesy of William Tullo, OD.)
