About Eye - Keratoconus

KERATOCONUS

Keratoconus (kerato –horn, cornea & konos-cone) is a degenerative disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve . As keratoconus progresses, the cornea bulges and thins, becoming irregular. The progression of KC is unpredictable. It is generally slow and can stop at any stage from mild to severe.

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Etiology (Causes) of Keratoconus

The cause is unknown but the tendency to develop keratoconus is probably present from birth.Keratoconus is thought to involve a defect in collagen, the tissue that makes up most of the cornea .There is also systemic& an ocular associations.

Systemic disorder include Down,Turner,Ehlers-Danols & Marfan syndromes, atopy, osteogenesis imperfecta, mitral valve prolapsed & mental retardation.

Ocular associations include vernal keratoconjunctivitis, blue sclera, aniridia, ectopia lentis, leber congenital amaurosis, retinitis pigmentosa & persistent eye rubbing.

What are the symptoms of Keratoconus?

  1. The typical patient with undiagnosed keratoconus complains of deteriorating vision, usually in one eye first, both at distance and near.
  2. Near visual acuity may improve if the patient squints or holds printed material closer.
  3. Keratoconus patients often report multiple images or ghosting of images and often relate a history of frequent refractive correction changes without much improvement in visual acuity.
  4. Patients may also report irritating symptoms such as intolerance to glare, photophobia and a recurrent foreign body sensation.
  5. Even with appropriate contact lens correction, keratoconus patients often report fluctuating vision throughout the day and from day to day, although the measurements of visual acuity in keratoconus patients are highly repeatable.

Exams and Tests

  1. Keratoconus is frequently discovered during adolescence. It can usually be diagnosed with slit-lamp examination of the cornea. Early cases may require a test called corneal topography, which creates a map of the curvature of the cornea.
  2. When keratoconus is advanced, the cornea may be thinner in areas. This can be measured with a painless test called pachymetry
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Treatment

  1. Spectacles in early cases to correct regular & mild irregular astigmatism.
  2. Contact lenses: In early stages of keratoconus, soft contact lenses can suffice to correct for the mild astigmatism. As the condition progresses, these may no longer provide the patient with a satisfactory degree of visual acuity, and most clinical practitioners will move to managing the condition with rigid contact lenses, known as rigid gas-permeable, or RGPs. RGP lenses provide a good level of visual correction, but do not arrest progression of the condition.
  3. Some patients also find good vision correction and comfort with a "piggyback" lens combination, in which gas-permeable rigid lenses are worn over soft lenses, both providing a degree of vision correction One form of piggyback lens makes use of a soft lens with a countersunk central area to accept the rigid lens.
  4. Scleral lenses are sometimes prescribed for cases of advanced or very irregular keratoconus; these lenses cover a greater proportion of the surface of the eye and hence can offer improved stability. The larger size of the lenses may make them unappealing or uncomfortable to some; however, their easier handling can find favour with patients with reduced dexterity, such as the elderly
  5. Surgical options: Corneal collagen cross linking with riboflavin (C3R) Corneal cross linking is the newest development in the treatment of keratoconus and as such it holds a lot of promise. Quite simply, C3R involves treating the cornea with riboflavin and then activating its collagen cross linking properties with ultraviolet light. C3R improves the strength of the cornea by increasing the linking between collagen fibers. The result of this increased cross linking is that it increases the strength of the cornea and often causes some corneal flatten.A one-time application of riboflavin solution is administered to the eye and is activated by illumination with UV-A light for approximately 30 minutes. The riboflavin causes new bonds to form across adjacent collagen strands in the stromal layer of the cornea, which recovers and preserves some of the cornea's mechanical strength. The corneal epithelial layer is generally removed in order to increase penetration of the riboflavin into the stroma.
  6. Corneal ring segment inserts: A recent surgical alternative to corneal transplant is the insertion of intrastromal corneal ring segments. A small incision is made in the periphery of the cornea and two thin arcs of polymethyl metha acrylate are slid between the layers of the stroma on either side of the pupil before the incision is closed. The segments push out against the curvature of the cornea, flattening the peak of the cone and returning it to a more natural shape. The procedure, carried out on an outpatient basis under local anaesthesia, offers the benefit of being reversible and even potentially exchangeable as it involves no removal of eye tissue.
  7. keratoplasty

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