OPTOMETRY. I COMMENTARY I Contact lens fitting following corneal graft surgery. Clin Exp Optom 2003; 86: 4:

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1 OPTOMETRY I COMMENTARY I Contact lens fitting following corneal graft surgery Clin Exp Optom 2003; 86: 4: Loretta B Szc~otka'~ OD MS FAAO (DipCL) Richard G Lindsay+$ BScOptom MBA FAAO (DipCL) FCLSA FVCO Department of Ophthalmology, Case Western Reserve University Contact Lens Service, University Hospitals of Cleveland, Ohio t Department of Optometry and Vision Sciences, The University of Melbourne Optometrist, East Melbourne Received: 6 January 2003 Revised: 17 March 2003 Accepted for publication: 23 March 2003 Contact lens fitting may be required following keratoplasty for either optical or therapeutic reasons. Optical indications for contact lens fitting include the correction of irregular astigmatism, high regular astigmatism, anisometropia and secondary aniseikonia, as well as simple ametropia, where the patient desires to wear contact lenses in preference to spectacles. Therapeutic lenses are not routinely fitted following kerate plasty, although this management is advised in certain cases, such as when there are protruding sutures or epithelial healing is impaired. Designing a contact lens for a patient who has undergone keratoplasty will require the practitioner to carefully assess all the relevant features of the corneal graft. In this regard, there are many factors that need to be considered including the diameter of the graft zone, the topographical relationship between the host cornea and donor cornea, the corneal (graft) toricity and the location of the graft. Special designs, such as reverse geometry lenses, or more complex contact lens modalities, such as piggyback contact lens systems, may be required to achieve success in fitting. Key words: contact lens, corneal astigmatism, donor cornea, host cornea, keratoplasty Keratoplasty involves the replacement of abnormal host tissue by donor corneal tissue. The graft may be partial thickness (lamellar), whereby a thin posterior stroma1 layer, Descemet's membrane and endothelium are preserved, or full thickness (penetrating), in which the entire thickness of the cornea, including the endothelium, is replaced. While the majority of grafts performed are full thickness,')* lamellar keratoplasty provides the advantage, particularly with respect to contact lens fitting, of a significantly lower risk of endothelial rejection. Improving visual acuity is by far the most common indication for keratoplasty. Corneal grafting may also be performed for tectonic, therapeutic or cosmetic reason~.~ The results from the Australian Corneal Graft Registry (ACGR) reveal that five main categories-specifically keratoconus, bullous keratopathy, failed previous graft, corneal dystrophy and herpetic eye disease-account for 88 per cent of all indications for grafting, with the most common being keratoconus. Patients with keratoconus were also shown to have the best prognosis with respect to graft survival.' Interestingly, in the USA the most common indication for corneal grafting is pseudophakic corneal oedema, which accounted for approximately 20 per cent of all penetrating keratoplasties in Corneal ectasias/thinning disorders were next, accounting for approximately 16 per cent of all penetrating keratoplasties. Keratoconus was the most common indication for lamellar keratoplasty, although this procedure is still rarely performed with only about 250 performed in the USA in 2001 out of a total of approximately 30,000 corneal transplants.' Contact lens fitting may be required following keratoplasty for either optical or therapeutic reasons. Optical indications for contact lens fitting include the correction of irregular astigmatism, high regular astigmatism, anisometropia and secondary Clinical and Experimental Optometry 86.4 July

2 Contact lens fitting after keratoplasty Szczotka and Lindsay aniseikonia, as well as simple ametropia where the patient desires to wear contact lenses in preference to spectacles. In the circumstance of refractive anisometropia, contact lenses are the optical correction of choice because they do not induce relative spectacle magnification and so help to limit the image size differential, which is unavoidable with spectacle correction. To assess the ability of a patient to function binocularly without aniseikonic symp toms, a good rule of thumb is to apply 1.5 per cent magnification per dioptre of disparity between the two eyes. If an image differential of greater than five per cent exists, this would be likely to induce aniseikonia and so contact lenses are recommended regardless of whether the cornea graft has an irregular contour. Therapeutic lenses are not routinely fitted following keratoplasty, although this management is advised in certain cases, such as when there are protruding sutures or epithelial healing is impaired. Both types of contact lens application for postkeratoplasty patients will be discussed in this paper. THERAPEUTIC CONTACT LENS FITTING Therapeutic lenses may be required following corneal graft surgery where epithelial healing is impaired, for example from ocular surface abnormalities as in Stevens- Johnson syndrome. In this situation, a hydrogel (soft) bandage lens can help prevent trauma to the epithelium by the lids during blinking. A soft lens can also be used in the immediate post-operative period to cover wound leaks or dehiscences that may develop. In most cases, a small leak can be sealed with a bandage lens without the need for surgical interventi~n.~ Protruding sutures (Figure 1) can cause significant discomfort to the patient and can act as a site for infection and stimulate vessel growth. If the sutures cannot be removed promptly by the surgeon, this problem is usually best managed by the use of a soft bandage lens until it is appropriate for the sutures to be remo~ed.~ A soft lens will be required to serve as a bandage in virtually all cases of post-keratoplasty therapeutic lens fitting. In the early stages after keratoplasty, when a therapeutic lens is most likely to be needed, most grafts are flatter thanand relatively proud or sunken with respect to-the host cornea. Complete corneal coverage is also essential when fitting a therapeutic lens onto a corneal graft. In view of this, post-keratoplasty therapeutic lenses usually will have a flatter (larger) back optic zone radius (BOZR) and total diameter (TD) than would be used for a conventional soft lens fitting.4 In addition, the oxygen permeability of the lens material should be high enough to help reduce the risk of physiological complications that might occur as a result of corneal hypoxia. Disposable soft lenses sometimes can be used therapeutically on corneal transplants. The Soflens 66 (Bausch and Lomb, Rochester, NY) disposable lens is a good lens to use in this situation as its reverse geometry design-lens steeper in the periphery compared to the central optic zone-generally provides for better alignment with a proud graft. Disposable lenses are available in a range of medium to high water-content materials and, given that most therapeutic lenses will be relatively thin due to the incorporation of a negligible prescriptive power, they will generally ensure an adequate supply of oxygen to the cornea during lens wear.5 If signs of corneal hypoxia are noted with these lenses, then consideration could be given to using the new generation disposable silicone hydrogel lenses (especially for longer-term therapeutic wear) in view of their significantly higher oxygen transmissibility. Disposable lenses are manufactured as stock lenses, so they come in a limited range of parameters. With virtually all types of disposable lenses, the TD will be less than 14.5 mm and the BOZR somewhere between 8.3 and 9.1 mm. Postkeratoplasty therapeutic lenses often incorporate BOZR greater than 9 mm and TD as large as 17 mm, so the use of disposable lenses in this regard will not always be appropriate. OPTICAL CONTACT LENS F G In some cases, despite a technically successful corneal graft, the final visual acuity may be reduced due to the presence of a large degree of irregular astigmatism within the graft zone (Figure 2). Irregular astigmatism is the most frequent of all the optical indications for fitting contact lenses after penetrating keratoplasty. In the previously mentioned ACGR study, 20 per cent of corneal grafts had astigmatism greater than five dioptres. In turn, 18 per cent of these highly toric grafts had astigmatism, which could be classed as irregular. If the graft astigmatism is regular, spectacles may be prescribed or refractive surgery may be considered to decrease the amount of astigmatism. If the graft astigmatism is irregular, neither a spectacle correction nor a refractive procedure is likely to be contemplated and patients with high degrees of irregular astigmatism will usually require fitting with a rigid contact lens (or similar lens form) to optimise the visual acuity. If contact lenses are required to improve visual acuity, soft lenses are a poor option as, even in toric form, they cannot neutralise irregular astigmatism and the lower oxygen transmissibility in speciality lens designs is a limiting factor in the long-term use on full thickness transplants. The normal cornea is avascular and if new blood vessel growth is stimulated by contact lens-induced hypoxia, this immunologically privileged status is disrupted, which increases the risk of donor rejection. Designing a rigid contact lens for a patient who has undergone keratoplasty requires the practitioner to carefully assess all the relevant features of the corneal graft. In this regard, there are many factors that need to be considered including the diameter of the graft zone, the topographical relationship between the host cornea and donor cornea, the corneal (graft) toricity and the location of the graft.6 The diameter of the graft zone is usually between 7.5 and 8.5 mm. It has been shown that the survival rate of very small grafts (less than 7.00 mm diameter) and Clinical and Experimental Optomeuy 86.4 July

3 Contact lens fitting after keratoplasty Sznotka and Lindsay Figure 1. Slitlamp photograph of a corneal graft with a protruding suture at approximately 12 o clock figure 2. Topographical map of a corneal graft with significant irregular astigmatism. Note the oblate contour of the graft. of large grafts (greater than 8.5 mm diameter) is poorer than for grafts of intermediate size. If the graft size is too small, the edge of the graft may be within the pupillary zone, leading to flare and other related visual symptoms. If the graft size is large, the edge of the graft will be close to the limbal vasculature, hence increasing the chance of blood vessel infiltration into the donor cornea and subsequent rejection of the corneal graft. The size of the corneal graft can be an important factor in post-keratoplasty contact lens fitting. Donor buttons of 8.0 mm or greater may occasionally allow the practitioner to fit a small diameter (less than 8.0 mm) rigid gas permeable (RGP) contact lens, which positions itself within the region of the graft, although this fitting strategy usually is not very successful. Large diameter lenses (greater than 10.0 mm), which extend across both the donor and the host cornea, generally will be required in the majority of cases. With these larger lenses, it is preferable that the BOZD is larger than the graft zone so that the optic zone of the lens spans both the graft and the hostdonor j~nction.~ Corneal topography should guide the contact lens fitter on selecting the best design for the posterior surface of the rigid lens. Based on the results of videokera- toscopy, there have been five classic corneal contours described following keratoplasty: 1. prolate shape: regular astigmatism with a central red bow-tie pattern, which denotes a steeper central region and flatter periphery 2. oblate shape: regular astigmatism with a central blue bow tie, which denotes a flatter central region and steeper periphery 3. mixed shape: regular astigmatism, which extends through the topographic map 4. asymmetrical pattern with the two steepest hemi-meridians not symmetric and/or 180 degrees apart 5. steep-to-flat pattern, where the cornea is steepest on one side and becomes progressively flatter toward the other. The prolate shape can become one of the simplest or one of the most difficult graft contours to fit. If the central steepening simulates the prolate shape of the normal human cornea, normal rigid lenses incorporating conventional designs may be used. In fact, these patients probably have relatively good spectacle acuity and therefore, may not pursue contact lenses as a treatment option. However, some grafts that are steeper than the host cornea protrude slightly, such that they are termed proud. Proud grafts can make the task of contact lens fitting very awkward, due to the significant change in curvature at the donor-host junction. If the edge of the lens sits near this region, edge stand-off may occur, leading to patient discomfort and poor lens stability. If the lens covers this area, excessive bubble formation under the lens may be noted just adjacent to the edge of the graft zone.6 One option for dealing with a graft that is relatively proud is to use a rigid lens that incorporates a reverse geometry design.* Conventionally designed rigid contact lenses have progressively flatter curves as you move out towards the periphery, with the posterior central curve (BOZR) being the steepest curve. Conversely, rigid lenses incorporating a reverse geometry design will have one or more peripheral curves that are steeper (shorter radius) than the BOZR. In the majority of reverse geometry designs available today, the steeper peripheral curve is the secondary curve. Figure 3 is an example of a reverse geometry design rigid lens fitted to a cornea that has undergone penetrating keratoplasty. Occasionally, if the graft is extremely proud only a scleral or semi-scleral lens design will provide adequate stability. Figure 4 is an example of a semi-scleral 246

4 Contact lens fitting after keratoplasty Sznotka and Lindsay Figure 3. Fluorescein pattern of a rigid gas permeable lens with a reverse geometry design on a very proud corneal graft Figure 4. Significantinferior lens stand-off seen in the fluorescein pattern of a semi-scleral (Epicon) lens on an eye with a proud corneal graft Figure 5. Simulated fluorescein fitting pattern for an RGP lens with a reverse geometrydesign on a cornea with an oblate contour Figure 6. Topographical map of a tilted graft. Note the steeper hemi-meridian inferiorly. (Epicon) lens on a proud graft that continues to have significant lens stand-off in the periphery, thus highlighting the difficulty in ultimately finding a suitable lens for these patients. Reverse geometry lenses are also ideally suited for the oblate cornea. A corneal graft with this type of contour will be relatively flat centrally and steeper periph- erally (Figure 2), similar to a cornea that has undergone refractive surgery (for example, radial keratotomy, laser in situ keratomileusis) for the reduction of myopia. Conventional rigid lenses that are designed for the normal prolate shape of the cornea will generally show poor alignment on an oblate cornea.ya traditionally designed rigid lens fitted 'on-k' to this type 247 of cornea will generally demonstrate excessive edge lift as the steeper peripheral cornea falls away from the posterior surface of the contact lens. Conversely, if a traditional RGP lens is fitted to match the steeper peripheral cornea, the lens will be too steep centrally with the potential for bubble entrapment or lens adherence. Consequently, an oblate corneal contour

5 Contact lens fitting after keratoplasty Szczotka and Lindtay will usually require the use of a reverse geometry lens that aligns with the major curves of the corneal surface. To begin designing such a lens, match the central corneal curve or simulated keratometry values from videokeratoscopy with the BOZR of the lens over a chord diameter that is larger than the oblate graft. Then, using the axial topographic map obtained from videokeratoscopy, select the secondary and other peripheral curves based on the curvature of the mid-peripheral corneal region outside the relatively flatter central zone. The lens fluorescein fitting pattern should be similar to the simulation shown in Figure 5. Nearly all corneal grafts incorporate some degree of astigmatism. Deciding when to fit a rigid lens with a toric back surface to a graft incorporating mixed or asymmetric astigmatism is not always a straightforward task. In dealing with graft toricity, a spherical optic zone is often preferred to a toroidal optic zone if the amount of astigmatism is less than five dioptres and/or the astigmatism is localised to a small central area of the graft. Spherical optic zones work well if the remaining host cornea is regular and relatively spherical, whereas toric RGP lenses will demonstrate poor alignment on a spherical host cornea (assuming that the peripheral curves are also toric in form). Additionally, a rigid contact lens with a toroidal back optic zone has its principal meridians at right angles and so may not align very well on a graft exhibiting irregular astigmatism.6 The steep-to-flat graft contour is also commonly referred to as a tilted graft (Figure 6). This is often the most difficult shape to fit because of the tendency of the rigid lens to decentre over the steepest hemi-meridian of the cornea. However, these are the patients who would benefit most from successful RGP lens fitting because of the high degree of irregular astigmatism that accompanies this shape. Spherical lenses, as opposed to toric lenses, are usually the rigid lens design of choice. Successful RGP lens fitting involves using traditional parameter and design modifications to prevent the lens from decentring over the steeper hemi- meridian. The required lens modifications will depend on the location of the steeper hemi-meridian. For an inferiorly located steeper hemi-meridian, the design options include a larger (flatter) BOZR or a lenticular design with a minus carrier to minimise inferior lens decentration and a larger TD or BOZD to limit the amount of flare. If the steeper hemi-meridian is located nasally or temporally, again a larger TD and/or BOZD can be used to minimise the degree of flare, while using an aspheric design for the posterior surface of the lens may help to improve lens centration. When the steeper hemimeridian is located superiorly, increasing the weight of the lens is generally the best option and this can be done by incorporating a prism ballast into the lens, using a single cut (non-lenticular) design or choosing a lens material with a high specific gravity. As a rule when performing keratoplasty, most surgeons will attempt to centre the graft over the pupil, on the assumption that the centre of the pupil approximates the line of sight. In certain cases, such as pellucid marginal degeneration and greatly decentred inferior thinning in keratoconus, this may not be possible. O A graft zone that is significantly decentred with respect to the pupil (and hence the line of sight) can cause many problems for the graft patient. Visual symptoms such as flare and monocular diplopia may be experienced. Fitting with RGP contact lenses may exacerbate the problem due to the tendency of the lens to locate over the graft zone, such that it is decentred with respect to the pupil. This lens decentration may also decrease the level of comfort associated with the wearing of the lens. A possible solution is to design a lens with a decentred back optic zone. Alternatively, some other form of contact lens correction, such as a piggyback system, may be required to bring about satisfactory lens centration. A piggyback contact lens system consists of a combination of a soft lens (to aid with centration and/or improve comfort) and an RGP lens (to optimise vision), although this can be achieved in a number of ways. First, the piggyback lens may be one-piece, whereby the RGP centre is attached to a soft skirt (as is the case with the Ciba SoftPerm lens). This type of piggyback lens is not usually recommended for postkeratoplasty contact lens fitting, as the reduced oxygen transmissibility associated with the soft lens carrier increases the likelihood of corneal vascularisation and sub sequent graft failure. Second, the piggyback lens system can be created by fitting a soft contact lens (usually a disposable lens) underneath an RGP lens. This type of arrangement is generally utilised in cases in which fitting with just a rigid lens leads to areas of significant corneal insult due to a highly irregular graft topography. Placing a soft lens under the rigid lens helps to protect the cornea from excessive lens bearing and therefore minimises the possibility of complications associated with contact lens wear. Preference should be given to using the silicone hydrogel lenses in this situation due to their higher oxygen transmissibility. Finally, a piggyback lens system may consist of a soft carrier lens incorporating a central recess in which the RGP insert lens is placed (for example, Flexlens Piggyback). This piggyback lens system provides good lens centration and comfort. In addition, unlike the SoftPerm lens, which comes in only a limited range of parameters, this two-piece piggyback system can be custom made to specifications that the practitioner deems necessary. A high water content material should be used for the soft carrier and a highly gas permeable material should be used for the rigid insert, to maximise the oxygen transmissibility of this contact lens system? Extra care must be taken when prescribing contact lenses for post-keratoplasty patients. It has been shown that central corneal sensitivity is greatly reduced in eyes that have undergone corneal grafting. Consequently, these patients may not experience the normal discomfort caused by a corneal abrasion or other form of corneal compromise. This factor takes on greater significance because some degree of epithelial compromise will usually be noted on a corneal graft, especially around the donor-host interface where the uneven nature of the cornea prevents 248

6 Contact lens fitting after keratoplasty Szcrotka and Lindsay the formation of a smooth tear layer over the epithelium. Graft patients should be advised to have breaks from contact lens wear as often as possible to minirnise this epithelial insuk6 The clinician also needs to be vigilant for signs of graft failure or changes that may bring on this occurrence. Primary graft failure (which is rare) is characterised by marked folds in DesCemet s membrane and cloudiness of the graft from the first post-operative day.9 Late failure, denoted by an initially clear graft for at least two weeks with rejection generally occurring within the year, is usually the result of immune graft rejection. Signs of an allograft reaction may include keratic precipitates on the graft endothelium, ciliary flush, graft oedema, an endothelial rejection line and blood vessel penetration into the graft zone.3 Any sign of graft failure warrants immediate ophthalmological referral. Author s address: Richard Lindsay 6th Floor, 376 Albert Street East Melbourne VIC 3002 AUSTRALIA REFERENCES 1. Williams KA, Muehlberg SM, Bartlett CM, Esterman A, Coster DJ. The Australian Corneal Graft Registry: 1999 Report. Adelaide, McNeill J Eye Banking Statistical Report. Washington DC: Eye Bank Association of America, Casey TA, Mayer DJ. Corneal Grafting. London: WB Saunders Co; 1984: Woodward E. Contact lenses in abnormal ocular conditions. In: Phillips A, Speedwell L, eds. Contact Lenses, 4th ed. London: Butterworths; Brennan NA, Efron N, Weissman BA, Hams MG. Clinical application of the oxygen transmissibility of powered contact lenses. CLAOJ1991; 17: Lindsay RG. Post-keratoplasty contact lens management. ClinExp Optom 1995; 78: Schanzlin DJ, Robin JB. Corneal topography-measuring and modifymg the cornea. New York: Springer-Verlag; 1992: Lin ST. Application of the OK-3 lens design to corneal transplant patients. Optom Vis Sci (Suppl) 1993; 70: 83P. 9. Lindsay RG. Contact lens fitting after radial keratotomy. Clin Exp Optom 2002; 85: Lindsay RG. Pellucid marginal degeneration. Clin Exp Optom 1993; 76: Ruben M, Colebrook E. Keratoplasty sensitivity. Br J Ophthalmol1979; 63: