Aftercare complications 29 Chapter

References

1.Poggio EC, Glynn RJ, Schein OD, Seddon JM, Shannon MJ, Scardino VA et al. The incidence of ulcerative keratitis among users of daily-wear and extended-wear soft contact lenses. New England Journal of Medicine 1989;321(12):779–83.

2.Cheng KH, Leung SL, Hoekman HW, Beekhuis WH, Mulder PG, Geerards AJ et al. Incidence of contact lens associated microbial keratitis and its related morbidity. Lancet 1999;354(9174):181–5.

3.Schein OD, McNally JJ, Katz J, Chalmers RL, Tielsch JM, Alfonso E. The incidence of microbial keratitis among wearers of a 30-day silicone hydrogel extended-wear contact lens. Ophthalmology 2005;112(12):2172–9.

4.Stapleton F, Keay L, Edwards K, Naduvilath T, Dart JK, Brian G et al. The incidence of contact lens-related microbial keratitis in Australia. Ophthalmology 2008;115(10):1655–62.

5.Dart JK, Radford CF, Minassian D, Verma S, Stapleton F. Risk factors for microbial keratitis with contemporary contact lenses: a case-control study. Ophthalmology 2008;115(10):1647–54.

6.Dumbleton K. Adverse events with silicone hydrogel continuous wear. Contact Lens and Anterior Eye 2002;25:137–46.

7.Efron N. Contact lens-induced sterile infiltrative keratitis. Optician 1997;214(5606):16–22.

8.Blade KJ, Tomlinson A, Seal D. Acanthamoeba keratitis occurring with daily disposable contact lens wear. British Journal of Ophthalmology 2000;84:805.

9.Gasson AP. Visual considerations with hydrophilic lenses. Ophthalmic Optician 1975;15:439–48.

10. Port MJ. Contact lens surface properties and interactions. Optometry Today 1999;July 30, 27–35.

357

30.1 Refitting PMMA wearers

Although most of Section 30.1 relates specifically to refitting PMMA, many of the practical points also apply to refitting long-standing gas-permeable lenses.

30.1.1 Physiological problems caused by PMMA

PMMA lenses are now almost never fitted although they have, in many cases, been worn by long-standing patients for well over 40 years. These patients are very often quite happy with their lenses and it is only at an aftercare examination that the practitioner may detect corneal changes. In other cases, patients seek advice because of reduced wearing time, red eyes or depressed vision.

The more common changes found with long-term PMMA wear are:

•Epithelial oedema.

•Reduced corneal sensitivity.

•Central punctate epithelial staining.

•Chronic 3 and 9 o’clock staining.

•Stromal oedema.

•Folds in Descemet’s membrane.

•Endothelial polymegathism.

These changes are due to chronic lack of oxygen, drying of the corneal  tissue and the mechanical action of the lens. The combination of these  long-term effects produces the loss of tolerance known as ‘corneal exhaustion syndrome’.

©2010 Elsevier Ltd, Inc, BV

DOI: 10.1016/B978-0-7506-7590-1.00011-X

Section FIVE Management

30.1.2 Refitting with gas-permeable lenses

Refitting long-term PMMA wearers can prove difficult, especially where there are no previous details available. The procedure is further complicated because, however carefully measurement and fitting are carried out, changes are likely to occur as the cornea comes ‘off the influence’ of PMMA. The preferred course of action is to refit with modern gas-permeable lenses. It is usually more problematic to move directly from PMMA to soft lenses.

Problems of refitting

•The cornea may show considerable signs of oedema and distortion.

•‘K’ readings may be very different from the measurements when fitting   has ultimately been completed and may continue to change for several months. There may be considerable distortion or even permanent corneal warpage.

•Accurate refraction may be very difficult if not impossible with poor retinoscopy reflex and depressed visual acuity because of the corneal oedema.

•The BVP often requires more minus power after 1–3 weeks and the corneal astigmatism is likely to alter.

•It is often impossible to measure accurately the BOZR of a patient’s old, distorted lenses.

Refitting procedures

General points

•Patients should understand the possible difficulties and that refitting requires careful follow-up.

•They should come for their refitting appointment wearing the existing PMMA lenses, as with spectacle prescribing (see Section 30.2).

•The old lenses should be measured where possible and, if they exist,   old pre-contact lens spectacles should be examined. They are unlikely   to be accurate but offer clues to the original Rx and degree of astigmatism.

Fitting

•The PMMA lenses are assessed with white light and fluorescein, noting where improvements to the physical fitting may be made.

•‘K’ readings are taken as carefully as possible but they may be distorted, unreliably flat and show an artificial degree of astigmatism.

•An assessment of the refraction is made.

•The initial lenses used for refitting are based on ‘K’ readings but measurements of old lenses are taken into account. Much more reliance is

360

Additional aftercare procedures 30 Chapter

placed on the fluorescein appearance than ‘K’s, although this is also difficult because central oedema may give a conus-like fitting.

•Rigid gas-permeable lenses give better vision if steep fittings are avoided.

•Fitting both a larger optic and total diameter can often solve PMMA difficulties such as poor centration or flare.

•There is less 3 and 9 o’clock staining with narrower edge clearance.

•For patients with very tight lids, designs are avoided with narrow edge   lift, especially aspherics. There may be an increased possibility of lens adhesion.

Problems

A minority of patients cannot adapt to rigid gas-permeable lenses because of:

•Physical discomfort, relating to surface wetting properties and increased corneal sensitivity.

•Poor visual acuity, relating to lens flexure or distortion.

•Greasing and deposits problems.

•CLIPC.

If these problems cannot be resolved, the practitioner should consider changing to soft lenses after a further 6–8 weeks.

PRACTICAL ADVICE

•Avoid materials with low rigidity or very thin designs for patients with tight lids and toric corneas since lenses may flex and distort.

•Avoid brittle materials for initial refitting. Patients used to handling relatively robust PMMA are likely to have breakage problems. Similarly avoid materials which may scratch easily. Advise patients of a potentially shorter lifespan.

•Carefully specify centre and edge thickness where possible, to avoid lenses which are too thin or too thick.

•Refraction frequently shows an increase in minus of 0.25 to 0.50 D after about 2 weeks. Myopes should therefore be fully corrected and binocular additions are not usually given except with presbyopes.

30.1.3 Refitting with soft lenses

It is generally unwise to refit PMMA wearers directly with soft lenses since problems as the fitting progresses are much more significant. The same can apply when refitting long-standing rigid gas-permeable wearers.

•As the ‘K’ readings change the degree of astigmatism may alter in an unpredictable fashion. Initially good acuity may deteriorate within 2 or 3 days as corneal toricity changes.

361