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Keratoconus

Keratoconus

Overview

Keratoconus is a progressive, noninflammatory, bilateral or asymmetric ectatic corneal disease, characterized by stromal thinning and weakening that leads to corneal surface distortion.

The distorted cone shape of the cornea causes major changes in the refractive characteristics of the cornea (irregular astigmatism) that cannot be fully corrected with glasses. Progressing keratoconus necessitates frequent change of eyeglasses. Contact lenses may provide better vision correction and should be tried when eyeglasses are not satisfactory.

Symptoms

The following symptoms can point to keratoconus:

  • Blurred or distorted vision
  • Increased sensitivity to bright light
  • Diplopia or double vision
  • Halos around bright lights
  • Multiple unsatisfactory attempts to obtain optimum spectacle correction
  • Headaches due to eye strain

Causes

Although many theories have been proposed, there is no definitive cause of keratoconus. Possible causes include:

  • Genetics
  • A collagen deficiency
  • Overexposure to ultraviolet rays from the sun
  • Excessive eye-rubbing
  • Allergies
  • An injury to the eye
  • Diseases of the eye

Risk factors

These factors can increase your chances of developing keratoconus:

  • Family history of keratoconus
  • An atopic disorder
  • Vigorous eye rubbing
  • Lax eyelids
  • Certain connective tissue disorders
  • Down syndrome
  • Congenital disorders with poor vision

Diagnosis

After a thorough examination of the eyes, the doctor will measure cornea curvature to determine whether these symptoms are a result of keratoconus. Some of the tests that will be conducted may include:

  • Refraction (including retinoscopy)
  • Slit-lamp biomicroscopy
  • Corneal topography
  • Corneal tomography

Treatment

Treatment for keratoconus depends on the severity of the condition and how quickly it is progressing. The most common surgical options of keratoconus treatment include the following:

  • Collagen cross-linking (CXL)
  • Implantation of intrastromal corneal ring segments (ICRS)
  • Deep anterior lamellar keratoplasty (DALK)
  • Penetrating keratoplasty (PKP)

Ultraviolet corneal collagen cross-linking

Ultraviolet corneal collagen cross-linking is the only procedure that slows the progression of keratoconus. It is performed to increase the rigidity of the cornea.

Slowing, or possibly stabilizing, the progression of corneal ectasia is achieved by inducing additional cross-links within or between collagen fibers using ultraviolet and riboflavin. When exposed to ultraviolet A radiation, riboflavin produces oxygen free radicals that initiate the creation of new covalent bonds. These bridge the amino groups of collagen fibrils, increasing the rigidity of corneal tissue.

Collagen cross-linking is most effective in patients with progressive keratoconus who are aged 16-40 years and have a minimum corneal thickness of 400 microns, a maximum keratometry of < 60D, and no other known corneal diseases.

Current studies are showing good short-term results and some good long-term results 7-10 years postprocedure.

Intrastromal corneal ring segments

Intrastromal corneal rings are crescent-shaped plastic segments implanted into the corneal stroma to reduce corneal distortion.

Corneal inserts can restore a more normal corneal shape, slow progress of keratoconus and reduce the need for a cornea transplant. This surgery may also make it easier to fit and tolerate contact lenses. The corneal inserts can be removed, so the procedure can be considered a temporary measure.

Deep anterior lamellar keratoplasty

Deep anterior lamellar keratoplasty is a partial-thickness cornea transplant procedure which involves only the donor stroma, leaving the recipient’s own Descemet membrane and endothelium in place. Leaving the host endothelium intact significantly decreases the risk of endothelial rejection.

Currently, deep anterior lamellar keratoplasty represents around 20 percent of all corneal transplantations. Visual acuity results of deep anterior lamellar keratoplasty are similar if not slightly inferior to those of penetrating keratoplasty in patients who do not have deep central corneal scarring.

Penetrating keratoplasty

Penetrating keratoplasty is a full-cornea transplant. It is still the more commonly performed surgery used to treat keratoconus in patients whose vision is not correctable to better than 20/40. Penetrating keratoplasty yields good success rates, especially in eyes with endothelial dysfunction and central opacities, resulting in clear visual axes in greater than 90 percent of all cases. Penetrating keratoplasty for keratoconus exhibits excellent visual and survival results, but young patients may require one or more grafts during their lifetime.