Eye disease that affects the cornea and affects 1 in 2000 people, usually the disease is detected between 10 and 20 years old. We start to correct the vision with glasses and then when the cornea is
deformity we will put on rigid lenses permeable to oxygen to compensate and therefore improve vision.
This cornea is made up of 5 layers of cells.
The cornea will deform forward and take the shape of a cone and cause reduced vision and accompanied by astigmatism.
In the majority of patients, it affects both eyes and as the disease progresses corneal opacities will develop and decrease visual acuity.
This gives the impression of visual fog and distortion of the images and sometimes a feeling of dazzling with the light.
Prevalence of keratoconus :
Variable according to the authors : 0.4 to 0.6% (Dr T. DAVID), 0.15 to 0.6% (N. BIER and LOWTHER), 1 case in 2000 (RABINOWITZ), in France estimate of 30,000 cases (2000).
Impact of keratoconus on social and professional life :
The keratoconus wearer is corrected with astigmatic lenses at the start and obtains a vision greater than 8/10. But quickly, glasses do not maintain correct acuity and only wearing contact lenses can regain 90% of the old acuity.
Thanks to the wearing of contact lenses which are adapted and readjusted throughout life, the wearer of keratoconus maintains satisfactory acuity from far as well as from near.
Certain professions requiring an acuity greater than 8/10 will not be accessible.
The acuities of KC wearers are well above the acuities required for driving a car which requires acuity> 5/10 on the better eye and 1/10 on the worst eye.
Warning signs :
Rubbing of the eyes (66 to 73%) is observed in the questioning of subjects with KC.
Often there is an accentuated deformity on the side of the dominant hand. People with an allergic temperament (30%) complain of dry eyes and a sensation of foreign bodies, hay fever, asthma, eczema, spring conjunctivitis and other allergies.
It is absolutely not recommended to rub your eyes as this may increase the corneal deformity.
Etiology and evolution of keratoconus :
Keratoconus affects adolescents or young adults, most of the time without prior visual defect. The cornea, placed directly in front of the eye, is lubricated by the tears which protect it and nourish it mainly by the oxygen in the air dissolved in the tears.
The cornea must be perfectly transparent and regular; it provides 2/3 of the power of the eye and focuses images on the retina to ensure vision through the brain.
The thick cornea (500 µm in the center and 700 µm at the periphery) includes 5 layers: at the front, the epithelium (50 µm thick, the only corneal layer that regenerates), then Bowman's membrane, the stroma involved in the deformation of the keratoconus, Descemet's membrane, and the endothelium in contact with the aqueous humor in the anterior chamber of the eye.
The evolution by successive crises alters the vision of one eye, the 2nd eye always evolves with 1 or 2 stages of delay in 90% of cases of KC.
Average age of onset around 16 years after puberty
Age of detection: ≈ 20 - 30 years
Very variable course: KC progresses over 5 to 6 years, followed by a stable phase, then the possibility of course by more spaced crises.
In the most advanced cases of keratoconus (15% of KC), the too thin cornea presents areas of scars penalizing vision. A cornea transplant makes it possible to find a clear cornea and a relatively good acuity. Astigmatism usually persists. This is corrected by glasses or perfectly by contact lenses of specific custom geometries.
Correction of keratoconus by contact lenses :
The keratoconus cornea has an irregular and asymmetrical surface. The deformities can be centered in the pupil area and penalize vision very early on. The deformations are more often infero-temporal and variable diameter. The images seen by the subject are then scattered. We often take the comparison of a distorting mirror in which the image is rendered distorted.
The topography, the measurements and the preliminary examinations allow the contactologist to determine the shape and the power of the contact lens. It is placed on the cornea by capillary action thanks to the tears and the alignment of the precisely adjusted shape.
The anterior surface of the lens is symmetrical and regular, the rear surface of the lens is fitted to the irregular surface of the cornea. Tears fill the space between the back side of the lens and the cornea. In the lens wearer, a new optical system is then created by the whole "lens + tears + cornea".
This new optical system optically plays the role of a normal cornea with a smooth and regular front. The light rays which reach the eye now pass through the optical system thus created to focus correctly on the retina: optimal vision is regained.
Evolution of Keratoconus
- Suspected in irregular astigmatism and myopia progressing with moderate decrease in VA
- Keratometry: spokes 7.10 mm
- Difficulty aligning sights
- Videokeratoscopy: beginner cone
- Very curved spokes 6.50 to 7.00 mm
- Distorted sights
- Irregular astigmatism +++ (4- 5 D)
- Corneal thinning, deep stromal streaks
- A .V insufficient glasses
Keratometry 6.00 mm not measurable
- Extreme thinning of the top of the cornea
- Possible rupture of Descemet's membrane
- Central corneal edema
At stage IV
The base of the cone exceeds 7mm in the Charleux test
New generation of contact lenses for keratoconus scleral lens Maxilens Onefit:
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Criteria: Keratoconus, Corneal transplant, Dry eye syndromes, Corneal dystrophies.
The optical quality of a rigid lens with the comfort of a soft lens. Maxilens Onefit, the new scleral contact lens technology available from Dencott.
Made to your measure, with optical quality and the physiological tolerance of a rigid lens with the comfort and stability of a flexible lens, ultra comfortable with optimum vision correction results, the new scleral contact lens technology, since each eye is unique.
The sophisticated curvatures of the design create a protective tear layer between your eye and the lens. This multifunctional tear layer and continuously hydrate your eye while wearing.
|Contact lenses: the solution.|
American studies show the benefit of fitting keratoconus wearers with oxygen permeable lenses in order to give them the best visual comfort. (July 2012 ophthalmology notebooks).