Contact Lens Applications in Corneal Disease

Introduction

Since the early 1900s contact lenses have evolved from non-oxygen-permeable rigid lenses made of glass or polymethylmethacrylate (PMMA) to the comfort of modern lenses composed of soft silicone hydrogel (SiHy) materials. With the introduction of the first commercially available soft lens by Otto Wichterle in 1971, low-cost contact lenses became widely available for patients who were unable to tolerate wear of the hard, oxygen-impermeable materials. As the popularity of these lenses grew, so did the apparent need for improvement in physiologic performance. The continued advances in designs over several decades led to the development of newer lenses that are physiologically superior to their original soft lens counterparts, in that their constituent polymers allow more oxygen to reach the surface of the eye, thereby reducing the incidence of lens-related complications. While these new hyper-oxygen-transmissible lenses have been widely accepted into routine clinical practice for the correction of refractive error, they also offer significant advantages in the visual rehabilitation of patients with abnormal corneas who demonstrate an increased demand for oxygen, and for therapeutic use in wound healing and ocular surface disease. In the nonpathologic cornea, contact lenses are routinely used as the primary mode of vision correction. It is estimated that the population of contact lens users in the United States is nearly 40 million and that the current value of the worldwide contact lens market is approximately 7.5 billion (US) dollars.

Contact Lens Materials: Historical Overview

Historically, hard contact lenses, commonly prescribed until the early 1980s, were made of PMMA, an oxygen-impermeable rigid and inflexible material. In addition to the lack of comfort these lenses produced, complications driven by the diminished supply of oxygen to the central cornea included corneal warpage, vascularization, central corneal clouding or edema, and endothelial cell polymegathism. To increase comfort and oxygen supply to the cornea, soft hydrogel lenses were introduced.

Soft Lens Innovations

Contact Lenses As Bandage Lenses

Indications for therapeutic use of contact lenses as a bandage include support and protection of the cornea, management of pain, and to promote epithelial healing after abrasions or recurrent corneal erosions, after refractive surgery, after therapeutic interventions involving the ocular surface such as superficial keratectomy or corneal collagen crosslinking, and during hospitalizations for burns or mechanico-thermal trauma. Bandage lenses, which are primarily worn on an extended-wear basis in patients with preexisting epithelial defects, require the patient to be monitored for a host of complications arising from overnight wear, including hypoxia and risk of microbial infection.

Hydrogel and SiHy lenses are the mainstay for short-term bandage or therapeutic use because of ease of fitting, low cost, and inventories commonly kept on hand. With the increasing popularity of SiHys and the benefits of improved corneal physiology, however, SiHy lenses have become the preferred form. Recent studies evaluating the use of SiHys for pain relief, epithelial wound closure, and after refractive surgery report an increase in the rate of reepithelialization with SiHy lenses and decrease in ocular pain. ^, In a retrospective study examining the efficacy of SiHy lenses worn in a therapeutic modality, 91.6% of patients achieved pain relief and 83.78% demonstrated complete corneal recovery without complications. Although there is no clear recommendation regarding bandage lens design and material, as findings vary between the studies, it seems that the second generation of SiHys containing polyvinyl-pyrrolidone is preferred by patients. The examples of FDA approved disposable contact lenses for postoperative pain relief are Acuvue Oasys and Air Optix Night & Day (see Table 98.2 ). In the presence of an epithelial defect, a lens that ensures full corneal coverage with adequate movement with blink and sufficient oxygen permeability will support epithelium healing. A larger lens is typically more effective in corneas exhibiting high toricity or steeper than average curvature, since higher sagittal depth will stabilize lens fit and reduce excessive lens movement. Poor retention due to lid abnormality or significant corneal irregularity may require use of very-large-diameter bandage lenses. Kontur (Kontur Kontact Lens, Co., Hercules, CA) are 15–24 mm diameter hydrogel (HEMA) lenses offered in a variety of single base curves and bicurve designs. In cases of Boston keratoprosthesis implantation or corneal dellen, a large-diameter hydrogel lens is used to allow for improved surface hydration and prevent corneal melt. ^,

There are reports of the use of various therapeutic lenses including scleral lenses and the devices used in prosthetic replacement of the ocular surface ecosystem (PROSE) treatment for exposure keratitis during acute hospitalization or in outpatient care of persistent corneal epithelial defect. Any large-diameter RGP lens must be cleaned and reinserted daily. In some cases prophylactic antibiotics are used concurrently. Bandage lenses are also used in conjunction with cyanoacrylate tissue adhesive glue for corneal perforations.

Therapeutic Uses for Contact Lenses

Contact lenses can be used on a long-term therapeutic basis to provide relief for a wide range of ocular surface disorders. Therapeutic lenses function to protect the epithelium in instances of inadequate lid or blink function, support epithelial function, reduce desiccation, and aid in pain control. An improvement in visual acuity is not the primary aim of therapeutic contact lenses, but it can be an advantageous “side effect” that is a driver for continued wear. Indications for the use of therapeutic contact lenses, include support of the ocular surface after chemical burns, persistent or recurrent epithelial abnormalities after cancer treatment, lid irregularities, bullous keratopathy, severe ocular surface disease such as keratoconjunctivitis sicca, ocular cicatricial pemphigoid, Stevens-Johnson syndrome, and ocular chronic graft-versus-host disease. ^{, ,} A detailed summary of therapeutic indications for contact lens wear is given in Table 98.3 .

The most common lenses used for therapeutic measures are conventional hydrogel and SiHy lenses, large-diameter hydrogel lenses, and large-diameter RGP lenses. The last decade has brought greater appreciation of the value of large-diameter RGP lenses for treatment of advanced ocular surface disease. These lenses are classified as corneo-scleral, mini-scleral, or scleral based on diameter and characteristics of fit. Use of such lenses was previously limited by the low oxygen transmissibility of the available lens materials and difficulty in manufacturing on a large scale. Scleral lenses made of newer hyper-oxygen-transmitting materials using lathe-cut designs have proven useful in ocular surface disease. ^{, ,} The advantage of using scleral lenses in severe ocular surface disease derives from the fact that the lenses rest on the sclera and vault over the cornea and limbus, forming an aqueous reservoir that continuously bathes the damaged epithelium ( Fig. 98.1 ). This aqueous buffer protects the eye from the mechanical friction of the eyelid during blinking, and maintains the eye in a well-hydrated environment. Scleral lenses are fitted by using a diagnostic set of preformed lenses and then communicating changes in lens specification to the manufacturing laboratory. Computer-aided design and computer-aided manufacturing (CAD/CAM) capabilities have allowed higher degrees of customization, including quadrant specific back surfaces and front surface cylinder correction. Innovations in lens manufacture have allowed for a modernization of the historical molding approach with CAD/CAM design, ocular surface profilometry, where the curvature of the anterior eye surface encompassing the corneo-scleral area is measured and EyePrintPRO impression technology (EyePrint Prosthetics, Lakewood, CO) in which an impression mold of the cornea and scleral is created and then transferred to the manufacturing lathe by high-precision scanning device. Care should be taken when fitting to ensure there is no contact apically or at the limbus, no impingement into the limbal conjunctiva, and no blanching of underlying episcleral blood vessels. Lens suction can be reduced by the incorporation of fluid-ventilated channels to allow for adequate tear exchange.

PROSE is a treatment approach using large-diameter RGP scleral lens prosthetic devices in which the clinician uses the CAD/CAM system directly to design lenses for the treatment of complex corneal disease. PROSE treatment has been shown to be clinically effective and cost-effective across a broad range of diagnoses including ocular surface disease. ^, Success with scleral lenses and with PROSE treatment has been specifically reported in ocular cicatricial pemphigoid, Stevens-Johnson syndrome, atopy, as well as in cases of exposure, lagophthalmos, and limbal stem cell dysfunction in the setting of treatment for cancer. ^, Therapeutic contact lens wear plays an important role in the management of chronic ocular graft-versus-host disease, with silicone-hydrogel lenses, ^, scleral lenses, and PROSE treatment demonstrated to improve vision, comfort, and quality of life for these patients.