MENU

Posts Tagged ‘eye surgery’

Keratoconus Causes and Treatment Options

Saturday, July 31st, 2010

By: Clark Chang, OD, MS, FAAO

Keratoconus Causes

Keratoconus is a non-inflammatory, progressive corneal condition associated with corneal thinning, weakening, and steepening, resulting in corneal optical irregularities (cone shape) and poor vision. An incidence rate of 1:2000 has been reported with no known sexual or ethnic predilection. In addition, familial inheritance has been reported in 6-24% of cases and co-morbidities such as atopic disease and connective tissue diseases have also been reported in the literature. Thus, genetic predisposition, acute eye allergies, and eye rubbing (often as allergic response) have all been proposed as potential underlying causes of keratoconus development. However, no definite causative factor(s) have been proven.

As keratoconus progresses in severity, the increasingly irregular shape of the eye causes optical side effects known as higher order aberrations (think of static noise for TV signals). These aberrations are primarily responsible for the reduction in one’s visual functions.  Corneal transplant has traditionally been utilized as the choice of medical treatment for the misshapen cornea. However, the reconstructed tissue interface does not always restore the cornea to its normal (spherical) shape, which means contact lenses are still needed to treat keratoconus after corneal transplantation1. Therefore, with the recent advancements in contact lens technology, non-surgical management methods have been recognized as the leading treatment choice in visual rehabilitation for keratoconus patients. Surgical options are currently being preserved for individuals who either cannot tolerate contact lenses or cannot achieve satisfactory vision with contact lenses2.

Keratoconus Contact Lens Treatment Options

Rigid Gas Permeable lenses (RGP) provide good visual outcomes, which make it the most widely utilized method in rehabilitating an irregular corneal surface. The firm structure of an RGP lens allows a layer of tear fluid to form beneath the lens; the tear layer fills in the irregularities between the cornea and the lens, and the combination of the smooth outer lens surface and the tear layer neutralizes the visual distortions. However, the advantages of good visual outcome and ease of lens handling may not always outweigh the amount of time it takes to adapt to RGP lenses and the issues of discomfort and the potential for RGP lenses to “pop out” of the eye. Therefore, alternative non-surgical treatment options have been developed to overcome such issues.

Because most soft lens materials are flexible they drape over the cornea. If the cornea is irregularly shaped, a soft lens will take the shape of the irregularities hence, this treatment option is only used for patients with very mild keratoconus. Nonetheless, recent custom soft keratoconus lens designs employ enhanced lens thickness in an attempt to mimic the optical benefits offered by RGP lenses. While oxygen permeability may be a concern until new material becomes available, the soft keratoconus lens provides a viable alternative for patients with mild to moderate keratoconus who cannot tolerate an RGP lens.

RGP intolerance mainly stems from irritation caused by the lens touching the eye.  A carefully selected bandage soft lens can be placed under the RGP lens in a piggyback system, which decreases irritation and helps stabilize the RGP lens on the eye. However, handling the two-lens system can be complex and inconvenient as there is a potential for reduced oxygen supply to the eye3.

Hybrid lens technology has enabled the bonding of an RGP lens with a soft lens so a single lens system offers both improved visual quality and increased wearing comfort. The recent advances in the 4th generation hybrid lens, ClearKone®, utilize a uniquely designed RGP lens shape to expand on its previous fitting parameters to include patients through all stages of keratoconus. Fitting success rates up to 86.9% have been reported utilizing hybrid lens platforms on keratoconus patients.

Recently improved oxygen permeability in RGP lens materials led to the clinical resurgence of scleral lenses. Scleral lenses comprise the largest diameter lenses within the family of non-surgical treatment options. A scleral lens design can often be more comfortable than its smaller RGP counterpart because a scleral lens design allows its lens edge to rest on sclera (white part of the eye), which has much lower sensitivity than one’s cornea. In addition, similar to the 4th generation hybrid lenses, sclera lenses are designed so the lens does not bear on the cornea, which minimizes irritation. Up to a 93% fitting success rate has been described with modern scleral lens designs1.

Because of the larger lens diameters in both the hybrid and scleral lenses, in comparison to the conventional RGP lenses, the insertion and removal process is different and requires practice during the initial adaptation period. This can hold true even for patients that have worn contact lenses before.

A well-fitted contact lens not only defers the need for more invasive surgical procedures but also significantly improves the quality of one’s vision and life. However, this process requires the combined ingredients of a physician’s clinical expertise and a patient’s determination. Further, it is essential for both the physician and the patient to recognize that no single lens design currently encompasses the complexity of all fitting situations. An open and honest discussion regarding one’s visual expectations and daily functional tasks performed in real life environment can be meaningful in the selection of a tailored management choice from the many non-surgical options that exist today.

Reference

1. Rosenthal P. Evolution of an Ocular Surface Prosthesis. Contact Lens Spectrum. 2009 Dec: 24(12):32-38

2. Garcia-Lledo M, Feinbaum C, Alio JL. Contact lens fitting in keratoconus. Compr Ophthalmol Update. 2006 Mar-Apr; 7(2):47-52.

3. Rosenthal P. Evolution of an Ocular Surface Prosthesis. Contact Lens Spectrum. 2009 Dec: 24(12):32-38.

4. Garcia-Lledo M, Feinbaum C, Alio JL. Contact lens fitting in keratoconus. Compr Ophthalmol Update. 2006 Mar-Apr; 7(2):47-52.

5. Nau AC. A comparison of Synergeyes versus traditional rigid gas permeable lens designs for patients with irregular corneas. Eye Contact Lens. 2008 Jul;34(4):198-200.

6. Abdalla YF, Elsahn AF, Hammersmith KM, Cohen EJ. SynergEyes lenses for keratoconus. Cornea. 2010 Jan;29(1):5-8.

Contact Lenses vs. Surgery for Keratoconus

Saturday, July 31st, 2010

Contact lenses with a rigid surface are the undisputed gold standard for restoring vision in keratoconus.  Despite recent advances in surgical treatment — including collagen cross-linking, intracorneal ring implants (Intacs), and partial-thickness corneal transplants — none of the currently available surgeries can make the distorted keratoconic cornea quite as smooth as the surface of a rigid contact lens.  The uniform surface of a rigid lens masks the distorted, irregular cornea in keratoconus, allowing light to properly focus into the eye.  Simply put, the rigid surface neutralizes the optical turbulence of the keratoconic eye.  This is why many of the top corneal surgeons first refer their keratoconus patients to a contact lens specialist before operating.  Of course surgical treatment has its place.  However surgery for keratoconus often has a secondary role in relation to less invasive contact lens treatments.

A historical challenge with rigid or “hard” contact lenses is that some wearers, even those without keratoconus, have difficulty overcoming the initial awareness of the lens edge interacting with the eyelid.  If you have keratoconus and can’t wear even optimally prescribed rigid lenses, you may be stuck between a rock and a hard place.  That’s because glasses and corneal surgery by themselves can’t approach the quality of vision afforded by rigid optics, at least not typically.  Furthermore, while soft contacts are initially more comfortable than their rigid counterparts, the soft material conforms to the irregular “peaks and valleys” of the keratoconic cornea, leaving the visual distortions largely unaddressed.

So what can your eye doctor do in the aforementioned situation?  Your doctor may recommend UltraHealth or ClearKone® hybrid contact lenses which combine the clarity of a rigid center with the comfort of a soft outer skirt.  These  lenses were designed specifically for keratoconus.  For selected patients, properly prescribed UltraHealth  lenses can afford a new-found freedom that no other treatment can approach.  UltraHealth  is an important option for some keratoconus patients who are unable to wear rigid lenses.  Yet UltraHealth  also has a role for many other keratoconus patients, especially those active in sports where resistance against lens dislodgement and visual stability are desirable.  Many of the contact lens specialists at the forefront of keratoconus treatment are certified to prescribe UltraHealth.  These contact lens specialists tend to interact regularly with corneal surgeons, using a team-approach to treat keratoconus both non-surgically and surgically as dictated by the particulars of each case.

Another alternative is scleral lenses, which are rigid contacts that are unusually large — larger in diameter than most soft contacts.  Scleral lenses often provide improved initial comfort over smaller diameter rigid lens designs, however they can require greater expertise by the practitioner and patient for successful wear.

For those already wearing more common rigid lenses, but who are experiencing the unavoidable rubbing on the sensitive corneal surface from the lenses, your eye doctor may prescribe a “piggyback” system.  In piggyback systems, breathable soft lenses are worn underneath the rigid lenses not for improving vision, but for protecting against mechanical chaffing and the resulting discomfort.  Your eye care professional can determine the appropriate contact lens modality for your specific circumstance, including whether lens wearing discomfort is due to sensitivity of the lens edges, lens chaffing of the cornea, or some other reason.

Ultimately, the practitioner’s experience and skill are more important than the contact lens design used for treating keratoconus.  Many eye doctors do not routinely prescribe medically-necessary contact lenses and will refer you to one of their colleagues with such expertise.  Since the pattern of corneal distortion in keratoconus is as unique as a fingerprint, there isn’t a single lens design that works for every eye.  Contact lens prescribing for keratoconus is a process which can span many visits before all refinements to the lens parameters are completed.  Due to the chair-time required and custom nature of the prescribing, it’s not uncommon for the services and lenses to cost over $1,500 without third party coverage.  Many medical insurances fail to understand that contact lenses for keratoconus are non-elective and medically-necessary for rehabilitating vision.  Consequently, keratoconus patients often shoulder most of the financial responsibility for their contact lens treatment.

Surgical Treatment Options for Keratoconus

Tuesday, July 27th, 2010

Medical and surgical options for the treatment of keratoconus are also expanding and improving. Corneal transplantation (penetrating keratoplasty or “PK”) has been utilized for the surgical management of keratoconus for many decades. The criteria for PK surgery typically is either the development of corneal scaring that reduces best corrected vision (even with contact lenses) or intolerance to contact lens wear (due to poor comfort or the inability to achieve a stable fit). Modification and improvement in surgical techniques has made PK much more successful. It should be noted however that keratoconus patients undergoing PK most often still require contact lenses to provide optimal vision. It is the exception to the rule to find patients who do not need some form of contact lens correction following PK, and even rarer to find a patient who does not need any type of vision correction after this surgery.



Intacs Corneal Segments

Click to enlarge



Intacs (by Addition Technology) is a relatively newer surgical method to address the corneal irregularity found in keratoconus. It involves the implantation of tiny plastic segments within the cornea. The result is to make the optical surface of the cornea relatively more regular, thus reducing the degree of vision distortion. This technology is only indicated for keratoconic corneas without scaring, yet have become contact lens intolerant. Results with Intacs have been encouraging, but once again are not a total solution for this disease. As with PK, patients who have had Intacs implanted most often still require contact lens correction for maximum vision. By making the corneal surface more regular contact lens fitting may be more successful following Intacs.

The newest development in the medical treatment for keratoconus is termed “Collagen Crosslinking with Riboflavin”. It involved the exposure of the cornea to riboflavin (vitamin B2) and ultraviolet light for a period of time. The result is a change in the crosslinking of collagen fibrils within the substance of the cornea. For some patients this treatment strengthens the cornea and therefore slows down or halts the progression of keratoconus. For some more fortunate patients this treatment may also improve corneal surface regularity. Numerous studies evaluating this so far non-FDA approved procedure are going on throughout the United States.

Keratoconus is a corneal disease that results in progressive visual distortion. Technologies in contact lens correction, medical treatment, and surgical options for keratoconus continue to improve. The primary treatment for the disease is with specialized contact lenses. Seeing an eye care professional who is skilled and experienced in the diagnosis and management of keratoconus provides the best opportunity to experience the best vision possible.

Article Written by: S. Barry Eiden, OD, FAAO

President and Medical Director of North Suburban Vision Consultants, Ltd.

Website: http://www.nsvc.com

EyeVis Eye and Vision Research Institute

Immediate Past Chair of the Contact Lens and Cornea Section of the American Optometric Association


« READ “Non-Surgical Treatment Options”

Scroll Up