by Eiman Atia, Senior Optometry Student at the New England College Of Optometry
Stephanie Sturgis, Senior Optometry Student at the Pennsylvania College Of Optometry
Scleral lens technology has been around since 1888 and was first developed in Germany. However, the concept was first put on paper in the 15th century by Leonardo Da Vinci. They were the first contact lens to be developed but today they remain a highly under-utilized medical device. There are many anterior segment conditions that warrant usage of a scleral lens such as keratoconus, pellucid marginal degeneration, other atypical cones, dry eyes and Steven Johnson Syndrome. People who develop these conditions may be led to believe that the only option to address these issues is through invasive surgery. Some of these surgeries include LASIK, RK, ALK, CK, PRK, Intacs, and other types of corneal transplants. Of course with every surgery there are risks and complications and sometimes these surgeries do not always have the desired outcome. This paper will explore these procedures and their post-surgical complications that may indicate usage of scleral lenses.
More recently, refractive surgery has been a popular option for those who wish to discontinue wearing glasses or contact lenses to achieve clear vision. The most common refractive procedure is laser assisted in-situ keratomileusis, otherwise known as LASIK. During this procedure, a topical anesthetic is used and an excimer laser is used to create a flap in the epithelial layer of the cornea. Once this flap is created, it is folded back and the laser removes some tissue underneath the flap to permanently re-shape the cornea and correct for the patient’s refractive error. Once the tissue is removed, the flap is then put back into place and the epithelial tissue is left to heal on its own. The amount of tissue removed is generally calculated based on the patient’s prescription and the thickness of their cornea. The eye is then usually patched overnight to prevent any rubbing or mechanical disturbance that would cause delayed healing. LASIK is an outpatient procedure that takes approximately 10-15 minutes per eye. Patients can expect to see their visual results in a few days after surgery, and sometimes can take months to see results. In order to be considered to have this surgery, it is generally recommended that the patient is at least 18 years of age and has a stable prescription. For some patients who have myopia (nearsightedness), their prescription may not stabilize until their mid to late 20s. Other contraindications for LASIK include diabetes, rheumatoid arthritis, lupus, glaucoma, herpes or cataracts, and pregnant or breastfeeding women. Patients should also take into account that once they hit presbyopic age, (around age 40), they will be dependent on reading glasses regardless of the LASIK procedure. Patients should also bear in mind that sometimes after the surgery, another LASIK procedure is needed to correct for residual refractive error. Some other symptoms that patients may experience after LASIK include glare, halos, dry eyes, decreased contrast sensitivity, light sensitivity, and poor night vision. In some other instances, complications may arise after surgery including permanent vision loss or decreased vision due to irregular astigmatism, flap complications such as epithelial ingrowth, diffuse lamellar keratitis( DLK), keratectasia, dry eyes, eye infections, haze, ocular pain and so on.
Scleral lenses not only correct for post-LASIK complications such as irregular astigmatism, corneal ectasia and other types of compromised corneas by the optics explained above, but they can also serve as protection and relief for those with dry eyes due to LASIK, by being in a constant moist environment throughout the day.
Radial Keratotomy is one of the earliest refractive eye surgeries which was introduced in 1978. During this procedure numerous incisions are made throughout the periphery of the cornea to correct for the refractive error. RK is intended for people with refractive errors ranging from one to four diopters of myopia. RK is not a very common procedure now as more modern techniques using excimer lasers are more accurate and have better predictability in their surgical results. In general, a good candidate for RK is quite similar to LASIK criteria. Contraindications are similar as well and include diabetes, autoimmune disease, and HIV/AIDS, herpes, glaucoma, pregnancy and dry eyes. In this type of eye surgery, it is strongly contraindicated in those with family or personal history of corneal disease. One of the biggest drawbacks of RK is that it may result in symptoms such as fluctuating vision throughout the day, halos, starbursts, and glare. Another drawback is that the prescription after surgery is not as stable as that of LASIK or PRK, and there tends to be a hyperopic shift in refractive error after a few years. The incisions from the surgery never heal. This leaves an open wound, which leads to more long term risk of infection. If the infection becomes untreatable, the only option left may be to receive a corneal transplant.
Due to the open wounds and possible fluctuating vision after surgery in some patients, soft contact lenses would potentially make these concerns an even larger issue. Since scleral lenses have a liquid interface between the lens and cornea, they help compensate for the fluctuation of vision throughout the day and also vault over the compromised cornea, therefore providing comfort and improved vision for these patients. Since the scleral lens vaults over the entire cornea and the cornea is cushioned in liquid it is protected from external insult.
Automated Lamellar Keratoplasty is an outdated refractive procedure similar to LASIK except that a microkeratome is used to remove tissue from the cornea instead of a laser. It is outdated because it is not as accurate as current methods of reshaping the cornea. A flap is created in this procedure and the underlying tissue is taken out to reshape the cornea, just as in LASIK. The recovery time is about 24 hours, however, the vision may not stabilize until weeks later. Candidacy and side effects are similar to LASIK as well. It can correct nearsightedness with refractions from -5.00 to -8.00. This procedure has been known to serve well for those in need of higher vision corrections but as said before, is less accurate.
Another procedure performed for those who are farsighted or hyperopic is known as Conductive Keratoplasty (CK). In this surgery, instead of a laser, a radio frequency energy wave gently remolds the cornea. The radio wave frequency used creates a thermal effect that shrinks the stromal layer in the cornea to re-shape the tissue. According to the FDA an ideal candidate is a patient who is over the age of 40 who has minimal difference between their manifest and cycloplegic refraction, about 0.50 D or less. The range of refractive error that can be treated ranges from +0.75 to +3.25 and astigmatism less than 0.75 D after a cycloplegic eye exam. A good candidate is also one who has had adequate distance vision since birth and can tolerate mild distance blur following the procedure. Contraindications for CK include those mentioned under LASIK and ALK as well as corneas with less than 560 microns in the periphery, or those on any systemic or ocular medications affecting the eyes.
Photorefractive keratectomy is a refractive procedure similar to LASIK in that an excimer laser is used to reshape the cornea. The difference lies in that there is no flap created in the PRK procedure. The laser is instead applied directly to the surface of the cornea. This accounts for a longer recovery period than LASIK would because the epithelial layer has to regenerate and replace the lost tissue. Usually it can take a few weeks to several months for patients to achieve their best corrected vision with this procedure. With LASIK, visual results are seen almost immediately whereas in PRK the improvement in vision will take much longer to occur because the epithelium has to regenerate. This procedure is used for all refractive errors including myopia, hyperopia, and astigmatism. The candidacy for this procedure, as well as the side effects are the same as LASIK. In preparation for the procedure the patient must refrain from wearing all types of contact lenses for a couple weeks before the procedure to ensure the cornea is in an unaltered state. After the surgery a bandage contact lens is placed on the cornea for 4-5 days to allow the epithelium to heal. Corneal ectasia is a common side effect in LASIK but it tends to be much less common after PRK procedures. If corneal ectasia were to occur a scleral lens would be the ideal management option for the patient.
Intacs were approved in 2004 by the FDA to help treat keratoconus and have also been used to help correct prescriptions in those who are nearsighted. These small semi-circular plastic rings are inserted in the stromal layer of the cornea to flatten its shape and essentially get rid of the keratoconus and myopia by altering the shape of the cornea or moving the cone, thus smoothing over the irregularities. This procedure involves making a small incision in the surface of the cornea while the eye is under anesthetic. The layers of the cornea are separated to ensure proper positioning of the Intacs. An instrument is used to assist in proper alignment of the Intacs. A suture is then used to close the incision and the healing process will begin. Glasses or contacts may still be required after this surgery takes place. Complications of Intacs include over or undercorrection, neovascularization near the incision site, migration of the Intacs toward the wound or extrusion of the Intacs. The best candidate known for this type of surgery are those who have keratoconus but cannot tolerate contact lenses and whose corneas are clear. The main purpose of Intacs is to help improve visual acuity because they will not cure keratoconus but can postpone the need for invasive surgeries such as corneal transplants. Despite improving visual function, Intacs will not prevent further stromal progression in keratoconus.
Scleral lenses can be used as an alternative to all of the above procedures as well as a post-surgical option to the above procedural complications. Scleral lens technology is a well-known, but underutilized medical device for patients who either have irregularly shaped corneas from disease or have who have experienced surgical trauma. These post-surgical patients with complications are sometimes left with fear and doubt that no option exists to improve their loss of vision. These distortions cannot always be corrected with the conventional methods of soft contact lenses, RGP contact lenses and glasses. Soft contact lenses are not a good option for irregular corneas because they mold to the same shape of the irregular cornea, causing light coming in to the eye to be scattered and form an unclear image. For those with dry eyes, they are also not well tolerated. RGPs are a better option than soft lenses because they are a harder material that can be custom made to essentially mask the irregularities of the damaged cornea. The tear film that sits underneath the lens negates the irregularity of the cornea as well, giving a smooth surface for light to focus on the back of the retina, forming a sharp image. These lenses have a smaller diameter and can sometimes be very uncomfortable and hard to adapt to. They do, however, provide good optics and crisper vision. Scleral lenses are another type of hard contact lens whose optics function similarly to that of RGPs. Scleral lenses differ in that they have a larger diameter, allowing them to vault over the cornea and sit on the sclera, the white of the eye, instead of the cornea. This provides better initial comfort and allows for an easier adaptation period than RGP lenses. The scleral lens is inserted in the eye with saline which acts as a liquid interface between the scleral lens and the cornea. Since the lens and liquid interface form a smooth surface, light will not be scattered and halos and glare can be eliminated. They can also be used to treat the over or undercorrection induced by surgery that eyeglasses and soft lenses cannot mask. As explained above, these lenses can be used to protect the eye from environmental irritants such as air conditioning, allergens and dust in those who have open wounds from surgeries such as RK, as well as those with dry eye. Keratectasia is a corneal condition that can result from non-surgical disease such as keratoconus, keratoglobus and pellucid marginal degeneration, as well as post-refractive surgeries including LASIK, PRK, RK, ALK, and CK and Intacs. During surgery, the corneal wall is made thinner and the pressure from internal forces from the eye can cause this malleable soft tissue to become distended and protruded. The only way to manage and achieve acceptable vision when this happens, is to have a scleral lens vault over this changing tissue. The concept of vaulting over changing tissue is also why these lenses work well for those who have had migration or extrusion from Intacs. If vision is improved with these lenses, there is absolutely no indication for a corneal transplant.
Patients who have had LASIK, RK, ALK, CK,PRK, and Intacs complications should consider scleral lenses as a first line treatment before considering more invasive procedures. A scleral lens can substitute for a corneal transplant by essentially replacing the irregular corneas with as a new optical surface. This new optical surface can serve to get rid of the symptomatic side effects of halos, glare, and dryness that may arise from these procedures. As mentioned earlier, conventional methods for correcting refractive error are not sufficient for these types of complications. Scleral lenses may be one of the only options readily available to treat these conditions without having to undergo surgery again and risk greater complications.
Scleral lenses have many other indications such as cosmetic, sports vision aid including those involved in activities such as swimming, and other settings with dust or dirt. They can be used as a protective device over corneal transplants and also have promising future implications of being used as a drug vehicle to the front surface of the eye. Scleral lenses are under-utilized and should be considered a first-line treatment/management for anterior segment conditions and complications.
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