Section three Hydrogel and silicone hydrogel fitting

with conventional lenses, particularly with daily disposables in low powers of less than −2.00 D. This applies even to experienced wearers of conventional lenses, who sometimes discontinue for this reason.

PRACTICAL ADVICE

Where patients experience difficulty with handling, initially use disposables of a different make with a lower water content or greater modulus; they can subsequently be switched to the preferred design. Alternatively, patients can be given high powered lenses for practice purposes to make insertion easier and give confidence.

Solutions

Except in cases of known allergy or sensitivity, the modern generation of multipurpose solutions (Section 26.3.1) is generally recommended for use with disposable lenses. Many solutions systems now include new cases and monthly patients should be encouraged to replace the case at the same time as the lenses. Despite the simplicity of use for one-bottle systems, it is essential to stress the importance of proper lens cleaning and disinfection. Patients often assume that disposability equals minimal lens care and the ‘no-rub’ approach is to be deprecated.

Where patients use monthly disposables on an irregular basis they may not be prepared to change them every month. In these cases, the life of the lenses can be regulated according to the usage of a typical one month bottle of soaking solution.

Aftercare

•Aftercare follows the normal principles described in Chapters 28 and 30 for both daily and extended wear.

•Careful observation is required where fittings may be marginal due to limitations in lens parameters.

•Intervals for routine aftercare visits can be arranged to coincide with the dispensing of lens supplies at 3 or 6 months.

•A full aftercare examination is required every 12 months.

•Aftercare visits represent a good opportunity to improve marginally successful fittings with newly introduced materials, parameters or a different make of lens.

18.6 Practice management

The main disadvantage of disposable lenses is the need for careful management of lens supplies.

•For patient simplicity, the ideal replacement interval should be 1, whether this is 1 day, 1 week or 1 month.

•Where a 2-weekly schedule is used, lenses can be replaced on the 1st and 15th of the month.

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•Where possible, supply lenses in units of 6 rather than 3 months. This means that administrative dealings with patients and laboratories occur twice instead of four times a year.

•Computer systems can be used to deal with automatic supplies from laboratories and to select patients from the practice database. It is frequently difficult, however, to ensure that dates coincide. There are, in fact, three time scales to correlate, determined by: (1) the laboratory, which may well work on only a 12-week quarter; (2) the practice, which should depend on the practitioner’s recommendation to the patient; and (3) the patient, who may be accurate with lens usage, behind schedule by extending the lens lifespan, or ahead because of lens breakage or loss.

•Consider supplying lenses from a practice stock rather than relying on an inflexible laboratory computer system.

•Many practices use standing orders or direct debits to control patient fees.

PRACTICAL ADVICE

The three key pieces of information required for each patient are:

(a)The mode of wear (daily, flexible or extended).

(b)The replacement interval (weekly, fortnightly or monthly)

(c)The quantity of lenses to be supplied.

These details can be noted on the record card in the following simple fashion:

Daily/2-weekly/6 monthly

To indicate lenses worn on a daily basis, replaced 2-weekly and supplied in units of 6 months.

Extended/monthly/3 monthly

To indicate extended wear lenses, replaced monthly and supplied in units of 3 months.

18.7 Other uses for disposable lenses

The low unit cost of disposables means that they have other very useful clinical applications apart from normal daily and extended wear.

•As trial lenses, since most soft lenses are no longer re-used.

•Low-cost temporary replacements in an emergency.

•Maintaining soft lens wear when CLIPC is causing rapid deposits.

•Short-term use in the hay fever season to avoid CLIPC.

•Periodic use for patients working with VDUs intensively but intermittently.

•To give a lengthy tolerance trial for contact lenses in general (e.g. can the patient cope with handling and disinfection?).

•To give an extended assessment of contact lens vision (e.g. can uncorrected astigmatism or monovision be tolerated?).

•Temporary lenses for patients undergoing orthokeratology (see Chapter 14).

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•Temporary lenses for patients ceasing rigid lens wear prior to cataract or refractive surgery.

•As a means of assessing children who require soft lenses.

References

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

2.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.

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

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Hydrogel and silicone hydrogel fitting three

Silicone hydrogels 19CHAPTER

Silicone hydrogel lenses were first introduced to the UK by Bausch & Lomb and CibaVision during 1999 with the key advantage of extremely high oxygen permeability. They were initially launched as the first of an entirely new generation of materials for 30 days extended or continuous wear. It was originally thought that they would prove much safer in this respect with a significant reduction in serious adverse ocular responses. Current evidence, however, has shown that with overnight wear the incidence of corneal infection with silicone hydrogel lenses is similar to that for traditional hydrogels but the severity is less.1

It was soon recognized that there were a great many advantages for silicone hydrogels for purely daily wear. They have gradually entered contact lens practice for routine daily wear and, with the introduction of more complex designs (Section 19.3), they are now frequently the lens of first choice.

With silicone hydrogels, a lower water content does not equate to a lower Dk. Since the majority of oxygen is transported through the silicone component of the material, the higher the water content the lower the Dk and vice versa.

The early, first generation materials with low water content had a high modulus with greater rigidity. This proved uncomfortable for some patients used to softer hydrogels and gave a higher incidence of arcuate staining. A so-called second generation of materials was introduced with a lower modulus which has successfully overcome these problems. More recent lenses are derived from materials with both a low modulus and a higher water content to improve comfort still further. These are sometimes referred to as third generation silicone hydrogels. Table 19.1 shows the range of lenses currently available.

©2010 Elsevier Ltd, Inc, BV

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