Keratoconus | Eye Doctors Contact Lenses and New Options for Treatment

Keratoconus Courtesy of Indiana University Department of Ophthalmology

Keratoconus is an eye disease that causes vision to gradually worsen over time, as the transparent corneal tissue that covers the front of the eye thins and bulges forward, forming the cone shape that keratoconus is named for. Rapid increases in nearsightedness and astigmatism are common with frequent changes in your eyeglass prescription. Scarring of the cornea can also occur resulting in significant vision loss.

Keratoconus Symptoms Your Optometrist may discuss

• The appearance of long linear light streaks in your eyesight at night

• Visual Glare and halos around lights, especially car headlights and taillights at night

• Double Vision

• Distorted Vision

• Blurry Vision making it difficult to read

• Ghost like eye images of white light surrounding objects you are viewing, sometimes noticed as multiple dots when viewing on small light image-can be seen with one eye

• Eye Sensitivity to light

• Eye Doctors Agree Keratoconus usually show up most commonly between the teenage years of 16 up to age 30

When this corneal eye disease manifests at earlier ages optometrists often find a more aggressive form with ongoing, frequent changes in your eyeglass or contact lens prescription. The best guess is the occurrence rate is about 1 in 2000 people. It is hard for eye doctors to pin down the exact rate of this eye disease because it can be very mild and remain undiagnosed, especially when it burns out early (form fruste), or stops progressing after several years. Corneal Keratoconus creates irregular astigmatism, causing curvatures on the cornea tissue that are not nice smooth curves. Instead the eye curvature resembles the surface of a potato with dips and valleys on a very irregular shape. This type of shape makes it very difficult for your optometrist to prescribe an eye prescription for eyeglasses that results in clear vision. The lenses would have to be made in very strange shapes to result in clear vision. Even lenses that have been designed in this manner are rendered ineffective the moment your eyes look off the center of the lens. Irregular astigmatism also occurs without kerataconus, but it does not tend to progress and result in the characteristic steepening of the cornea resembling a cone shaped area. Usually kerataconus presents in one eye and over time well over half of the eye patients will have both eyes involved.

The cause of Kerataconus and the changes in the cornea are surprisingly not well known by the optometric research clinics at this time. In the past, much speculation centered around eye rubbing and ocular allergies. Some eye physicians have speculated that Keratoconus is triggered by eye rubbing that starts an inflammatory cascade in the cornea. Frequent eye rubbing also could cause mechanical tissue breakdown in areas of the cornea that are already compromised. Research by eye doctors has shown between 6-8% of patients with kerataconus have a family history, indicating there is a genetic component in some cases. Several areas of chromosomes have been identified as potential genetic markers and are being investigated further. Also, certain eye diseases such as retinitis pigmentosa, retinopathy of prematurely (damage to the retina tissue in the back of the eye from premature birth), Leber’s congenital amaurosis (a degenerative disease of the optic nerve), and vernal keratoconjunctivitis (a type of allergic eye disease which creates itchy eyes and frequent) appear to have some correlation. Some disease of the body also have a degree of co-occurrence with Keratoconus- Ehlers-Danlos syndrome, Down syndrome, osteogenesis imperfecta, pseuodoxanthoma elasticum), mitral valve prolapse in the heart, Laurence-Moon-Biedl syndrome, Rieger’s syndrome and neurofibromatosis. Several of these diseases interfere with normal collagen development and may precipitate kerataconus by disrupting collagen development in the cornea.

The changes to the cornea from Keratoconus are mostly unknown. The cornea consists of 5 layers and is about 1/2 mm thick (550 microns or about the width of 5 human hairs). The epithelium layer is the surface layers of cells. Underneath the eyes epithelium layers is a thin basement membrane sitting on the anterior limiting membrane, also know as bowman’s membrane. The bulk of the corneal thickness is in the stromal layer, where the collagen protein fibers run across the cornea, adding the tensile strength. Tensile strength is the degree a material can be stressed and still return to it’s original state and shape. Collagen is the memory material of the cornea. The structure of collagen changes in the center area of the cornea with shorter fibers, that cross more, run at different angles, run though each other, form connections to Bowmans membrane, and also form connections originating from Bowman’s membrane. It has been suggested from research by Jan P.G. Bergmanson, OD, PhD, PhD h.c, DSc, & Jessica H. Mathew, OD that this alteration in structure near the central cornea may help explain the nature of Keratoconus in the future, With shorter fibers running in differing directions with various connections the central cornea would seem to be more prone to breakdown of the normal collagen structure. Optometrists have found the bulging cone area characteristic of Keratoconus cones usually form close to the central cornea, slightly inferior, which seems to substantiate the altered central corneal tissues may play a part in the eye condition. Early changes may occur in the surface epithelial cells disrupting the basement membrane. When keratoconus begins, whatever the cause may be, enzymes increase and start damaging the epithelial basement membrane. This is the membrane formed underneath the lowest level of epithelial cells. Subsequent breaks in the corneal anterior limiting membrane occur and the cornea starts to thin centrally, probably due to the susceptibility of the different surface anatomy of the collagen fibers under lying Bowman’s membrane. As these breaks occur the surface epithelial cells can contact the stromal level of the cornea where most of the structural framework of this eye tissue is located. Small proteins called cytokines are released and alter the fluids around the cells, leading to scarring of the cornea.  Stromal fibers may move through the anterior limiting membrane. Whatever the cause, a disruption of the normal collagen structure causes the memory shape to lose its capacity and irregular shaped corneas to subsequently develop. There are indications of changes in the different enzymes that degrade proteins and induce changes in the collagen and the spaces surrounding the cells in the cornea. Cathepsins are one type of protein that increase as kerataconus starts to occur. These could lead to destruction of the so called extra cellular matrix, the substances surrounding the cells and lead to degenerative effects in the cornea.
They may also indirectly cause a reduction in the antioxidants and increase oxidative damage to the cornea, another theory that has been proposed. Matrix metalloproteinase-2 is also activated and changes the extra cellular matrix surrounding the corneal cells. Keratocytes are numerous cells in the cornea that produce the collagen for the fibers and the extracllular matrix components, turning mostly dormant by birth. In Keratoconus they have been observed to have increased apoptosis (increased programmed cellular death). There us a reduction in the number of collagen fiber and they also reduce in diameter. Most likely, keratoconus will be found to be several different disease processes and also multifactoral. Multifactoral eye diseases have multiple factors that combine to create the eye condition. For instance, the different collagen structure in the central cornea makes the eye susceptible, changes in enzymes may alter the tissues and start causing minor breakdowns in the epithelial surface cells, enzyme changes may lead to increased oxidative stress further weakening the eye tissue, and constant rubbing of the eyes may push the eyes over the edge by inducing mechanical damage to the eye tissues that could only occur with a compromised cornea. A genetic alteration of the cornea could make the cornea of the eye more susceptible to the entire chain of events.

Your eye doctor will initially treat Keratoconus with contact lenses

Treatment of Keratoconus usually begins with a rigid gas permeable contact lens when vision can no longer be maintained clearly with spectacle lenses. Sometimes, a gas permeable lens will be fit over the top of a soft contact lens in a piggyback contact lens fitting, with a soft contact lens and a rigid gas permeable contact lens on top of it. While used years ago, piggyback contact lens fittings fell out of favor due to the complications from reduced oxygen flow with older soft contact lenses. With the new super oxygen permeable silicone hydrogel soft contact lenses, it is enjoying a small resurgence. It is primarily used to increase eye comfort for the keratoconic eye patient. There are also combination contact lenses available today, such as the SynergEyes contact lens that is a rigid contact lens with a soft skirt attached surrounding the lens. The primary issue with Keratoconic contact lens fittings is matching the steeply curved cone with the surrounding flatter eye tissue, while dealing with the irregularities of curvature that are present. While custom mapping technology is highly touted as the way to achieve the required fit, the truth is observation of contact lenses on a keratoconic eye by an optometrist and adjustments based on how dyes accumulate under the contact lenses is still the most accurate method to achieve an excellent final fit. Due to the drastic changes in curvature the contact lenses require multiple different curves as you move toward the edge of the lens. While many different lenses have been developed with special names as the ultimate Keratoconus contact lens, they are all variations on the basic concept of a steep contact lens center and a gradient of changing curvatures to the edge. Rigid contact lenses work because the light bending capacity of the tears is very close to the light bending capacity of the cornea. The tears fill in between the irregular eye surface and the smooth surface on the back of the lens. This essentially removes the irregular astigmatism and nearsightedness by utilizing the back contact lens surface as a new regular surface where light is altered, and often restores the corrected eyesight close to 20/20. Eye glasses may only achieve 20/40 vision or much worse because the irregular surface remains. Occasionally Scleral rigid gas permeable lenses are used. These are gas permeable lenses larger than normal that extend out onto the white part of the eye. All contact lenses today are gas permeable, or designed to let air pass through to keep the cornea healthy. Soft contact lenses are usually not referred to as gas permeable because of historical changes. Hard lenses were the first contact lenses and they were made of a material that passed no oxygen through the lens. When changes were made to the polymers used to make hard contact lenses that allowed them to breathe or pass needed air to the underlying cornea, they were renamed rigid gas permeable contact lenses. Rigid because they are still a hard material with only 1-2% water, and gas permeable because unlike the older hard contact lenses they now transmitted air to the eyes. Soon they became called by the acronym of RGP’s to save a few words (even prior to the texting era). With time they also came to be referred to as gas perms, in spite of the fact that all soft contact lenses are also gas permeable. Soft contact lenses are never rigid however, as they normally are composed of about 50% water. This softness comes at the price of increased flexibility and they drape across the eye, imitating the irregularities of a Keratoconic cornea and do not correct the vision back to optimum levels. Once your eye doctor has achieved an excellent fit and optimized your contact lens prescription, there may be frequent changes in your contact lens prescription as the Keratoconus goes through progressive changes.

Your Eye Doctor May Be Able to Avoid Corneal Transplants

While only 10-20% of eyes will undergo ongoing serious changes, they do present challenges to fitting contact lenses on eyes with Keratoconus. At some point, scarring of the cornea can start to occur and patients become intolerant to contact lenses. In years past, the only remaining option was a corneal transplant. While corneal transplants enjoy a relatively high success rate, there are still risks and problems. Recently there have been some new exciting options starting to evolve.

Permanent Contact Lenses-Intacs

Intacs are small rigid half rings similar to portions of a gas permeable contact lens that are implanted in the cornea. They were originally developed to reverse nearsightedness, but did not prove as effective as originally thought and were replaced by LASIK eye correction procedures. A few years ago they found a new use in stabilizing Kerataconus. They are not a cure for Keratoconus, but can restore some more regularity and allow some patients to continue contact lens wear while avoiding a corneal transplant. They also appear to have some effect in decreasing the rate of change in Keratoconus. While they are promoted as being completely removable and reversible if patients have problems, this is not entirely true. About 10-15% of Intacs cause some complications and issues that cannot be resolved if they are removed. Still, it is a better option than jumping straight to a corneal transplant.

Keratoconus Corneal collagen cross-linking therapy

Corneal collagen cross-linking therapy (CXL) is intended to stabilize the tissue by forming more bonds between the existing collagen fibers and also increasing the size of the fibers, making the cornea much firmer and less likely to continue deforming. It involves pretreatment the cornea with riboflavin (Vitamin B2) for 30 minutes then using radiation from the ultraviolet A band light spectrum (normally around 370 nanometers) to increase the cross links over about a 30 minute period. While it has been more extensively in Europe, it is starting to enter the U.S. market. The riboflavin acts to keep the UVA from completely passing through the cornea so the UV can act to create more cross links. Riboflavin also may have a photo reactive effect that further increases cross linking of the collagen bands. Questions still surround this treatment. It is not an FDA approved treatment in the United States but is undergoing clinical trials, and currently is used off label as a treatment for Keratoconus. The FDA (Food and Drug Administration) regulates drugs and medical devices but not doctors. Any procedure that uses drugs or medical devices can be performed by a doctor if you are properly informed, share in the decision, and it has an acceptable possibility of helping. The riboflavin still allows a significant amount of UVA to pass through the cornea. This could potentially increase future risks for cataract development. UVA with riboflavin is cytotoxic (damaging to cells) and can damage the endothelial cells that line the back of the cornea and are vital for its long term health. Corneal thickness needs to be factored to keep this type of damage far enough away from the endothelium cells of the cornea. A minimum corneal thickness of 400 microns has been suggested but a better choice would be 450 to 500 microns. Cellular damage to the keratocytes, changes to the matrix of the cornea, and changes to the epithelium do occur in the cornea after the procedure. Normally they regenerate over the next 6 months. Riboflavin has poor penetration into the cornea so the surface layers of epithelium cells need to be removed. It is unknown if the effect of increased rigidity created by this treatment will last indefinitely, or if there are any other long term problems from increasing the cross linking and rigidity of the cornea. Some cases of persistent haze, infections, and increased eye pressure reading have been noted. The increased eye pressures are presumably an artifact since we know thicker (more firm) corneas read artificially high with most current glaucoma instruments. With careful consideration about the stage of Keratoconus and treatment of the eye at the appropriate stage, cross linking of collagen fibers in the cornea appears to be a great addition to eye doctors armetarium in treating keratoconus. While it may improve the condition mildly in many patients, it should always be considered as a stabilizing treatment and not a curative treatment.

Future therapies will evolve. Cross linking collagen therapy is still in its infancy. Stem cell and genetic treatments may be seen at some time. Someday we will no longer be treating Keratoconus but acting to prevent it from ever distorting peoples vision and lives.