Keratoconus

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Bulging Cornea

Keratoconus (bulging of the cornea) is the most common type of corneal dystrophy, in which the cornea thins and protrudes, gradually takes on a conical rather than the normal rounded shape. Because the cornea is the first point of focusing light that comes into the eyes, vision is distorted. The condition often starts in puberty, and it is reported by teens who come to their eye doctor because their vision is poor. It then progresses gradually into adulthood and eventually stabilizes. Severe astigmatism can result causing poorer vision. Consequently, keratoconus is often mistaken for astigmatism.

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About the Cornea

Six layers make up the structure of the cornea.

The epithelium, the outermost layer, is a thin layer of protective cells.

The Bowman's layer contains collagen fibers that help maintain the cornea's shape.

The Dua layer is a strong, thin, air-proof layer of collagen.

The corneal stroma is transparent but very fibrous and tough. It is the thickest layer of the cornea. It is a special tissue (mesenchymal) composed of organized layers of types I and V collagen with fibroblast cells between the layers. These cells secrete a matrix to maintain both strength and transparency.

Descemet's membrane is comprised of IV and VIII collagen fibers. If this layer is damaged (as in Fuch's dystrophy), a corneal transplant may be required. If this membrane fails, then the cornea becomes increasingly cloudy.

Corneal endothelium is the "basement" of the cornea on which the other layers and membranes are seated.

Nerve fibers. The cornea is tightly populated with nerve fibers, making it the most sensitive of all tissues: 20-40 times more sensitive than the root of your tooth.

Types of Keratoconus

The different types of keratoconus determine where the area of bulging is occurring. A technique known as corneal topography measures the contour of the cornea. Normal corneal topography displays a regular and uniform surface without strong declivities.

Forme frust. The irregularities are mild, and neither slit-lamp exams nor corneal topography will show abnormalities; but by considering the results of these techniques along with normality and biomechanical status, the doctor can screen for this early form of keratoconus. The patient does not notice symptoms, and the condition is correctable with glasses or soft contact lenses.

Nipple cone. There is a small isolated area of bulging at, or near, the center of the cornea. Vision can be significantly distorted however, because the area of bulging is very near the pupil.

Oval cone. This is the most common form. With the development of the oval (or sagging) cone, comes more difficulty in fitting contact lenses, along with scarring and corneal hydrops (rupture of the cornea). The bulging is more to the side of the cornea rather than the center, but it continues into the center where it distorts vision. Special types of contact lenses can correct vision.

Globus cone. This condition has significant thinning and bulging, covering 75% of the cornea. It is the most severe form and is also uncommon. It typically requires a corneal transplant.

What Happens?

Dua's layer helps control the flow of fluid from the eye, contributing to the functioning of the sieve-like trabecular meshwork in the periphery of the cornea. A poor functioning trabecular meshwork can lead to glaucoma. Tears developing in the Dua's layer contribute to fluid build-up. Additionally, in cases of severe bulging, a tear in the Descemet's membrane can also develop, allowing fluid from inside the eye to permeate the cornea.

When tears develop in the thin Dua's and Descemet's layers the Bowman's layer begins to deteriorate. The damage results in fluid that, from inside the eye, permeates the cornea.

Furthermore, researchers have found that the damaged cornea shows signs of oxidation damage to the Bowman's layer caused by free radicals. The cells create a common antigen-related protein (LAR) that is not found in normal corneas. It is felt that if cornea membrane cells are only partially damaged, they can heal, but over time corneal cells can die, causing vision loss.

These changes result in severe haziness, which is often accompanied by blister like lesions of the superficial cornea, resulting in impairment of vision and discomfort.

Symptoms

Symptomatic abnormalities include deterioration of cornea cells, collagen fibers and membranes, mitochondria swelling, and protein synthesis abnormalities. These alterations take place both within the cells and in the spaces between cells.4

  • Visual distortion with and without eyeglasses.
  • Standard contact lenses do not fit well.
  • Multiple images (monocular polyopia)
  • Glare from lights
  • Light sensitivity
  • Poor night vision

Keratoconus

Causes

There are several apparent causes. It may be develop due to tears in the Dua layer which allow fluid buildup. The cornea tissue may thin due to the deterioration of the Bowman's Layer -- it is not inflamed but exhibits signs of free radical damage.1

Researchers have found that the damaged cornea shows signs of oxidation damage to the Bowman's Layer caused by free radicals. The cells create an enzyme called "leukocyte", a common antigen related protein (LAR) that is not found in normal corneas. It is felt that if cornea membrane cells are only partially damaged they can heal, but over time corneal cells can be killed causing vision loss.

With the 2013 discovery of the Dua's layer, it is also thought that a tear in this thin, tough layer may allow fluid to leak, creating pressure on the cornea (acute hydrops).

  • Oxidative damage by free radicals.5, 6
  • Allergies Approximately 40-50 percent of keratoconus patients have allergies. Allergies may be a contributing factor.7
  • Magnesium deficiencies are linked to keratoconus. Researchers have found that alterations to cells and molecules in the eyes of patients with keratoconus are similar to the alterations caused by magnesium deficiency.4 Alcoholism, pregnancy, diabetes, hyperthyroidism, diuretics and stress can lead to a magnesium deficiency. Low magnesium can cause a thinning of elastic membranes such as the cornea.
  • Genetic disposition is a risk factor (when family members have had this condition). Six genes are associated with keratoconus. 8
  • Those with Downs syndrome have a 6 times greater risk of keratoconus. Five to 8% of Downs patients have keratoconus.2
  • African Americans and Latinos have a 50% greater rate as compared to the white population.
  • Respiratory conditions. Those suffering from sleep apnea and asthma are at greater risk.
  • Other vision conditions associated with keratoconus include retinitis pigmentosa and Leber's disease.
  • Other factors such as chronic eye rubbing and wearing hard contact lenses are associated with keratoconus.

Conventional Treatment

Contact lenses can be fitted by a specialist who fits contacts for keratoconus. Soft lenses can be used in the early stages and help hide the effects of irregularities in the cornea. Gas permeable (GP) lenses can be used when soft lenses are not sufficient; they cover a larger area of the cornea needed to provide a good fit. Piggyback lenses can be used if the patient is intolerant of the GP lenses. A soft contact lens is first fitted for the patient, then, a gas permeable lens is made to fit over the soft lens. Scleral contacts are most often used for treatment compared to gas permeable. Their vaulting effect of the central bulge is important and more comfortable than GP lenses.

Surgery may be recommended when the above options do not work. Intacs can be implanted to enhance the stability of the cornea and achieve a more stable fit. Cross linking is the only FDA-approved treatment for halting the progression of keratoconus. It involves administering riboflavin (vitamin B2) eye drops and UVA light in carefully selected parameters that strengthen the front layers of the cornea (clear covering of the eye) and avoid damage to the back part of the eye.

If keratoconus is severe, a corneal transplant, (penetrating keratoplasty), is recommended by eye doctors in 25% of cases. With the discovery of the Dua layer, surgeons are more able to pinpoint location and so avoid damage to the corneal stroma. The femtosecond laser technology’s accuracy additionally reduces surgical injury.

Self Help Information

Since we consider most eye conditions to be a reflection of the health of the whole body, lifestyle choices and diet can play a major factor in getting and maintaining good vision.

MSM eyedrops9 and certain nutrients such as N-Acetyl-Cysteine and Vitamin C may help slow down development of keratoconus and support corneal health.

  • Homeopathic eye drops are helpful.
  • Wear 100% UVA and UVB protecting wraparound sunglasses with a brimmed hat when you are outside.
  • Supplementation with nutrients and eyedrops that have been found to be helpful to protect vision.
  • Diet & lifestyle - see our recommendations for healthy eyes for detailed information.

Related Conditions

  • Keratoglobus - also known as megalocornea, occurs when the cornea thins at the edges and changes to a more globular shape due to deteriorating cornea structure.
  • Pellucid marginal degeneration - this is another degenerative condition in which the bottom edge and side margins of the cornea become thinner.
  • Posterior keratoconus - in this condition the back of the cornea deteriorates and thins.
  • Acute hydrops - occurs when swelling occurs due to leakage in the Descemet's membrane (see the image above). Sometimes the cornea tears or is scarred.
  • Descemetocele - formation of a descemetocele occurs when the Descemet membrane bulges due to cornea damage caused by infection or corneal ulcer.
  • Pre-Descemet's dystrophies - here, the stroma layer of the cornea develops opaque areas and lesions can form.

Keratoconus News

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Footnotes and Sources

1. http://www.nkcf.org/en/research.html
2. http://en.wikipedia.org/wiki/Keratoconus
3. http://www.mskcc.org/cancer-care/herb/n-acetylcysteine
4. Thalasselis, A. (2005). The possible relationship between keratoconus and magnesium deficiency. Ophthalmic Physiol Opt, Jan;25(1):7-12.
5. Armal, E., Peris-Martinez, C., Menezon, J.L., Johnsen-Soriano, S., Romero, F.J. (2011). Oxidative stress in keratoconus? Invest Ophthalmol Vis Sci, Nov 4;52(12):8592-7.
6. Toprak, I., Kucukatay, V., Yildirim, C., Kilic-Toprak, E., Lilic-Erkek, O. (2014). Increased systemic oxidative stress in patients with keratoconus. Eye (Lond), Mar;28(3):285-9.
7. Sharma, N., Rao, K., Maharana, P.K., Vajpayee, R.B. (2013). Ocular allergy and keratoconus. Indian J Ophthalmol, Aug;61(8):407-409.
8.Woodward, M.A., Blachley, T.S., Stein, J.D. (2016). The Association Between Sociodemographic Factors, Common Systemic Diseases, and Keratoconus: An Analysis of a Nationwide Health Care Claims Database. Ophthalmology, Mar;123(3):457-65.
9. Kim, Y.H., Kim, D.H., Lim, H., Baek, D.Y., Shin, H.K., et al. (2009). The anti-inflammatory effects of methylsulfonylmethane on lipopolysaccharide-induced inflammatory responses in murine macrophages. Biol Pharm Bull, Apr;32(4):651-6.
Other sources:
GeneCardsSuite. Corneal Stroma. Retrieved Feb 8 2018 from https://discovery.lifemapsc.com/in-vivo-development/eye/corneal-stroma.
Ueki, R., Maeda, N., Fuchihata, M., Koh, S., Kitaoka, T., et al. (2014). Differentiation of forme fruste keratoconus from normal cornea using parameters of corneal tomography, aberration, and biomechanics. IVOS, 55(13): 3705.
H. S. Dua, L. A. Faraj, M. J. Branch, A. M. Yeung, M. S. Elalfy, D. G., et al. (2014). The collagen matrix of the human trabecular meshwork is an extension of the novel pre-Descemet's layer (Dua's layer). Br J Ophthal, May;98(5):691-7.
Carracedo, G., Recchioni, A., Alejandre-Alba, N., Martin-Gil, A., Crooke, A., et al. (2015). Signs and Symptoms of Dry Eye in Keratoconus Patients: A Pilot Study. Curr Eye Res, 40(11):1088-94.
National Keratoconus Foundation