Computer technology and biotechnology have improved our understanding of keratoconus over the past few years.
Keratoconus (ie, Greek derivitate, conical cornea) may be defined as a noninflammatory ecstatic corneal disorder.1,2 The treatment is mainly optical in early and moderate cases, however, surgery is required in advanced cones, as spectacles insufficiently compensate for the optical effects produced by irregular astigmatism. Rigid gas permeable contact lenses give satisfactory visual results in most cases, however, obvious practical and clinical concerns (ie, contact lens intolerance and contact lens-related problems)3-5 remain. Adequate tear exchanges, optical clearance and gas permeability of the system are essential to provide enough oxygen and to avoid hypoxic damage and scarring of the apex of the diseased cornea.
Keratoplasty — penetrating and lamellar — is, from the surgeon's point of view, a radical solution. The risk of postoperative sight-threatening complications, listed below, must be considered before determining to proceed with the surgery:1,6,7
• Functional recovery following corneal transplantation is usually long and often lasts >1 year.
• Medications (eg, corticosteroids and sometimes antimetabolites) are needed for several months postoperatively.
• Surgical and postsurgical graft survival/rejection and endothelial cell loss/rejection varies between patients. For example, a 20-year-old patient faces a limited duration of graft vitality. Graft survival decreases when combined with other factors (eg, atopy, 10 years survival rate of 75%; Down syndrome, 10 years survival rate of 65%).
• The peripheral ring of the recipient cornea consistently remains a potential source of recurrence. About 56% of keratoconus eyes successfully treated with penetrating keratoplasty (PK) showed progressive development of astigmatism 10 to 15 years after surgery.
• Poor availability of optimum quality donor tissue in countries where the culture of donation is low (eg, Middle Eastern countries).
• Postoperative ametropia.
• The need for additional correction (eg, contact lenses, LASIK, PRK, relaxing or
wedge incisions or toric phakic IOLs) to correct for posttransplantation refractive errors. An estimated 30% of eyes, post-PK, have >5.00 D of astigmatism.
A SOLUTION WITH MINIMAL RISK
The majority of keratoconic patients are younger and in their highest life activity. Patients want a minimal risk solution that gives high quality of vision, rapid rehabilitation and minimal discomfort and pain.8-10 Generally, well-informed patients are reluctant to undergo corneal transplantation. Surgeons should consider it as the last resort. Patients and surgeons should be interested in a more conservative alternative that delays corneal grafting.6,9
In my practice, we implanted intracorneal ring segments (Intacs; Addition Technology, Des Plaines, Illinois) in 127 keratoconic patients (186 eyes). We currently have 5-year follow-up results. Preoperative and postoperative assessment included slit lamp examination, UCVA and BCVA (decimal chart), corneal topography (Topographic Modeling System [TMS 2]; Tomey, New York, New York), central and peripheral corneal thickness using ultrasonic pachymetry (DGH-1000, DGH Technology, Exton, Pennsylvania) and Optical Path Difference (OPD) Scan (Nidek, Tokyo, Japan) where Zernike graph with the total and differential ocular aberrations were compared.
Patients had stage one or two keratoconus based on Amsler-Krumeich classification, with clear central corneal, BCVA >0.2, central pachymetry >400 µm and intolerance to contact lenses. The surgical procedure was done under topical anesthesia, using the 10-step prolate method (Addition Technology). The incision was always made in the steepest meridian (Figure 1).
The average age of patients was 28.9 ±6.2 years. A total of 63.5% (118 of 186 eyes) were bilaterally implanted and 36.5% (68 eyes) received unilateral Intacs implantation. Preoperative mean keratometric reading was 52.53 D (range, 47.00 D to 55.60 D), and postoperative readings can be found in Figure 2. Notice the fluctuation in the k readings during the first 3 months. This may represent stabilization of the cone after the curve is steady and stable. In terms of UCVA, 15.6% of patients gained more than three lines and 69.7% gained one to three lines, meaning a total of 85.3% of patients gained lines compared with their preoperative UCVA. At 5 years postoperative, these statistics were 11.9%, 73.3% and 85.2%, respectively (P<.01) (Figure 3).
In terms of BCVA, 19.7% of patients gained more than three lines and 68.2% of patients gained one to three lines. A total of 87.9% of patients gained lines compared with their preoperative BCVA. Results at 5 years postoperative were 13.2%, 72.9% and 86.1%, respectively (P<.01) (Figure 4).
Corneal topographic surface quality indices suggested that surface regularity improved, and surface asymmetry was reduced with treatment (Figure 5). Postoperative minimum simulated keratometric readings were approximately 4.00 D less than the baseline. Figure 5b shows one patient's changes in corneal topography for 5 consecutive years. Wavefront technology (Figure 6), as measured by the OPD Scan, showed a decrease in both lower and higher order aberrations.
There were no intraoperative complications, except for one case where suction was impossible due to subconjunctival hemorrhage produced by the fixation forceps during incision making. This case was postponed and redone after subsiding of the subconjunctival hemorrhage and sustained no complication. One case of corneal vascularization (0.53%) appeared 18 months post-Intacs in a patient who used soft contact lens. Two rings (1.07%) were explanted, one due to direct ocular trauma 6 weeks postsurgery and the other due to continued progression of the cone 1 year postsurgery. Both Intacs were easily removed under topical anesthesia through the original incision. Both patients underwent a successful deep anterior lamellar keratoplasty 4 weeks post-Intacs removal. No eyes lost any lines as regards their preoperative UCVA and BCVA.
DECREASE CORNEAL ABNORMALITY
Set clear goals before using intracorneal ring segments for the management of keratoconus. They should not be used to eliminate the disease, only to decrease corneal abnormality. Our primary goals were to (1) convert contact lens intolerant patients to contact lens tolerant, (2) delay or stop the progression of the disease and (3) prevent the need for corneal transplant. Another goal included a decrease in corneal surface irregularity (ie, transition from rigid to soft contact lenses).11,12
In our study, corneal topographic maps qualitatively demonstrated reduction of corneal ectasia and improved cone height in all eyes. The flattening effect, together with decreased corneal surface irregularities, enabled soft contact lens use in most patients.
Intracorneal ring segment implantation decreased the incidence of lower and higher order aberrations, as measured by the OPD scan. Some patients who did not have postsurgical quantitative vision improvement reported decreased glare and improved vision quality, which may be attributable to decreased higher-order aberrations.13-16
The use of Intacs for early or moderate keratoconus achieves reshaping the abnormal cornea without removing corneal tissue or touching the central cornea.7,9,12 The central cornea in these patients is clear, and corneal thickness is borderline. Stability is a critical issue for any surgical intervention. In our study, postoperative results demonstrated that spherical and astigmatic errors — together with UCVA, BCVA and keratometric readings — improved in 85% of eyes over preoperative baseline measures and remained stable over the 5-year follow-up.8 Use of a portable corneoscope or operating microscope-mounted topography unit may be valuable for refining the corrective effect achieved by Intacs inserts in individual cases.
Intacs are a minimally invasive technique for reducing the corneal steepening and surface irregularities.12 Intacs may also be used to (1) smoothen corneal surface postcomplicated refractive surgery and (2) support the cornea in pellucid marginal degeneration.17-23 Refractive adjustments can be made during the procedure by replacing the original Intacs inserts choice with a thicker or a thinner one.5,24-27
Some investigators have found it unclear whether Intacs prevent progression of the cone or eliminate the need for keratoplasty. In our study, cone progression occurred in only one eye (0.53%) and the Intacs was removed. Patient selection remains the key point in successful implantation. If intracorneal ring segments are implanted in patients with unclear central corneas, the cone will progress; corneal decompensation has already started.9,12
Should keratoplasty become necessary, we advise separately removing Intacs beforehand. Conducting keratoplasty simultaneously to Intacs removal may induce undesirable postoperative astigmatism.7,10
Neovascularization may occur in long-term contact lens wearers and/or neovessels (Figure 7). Neovessels responded to stopping contact lens wear and did not progress. When the incision is performed on the temporal meridian, vessels are uncommon. Our incision is made in the steep meridian, and we advise considering corneal dimensions, pupil location and placing the incision farthest from the limbus as possible.5,6,10
Intacs are reversible, well-tolerated and exchangeable. They provide improved outcomes for patients, should the desired effect not be achieved with initial selection of inserts thickness. Modulation of postoperative outcomes with Intacs exchange warrants more studies.
The behavior of keratoconus tissue in the natural state and after ring implantation is not fully understood because no keratoconus eye is the same. Clinical and refractive data show that Intacs, for the management of keratoconus, may benefit carefully selected patients. We stress the importance of fully explaining surgical objectives with each patient.
Tarek A. Ibrahim, MD, PhD, is an ophthalmology lecturer, in Rio and Cairo, Egypt, and medical director and chief of the cornea and refractive surgery department at the Magrabi Eye Center, in Dammam. He states that he has no financial interest in any product or company mentioned. Dr. Ibrahim may be reached at tarekan@hotmail.com.
Up Front | Jul 2006
After 5 Years Follow-Up: Do Intacs Help in Keratoconus?
With careful patient selection and full explanation of surgical objectives, Intacs are useful for the management of keratoconus.
Tarek A. Ibrahim, MD, PhD
