Corneal ectasia is a group of disorders characterized by corneal weakness or thinning, in which protrusion of the cornea leads to irregular astigmatism and poor visual acuity. It comprises primary conditions such as keratoconus, keratoglobus, and pellucid marginal degeneration and secondary or iatrogenic corneal ectasia occurring after refractive surgery. 1,2
A progressive degenerative noninflammatory ectatic disease, keratoconus compromises the integrity of collagen matrix in the corneal stroma. Its hallmark characteristic is localized cone-shaped bulging with thinning at the site of the cone. This condition leads to the development of irregular astigmatism and steepening of corneal curvature that can cause myopia. 3 Keratoconus usually affects both eyes, although only one eye may be affected initially. Typically, an affected patient in his or her teens or 20’s seeks consultation for progressive visual blurring and/or distortion. Photophobia, glare, monocular diplopia, and ocular irritation are other presenting symptoms. 4
AIM OF MANAGEMENT
Keratoconus treatment strategies (Figure 1) have two goals: (1) stopping or delaying progression and (2) restoring visual acuity.
CXL. At our center, corneal collagen crosslinking (CXL) is the preferred treatment in all eyes with documented progression of ectasia on topography. Our epitheliumoff CXL technique takes 5 minutes. In eyes with early keratoconus and good BCVA, CXL is performed as a standalone treatment, and spectacles or soft contact lenses are prescribed if further correction is warranted. In eyes with more advanced keratoconus, we often perform a combination treatment, with CXL and intrastromal corneal ring segment (ICRS) insertion completed in the same session. 5-8
Corneal topography measurements are taken every 3 months for 1 year to ensure corneal stability. If at that time the patient presents with a stable refraction, he or she is scheduled for follow-up every 6 months. Low degrees of residual myopia can later be addressed with PRK; alternatively, refractive lens exchange or phakic IOL implantation are options in highly myopic eyes. A toric IOL or toric phakic IOL can be used when the cylinder is more than -3.00 D. 9
Keratoplasty. In eyes with poor BCVA due to keratoconus, spectacles and soft contact lenses cannot restore high-quality vision. Rigid gas permeable (RGP) lenses are a possible alternative, given good patient compliance; 10 however, many keratoconus patients have ocular comorbidities, such as vernal keratoconjunctivitis or allergic seasonal conjunctivitis, that can make tolerance of RGP lenses poor. 11,12 In these cases, we perform keratoplasty (deep anterior lamellar keratoplasty; DALK) or implant ICRSs, using the femtosecond laser for tunnel creation.
We perform DALK if the patient has any of the following: apical corneal scar, very steep cornea (maximum keratometry [K] more than 65.00 D), or a thin cornea at the site of ICRS insertion. 13-15 In eyes with deep corneal opacities, penetrating keratoplasty (PKP) may be needed.
ICRSs. Patients with poor BCVA and contact lens intolerance are good candidates for ICRSs, provided the central cornea is clear and peripheral corneal thickness at the incision site is more than 450 μm. 16-20 Patients with corneal haze or opacity, severe keratoconus (K greater than 65.00 D), acute hydrops, or active or recent ocular infection or inflammation are not candidates for ICRS insertion.
Our preferred ICRS is the Keraring (Mediphacos), and we select the ring size and thickness according to the manufacturer’s nomogram. 21 CXL is performed in the same session unless the eye has undergone CXL previously or there is no documented keratoconus progression.
PREOPERATIVE EVALUATION, PATIENT COUNSELING
Preoperative evaluation. This includes detailed ocular and medical history and a complete ophthalmic examination including UCVA, manifest refraction BCVA, and slit-lamp examination to exclude corneal opacity or inflammation. Scheimpflug imaging can be used to obtain K readings and corneal thickness at the thinnest point, 22,25 and anterior segment optical coherence tomography (OCT) can be used to measure corneal thickness at the incision site (Figure 2).
Patient counseling. During patient counseling, a full explanation of the nature of the disease and its prognosis is mandatory. The etiology of the disease, the genetic background, and the role of chronic eye rubbing should also be explained, as well as the treatment options. All patients undergoing CXL should understand clearly that the aim of the procedure is to stop progression, not to restore visual acuity. Patients should receive full information about each procedure and should know that they may need glasses after their refraction stabilizes. They must understand that all procedures are performed with the aim of avoiding or delaying the need for keratoplasty.
Laser-assisted tunnel creation and Keraring insertion. The procedure is done under topical anesthesia, with the patient in a supine position. The eyes are sterilized with povidoneiodine and draped, and a speculum is inserted. After a contact lens is placed on the eye and the patient-supporting system is moved to the treatment position, the eye is positioned against the patient interface, and suction is initiated. Careful placement and inspection of the contact glass can help to ensure proper centration; however, the laser’s software can compensate for a small degree of decentration.
At our center, we use the VisuMax femtosecond laser (Carl Zeiss Meditec) to create one or two ICRS tunnels at 80% corneal depth (Figures 3 and 4).26,27 The femtosecond laser also creates the incisions for ICRS insertion, preferably on the steepest axis (Figure 5); the axis of manifest refraction is used if the patient’s BCVA is better than 0.5. Normally two incisions are needed per channel, one on each end, but a 210° ICRS requires only one.
The appropriate size, thickness, and number of ICRSs depend on the patient’s manifest refraction, both spherical and cylindrical components. Insertion is done after channel creation, under a full aseptic technique and with the aid of forceps (Figure 6) and Sinskey hooks placed through dialing holes at both ends of the segment. Each ICRS is centered in the middle of its tunnel, equidistant from both incisions (Figure 7). If a single ICRS is used, it is inserted inferiorly; if two are used, the largest is inserted inferiorly. The procedure time is approximately 18 seconds.
CXL. There are currently two methods for CXL, epithelium-on and epithelium-off. We prefer removing the central corneal epithelium to allow better diffusion of riboflavin into the stroma. The following procedure description assumes epithelial removal before CXL.
Approximately 30 minutes prior to irradiation, riboflavin 0.1% is applied once every 5 minutes. Irradiation is then performed for 5 minutes with ultraviolet-A (UV-A) light (wavelength, 370 nm) with an irradiance of 18 mW/cm2 (equal to a dose of 5,400 mJ total energy) at a distance of 5.0 ±0.5 cm. Riboflavin application continues during UV-A irradiation. At the end of irradiation, the device switches off automatically.
Topical antibiotics, moxifloxacin, a steroid such as prednisolone, and artificial tears are prescribed for use every hour on the first postoperative day. Antibiotic dosing is then decreased to once every 4 hours for 10 days. The steroid is gradually tapered, and use of artificial tears every 4 hours should continue for about 1 month. Analgesics are prescribed only for patients who undergo CXL.
All patients must be advised to avoid eye rubbing, and bandage contact lenses should be removed once epithelial healing is complete. This is typically done around postoperative day 3.
After surgical intervention for keratoconus, visual acuity is likely to fluctuate for 1 to 3 months before stabilizing; therefore, strict follow-up is mandatory. In our practice, we see patients at 1 week; 1, 3, and 6 months; and 1 year postoperatively.
During each follow-up, a complete ophthalmic examination including visual acuity measurement, refraction, and corneal topography is performed. Anterior segment OCT is done in eyes with ICRSs once, at 1-week follow-up, to detect the depth and position of the ICRSs. During follow-up, patients are instructed to avoid eye rubbing, and any ocular allergy is treated appropriately.
Moones Abdalla, MD, is a cornea fellow at the Cornea Center, Alexandria, Egypt. Dr. Abdalla states that he has no financial interest in the products or companies mentioned. He may be reached at e-mail: moones_fathi@ hotmail.com.
Ahmed Elmassry, MD, is Professor of Ophthalmology at Alexandria University, Alexandria, Egypt. Dr. Elmassry states that he has no financial interest in the products or companies mentioned. He may be reached at e-mail: firstname.lastname@example.org.
Osama Ibrahim, MD, is a Professor of Ophthalmology at Alexandria University, Alexandria, Egypt. Dr. Ibrahim states that he is a consultant to Carl Zeiss Meditec. He may be reached at e-mail: email@example.com.
Amr Said, MD, is an Assistant Lecturer of Ophthalmology and a cornea fellow at Alexandria University, Alexandria, Egypt. Dr. Said is responsible for the work in this article and states that he has no financial interest in the products or companies mentioned. He may be reached at e-mail: firstname.lastname@example.org.
- Rabinowitz YS. Keratoconus. Surv Ophthalmol. 1998;42:297-319. 2.Krachmer JH, Feder RS, Belin MW. Keratoconus and related noninflammatory corneal thinning disorders. Surv Ophthalmol. 1984;28:293-322.
- Krachmer JH, Mannis MJ, Holland EJ. Cornea: Fundamentals, Diagnosis, and Management. 3rd ed. Philadelphia; Elsevier Inc.: 2011.
- Lee LR, Hirst LW, Readshaw G. Clinical detection of unilateral keratoconus. Aust N Z J Ophthalmol. 1995;23:129-133.
- Wollensak G. Crosslinking treatment of progressive keratoconus: New hope. Curr Opin Ophthalmol. 2006;17:356-360.
- . Kohlhaas M, Spoerl E, Schilde T, et al. Biomechanical evidence of the distribution of cross-links in corneas treated with riboflavin and ultraviolet A light. J Cataract Refract Surg. 2006;32:279-283.
- Wollensak G, Spoerl E, Seiler T. Stress-strain measurements of human and porcine corneas after riboflavin-ultraviolet- A-induced cross-linking. J Cataract Refract Surg. 2003;29:1780-1785.
- Goldich Y, Marcovich A, Barkana Y, et al. Safety of corneal collagen cross-linking with UV-A and riboflavin in progressive keratoconus. Cornea. 2010;29:409-411.
- Kremer I, Schochot Y, Kaplan A, Blumenthal M. Three year results of photoastigmatic refractive keratectomy for mild and atypical keratoconus. J Cataract Refract Surg. 1998;24:1581-1588.
- Edrington TB, Szczotka LB, Barr JT, et al. Rigid contact lens fitting relationships in keratoconus. Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Group. Optom Vis Sci. 1999;76:692-699.
- Ihalainen A. Clinical and epidemiological features of keratoconus. Genetic and external factors in the pathogenesis of the disease. Acta Ophthalmol (Copenh). 1986;64(Suppl):178.
- Wachtmeister L, Ingemansson SO, Moller E. Atopy and HLA antigens in patients with keratoconus. Acta Ophthalmol (Copenh). 1982;60:113-122.
- Kirkness CM, Ficker LA, Steele AD McG, Rice NSC. The success of penetrating keratoplasty for keratoconus. Eye. 1990;4:673-688.
- Paglen PG, Fine M, Abbott RL, et al. The prognosis for keratoplasty in keratoconus. Ophthalmology. 1982;89:651-654.
- Terry MA. The evolution of lamellar grafting techniques over twenty-five years. Cornea. 2000;19:611-616.
- Ruckhofer J, Stoiber J, Alzner E, et al. One year results of European multicenter study of intrastromal corneal ring segments. complications, visual symptoms, and patient satisfaction. J Cataract Refract Surg. 2001;27:287-296.
- Shabayek MH, Alió JL. Intrastromal corneal ring segment implantation by femtosecond laser for keratoconus correction. Ophthalmology. 2007;114:1643-1652.
- Coskunseven E, Kymionis GD, Tsiklis NS, et al. One-year results of intrastromal corneal ring segment implantation (KeraRing) using femtosecond laser in patients with keratoconus. Am J Ophthalmol. 2008;145:775-779.
- Ertan A, Kamburoglu G, Bahadir M. Intacs insertion with the femtosecond laser for the management of keratoconus: One-year results. J Cataract Refract Surg. 2006;32:2039-2042.
- Coskunseven E, Kymionis GD, Tsiklis NS, et al. Complications of intrastromal corneal ring segment implantation using a femtosecond laser for channel creation: a survey of 850 eyes with keratoconus. Acta Ophthalmol. 2011;89:54-57.
- Kirkness CM, Ficker LA, Steele AD McG, Rice NSC. The success of penetrating keratoplasty for keratoconus. Eye. 1990;4:673- 688.
- Scheimpflug principle. http://en.wikipedia.org/wiki/Scheimpflug principle. Accessed April 9, 2012.
- Neuhann TH. Pentacam system’s over view: understanding its benefits. Highlights of Ophthalmology. 2007;35:1.
- Belin MW. Next generation technology for the cataract & refractive surgeon. Cataract & Refractive Surgery Today. 2005;(1):S7.
- Belin MW, Holladay JT, Ambrósio Jr R. Why cataract and refractive surgeons need the Pentacam. Cataract & Refractive Surgery Today. 2006;(1)S1-S12.
- Lubatschowski H. Overview of commercially available femtosecond lasers in refractive surgery. J Refract Surg. 2008;24:S102-S107.
- Mediphacos website. www.keraring.com. Accessed on June 5, 2011.