How the eye functions
To comprehend keratoconus, we must first understand how the eye enables us to see, and what role the cornea plays in this process.
To appreciate how the eye functions, imagine yourself as a beam of light reflected from a 100-foot tree into the eye of a living person. You are the image of the tree, traveling at the speed of light and about to enter an obstacle course on your way to the brain of the observer. Your first encounter is your passage through the clear convex cornea which bends (refracts) you and slows you down. It also shrinks you to manageable size (little larger than a nickel). Next you squeeze through a round, adjustable opening, the pupil, formed by a colorful membrane, the iris, which, if you are too bright, will reduce your intensity. You now encounter a rather dense but transparent medium, the lens, which not only bends you even more, but unceremoniously turns you upside down and aims (focuses) you at the back of the eye, the retina, which you strike after passing through a clear, sticky, gel-like substance, the vitreous humor.
You are now the inverted image of a 100-foot tree shrunk to the size of a postage stamp and flattened against the retina. But not for long! Instantly you are transformed from a beam of light into an electrical impulse, and flashed along the optic nerve from the retina to the brain, where you are perceived as a 100-foot, three-dimensional, right-side-up tree. And all of this in a tiny fraction of a second.
To recap: the cornea is the clear, transparent front covering which admits light and begins the refractive process, and also keeps foreign particles from entering the eye. The pupil is an adjustable opening that controls the intensity of light permitted to strike the lens, which focuses light through the vitreous humor, a clear gel-like substance that fills the back of the eye and supports the retina. The retina receives the focused image from the lens, and transforms this image into electrical impulses that are carried by
the optic nerve to the brain.
We are primarily concerned with the cornea, and an affliction of the cornea known as keratoconus.
The eye is enclosed by a tough white sac, the sclera. The cornea is the transparent window in this white sac which allows the objects you are looking at to be carried in the form of light waves into the interior of your eye.
The surface of the cornea is where light begins its journey into the eye. The cornea’s mission is to gather and focus visual images. Because it is out front, like the windshield of an automobile, it is subject to considerable abuse from the outside world. Particles of dust and grit inevitably find their way onto our outer eyes and irritate them, thereby stimulating the production of tears to wash foreign material away.
“A minute corneal scar can impair vision”
The cornea is masterfully engineered so that only the most expensive manmade lenses can match its precision. The smoothness and shape of the cornea is as vitally important to its proper functioning as is its transparency. If either the surface smoothness or the clarity of the cornea suffers, vision will become distorted.
Although appearing to be one clear membrane, the cornea is actually composed of five distinct layers of tissue, each with its respective function. The thin outer layer, or epithelium, is a reliable barrier against corneal infection and usually must be damaged before an infectious agent can get a start in the middle layer (stroma) of the cornea, which is made of collagen (connective tissue).
“The cornea refracts and protects”
We can tolerate very large scars on our bodies with no concern except for our vanity. Not so the cornea! Even a minor scar can impair one’s vision. No matter how well the rest of the eye is functioning, if the cornea is scarred, clouded or distorted, vision will be affected.
What is Keratoconus?
The word keratoconus is formed from two Greek words: kerato, meaning cornea, and konos, meaning cone. Keratoconus, or conical cornea, is a condition in which the normally round shape of the cornea is distorted and a cone-like bulge develops, leading to progressive nearsightedness and irregular astigmatism and significant visual impairment. This distortion has been compared to viewing a street sign through your car windshield during a driving rain storm. As the KC progresses, the cornea bulges and thins, becoming irregular and sometimes forming scars.
What causes Keratoconus?
The causes of this affliction are still unknown despite our long familiarity with it. There has been no shortage of speculation or study and numerous theories have been proposed.
One scientific view is that keratoconus is developmental (i.e., genetic) in origin. This suggests that it is the consequence of an abnormality of growth, essentially a congenital defect. Another is that KC represents a degenerative condition. Still a third postulation is that KC is secondary to some disease process. This idea sprang from the fact that it can occur in children who are not robust, and it usually affects both eyes. Another less widely held hypothesis suggests that the endocrine system may be involved. This idea gained some credence from the usual appearance of the disease at puberty.
Hereditary influences in KC are suggested by studies which show that about 7% of patients have other family members with the disease. Unless you can find evidence of KC in successive generations of your family, there is only a 1 in 10 chance of your having an offspring with some degree of keratoconus.
Environmental factors such as excessive eye-rubbing can contribute to corneal thinning and distortion.
Who gets keratoconus?
Signs & Symptoms
The main symptoms of keratoconus are the following:
- Blurred vision.
- Distortion of images.
- Progressive nearsightedness and irregular astigmatism (frequent changes in eye glass prescription or vision that cannot be corrected with glasses).
- Double vision when looking with just one eye.
- Frequent eye rubbing.
Keratoconus diagnosis
Keratoconus, especially in the early stages, can be difficult to diagnose and all of the above symptoms could be associated with other eye problems. Simply recognizing symptoms does not by itself diagnose keratoconus.
Keratoconus diagnosis requires excellent scientific competence, significant clinical experience, detailed examination and specialized diagnostic equipment.
Measurements required for keratoconus diagnosis:
- Optical coherence tomography – corneal and epithelium pachymetry mapping
- Computerized corneal topography
- Manifest refraction and proper history, including change in eye glass prescription, decreased vision, history of eye rubbing, medical problems, allergies, sleep patterns
- Slit-lamp biomicroscopy of the anterior segment (classic signs: Fleischer’s ring: an iron colored ring surrounding the cone, Vogt’s striae: stress lines caused by corneal thinning, Apical scarring (scarring at the apex of the cone)
Specialized diagnostic equipment
- Anterior Segment Optical Coherence Tomography (OCT RTVue): OCT-derived epithelial mapping (across a 9-mm wide corneal area) is a critical diagnostic tool in early and advancing keratoconus. The corneal epithelium has a compensation function, trying to “cover” stromal surface irregularities. In keratoconic eyes the epithelium becomes thinner over the cone and correspondingly thicker over the flatter areas.
- Anterior Eye Segment Tomography (Pentacam Scheimpflug rotating camera): Rotating camera Scheimpflug imagery provides a multitude of corneal refractive (keratometric), topometric, tomographic, and pachymetric data. In addition, specific anterior-surface irregularity indices (the index of surface variance and the index of height decentration) are sensitive criteria in the diagnosis, progression, and surgical follow-up of keratoconus.
- Placido Disc Topography (videokeratography): This diagnostic device delivers anterior corneal elevation data and gives detailed description of the shape and power of the cornea.
- Cassini Multicolored-Spot Reflection Topography: This innovative technology provides true corneal shape analysis in regular and irregular surfaces and in corneal scarring. Measures anterior surface aberrations and posterior curvature and elevation measurements. Provides submicron accuracy in the axis and amount of corneal astigmatism and includes several keratoconus-specific data, such as the Klyce indices of surface asymmetry index and surface regularity index.
How Is Keratoconus Treated?
The main objective in treating keratoconus is to arrest its progression. Depending on the stage of keratoconus and the age of the individual, the current treatment options for keratoconus management are the following:
1. Corneal Cross-Linking (CXL): There are actually two elements involved in the cross-linking process: ultra violet radiation and vitamin B2, also known as riboflavin. A solution of vitamin B2 is administered topically to the cornea and then activated by ultraviolet-A light. The effect of UVA light on the riboflavin creates new bonds between collagen fibrils in the stroma, conferring new mechanical strength on the cornea and stopping disease progression.
2. PiXL (Photorefractive Intrastromal Cross-Linking): Customizable, differential CXL application in specific areas of the cornea, indicated for keratoconic or ectatic corneas in which CXL is desired to be combined with a customized refractive intervention of myopia and/or cylinder without tissue removal. The cornea is treated with the KXL-II device with a customized variable fluence pattern to reflect 15J of energy in a small trapezoid area matched to the thinnest part of the cornea, then 10J in a broader trapezoid area, surrounded by a 7mm round OZ that was allocated to receive 5.5J of total energy. Laservision was the fist team worldwide to introduce this innovative application.
3. Athens protocol procedure: Our technique combines simultaneous topography-guided partial PRK with corneal CXL and is proven to be a safe and effective approach for normalizing the cornea and enhancing the visual function of eyes with ectatic conditions. Combined CXL with topography-guided, partial PRK can address high amounts of irregular astigmatism in these eyes. The goal of our treatment is to both stabilize the cornea, thus arrest keratoconus progression and to reduce the irregularity of the surface. This is a therapeutic and not a refractive procedure that allows visual improvement either unaided or aided with spectacles and/or contact lenses. Our scientific team was the first to introduce the Athens Protocol Technique, which is now internationally recognized. We have contributed many of the evolutionary steps of the cornea cross-linking since 2001 and our bibliography includes numerous publications, papers, as well as worldwide meeting presentations.The Athens Protocol treatment is simple, the patient receives topical anesthesia and by the end of the procedure a bandage contact lens is fitted to reduce discomfort. There might be a slight burning sensation, pain and photosensitivity the first 2 days but these symptoms are totally normal and temporary. The bandage contact lens is removed three to four days after the initial treatment and the patient may return to his normal daily activities within a week.
4. Intracorneal ring segments (ICRSs): These inserts appear to significantly shift the shape of the cornea and may provide significant visual rehabilitation. They are made of PMMA (polymethylmethacrylate) and they are implanted in the deep peripheral corneal stroma to modify the corneal curvature. This procedure does not involve corneal tissue nor does it invade the central optical zone. The insertion is performed under topical anesthesia.
5. Penetrating Keratoplasty (PK) (corneal transplant): The patient’s cornea is discarded and replaced with a fresh donor cornea. This procedure is associated with significant morbidity, as usually it takes about a week for the patient to return to normal everyday life and months, if not years, before that eye can be adequately visually rehabilitated. It is noted that, despite the use of this drastic procedure, visual rehabilitation may still necessitate additional repair and/or refractive procedures in order to reduce the very common irregular astigmatism and high postoperative anisometropia associated with penetrating keratoplasty. Long-term graft survival in keratoconic eyes declines rapidly after the second decade because the endothelial cells of the donor cornea tend to be slowly rejected by the host.
6. Deep Anterior Lamellar Keratoplasty (DALK): The outer layers of the patient’s cornea are removed and replaced with a partial thickness of donor tissue. This operation has the advantage that the graft cannot fail from endothelial rejection, but is suitable for patients in whom the inner endothelial layer is still healthy. This procedure may be combined with collagen cross-linking on both tissues for greater corneal stabilization.
Post-operative instructions after Athens Protocol procedure
Eye drops Use
- Always wash your hands before putting in the drops.
- Shake the bottles thoroughly prior to each drop .
- There is no preference as to which medication drop is applied first, just remember to wait 2-3 minutes between each eye drop.
- You may experience a medicinal taste in the back of your throat after putting in drops, this is normal.
- Eye drops are not applied during night time.
- Be careful not to touch the eye with the bottle.
- Eye drops are applied over the bandage contact lenses that have been inserted after the operation. The eye surgeon will take the lenses off in 3-4 days. If they fall out, contact us immediately.
- Keep eye drops in a cool place, away from heat, moisture and direct sunlight.
After the operation, please keep your eyes closed, as much as possible.
Precautions
- It is very important to pay attention to your eyes hygiene for ten days after the operation.
- Avoid rubbing, bumping, or scratching your eyes.
- A pair of eye shields is provided in your “post-operative care kit”. The shields are to be worn at night or during naps with the pointed part of the shield pointing towards the nose. A roll of tape is included in the kit to apply the shield for subsequent nights.
- Do not swim/ work out for ten days after the operation.
- Do not rinse your eyes with water. Wash your hair leaning backwards keeping your eyes closed like being at hairdresser’s.
- Avoid facial cosmetics, makeup, mascara and colored contact lenses for ten days after the operation.
- Do not drive until you are confident with your vision.
- UV blocking sunglasses required when outdoors after surgery for two months.
- foreign body sensation
- pain
- blurred vision
- itchiness
- lacrimation
- redness
- eyelid swelling
- light sensitivity
- headache
