Therapeutic Contact Lenses

Introduction

Contact lenses can be used for therapeutic purposes to manage a wide range of ocular conditions. When so fitted, they are referred to as therapeutic contact lenses (TCLs) or bandage lenses. TCLs are fitted mainly to protect or promote healing of the cornea, as well as to provide relief from pain and discomfort. They can range from daily disposable lenses to specialist lenses such as scleral lenses, and although not primarily fitted for refractive correction, this can be incorporated to enhance visual rehabilitation. Development of contact lens materials and modalities and advances in novel technologies such as drug delivery have expanded the scope of TCL practice.

Indications for Therapeutic Contact Lens Fitting

The main indications for fitting a therapeutic lens are:

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pain relief
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promotion of corneal healing
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mechanical protection
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structural support or splint
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maintaining corneal hydration
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maintenance of fornices
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drug delivery.

In practice, a combination of these effects may be achieved, but pain relief has been shown to be the most common indication for TCL fitting ( ).

Lens Types and Selection

All types of contact lens and modality can be considered for therapeutic use, and their fitting is described elsewhere in this book. Selection of an appropriate lens is determined mainly by understanding the primary ocular condition, the indication for fitting and the duration of wear. An ideal lens will address one or more of the indications above and have minimal adverse effects. Factors which need to be considered in the selection of the lens type are discussed in the following sections.

Lenses are fitted in the same way as for refractive conditions but extra care is needed to ensure that damage is not caused to an already abnormal ocular surface. Where the eye is particularly painful, instilling a local anaesthetic such as proxymetacaine may be necessary to relax the eye enough to insert the lens.

Decide on the best type of TCL to use (see below). Measure the eye to be fitted or if that is not possible, the fellow eye, before selecting the optimum size of lens.

Oxygen permeability

The physiological requirements of a diseased eye can be quite different from a normal eye. In many ocular conditions requiring a therapeutic lens, corneal physiology may be affected by damage to the tissues involved in oxygen transport, e.g. endothelial dystrophies. Also, in many applications, the TCL is worn on a continuous-wear basis. In general, the use of materials with greater oxygen permeability is indicated to reduce the degree of hypoxia ( ), and silicone hydrogel lenses have become a popular choice for therapeutic use especially when the primary goal is corneal healing. Semi-scleral and scleral lenses are now available in gas-permeable materials, which have increased their therapeutic application.

Tear film and distribution

The tear film and distribution can be affected to varying degrees in diseased eyes. The ocular surface may become irregular, affecting tear distribution, or tear production may be limited. In drier eyes, the wetting angle of the material or tear distribution across the lens will be important in lens selection. In eyes with severe ocular surface disease or exposure, maintenance of a tear reservoir behind the lens to hydrate the cornea will be the main factor for consideration ( ).

Mechanical effects

Fitting a contact lens onto an already diseased eye may produce effects such as low-grade mechanical trauma to the corneal epithelium and the following should be considered:

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Adequate lens movement is necessary but, if excessive, it may exacerbate pain and delay healing of the epithelium.
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With soft lenses, the modulus or ‘stiffness’ of the lens may affect epithelial integrity, with some stiffer silicone hydrogel lenses causing more mechanical trauma to the epithelium.
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Silicone hydrogel lenses with a higher modulus can be useful for improved visual performance ( ) but may be less comfortable due to the mechanical effect of a stiffer lens on the diseased epithelium.
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Disposable hydrogel lenses can be useful, particularly for pain relief and promotion of corneal healing as they have a low modulus. They are a low cost option if very frequent replacement or temporary use is required.
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Semi-scleral and scleral lenses fitted with corneal clearance and limited movement will reduce the mechanical effect on the cornea but the conjunctiva can be compressed or can prolapse ( ).

Coverage

The total diameter (TD) of the TCL is important to address the main indication for use. The lens should have an appropriate diameter to aid centration and ensure adequate movement but should also cover the affected area when promoting healing and when mechanical protection or maintenance of the fornix is required. For example, when using a soft lens, the TD of the lens should be large enough to cover the limbus completely and provide optimum movement during versions. In some conditions the TD will need to be increased to cover a surgical site or to aid the healing of peripheral or conjunctival lesions (see below). When a lens is required to maintain the fornix, typically a scleral lens, it should be of large enough diameter to prevent the formation of symblepharon.

Conditions That Can Benefit From the Use of Therapeutic Contact Lenses

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