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Definition of Keratoconus: The word keratoconus is derived from Greek and Latin. Kerato means cornea and conus means cone shaped. It is a bilateral, progressive, asymmetric, non-inflammatory thinning and ectatic condition of the cornea, resulting in a high degree of irregular myopic astigmatism.

Prevalence: Keratoconus is estimated to occur in 1 out of every 2000 persons in the general population. There appears to be no significant preponderance with regards to either men or women.

What is the usual age of onset of keratoconus?

The onset of keratoconus is between the ages of 10 and 30. The changes in the shape of the cornea usually occur slowly over several years.

Symptoms: Symptoms depend on the severity of the disease. The most common symptoms include:

• Blurred vision.

• Distortion of vision.

• Photophobia.

• Glare.

• Eye Irritation and itching.

• Frequent spectacle power changes.

• Inability to wear contact lenses.

Causes:

The cause of keratoconus remains unknown, although recent research seems to indicate the possible causes include:

• Keratoconus is thought to involve a defect in collagen, the tissue that makes up most of the cornea.

• Keratoconus have a genetic component and studies indicate that about 8% of patients have affected relatives.

• It happens more often in people with certain medical problems, including certain allergic conditions.

• Some think that chronic excessive eye rubbing can cause of keratoconus.

Classification:

(A)Based on keratometry reading:

  1. Mild: Keratometric readings are less than 45D in both meridians.

  2. Moderate: Keratometric readings are between 45D and 52D in both meridians.

  3. Advanced: Keratometric readings are between 53D and 62D in both meridians.

  4. Severe: keratometric readings are in both meridians more than 62D.

(B)Based on morphologic shape:

  1. Nipple Cones: Characterized by their small size (5 mm) and steep curvature. The optical centre is often either central or para-central and displaced inferonasally.

  2. Oval Cones: Which are larger (5-6 mm), ellipsoid and commonly displaced inferonasally.

  3. Globus Cones: Which are largest more than 6mm and may involve over 75% of the cornea.

Clinical Features:

  1. In early stage, impaired vision in one eye caused by progressive Irregular myopic astigmatism with steep keratometry reading.

  2. Scissor reflex on retinoscopy.

  3. Ophthalmoscopically shows an “Oil droplet reflex”.

  4. Munson sign-Bulging of lower lid in down gaze.

  5. Fleischer Ring-Epithelial iron deposits at the base of the cornea. Mechanism of iron deposition is not clear understood. It may be uneven distribution of tears.

  6. Progressive Central or paracentral stromal thinning with inferior apical protrusion.

  7. Vogt striae-Fine deep vertical stromal folds which temporarily disappear on digital pressure.

  8. Rizutti sign-conical reflection on the nasal cornea when light is shone from the temporal side.

  9. Prominent corneal nerves.

  10. Acute Hydropes-Corneal edema resulting from tears Due to ruptures of the descemet`s membrane and acute seepage of the aqueous humor into the corneal stroma and epithelium. These breaks usually heal within 6-10 weeks and the edema gradually clears.

  11. Variable corneal scarring, depending on severity of the disease.

Associations: The ocular and systemic associations of the keratoconus include:

Ocular:

• Vernal conjunctivitis.

• Blue sclera.

• Aniridia.

• Ectopia Lentis.

• Retinitis Pigmentosa.

• Leber congenital amaurosis.

Systemic:

• Down syndrome.

• Ehlers-Danols syndrome.

• Marfan syndrome.

• Atopic dermatitis.

• Osteogenesis imperfecta.

Exams and Tests:

Visual acuity testing: Visual acuity is an indication of the clarity or clearness of one’s vision. It is a measurement of how well a person sees.

Refraction: The refraction test is an eye exam that measures a person’s prescription for eye glasses or contact lenses.

Slit Lamp examination: The slit lamp is an instrument consisting of a high-intensity light source that can be focused to shine a thin sheet of light into the eye. The slit lamp examination provides a stereoscopic magnified view of the eye structures in detail, enabling anatomical diagnoses to be made for a variety of eye conditions like keratoconus.

• Corneal topography: Corneal topography, also known as photokeratoscopy or video-keratography, is a non invasive imaging technique for mapping the surface curvature of the cornea. The three-dimensional map is a valuable aid. It is also used in the diagnosis and treatment of a number of conditions; in planning refractive surgery such as LASIK and evaluation of its results; or in assessing the fit of contact lenses or to diagnose keratoconus.

Treatment:

Optical:

Spectacles: In the early stages of the keratoconus, spectacles are usually successful in correcting the myopia astigmatism associated with the keratoconus. But in severe cases it does not give good quality of vision due to high amount of corneal toricity.

Contact lenses:

  1. Soft contact lenses: In the early stages of the keratoconus soft contact lens is helpful. Because soft contact lens give good comfort. But in advanced stages soft contact lenses cannot correct irregular astigmatism. So, soft contact lenses are not useful in advanced stages of keratoconus.

2. Rigid Gas Permeable contact lenses (RGP): As the condition advances, the cornea becomes highly irregular and vision is no longer adequately corrected with spectacles and soft contact lenses. Rigid gas permeable contact lenses are then required to provide optimal visual acuity. Rigid gas permeable lenses enables to vault over the cornea, replacing cornea`s irregularities by filling tears between cornea (front surface of the eye) and back surface of the RGP lenses with a smooth, uniform refracting surface to improve vision.

3. Piggy back contact lenses: Ideal fitting of a rigid gas permeable contact lens over a cone-shaped cornea can sometimes is not possible. To get good fitting and good visual outcome some practitioner use piggyback contact lens. This method involves placing a soft contact lens, such as one made of silicone hydrogel, over the eye and then fit a RGP lens over the soft contact lens.

4. Rose-K Lens: Rose-k lens was introduced by Dr Paul rose in 1995. This lens is world’s most frequently prescribed gas permeable lens for keratoconus. This lens has complex geometric design. Here six different curves at back surface of the lens and decreasing optic zone as base curve steepens. The material of the lens is Boston.

5. Boston sclera contact lens: In advance case of keratoconus to delay the surgery Boston sclera contact lens is very helpful. It is made of material that allows oxygen to pass through to the eye, larger diameters (15 to 24mm), edges rest on the sclera or white portion of the eye and the central optic zone (12mm) is designed to completely vaults over the irregularly shaped cornea. These larger lenses also are more stable than conventional gas permeable contact lenses.

Surgical:

Penetrating Keratoplasty: In about 15% of cases, the keratoconus progresses to the stage where corneal transplantation is required to achieve better vision.

Corneal Collagen Cross-linking with Riboflavin (C3-R): A new, minimally invasive procedure called Corneal Collagen Cross-linking with Riboflavin (vitamin B) and ultraviolet-A (UVA 365nm) is called C3-R.

The treatment is performed in operation theatre under complete sterile conditions. Usually one eye is treated in one sitting. The treatment is performed using anesthetic eye drops. The surface of the eye (cornea) is treated with application of Riboflavin eye drops for 30 minutes. The eye is then exposed to UVA light for 30 minutes. The combination of Riboflavin drops and ultra violet light that react with the tissues in the cornea, strengthening them by creating more ‘cross-linking’ among them. The resulting increased stiffness and rigidity of the cornea, stabilizes corneal ectasia. Hence, the treatment takes about an hour per eye. After the treatment, antibiotic eye drops are applied; a bandage contact lens may be applied, which will be removed after few days.

However one need to understand that Collagen cross-linking treatment is not a cure for keratoconus, rather, it aims to slow the progression of the condition. However following the cross-linking treatment it makes the patient more comfortable to wear contact lens.

Complications of keratoconus:

• Patients with even borderline keratoconus should not have laser vision correction. Corneal topography is done before laser vision correction to rule out people with this condition.

• There is a risk of rejection after corneal transplantation, but the risk is much lower than with other organ transplants.

When to Contact a Medical Professional?

Young persons whose vision cannot be corrected to 20/20 or 6/6 with glasses should be evaluated by an eye doctor experienced with keratoconus.

Does keratoconus affect both eyes?

Yes, keratoconus generally affects both eyes. Keratoconus is basically a bilateral condition; the degree of progression for the two eyes is often unequal.

Does keratoconus cause blindness?

Keratoconus does not cause total blindness. However it can lead to significant vision impairment resulting in legal blindness.

Prevention:

There are no preventive measures. Some specialists believe that patients with keratoconus should have their eye allergies aggressively treated and should be instructed not to rub their eyes.



Source by Subrata Roy

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