Contact lens fitting over intrastromal corneal rings in a keratoconic patient

Transcription

1 Contact lens fitting over intrastromal corneal rings in a keratoconic patient Larisia Hladun, O.D.* and Michael Harris, O.D., J.D., M.S. University of California at Berkeley. College of Optometry. Berkeley. California * DL Hladun is currently affiliated with Airdrie Eyecare Centre, Airdrie, Alberta, Canada Background: lntrastromal corneal ring segments have been used as a refractive surgev method for treatment of myopia. More recently, attempts have been made to use this surgical procedure in patients with keratoconus. Case Report: A 51-year-old man with keratoconus came to the clinic for a contact lens refit. He had undergone surgical insertion of intrastromal corneal rings in his right eye 7 months earlier in an attempt to obtain acceptable vision without contact lenses. At the time of presentation, the patient was not satisfied with his vision in the right eye and requested an attempt to improve his vision with a contact lens. The resulting corneal shape after surgery presented some complicat~ons, but the patient was able to achieve vision and adequate comfort in his right eye with a piggyback contact lens system. Conclusions: Insertion of intrastromal corneal rings may be beneficial in patients with early keratoconus or who are contact lens-intolerant. However, patients with more-advanced keratoconus are not likely to achieve adequate vision after the surgery and will require a contact lens. In addition, changes in the corneal anatomy created by the intrastromal rings may make contact lens fitting more challenging. The corneal irregularity may be exacerbated due to drastic variations in corneal elevation over the intrastromal ring and directly adjacent to the ring. This irregularity in elevation leads to difficulty in centering the lens on the eye and problems with bubbles forming under the contact lens over areas of corneal depression. When successfully fitted, contact lenses over intrastromal corneal rings can improve vision significantly. Key Words: Contact lenses, corneal surgery, implants, intrastroma1 corneal rings, keratoconus, prostheses Hladun L and Harris M. Contact lens fitting over intrastromal corneal rlngs in a keratoconic patient. Optometry 2004;75: K eratoconus is a non-inflammatory degeneration that results in thinning of the cornea. Patients may manifest symptoms of blur, ocular irritation, photophobia, and glare.' High levels of irregular astigmatism may be revealed with retinoscopy (scissor reflex), subjective refraction, keratometry, and corneal topography. Slit-lamp biomicroscopy may reveal the following findings: corneal protrusion, stromal thinning, Fleischer's ring (superficial iron ring surrounding base of cone), Vogt striae (in posterior stroma), and corneal scarring. ' In the early stages of the disease, patients often achieve acceptable vision with spectacle correction. However, as the thinning and irregularity of the cornea advance, other options need to be considered. Rigid gas-permeable lenses are generally the primary choice for patients with advancing keratoconus. The tear layer fills in the irregularity between the cornea and the contact lens, allowing patients to achieve significantly improved vision, as compared to the best spectacle correction. As keratoconus progresses, a point may be reached when the patient is unable to achieve acceptable vision or comfort with contact lenses. In the United States, the most-common surgical option for these patients is penetrating keratoplasty.' Other surgical procedures that have been performed for keratoconic patients are thermokeratoplasty, lamellar keratoplasty, epikeratophakia, and insertion of intrastromal corneal rings (ICR) or 1ntacsB.l The insertion of IntacsB is a fairly recent surgical procedure, originally designed for the treatment of myopia. The U.S. Food and Drug Administration approved IntacsB in Apd 1999 for the treatment of my~pia.~ Wo arcs of polyrnethylmethacrylate (PMMA) VOLUME 75lNUMBER 11JANUARY

2 C L I N I C A L CARE In a similar study, Siganos et al.7 also selected keratoconic patients with clear central corneas and contact lens intolerance. W o Intacm segments of 0.45 mm thickness each were inserted into 33 eyes in an attempt to maximize corneal flattening. Results indicate a gain of between one to six lines of bestcorrected visual acuity (BCVA)in 25 eyes. Four eyes experienced a one- to two-line loss and four eyes maintained their BCVA. In addition, three patients elected to have the segments removed due to unsatisfactory resulk7 filure 1 Inferior IntacB in 0 D. cornea are inserted to a depth of 68% of the cornea based on pachymetry readings. When the IntacB is inserted into the cornea, it separates the corneal lamellae and creates a shortening of the arc length that is proportional to the thickness of this spacer element.3 The rings are available in a variety of different thicknesses in order to correct varying degrees of low-tomoderate myopia. The relationship between the thickness and the dioptric correction has been shown to be 0.70 D per 0.05 mm thickness i n ~ r e m e n t. ~ Colin et al.5 evaluated the effect of Intacsm in keratoconic patients. Criteria for patient selection included the following: clear central corneas, contact lens intolerance, best-corrected visual acuity with spectacles or contact lenses of or better, and corneal thickness of more than 400 pm at the location of the segments. The experimental protocol was to use a thicker segment (0.45mm) inferiorly to lift the cornea and a thinner segment (0.35 mm) superiorly to flatten the cornea and reduce the asymmetric a~tigmatism.~ Results from ten keratoconic eyes indicated a mean keratometric flattening of 5.0 D.5 Rvelve-month postoperative results indicated a mean uncorrected visual acuity of 0.35 logmar (Snellen Equivalent, approximately 20150) as compared to the preoperative uncorrected visual acuity of 1.05 logmar (approximately201200).in addition, average best-corrected spectacle acuity was improved by approximately two lines of a ~ u i t y. ~ In general, fitting an irregularly shaped cornea with contact lenses is more challenging than fitting a normal prolate cornea. Irregularly shaped corneas may result from diseases such as keratoconus, corneal scars due to trauma or disease, refractive surgery procedures (LASIK, PRK, Intacsm), or corneal transplants. Regardless of the cause of the irregularity, rigid gas-permeable (RGP) lenses are the contact lenses of choice, since the tear layer fills in the area between the contact lens and cornea, thus eliminating much of the irregularity of the optical system. There are several main concerns to address when fitting post-surgical corneas with contact lenses. One concern is obtaining adequate lens centration, since RGP lenses tend to center over the steepest area of the cornea. Since this is probably not the center of the post-surgical cornea, the lens diameter may need to be increased in order to obtain adequate corneal coverage and improve centration. A second concern is maintenance of an adequate oxygen supply to the cornea, in order to prevent neovascularization. Although this is of higher concern in patients who have undergone penetrating keratoplasty rather than refractive surgery, it is still important to consider a lens material with a moderately high dk. This will maximize oxygen transmission while still maintaining lens integrity. A third concern is a careful evaluation of the fluorescein pattern during the fitting process. Areas of excessive bearing on the cornea may result in contact lens-induced scarring and corneal warpage if decentered, while areas of excessive fluorescein 49 V O L U M E 75lNUMBER 11JANUARY 2004

3 C L I N I C A L CARE 1 a 65.5 C.) & Axial Power Keratometric - A A L MunPm 584 t81d 50YIIone kreg t226d RplDm(r 3 2 m nmsd 318m@(-l 4.00) N t%tk$'8'eia. K q ( k H w Power 6Q2! 12 Merldran Rad~us rnm D 1 5 D Color Steps CopyrlgM Bausch & Lomb Surglcal om pooling could lead to bubbles or dimple veiling, thus impacting vision and the health of the cornea. Case Report A 51-year-old man came to the clinic with an interest in being refit with contact lenses. He reported being diagnosed with keratoconus 30 years earlier and had been wearing RGP contact lenses since the time of diagnosis. Seven months earlier, he discontinued contact lens wear in his right eye and underwent surgical insertion of Intacsm(see Figure 1).His hope was that the procedure would improve his vision significantly and also stabilize the advancement of keratoconus. The surgical center identified his BCVA with contact lenses before surgery as O.D. and O.S. After the surgical procedure-although he noted some subjective improvement in his uncorrected vision-his vision was not functionally adequate; the visual acuity in his right eye with the IntacsBin place was with no correction and best-corrected with spectacles. Preoperative data received from the surgical center indicated the patient had variable refractions in his right eye before the surgery. The surgical plan was AC-X-CMS003 to aim for a treatment of x 120. An Intac@ size of 0.25 mm was placed superior nasal to the cone center, and an Intac@size of 0.35 mm was placed inferior temporal to the cone center. The corneal thickness was measured by pachyrnetry to be 520 microns centrally and 591 microns peripherally in the 14adegree axis. The Intacb were placed at a depth of approximately 66% of this peripheral thickness (a depth of 390 microns).the overall position of the Intacb was inferior temporal within the cornea, circling the steepest area of the cornea. In his left eye, the patient was wearing a 4-yearold RGP with which he was able to achieve vision. The parameters of this lens were D (6.88 mm)l Dl 8.5. The lens fit was flat, with excessive central bearing (60%bearing). A corneal scar was present, with surrounding edema and staining. Corneal topography (Orbscan@) results at the time of contact lens fitting indicated simulated K readings of 56.60@161 and 63.0@071 for the right eye. The topography pattern indicated a C-shaped area of steepening associated with the placement of the Intacs@,as well as an area of inferior temporal steepening associated with the keratoconus (see Figure 2). 50 VOLUME 75lNUMBER 11JANUARY 2004

4 C L I N I C A L CARE m Axial Power Keratometric LL L i L -OM1 33m ~ ~ D S r mi m q c o r,. l o ) KD(E~X~~OIMI K*rp.C1IEQ 045,005 - Power Mendian Radus 82 Sl) D m D Color Steps C O ~ ~ T I ~M Bausch B Lomb surgical 01 The simulated K readings for the left eye were and The pattern indicated a large zone of steepening inferior to the corneal center (see Figure 3). Contact lens fitting The patient was interested in pursuing contact lens fitting for his right eye to improve his vision. He was also advised that his left lens needed to be refit, since his current lens was fitting poorly and causing irritation to his cornea. Unfortunately, no photographs are available to demonstrate the fitting process, because the patient was extremely photophobic and we were unable to obtain clear photographs. Burger Kone@trial lenses were used in the fitting procedure. These lenses are designed specifically for fitting keratoconic patients. The trial lens set has two diameters: flatter lenses are 8.8 mm in diameter and steeper lenses are 8.4 mm in diameter. The base curves in the fitting set are in 1 D steps of increasing steepness and the power varies accordingly, with 1 D steps of increasing minus power. This is of great benefit in the process of trial lens fitting, since the over-refraction found VOLUME 75lNUMBER 1IJANUARY 2004 AGX-CMSOO3 with the first trial lens will theoretically be the same for other trial lenses. The initial trial lens selected for the right eye was Oxyflow-30B (F30) D (5.63 mm)l x x 0.4. This base curve (BC)was selected because it approximated the average of the simulated K readings found with the OrbScanB. Manual keratometry values were also attempted, but due to extreme distortion, only an estimate of 60 D could be determined. After allowing the right trial lens to settle for 15 minutes, the fluorescein pattern was evaluated as follows: central bubble (varied in size with blinks), light touch superior, good peripheral system, inferior decentration. The visual acuity (VA) was 20130, with a spherical over-refraction (SOR) of D. The lens was initially assessed as too steep and a lens 1 D flatter was inserted: F D (5.72 mm)/ x x 0.4. The fluorescein pattern was evaluated as follows: paracentral bubble (disappears with solid blink), touch over superior IntacB, good peripheral system, excessive nasal decentration. This lens was assessed to be decentering due to the flat fit over the peak corneal area. The steeper lens was

5 judged to be a better fit overall and the following lens was ordered: F D (5.63 mm)l x x 0.4. At the dispense appointment, the lens was evaluated to have a narrow peripheral system and the patient accepted an SOR of D for a subjective improvement in VA. Before the patient left with the lens, the peripheral system was modified in office to 11.0 x 0.4 for improved peripheral clearance. The patient began wearing the lens and returned for a follow-up visit the following week to reassess the fit and vision. Since the patient consistently accepted SOR, a new lens was ordered with the appropriate power. In addition, this lens was ordered in a slightly larger diameter and steeper BC in an attempt to improve centration and minimize bearing on the cornea. The peripheral system was also varied from the initial trial lens in order to maximize tear exchange. The final lens had the following parameters: F D (5.58 mm)/ Dl x x x ct. With this lens, the patient was able to achieve visual acuity. The fluorescein pattern indicated slight central clearance, mid-peripheral touch, and a good peripheral system. However, due to the topography of the cornea with the Intad present, a bubble of varying size was constantly present just above the corneal ridge created by the lower IntacB. At times, the bubble was a single large bubble and at other times it was broken down into a zone of tiny bubbles. This did not interfere with vision because it was located inferior to the visual axis. A second problem was an area of bearing on the epithelial surface overlying the inferior IntacB. The main concern was that the epithelial surface of the cornea could erode due to the constant rubbing of the contact lens. The patient was advised to return for followup in two weeks to assess the impact of the area of bubbles and the bearing on the cornea. Unfortunately, the patient did not return for his scheduled appointment, but came in with symptoms of irritation and light sensitivity in the right eye a few weeks later. Corneal evaluation indicated an area of dense staining with surrounding corneal edema overlying the inferior Intad. There were no cells or flare present and the VA remained stable. After contact lens wear was discontinued in the right eye for a week to allow the cornea to heal, the patient was refit into a piggyback con- tact lens system in his right eye. This system used a 1-Day AcuvueB D with the same RGP previously worn. A 1-day disposable soft contact lens was selected over a 2-week disposable lens because the patient had a history of allergic reactions to several contact lens solutions. The patient discarded the Acuvuem lens every evening when he removed his contact lenses. Follow-up visits at 1 week and 3 months indicated the patient adapted well to the piggyback system, with no complaints of irritation and no corneal staining. The left eye, without an IntacB, was considerably simpler to refit. An initial lens of D (6.25 mm) base curve was ordered, but due to excessive touch on the area of scarring, a steeper lens was ordered after a follow-up visit. A satisfactory fit was achieved with a lens with the following parameters: F D (6.03 mm)l x x ct. The fluorescein pattern indicated slight clearance centrally with minimal touch on the scar, mild mid-peripheral bearing, and a good peripheral system. The patient was able to achieve visual acuity of and the area of previously noted staining and edema in the left eye resolved with the new lens. Discussion One of the major benefits of the IntacsB is that they are a reversible surgical procedure to correct myopia. Once removed, the cornea appears to return to its normal preoperative cur~ature.~ Another positive aspect is that the corneal shape remains prolate within the 5-mm optical zone after s~rgery.~ This helps minimize problems that result from spherical aberration caused by a change in shape. In addition, no significant changes in contrast sensitivity have been found after ~urgery.~ Although the surgical procedure is considered reversible and relatively safe, some complications and side effects have resulted. Possible problems that may result include the following: conjunctival hemorrhage at the site of insertion, perforation into the anterior chamber, anterior chamber reaction, infiltrative keratitis, reduced corneal sensation, induced astigmatismi4 thickening of the stroma within the central cornea, and epithelial thinning over the Inta~@.~ Hartman et al.1 found that intrastromal corneal rings in rabbits resulted in histological changes-such as epithelial atrophy over the rings, mild stromal inflammation, and fibrosisparticularly at the insertion site. In addition, the VOLUME 75lNUMBER 11JANUARY 2004

6 upper limit to myopia correction was found to be only -4.1 D with the thickest (0.45 mm) IntacB, rather than the original -5.0 D predi~tion.~ Various surgical procedures have been attempted in the past for treatment of keratoconic patients. Procedures that weaken the cornea, such as radial keratotomy (RK), photorefractive keratectomy (PRK), and laser in situ keratomileusis (LASIK), have been understandably unsuccessful as a treatment, since the corneas of keratoconic eyes are already thinned and weakened. Procedures aimed at strengthening the cornea, such as epikeratophakia,ll li~e-epikeratophakia,1~ and excimer laser lamellar keratoplasty of augmented thickness (ELLKAT), l3 have been somewhat more successful. Currently, penetrating keratoplasty (PKP) is the most-common surgical procedure used in treatment of keratoconus in cases in which the patient is contact lens-intolerant, has reduced visual acuity secondary to scarring, or is unable to achieve an acceptable contact lens fit due to the advancement of the disease. A study by Smiddy et al.14 revealed an excellent prognosis for visual acuity outcome with PKP surgery. Best-corrected visual acuity (with either spectacles or contact lenses) was in 55% of the subjects and ranged from to in 35% of the subjects. The goals to strive for in a complicated contact lens fitting are the same as with any contact lens fitting: maximize vision and comfort while maintaining corneal health. An ideal fit would result in a clearance fit that had no areas of bearing on the cornea or excessive pooling under the lens. However, with an irregular cornea, the ideal may be difficult to attain and a minimum amount of touch and pooling should be acceptable. The patient should also be followed at dmonth intervals to monitor for epithelial breakdown or changes to the fit. It is important to have a slightly wider peripheral system than on a standard RGP in order to promote good tear exchange and prevent binding of the RGP to the cornea. The lenses used in this fitting had a peripheral system width of 1 mm, in comparison to the more-common 0.5- mm width in standard RGP lenses. The material of the RGP is another consideration for post-surgical corneas or piggyback systems. The final lens material used in the right eye had a bk of 30, but use of a maferiai with a higher dk could be advisable-especially since the patient ended up in a piggyback system. A better choice would have been Oxyflow HDS@ with a dk of 58. This moderately high dk material maximizes oxygen transmission, while at the same time maintaining good lens stability in order to minimize contact lens warpage. Patient comfort is a necessary factor to consider during the fitting process. Since it is often contact lens-intolerant patients who elect to have surgical procedures such as intrastromal corneal rings inserted, comfort is a major concern. A lens that tends to decenter may be one source of the discomfort. Strategies for enhancement of centration are to steepen the lens to minimize areas of corneal touch andlor increase the diameter of the lens. Another strategy for improvement of patient comfort is to use a piggyback system with a soft contact lens underneath the RGP. Studies have shown that using a piggyback contact lens system in keratoconic patients can improve comfort, increase wearing time, reduce corneal erosions, improve corneal integrity, and maintain visual acuity.15-l7 Tsubota et al.18 found that combining an RGP lens with a high water-content soft lens was a safe system for keratoconic patients, with no signs of change to the corneal epithelium or endothelium over a 9-month period. However, in order to minimize the chances for development of neovascularization-especially if this system is used in a post-surgical cornea-one should consider use of a moderately high dk RGP lens. This will result in an increase in oxygen permeability, with no compromise to the ability of the lens to maintain its shape. Since the soft contact lens will have more wear and tear on it due to the movement of the RGP over its surface, using a 1-day or 2-week disposable lens is a good option. The advantage of the 1-day lens is that the patient need not concern himself with a lens care system for the soft contact lens; however, the cost may be a deterrent for some patients. Conclusion According to the studies published by Colin et al5x6 and Siganos et al.,7 there seems to be some benefit derived from insertion of IntacsB in keratoconic patients. The main benefits are a reduction in the mean keratometric values and an improvement in both uncorrected and best-corrected visual acuity. Although this gain is experimentally si&cant, the main issue is whether this gain is functionally significant to the patient. For the patient in this case VOLUME 75lNUMBER 11JANUARY 2004

7 report, an improvement of visual acuity to the level of was noticeable, but still did not provide him with adequate functional vision. It should also be noted that intrastromal corneal ring insertion would be a benefit only to patients with clear corneas. Any patients with central corneal scarring would not benefit from this procedure and would probably need to proceed with a penetrating keratoplasty. In addition, there seems to be no evidence that the insertion of IntacsB will result in any stabilization of the keratoconus or halt the progression of the disease. Another issue that arises is whether the insertion of IntacsB creates a change in the corneal anatomy that makes contact lens fitting more difficult than without the IntacsB. Since this patient was not seen in our clinic before his surgery, we were unable to assess whether we would have been able to adequately fit the patient and achieve acceptable vision with contact lenses. However, it was found that the areas of depression and elevation associated with the IntacB placement did create extra difficulties in the fitting because of the creation of bubbles and an area of epithelial erosion, respectively. Patients must be carefully assessed as to their expectations before undergoing the IntacB surgical procedure. This procedure may be a benefit for patients with early-stage keratoconus or patients who are contact lens-intolerant. If patients do not have significantly reduced visual acuity, an improvement of two lines of acuity may be a noticeable benefit to their lifestyle. However, if patients have advanced keratoconus and considerably reduced vision, the surgery may not be a realistic option to give them any functional improvements. On the other hand, for a patient who is contact lens-intolerant, this is a relatively safe procedure, with minimal side effects or complications, and patients may appreciate the gain in vision. If, however, it is likely that the gain in visual acuity is not going to be functionally sigmficant, the disadvantage of a more-complicated contact lens fitting needs to be weighed against the minimal benefits achieved. References 1. Krachmer JH, Feder RS, Belin MW. Keratoconus and related noninflammatory corneal thinning disorders. Sun, Ophthalmol 1984;28: Linebarger EJ, Song D, Ruckhofer J, et al. Intacs: the intrastromal corneal ring. Int Ophthalmol Clin 2000; 40: Burris TE, Baker PC, Ayer CT, et al. Flattening of central corneal curvature with intrastromal corneal rings of increasing thickness: an eye-bank eye study. J Cataract Refract Surg 1993; 19(Suppl) : Schanzlin DJ, Asbell PA, Burris TE, et al. The intrastroma1 corneal ring segments: Phase I1 results for the correction of myopia. Ophthalmology 1997; 104: Colin J, Cochener B, Savary G, et al. Correcting keratoconus with intracorneal rings. J Cataract Refract Surg 2000;26: Colin J, Cochener B, Savary G, et al. INTACS inserts for treating keratoconus. Ophthalmology 2001; 108: Siganos CS, Kymionis GD, Kartakis N, et al. Management of keratoconus with Intacs. Am J Ophthalmol2003; 135: Nose W, Neves RA, Schanzlin DJ. Intrastromal corneal ring-one-year results of results of first implants in humans: a preliminary nonfunctional eye study. Refract Corneal Surg 1993;9: Reinstein DZ, Srivannaboon S, Holland SP. Epithelial and stromal changes induced by intacs examined by threedimensional very high-frequency digital ultrasound. J Refract Surg 2001;17: Hartmann C, Rieck PW, Holzkamper C, et al. The intrastromal corneal ring in clinical refractive surgery: reference to results in rabbits eyes. Graefes Arch Clin Exp Ophthalmol 2000;238: McDonald MB, Kaufman HE, Durrie DS, et al. Epikeratophakia for keratoconus. Arch Ophthalmol 1986; 104: Krumeich JH, Daniel J, Knulle A. Live-epikeratophakia for keratoconus. J Cataract Refract Surg 1998;24: Buratto L, Belloni S, Valeri R. Excimer laser lamellar keratoplasty of augmented thickness for keratoconus. J Refract Surg 1998;14: Smiddy WE, Hamburg TR, Kracher GP, et al. Keratoconus-contact lens or keratoplasty? Opththalmology 1988;95: Soni PS, Gerstman DR, Horner DG, et al. The management of keratoconus using the corneal modeling system and a piggyback system of contact lenses. JAM OPTOM ASSOC 1991;62: Kok JH, van Mil C. Piggyback lenses in keratoconus. Cornea 1993; 12: Yeung K, Eghbali F, Weissman BA. Clinical experience with piggyback contact lens systems on keratoconic eyes. JAM OPTOM ASSOC 1995;66: Tsubota K, Mashima Y, Murata H, et al. A piggyback contact lens for the correction of irregular astigmatism in keratoconus. Ophthalmology 1994; 101: Corresponding author: Larisia Hladun, O.D. Airdrie Eyecare Centre 120 2nd Avenue, NE Airdrie, Alberta T4B2N2Canada 54 VOLUME 75lNUMBER 11JANUARY 2004