There is an impressive body of evidence in the recent literature that underscores the utility of scleral contact lenses for anatomic or visual rehabilitation of eyes with corneal and external ocular disease. Three groups of conditions that are otherwise difficult to treat have been reported to be successfully managed with this modality. These include ectatic corneal conditions, ocular surface disease, and irregular or high astigmatism. The success of scleral contact lenses stems from three factors: the retention of a precorneal tear reservoir under the contact lens; protection of the ocular surface from the lid margins, lashes, and the external environment; and the provision of a smooth refracting surface. These factors maintain corneal epithelial hydration, promote epithelial healing and maintenance, and enhance vision and ocular comfort. In spite of their potential to improve difficult-to-treat ocular surface conditions, scleral contact lenses likely remain an underutilized modality due to the ophthalmic community's lack of familiarity with their fitting and utility. This article describes the design of modern scleral contact lenses, summarizes the clinical conditions for which their use is valuable, and presents a synopsis of recent clinical experience with the lenses.
Design Features
While the concept of a sclera-supported contact lens has been discussed for well over 400 years, the first report of gas permeable scleral lens use was in the Journal of the British Contact Lens Association in 1983.1 Rigid gas permeable (RGP) materials are the mainstay of all current scleral contact lenses. Fenestrations in the contact lens to permit entry of an air bubble to improve corneal oxygenation were a standard design feature in many of the original Polymethyl-methacrylate (PMMA) scleral lenses. Although nonventilated designs are used for some current scleral contact lenses, fenestrations are still preferred for other scleral contact lenses to reduce negative pressure, thereby facilitating easier removal of these very large lenses. Removal of most scleral contact lenses and mini-scleral contact lenses frequently requires use of a suction cup. Corneal swelling studies have demonstrated that the cornea underlying a scleral contact lens shows a satisfactory level of corneal metabolism.
Scleral lenses are designed to vault the entire cornea and limbus and rest on the resilient and less sensitive sclera. These lenses are typically 20-24 mm in diameter and have a central optic that covers the entire cornea, a transitional zone that overlies the limbus, and a haptic that bears on the sclera. The ideal scleral contact lens fitting shows light alignment to minimal apical corneal clearance with limbus-to-limbus coverage of the corneal portion of the contact lens, no compression of the limbus, gentle resting of the far haptic edge on the sclera, and minimal movement on blinking. The large size of the scleral contact lens may be construed as a potential disadvantage but is something to which patients quickly adapt. Frank corneal edema and compromised endothelial function are contraindications to the use of scleral contact lenses, since they exacerbate the edema in such situations.
There are four types of scleral contact lenses: spherical, front-surface toric, back-surface toric, and bitoric.2 A scleral contact lens is worn on a daily-wear basis. Lens care consists of cleaning, wetting, and disinfecting with standard RGP solutions. Before wearing, the concave surface of the lens is filled with nonpreserved saline. Fitting strategies and classification are described in detail in a recent paper.2
One scleral contact lens variant is the mini-scleral or semi-scleral contact lens, which was introduced in the late 1990s.3-5 The diameter of mini-scleral lenses ranges from 14 to 17 mm, much smaller than the 20 to 24 mm diameter of scleral contact lenses. The EpiCon (UltraVision, Leighton Buzzard, England), which is no longer available, and now the SoClear lens (Dakota Sciences, Sioux Falls, S.D.) (previously MacroLens made by C & H Contact Lens, Inc., Dallas) and Jupiter lens (Innovations in Sight, Front Royal, Va.) are examples of mini-scleral lenses. Mini-scleral contact lenses have the optical and stability advantages of RGPs, along with the comfort of soft contact lenses. Patients find their care and handling similar to their previous corneal contact lenses.
The Boston Scleral Lens (Boston Foundation for Sight, Needham, MA), also known as the Boston Scleral Lens Prosthetic Device, is a custom designed scleral lens.6,7 The lens is fabricated using proprietary CAD-CAM design and lathe technology. This permits customization of the lens dimensions to optimize individualized lens fit. A unique feature of the lens is the presence of radial channels approximately 200 µm in depth in the bearing surface of the haptic to facilitate the aspiration of outside tears to prevent lens suction. This facilitates the maintenance of its expanded, oxygenated precorneal tear film with virtually no lens movement and without touching the cornea. Physiologic adaptation is improved by the use of the Equalens 2 (Oprifocon A, Polymer Technology Corp, Rochester, NY), which dramatically increases the amount of oxygen available to the cornea and conjunctiva.
Adequacy of fit is determined by direct assessment of corneal clearance with the slit beam and inspection of the vascular compression pattern under the haptic bearing surface.
Clinical Conditions
Scleral lenses vault the cornea to decrease mechanical corneal touch, provide a tear reservoir to improve signs and symptoms of dry eye, and provide optical correction of regular and irregular astigmatism similar to other RGP lenses. Clinical conditions for which such lenses are most useful include ectatic corneal diseases (keratoconus, keratoglobus, pellucid marginal degeneration, and postrefractive surgery ectasia), high refractive errors or irregular astigmatism (postcorneal transplant, pathological myopia and nanophthalmos, and post-trauma), and ocular surface disease (dry eye secondary to cicatricial disease, neurotrophic and exposure keratitis, and severe atopic eye disease).6,8,9,10 Scleral contact lenses potentially offer benefits for patients with high refractive errors and higher order aberrations by providing improved centration compared to other contact lenses, especially for patients with keratoconus, trauma, or ptosis or following penetrating keratoplasty or radial keratotomy.
Recent Clinical Experience
In a retrospective review of all patients who presented between 1999 and 2003 (1003 patients and 1560 eyes), Pullum et al9 reported that 59.9% had corneal ectatic disease, 18.7% were postcorneal transplant, and 11.3% had ocular surface disease (OSD). The lenses were worn on a daily-wear schedule in all except 21 eyes. The latter group included eyes with OSD in which overnight wear was permitted for a short period to promote epithelial healing. Prophylactic antibiotics were not used and there were no infections that were attributed to use of the lenses. Vision improvement in eyes with corneal ectasia was significant, but most patients achieved vision up to but not better than 20/30. In the group with high refractive errors following corneal transplantation, a large majority achieved 20/20 or 20/25 vision.
Rosenthal and Croteau6 reported a series of 875 eyes of 538 patients fitted over an 18-year period, the majority between 2000 and 2005. Vision improvement was the reason for the fitting in 501 eyes and OSD management in 374. In the former group, 262 eyes had keratoconus and 130 eyes were postpenetrating keratoplasty. Among the OSD patients , 210 eyes had Stevens-Johnson syndrome, 84 eyes had severe dry eye, and 34 eyes had neurotrophic keratitis. Twenty-two eyes were fitted primarily for management of persistent epithelial defects, and 13 of these eyes healed fully. Lenses were worn continuously in eyes with persistent epithelial defect (PED), and this was interrupted briefly at intervals of 48 to 72 hours. Two daily-wear patients developed bacterial keratitis and both healed with topical antibiotics and resumed wearing scleral contact lenses. Among those on an extended wear schedule, four of 22 eyes with PED developed bacterial keratitis requiring penetrating keratoplasty. All of these patients had PED secondary to limbal stem cell deficiency, and a drop of antibiotic and steroid were placed in the fluid reservoir of the lens. After this experience, the medication regimen was altered and a fourth generation fluoroquinolone was placed in the fluid reservoir in such cases; eight additional cases were successfully treated subsequently. Ocular pain and disabling photophobia seen in many patients with severe dry eye were significantly mitigated with scleral contact lenses. The authors have subsequently reported a significant symptomatic improvement in a recent series of 33 eyes with dry eye secondary to graft-versus-host disease.7
Margolis, Thakrar and Perez10 conducted a retrospective chart review of 10 eyes with advanced atopic keratoconjunctivitis (AKC) that were treated with rigid gas permeable scleral contact lenses. A postfitting follow-up period of 20.5 months demonstrated improvement in conjunctival hyperemia, corneal epithelial defects, and at least one line in Snellen vision in all patients. The authors concluded that scleral contact lenses were useful in managing OSD and visual rehabilitation in medically controlled advanced AKC.
In cases of significant residual refractive error and higher order aberrations (HOA) following refractive surgery, Gemoules and Morris11 found gas permeable mini-scleral Macrolenses able to reduce HOA to normal levels in 20 eyes of 10 highly symptomatic patients who had undergone refractive surgery. This prospective study demonstrated reductions of trefoil by 44%, HOA by 65%, combined coma by 71%, and spherical aberration by 82%.
Horizons and Vistas
The impressive results reported in the recent literature on the success of the use of scleral contact lenses in OSD have occurred with the use of nonpreserved saline in the corneal reservoir of the lens. This experience confirms the importance of protecting the cornea from desiccation and the protective effect of the lens from the shearing forces of blinking or keratinized lid margins, dilution of pro-inflammatory chemokines, and reduction of osmolarity of the precorneal tear lake. Conceivably, the therapeutic value of the liquid corneal bandage may be enhanced with a formulation consisting of growth factors and other biologically active proteins; this is an area that is likely to be explored in the future. The advent of nanotechnology also expands the potential therapeutic role of additives used for contact lens material formulations.
Scleral contact lens fitting is not part of the curriculum in most ophthalmic educational programs. This factor plays a large part in the relative lack of familiarity with this modality. The steady stream of reports confirming the value of these lenses supports their increased use. Incorporating information on scleral contact lenses into the contact lens curriculum of residents would help to increase the use of this modality.
There is compelling evidence in the literature that scleral contact lenses can provide good results for the challenging patient groups described in this review. We believe more widespread use of scleral contact lenses is likely in the coming years.
References:
1. Ezekiel DF. Gas permeable haptic lenses. J Br Contact Lens Assoc. 1983;6:158-161.
2. Visser ES, Visser R, van Lier HJ, Otten HM. Modern scleral lenses part I: clinical features. Eye Contact Lens. 2007;33:13-20.
3. Winkler T. Corneo-scleral rigid gas permeable contact lens prescribed following penetrating keratoplasty. Int Contact Lens Clin. 1998;25:86-88.
4. Vreugdenhil W, Geerards AJ, Vervaet CJ. A new rigid gas-permeable semi-scleral contact lens for treatment of corneal surface disorders. Contact Lens Anterior Eye .1998;21:85-88.
5. Ye P, Sun A, Weissman BA. Role of mini-scleral gas-permeable contact lenses in the treatment of corneal disorders. Eye Contact Lens. 2007;33:111-113.
6. Rosenthal P, Croteau A. Fluid ventilated gas permeable scleral contact lens is an effective option for managing severe ocular surface disease and many corneal disorders that would otherwise require penetrating keratoplasty. Eye Contact Lens. 2005;31:130-135.
7. Jacobs DS, Rosenthal P. Boston Scleral Lens Prosthetic Device for treatment of severe dry eye in chronic graft-versus-host disease. Cornea. 2007;26:1195-1199.
8. Pullum K, Buckley, R. Therapeutic and ocular surface indications for scleral contact lens. Ocul Surf. 2007;5:40-48.
9. Pullum KW, Whiting MA, Buckley RJ. Scleral contact lens: the expanding role. Cornea. 2005;24:269-277.
10. Margolis R, Thakrar V, Perez VL. Role of rigid gas-permeable scleral contact lenses in the management of advanced atopic keratoconjunctivitis. Cornea. 2007;26:1032-1034.
11. Gemoules G, Morris KM. Rigid gas-permeable contact lenses and severe higher-order aberrations in postsurgical corneas. Eye Contact Lens. 2007;33(6, pt 1):304-307.
Author Disclosure
Dr. Basti and Dr.Grohe state that they have no financial relationship with the manufacturer or provider of any product or service discussed in this article or with the manufacturer or provider of any competing product or service.
Dr. Basti's work is supported in part by an unrestricted grant from Research to Prevent Blindness to the department of ophthalmology at Northwestern University's Feinberg School of Medicine.