Corneal Collagen Cross-linking Treatment
Corneal collagen cross-linking induced by treatment of impregnating Riboflavin (B2) in to the cornea and exposure to ultraviolet-A light is a safe and effective, minimally invasive procedure both to reduce disease progression, increase the strength of the cornea and to improve upon the cornea’s optical properties in eyes with early keratoconus.
As long as keratoconus is diagnosed early enough – a stabilization of clinical findings and visual acuity can be achieved without a need for a corneal transplant or further progression.
It is the first treatment for Keratoconus. It treats the cause not the symptoms, therefore the number of penetrating keratoplasty surgeries can be significantly reduced in the future. The treatment is relatively easy and low in costs and is available through out the world. Avoiding advanced Keratoconus because of the problems it causes is what the aim is with this treatment.
The early use of the cross-linking treatment must be advised to the patient as an option for them to halt any further progression once Keratoconus has been diagnosed. So that they have a chance to avoid advanced Keratoconus and all the problems that it can cause with vision correction.
Spectacle Correction in Keratoconus
In the early stages of keratoconus, the patient’s refractive error can often be successfully managed with spectacle lenses. It is important to communicate to the patient that there is no evidence to support the theory that early contact lens intervention is of therapeutic benefit in preventing or lessoning the progression of the disease. However, wearing contact lenses typically provides the patient with better visual acuity than can be obtained with glasses by neutralizing the regular and irregular refractive errors induced by the condition. As keratoconus progresses, spectacle lenses often fail to provide adequate visual acuity, especially at night. This can be further complicated by the fact that the patient’s glasses prescription may change frequently and can be limited by the degree of myopia and astigmatism that must be corrected. Also, keratoconus is often asymmetric therefore full spectacle correction may be intolerable because of anisometropia and anisokonia. However, despite these limitations, spectacles can often provide surprisingly good visual results in the early stages of the condition.
Wave Contact Lenses
Wave Contact Lenses are Contact Lenses which are custom designed from your corneal “fingerprint”, its a new technology which is being used to aid for a better fit and visual accuracy. Corneal Topography equipment digitally maps your cornea with thousands of numbers. The doctor uses the map data and Wave-front special design software to create a custom lens that follows almost every tiny shape on your cornea. Custom designed lenses differ greatly from plain “mass produced” lenses. The doctor using Wavefront technology for contact lenses will specify the lens diameter and thickness for comfort and adjust the position of the optics for best visual performance. In all there are 26 different adjustments, offering infinite design possibilities. Keratoconus Post Refractive Patient’s are the most challenging to fit with off-the shelve contact lenses and most in need of Wave-front contact lenses custom “match the cornea” design philosophy.
- The successful fitting of contact lenses for keratoconus requires that three objectives be met:
- The lens-to-cornea fitting relationship should create the least possible physical trauma to the cornea.
- The lens should provide stable visual acuity throughout the patient’s entire wearing schedule.
- The lens should provide all day wearing comfort.
Although it may be impossible to meet all of these objectives for every patient, we should remain focused on utilizing all of the modern lens designs and fitting techniques at our disposal to achieve the best possible outcomes.
Surgical Treatments for Corneal Ectasia Since the 1950’s, penetrating keratoplasty has been the primary surgical procedure for treatment of keratoconus.
The decision to pursue keratoplasty is one that must be made by the individual surgeon and the patient. The factors that can influence the decision include:
- The patient can no longer tolerate or be fitted adequately with contact lenses.
- The contact lenses fail to provide adequate visual acuity due to corneal scarring.
- Sharp bilateral visual acuity is required for recreational or professional requirements.
It is important to recognize that certain patients are perfectly content with 20/50 to 20/60 (6/15 to 6/18) visual acuity. Over the years, these individuals have developed blur interpretation skills that allow them to function surprisingly well in their daily endeavors. The major limiting factor for these individuals is difficulty driving at night. For most surgeons, keratoplasty is not considered until contact lens options have been exhausted.
Surgery involves risks that include:
- Graft rejection,
- High post operative regular and/or irregular astigmatism, and
- Steep or flat grafts.
Patients should be informed that keratoplasty for keratoconus has a success rate of approximately 92% for a clear transplant on the first surgery and that occasionally a second or third transplant might be needed secondary to postoperative great rejection, infection, or wound healing complications. Patients should also be advised that following keratoplasty, approximately 85% of them will find it necessary to wear a contact lens to correct the surgically-induced regular and irregular astigmatism and anisometropia.
A lamellar graft (also known as DALK or a partial graft) replaces part, rather than all, of the thickness of the cornea. It can be used instead of a penetrating graft if the deeper layers of the cornea are healthy.
Intacs inserts are 150 degree PMMA ring segments that are placed in the peripheral stroma of the cornea, typically to correct myopia. However, the technique has also been recently US FDA approved for the treatment of keratoconus.
The inserts are designed to be placed at a depth of approximately two-thirds the corneal thickness and are surgically inserted through a small radial incision into a trough created within the corneal stroma. The inserts shorten the corneal arc length and have a net effect of flattening the central cornea. The amount of flattening is determined by the insert’s thickness. Rings are available in thicknesses of 0.250, 0.275, 0.300, 0.325 and 0.350 mm and are oriented horizontally in the cornea at 12 and 6 o’clock. Intacs are indicated for contact lens intolerant patients with early keratoconus who have minimal central stromal scarring.
In theory, the inserts are designed to flatten the central cornea and provide reinforcement for the peripheral cornea. The procedure may also decrease the cornea surface irregularity and improves the patient’s best-corrected visual acuity. It’s been reported that sometimes using one segment is sufficient and favorable. Ferrara Rings works in a similar way to Intacs, but there are some differences in when they are used, depending on the size of the flattening that needed and also the pupil size of the patient.
Ferrara Ring, which like Intacs have ring segments 150º of arc but have a smaller inner and outer diameter (4.4mm and 5.6mm) and are triangular in crosssection. They range in thickness from 0.2mm to 0.35mm in 0.05mm increments. Ferrara Rings are approved in Europe for Keratoconus.
CornealRing is another modified intracorneal ring system. It differs from the Intacs and Ferrara Rings in that it has a 5mm inner diameter and a fusiform shape that reduces the stress on the corneal stromal fibers. This is supposed to help reduce the problems associated with the other two systems.
Laser Surgery for Keratoconus
Clinicians typically rule out LASIK surgery for patients with keratoconus because of a greater risk for scarring and excessive thinning leading to possible post-LASIK ectasia. However, some surgeons have reported success in performing a smoothing procedure for patients over the age of 40 years with stable keratoconus. Candidates for the procedure are most often individuals with mild keratoconus who are contact lens intolerant and reluctant to pursue corneal transplant surgery.
Studies are now available where the patients have had a cross linking procedure simultaneous to the surface Laser surgery to reduce numbers or subsequently after the cross linking procedure.