Section SIX Children and therapeutic lenses

•They do not absorb foreign substances, so medication can be used without fear of contamination.

•Fluorescein can be used to ensure the optimum fitting.

Disadvantages

•Difficult to fit.

•Surfaces deposits. Six-monthly replacements are advisable.

•Lenses can be difficult to remove.

•Adhesion can occur with lenses fitted either too steep or too flat.

•Expensive.

32.10 Bandage lenses

32.10.1 Soft lenses

Soft bandage lenses usually have to be used on an extended wear basis to relieve pain and allow denuded epithelium to regain its normal structure. They are available in high water content soft lens materials and silicone hydrogels. They are usually of plano power, since they are not primarily intended for visual improvement. Lenses are not generally handled by the patient and may require replacing every 4–8 weeks because of deposits. They are ideally fitted from stock and are used in cases of:

•Chronic keratitis.

•Post-keratoplasty.

•Bullous keratopathy.

•Exposure keratitis.

•Recurrent erosions.

•Corneal perforation.

General considerations

•Biomimetic materials are better where there is a tear film problem because they dehydrate less, e.g. Proclear 8.60/14.20 plano (e.g. exposure keratitis).

•High water content is better where a painful eye needs several weeks of continuous wear, e.g. Menicon Soft 72: 8.50/14.50 plano (e.g. bullous keratopathy).

•Silicone hydrogels are best where the primary objective is wound healing, e.g. PureVision 8.60/14.00 plano for persistent epithelial defect.

•Where ‘K’ readings are not possible, a good starting point with a high water content lens is 8.50:14.50.

•Radii range from 7.80 to 9.50 mm, the flatter lenses often being made in the higher water content materials.

•Diameters vary between 13.50 and 16.50 mm, the larger lenses being made in the higher water content materials.

•Centre thickness varies between 0.10 and 0.25 mm.

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32.10.2 Limbal diameter rigid gas permeable lenses

Lenses are used for severe dry eye, corneal exposure and trichiasis. They also assist with wound healing and may offer pain relief.

Designs are bicurve or a spherical optic with aspheric periphery. BOZR range is 7.00 to 7.90 mm with a TD of 12.50 mm and the axial edge lift varies throughout the range. The aim is to achieve alignment or slight apical touch with broad edge clearance. The lens should:

•Cover the whole cornea to give complete corneal protection.

•Not flex.

•Allow a tear resevoir.

•Be made from a high Dk material.

32.11 Additional therapeutic uses

Drug-release lenses

Soft lenses or shields of a collagen material are used as a drug release mechanism.

Low-vision aid

A Galilean telescope can be of benefit to the low-vision patient, but its cosmetic appearance is improved by using a high minus contact lens as the eyepiece. The powers required to achieve a minimum 31.5 magnification are at least −25.00 D for the contact lens and +20.00 D for the spectacle lens. The problems are that the field of view reduces as the powers increase and movement of the contact lens causes apparent movement of the visual field. However, the technique has been used with occasional success.7

Veterinary lenses

Veterinary lenses (e.g. Cantor + Nissel) represent a good alternative to tarsorraphy to promote corneal healing. They can be used on the eyes of cats, dogs, horses and lions for a wide variety of conditions including symblepharon, bullous keratopathy, adnexal problems, indolent ulcers and following superficial keratectomy. Lenses usually have a 74% water content and TDs of up to 25 mm. They are marked with a coloured dot for ease of viewing on the eye.

References

1.Korb DR, Finnemore VM, Herman JP. Apical changes and scarring in keratoconus related to contact lens fitting techniques. Journal of the American Optometric Association 1982;53:199–205.

2.Shephard AW. Keratoconus contact lens fitting. Journal of the British Contact Lens Association (Scientific Meetings 1989), 1989;21–5.

3.Astin C. Fitting of keratoconus patients with bi-elliptical contact lenses. The Journal of the British Contact Lens Association 1987;10:24–8.

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4.Hood A. Advanced contact lens fitting part three: hospital contact lens practice. Optician 1997;214(5612):16–22.

5.Edrington TB, Barr JT, Zadnik K, Davis LJ, Gundel RE, Libassi DP et al. Standardized rigid contact lens fitting protocol for keratoconus. Optometry and Vision Science 1996;73(6):369–75.

6.Harsant R. Silicone hydrogel piggy-back fitting. Optician 2000;220(5766):34–6.

7.Speedwell L. ‘Yet it does move’ A successful and inadvertent Galilean telescopic system. Optometry Today 1986;26:109.

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