Keratoconus

Keratoconus is a non-inflammatory disorder of the cornea, which is characterized by the presence of a progressive deformation of its surface. The cornea gradually takes a “conical” shape (it expands by creating an extrusion), deforming the reflection formed in the fundus of the eye. A progressive thinning can also be observed, as well as scarring, and finally opacity in the area where the cone has been formed. What's important with keratoconus is that it causes a gradual, partial or total, diminishing of vision, which cannot be improved with glasses and can even lead to blindness.

In most cases, this deformation can be found in the lower half of the cornea and first appears as irregular astigmatism. Nevertheless, all cases of astigmatism are not exclusively due to keratoconus.
While keratoconus progresses, the only non-invasive method that gives the patient a normal vision is rigid contact lenses (semi-rigid keratoconic lenses or even rigid). If keratoconus continues to deteriorate then it is possible for a scar to be created at the center of the cornea.

Keratoconus – Causes 

Despite ongoing research, the causes of keratoconus are essentially unknown. It is generally considered a genetic disease caused by multiple factors, mainly irregularities in the structure or the metabolism of various segments of the cornea.

It used to be considered a rare disorder, perhaps because there weren't any diagnostic means to detect it in the early stages. Today we know that keratoconus is not so rare. There are more than 20,000 people in Greece with keratoconus (approximately 1 for every 2,000 people)..

It usually appears in adolescence and progresses relatively fast, while later the rhythm of deterioration decreases and stops at around 35 years of age.

It is believed that genetics, the environment and the endocrine system play an important role in the creation of keratoconus.

Keratoconus – Symptoms 

Ο Keratoconus appears in many cases to be asymptomatic (Forme fruste keratoconus) and its detection can occur during preoperative tests for refractive surgery.

The first signs of keratoconus are usually the increasing myopia and especially astigmatism, and also the need to change eyeglasses prescription, confused vision with image deformation or blurry vision that cannot be corrected with glasses.

Other symptoms include:

Decrease of visual acuity
Increase in light sensitivity
Difficulty in driving at night
Irregular astigmatism that can't be corrected with glasses
Light diffractions, halos, diplopia (double vision) in one eye, especially at night
Intolerance of soft contact lenses
Sudden decrease in vision due to hydrops
Headaches and general eye aches.
Irritation in the eyes, excessive scratching

Light defractions and difficulty in driving at night

The symptoms usually appear at the end of adolescence. The disease usually progresses slowly, within 10 to 20 years and then it stops progressing. It starts at around 15 years of age and its progress “freezes” after 35.

It usually presents itself as myopia that changes constantly and with increasing astigmatism. This initial change warns the ophthalmologist about the presence of keratoconus. Each eye is affected at a different degree. As the disease progresses, the vision can be deformed, as the cornea becomes more convex and scarring is formed.

Keratoconus – Clinical characteristics

Gradual corneal thinning, at about 1/3 of the corneal thickness. It is connected to low visual acuity, a result of the noted irregular astigmatism with high keratometric (Ks) values.
Indentation of the lower eyelid when the patient looks down (Munson's sign).
A Fleischer ring (epithelial iron depositions) can surround the base of the cone.
Fibrosis..
Visible corneal nerves.
Raised central protrusion that causes intolerance in the use of contact lenses (Proud nebula).
Corneal scarring in severe cases.
Hydrops.

Munson's sign	Acute hydrops in advanced keratoconus

Keratoconus, especially in its early stages, can be difficult to diagnose and all the symptoms above can be related to other vision problems. Consult with your ophthalmologist to verify a keratoconus diagnosis.

Keratoconus – Diagnosis

Patients in the early stages complain of diminished visual acuity. Physical examination does not always provide evidence for a positive diagnosis. However, keratometry can give altered parameters. The patient presents an irregular progressive astigmatism that previously did not exist. In more advanced stages, the diagnosis is easier and with the help of a slit lamp, the cornea can present the known conical form, as well as thinning and haze of its central area. Nonetheless, positive diagnosis occurs with the help of an electronic device and a test called “corneal map” (corneal topography). In this test, a 2D image of the corneal topography is taken and, based on that, we can diagnose even the subclinical forms (those that haven't presented any symptoms).

Keratoconus – Diagnostic tests  

Skiascopy:shows irregular scissoring reflections.
Direct ophthalmoscopy: shows an oil droplet reflex (Red reflex).
Photokeratoscopy or Placido's disk: presents irregularities on the rims of the reflected rings.
Keratometry:: (High Ks, mild54 D) initially shows irregular astigmatism where the main meridians are not separated by 90% and the images from the keratoscopy cannot be superimposed
Corneal topography: shows the anomaly on the surface of the eye. Disorders such as keratoconus can present an irregular convexity, before the biomicroscopic signs are made visible (which an ophthalmologist can diagnose clinically). In keratoconus, the color maps provide information on the position, size and crest curvature. The most recent topography systems can also test at the same time for the curvature of the rear surface of the cornea, whose irregularities seem to come before the front surface. Simultaneously we can test the corneal thickness in all its points with greater precision.

The thickness of the cornea is a measurement of prime importance for the treatment of our patient.

Ultrasound pachymetry(CCT usually < 450 μm).

Keratoconus – Treatment:

 Glasses or soft contact lenses can be used to correct mild myopia and astigmatism caused by the keratoconus in the early stages, however, after a certain degree a rigid, gas-permeable (RGP) contact lens will better correct keratoconic vision.

 Rigid, gas-permeable contact lenses(RGP ή GP) can correct vision as keratoconus progresses. The rigid material of the lens allows it to exercise pressure on the cornea, replacing the irregular shape of the cornea with a smooth, uniform refractive surface that will improve vision.

Intracorneal rings can be inserted in the corneal stroma to flatten it, by changing the shape and position of the cone

Corneal Crosslinking (CXL) is a new treatment option that aims to stop the progress of keratoconus.

 Surgical corneal transplantς becomes necessary in very advanced stages of keratoconus, due to scarring, excessive thinning or intolerance to contact lenses.

News about Keratoconus

Keratoconus and keratoconus treatment from the US Library of Medicine

Information on Keratoconus (Squidoo)

Keratoconus: A short history of the use of contact lenses to treat the symptoms of keratoconus

Keratoconus and Corneal Transplant (Causes, Symptoms, Treatment)

Keratoconus – Medical Encyclopedia

Keratoconus and INTACS – results from 12-month trials

Keratoconus: Treatment with microwave radiation

Keratoconus International Institute

Keratoconus: Causes, Symptoms, Treatment

National Keratoconus Foundation

Keratoconus – Information from Wikipedia

August is awareness month for keratoconus in the United Kingdom

Artificial Corneas give hope against Keratoconus

Keratoconus – Diagnosis, Treatment, Keratoconic contact lenses [pdf]

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