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Eye care information on diseases and treatments
Keratoplasty is a surgical opthalmic practice that corrects the curve of the cornea. It is used to fix hyperopia and hyperopic astigmatism. The process uses laser energy to heat up and shrink the collagen in the peripheral and paracentral areas. Ultimately the operation can level the peripheral cornea and make the central cornea steeper so vision is less distorted.
Types of Keratoplasty
There are two main types of keratoplasty and both share the advantage of not harming the retinal cells in the cornea –
1. Laser thermal keratoplasty (LTK) involves heating the cornea and extending its curve. However, this procedure’s drawback is that it weakens and the vision correction does not last. However this type of keratoplasty may become more advanced as time goes on and more research is done regarding these types of high heat techniques. LTK is also used in experimental cutting edge eye therapies such as wave front based therapy.
2. Conductive keratoplasty (CK) uses low-pulsed high-energy radio frequencies to make the cornea steeper. It works by shrinking and heating the collagen. CK is considered to be a viable option as it is more stable and even in terms of heat distribution
History of Keratoplasty
Dr. Gayet pioneered using heat to alter the corneal curvature in 1879. At that time, he used cautery to perform a crude form of Keratoplasty. This was done in tandem with research done by a researcher named Lans who in 1898 developed a treatment for astigmatism in rabbit eyes by altering the curve of the cornea. This process was common until Dr. Castroviejo developed a different process called penetrating keratoplasty in 1936.
In 1964 thermal kertoplasty was refined as an operative process even more when two doctors name Stringer and Parr discovered that the collagen in the cornea shrinks between ff and 58 degrees Farenheit. Since that time all kinds of devices, both laser and non-laser have been tested to create a collagen shrinking device. In the seventies the thermostatically controlled electric probe was developed with mixed results. However this probe is now only used as an accessory during a keratoplasty.
In the sixties a radio frequency problem called the Los Alamos probe was developed and along with a retractable wire probe. This was followed by the discovery of Carbon Dioxide lasers and a solid-state laser. Both were risky but the solid state laser showed promising results during keratoplasty procedures.
These solid state lasers, also known as tHo:YAG laser appliances gave surgeons a means to shrink the collagen without burning the cornea. This assurance also sped up the lesion healing process and did the surrounding tissues of the cornea the least harm.
The effect of heat on the cornea
When heat is applied to collagen it shrinks. This flattens the area and can improve vision.
There are two methods of applying heat to the cornea. They are central heating and peripheral heating.
Central heating involves applying heat to the diameter of the cornea, which can cause a hyperopic shift that can improve the refractive ability of the lens.
When it comes to peripheral treatments, a belt like area is flattened using heat so that the curve of the cornea is steepened. Whenever the cornea is steepened vision is improved as it betters the refraction power of the eye.
Heating the cornea can help all kinds of eye conditions including:
Astigmatism – When heat is used for astigmatism, the peripheral edge of the cornea is raised a long a single line. This causes the evolution of a flatter meridian and steepening of the cornea.
Hyperopia – Heating the cornea can help be part of a process of tailoring its surface so that it is flatter and the meridian near the visual axis of the cornea can be improved. In turn, sight will be improved.
The disadvantage of corneal collagen contraction treatments is that they are not permanent. The procedure needs to be done again and again. This because the cornea consistently produces fresh collagen.
At least three factors are believed to play a role in improving sight with the application of heat to the cornea. First of all the instrument used must be able to control the temperature of the collagen shrinkage temperature. The collagen stability in the eye is also a factor as is the keratocyte reaction in the eye itself. All three of these factors are prerequisites for a successful operation. If they are not in place the operation may burn the eye or result in even worse eyesight. However for the most part this operation is successful even if for just a short time.