Therapeutic use of silicone hydrogel lenses for the management of dry eye

Case report

CT, a 53-year-old female patient was referred to my practice for management of a very severe bilateral dry eye condition that was causing her extreme ocular discomfort and also noticeably affecting her vision due to the associated corneal epithelial changes. She had been first diagnosed as having the dry eye condition about three years earlier. Since that time CT had tried many various tear supplements to try and manage her condition, however none of these had been successful in reducing her symptoms. Surgical intervention, in the form of permanent occlusion of both lower puncta so as to maximize the retention of tears on the eye, had also been ineffective.

CT’s ocular history was notable for the fact that she was myopic, having first been prescribed a spectacle correction when she was 19. She had also worn soft contact lenses on an intermittent basis from age 27 until about 5 years ago, when she had ceased wearing contact lenses due to persistent problems with lens comfort. In particular, CT remembered that she had reached a stage where her eyes always felt ‘incredibly dry’ whenever she was wearing the lenses. At the time of ceasing contact lens wear, CT was wearing disposable high water content (not silicone hydrogel) soft contact lenses.

Thorough questioning revealed no other ocular problems, present or past. Familial ocular history revealed no significant findings. The patient's general health was excellent and had always been so. There was no allergic history and she was not taking any medication on a regular basis.

Spectacle refraction of R -4.00/-0.25 x 80, L -4.50/-0.75 x 95 gave visual acuities of R 6/7.5=, L 6/9.5+. A +2.00 D addition provided CT with near acuity of N5.

The keratometry readings were as follows:

RE  42.50 (7.94) @ 175          LE 42.37 (7.97) @ 180
      42.75 (7.89) @ 85                42.12 (8.01) @ 90

The keratometry mires were slightly irregular and showed mild distortion.

Slit-lamp examination confirmed CT to have a marked bilateral dry eye condition. The fluorescein tear breakup time (BUT) was less than 3 seconds in both eyes and the lid margin tear meniscus height was greatly reduced, being less than 0.2 mm right and left. Overall, the quality of the tear film in both eyes was extremely poor. Significant damage to the ocular surface was noted with fluorescein staining revealing a severe epitheliopathy in both eyes extending over about the central 5 mm of the cornea. The bulbar conjunctiva was slightly hyperaemic bilaterally, otherwise the conjunctiva and eyelids showed a healthy appearance. No other abnormalities were noted on ocular examination.

CT’s ocular soreness and reduced visual acuity in both eyes was considered to be due to her marked bilateral corneal epitheliopathy resulting from her dry eye condition. The mechanism for the reduced visual acuity was believed to be an irregular corneal surface associated with the changes to the corneal epithelium.

CT was subsequently prescribed a pair of disposable silicone hydrogel (Focus Night and Day) contact lenses incorporating the prescription R 8.6/13.8/-4.00, L 8.6/13.8/-4.50 that provided her with visual acuities of R 6/7.5+, L 6/7.5. She was advised to wear these lenses on an extended wear basis of 6 nights in, 1 night out with lens replacement monthly.

CT was reviewed regularly over the next 3 months at the end of which time the corneal epitheliopathy had fully resolved in both eyes. The tear film quality was still poor with a tear BUT of 4 seconds observed bilaterally. Corrected visual acuities were now R and L 6/6 with both spectacle and contact lens correction. CT was advised to continue wearing the disposable silicone hydrogel lenses on the same extended wear regimen of 6 days and nights to help maintain the integrity of her corneal epithelium.

Discussion

Contact lenses are often used as a therapeutic device in clinical practice. Contact lenses can be fitted therapeutically to alleviate pain or discomfort, or to assist the healing of injured or diseased ocular tissue.(1) For the latter, if there is marked corneal epitheliopathy present then the best correctable visual acuity with spectacles may be reduced due to the irregular corneal surface; in this situation, the use a therapeutic contact lens may not only promote healing but also lead to an improvement in visual acuity.

Therapeutic contact lenses are used to treat many different anterior eye conditions including dry eye, bullous keratopathy, recurrent corneal erosions, Fuchs’ endothelial dystrophy, epithelial basement membrane dystrophy (EBMD), filamentary keratitis, Thygeson’s superficial punctate keratitis and neurotrophic keratopathy. Therapeutic lenses can also be prescribed following ocular surgery, such as penetrating keratoplasty and corneal refractive surgery, to assist epithelial healing and to alleviate pain.(2) Note that the majority of therapeutic contact lenses are worn overnight (i.e. they are used on an extended wear basis) as this mode of lens wear is generally required for continuous pain relief and/or complete healing of the ocular surface disorder. In addition, extended wear is preferable where lens insertion and removal may be associated with epithelial trauma, pain and an increased risk of corneal infection.(3)

Disposable soft lenses are the most commonly used therapeutic lenses. Either conventional hydrogel or silicone hydrogel lenses may be employed, although silicone hydrogel lenses are the preferred option for this role for a number of reasons. Firstly, as was stated previously, most therapeutic contact lenses are used on a continuous wear basis. The oxygen transmissibility of conventional hydrogel lenses does not meet the minimum requirement to avoid corneal swelling in overnight wear; silicone hydrogel lenses have a much higher oxygen transmissibility such that they easily exceed the minimum level required for overnight wear.(4) Secondly, maximizing the oxygen transmissibility is particularly important for therapeutic applications in which the primary aim is corneal healing, because corneal oxygen requirements are greater when healing and repair processes are taking place.5 Thirdly, silicone hydrogel lenses generally have a lower water content than conventional hydrogel lenses. As a result, silicone hydrogel lenses are less likely to dehydrate on the eye and they will be affected less by a poor quality tear film.(2)

Therapeutic contact lenses are generally only considered in the treatment of dry eye when other modes of therapy (such as tear supplements and punctual occlusion) have failed(2) or when there is significant ocular surface disease as a result of the dry eye condition. Therapeutic contact lenses are commonly prescribed for dry eye as an adjunct to healing – as in this case – whereby the lens permits re-epithelialization to occur beneath it, protects vulnerable new epithelial cells from the action of the eyelids and helps to maintain the presence of a precorneal tear film.(2) A silicone hydrogel lens would usually be the first choice when fitting a therapeutic lens for a dry eye condition, for the reasons outlined in the previous paragraph. Scleral and corneal lenses may also be considered when there is marked ocular surface disease and associated corneal irregularity.(1,2) There is a higher risk of corneal infection secondary to contact lens wear in dry eye, so patients with dry eye who are prescribed therapeutic contact lenses for their condition must be monitored closely on a regular basis.

Studies have shown that the therapeutic use of silicone hydrogel lenses for the management of ocular surface disorders is relatively safe and effective.(3,5) The silicone hydrogel lenses should be fitted with plenty of movement so as to help promote tear exchange beneath the lens. Corneal coverage should be complete and there should be no compression of the limbal vessels. The lenses should be replaced according to the lens replacement schedule recommended by the manufacturer of the lens. A lens wear regimen of 6 days and nights is most commonly used when therapeutic lenses are to be worn on a continuous basis(5), although other extended wear schedules such as 14 days and 30 days are sometimes used depending on the circumstances.

References:

1. Buckley RJ. Therapeutic applications (Chapter 30). In Efron N, ed. Contact Lens Practice. London: Butterworth-Heinemann, 2002.
2. Hickson-Curran SB. Contact lenses in other abnormal ocular conditions (Chapter 26) In Phillips AJ, Speedwell L, eds. Contact Lenses 5th ed. London: Butterworth-Heinemann, 2006.
3. Kanpolat A, Ucakhan OO. Therapeutic use of Focus Night & Day contact lenses. Cornea 2003; 22, 726-734.
4. Holden BA, Mertz G. Critical oxygen levels to avoid corneal oedema for daily and extended wear. Invest Ophthalmol Vis Sci 1984; 25: 1161-1167.
5. Ambroziak AM, Szaflik JP, Szaflik J. Therapeutic use of a silicone hydrogel contact lens in selected clinical cases. Eye & Contact Lens 2004; 30: 63-67.