Most patients have never heard of a condition called keratoconus; some may hear it for the first time when they go for a LASIK surgery evaluation.
While it is a relatively rare condition, it can have a significant impact on the quality of life of those diagnosed. Though we are still not sure of the exact etiology, there have been many advancements in treating and managing the disease.
What is keratoconus?
Keratoconus means cone-shaped cornea. It’s a bilateral and asymmetric disease that causes progressive thinning and steeping of the cornea.
The disease results in irregular astigmatism and decreased vision. Keratoconus begins when a patient is in their twenties or thirties. The prevalence is estimated to affect between 0.2 and 4,790 per 100,000 persons and the incidence is 25 cases per 100,000 persons/year.
The patient may present with progressive changes in the quality of their vision. Changes are present in all the corneal layers. With advanced progression, thinning of the corneal stroma, rupture of the anterior limiting membrane of the cornea, and thinning of the central/paracentral cornea can be observed.
When a doctor looks in the microscope, they may see Fleischer’s ring, a circle of iron deposition in the epithelium, and/or Vogt’s striae, fine vertical lines produced by compression of Descemet’s membrane. With significant progression, Munson’s sign, a V-shaped deformation of the lower lid, becomes noticeable as the patient looks down.
Though less common, corneal hydrops, breaks in the corneal membrane, can occur causing corneal swelling, vision loss, and pain.
What is the cause of keratoconus?
Eye inflammation is thought to play a role in the development of the disease. Environmental, genetic, or a combination of factors may cause keratoconus. The exact cause is unknown and varies between individuals. Detecting keratoconus can be difficult and is most often diagnosed by corneal topography, which is a mapping of the cornea.
Environmental factors that may lead to the development of keratoconus include eye rubbing, the development of allergic diseases such as allergic rhinitis, asthma, atopic dermatitis, sun exposure, and geography. Refractive surgeries like LASIK may also cause patients to develop keratoconus if too much corneal tissue is removed for the procedure.
Genetics has always been considered a factor in the development of keratoconus. Patients with genetic syndromes like Down’s and Ehler-Danlos syndrome, those of Middle Eastern and Asian ethnicity, twins, and those with a first-degree relative who has the disease are more at risk for developing keratoconus themselves. In fact, someone who has a relative with keratoconus has a 15 to 67 times greater risk of developing keratoconus than an individual with no family history of the disease. Severe genes have been implicated in disease development.
What are the risk factors for the development of keratoconus?
Keratoconus is a multifactorial disease, but a family history of keratoconus, rubbing your eyes, eczema, asthma, and allergy are major risk factors for developing keratoconus.
What are the current treatments for keratoconus?
The treatment for keratoconus depends on the severity of the disease and its progression. Mild cases are typically treated with spectacles, moderate cases with contact lenses, and if cases cannot be managed with scleral contact lenses, patients may require corneal surgery.
Contact lenses can be hard or soft lenses. A patient may wear one or the other depending upon the stage of the keratoconus. Hard lenses often provide better lens stability and vision than soft lenses.
The optics of a hard contact lens are superior when compared to a soft lens. Another option is a hybrid lens, a hard lens on a soft lens skirt. Hybrids provide the exceptional vision of a hard lens combined with the comfort of a soft lens.
Soft contact lenses
Usually, keratoconus management will begin with soft contact lenses when the vision becomes too distorted with glasses. Soft lenses provide adequate vision for a period of time until the disease progresses, and the amount of astigmatism becomes either too high or unstable for a soft lens.
Hard contact lenses
Historically, patients with keratoconus were fit in a hard lens called a rigid gas permeable lens or RGP lens; however, today, scleral lenses have become the preferred option by most doctors. Many insurances will cover these types of lenses for patients with keratoconus if their vision can be improved by a few lines on the chart.
Rigid gas permeable
Before the introduction of scleral lenses, patients with keratoconus were fit in a rigid gas-permeable lens. The lens rests on the cornea, without compressing the corneal cone, and provides enhanced visual clarity. Comprised of many nerves, the cornea is extremely sensitive, and RGPs can be uncomfortable and difficult for a patient to wear.
Scleral lenses are used by most eye doctors to manage keratoconus. Scleral lenses bridge over the top of the cornea and sit on the cushy part of the eye called the sclera. They offer optimal vision like a RGP lens, but significantly improved comfort.
Most patients are unable to feel them in the eye. The lenses are filled with a non-preservative solution to bathe the eye in fluid throughout the day making them a great option for patients with dry eye. Study data has demonstrated scleral lenses are safe and effective for patients with keratoconus.
Surgery may be recommended to slow the progression of keratoconus or if scleral contact lenses are no longer able to provide sufficient vision for patients.
Over the last two decades, corneal crosslinking (CXL) has been the sole option to stop the progression of keratoconus. CXL stiffens the cornea using a combination of ultraviolet-A light, oxygen, and a chromophore (vitamin B2, riboflavin).
Epi-off CXL is a procedure where the epithelium is removed and results in pain as the epithelium regrows, hazy vision, an increased risk of infection, and longer recovery time. Currently, epi-off CXL is the only procedure that is FDA-approved, but epi-on is expected to be approved in 2023.
A corneal transplant is considered when all other therapies have failed. A corneal transplant can be complete or partial.
Penetrating keratoplasty (PK) was the surgery of choice for keratoconus for over seven decades. However, the selective removal of tissue is now preferred by surgeons. Anterior lamellar keratoplasty (ALK) is now the preferred treatment of choice because of reduced graft rejection, fewer long-term complications, and better graft survival.
Although we still have a lot to learn about keratoconus, we have more advanced management and treatment options than years prior. With FDA approval for epi-on CXL expected this year, patients with keratoconus will have an easier and less painful way to stabilize the disease.
If you are a patient with keratoconus and unhappy with your current contact lenses, be sure to discuss scleral lenses with your eye doctor.