Lenses for presbyopia 24 Chapter

Quality of vision

•The use of high and low contrast visual acuity charts gives a useful idea of possible success.

•Low contrast charts will show the difference between spectacles and contact lenses and so may also give some indication of success.

•It is useful to have available in the consulting room common near vision tasks such as a VDU, different contrast papers, and needles and threads.

•A wide range of lighting in the consulting room aids assessment.

•A glare source can be utilized to illustrate potential problems.

GENERAL ADVICE

•Have available a variety of soft bifocals in order to fit the majority of suitable patients.

•It is essential to use trial lenses to obtain an idea of potential success for any particular type of bifocal.

•Try different combinations of bifocals and single vision lenses according to eye dominance.

•Avoid fitting poor lens handlers because of the potential expense with breakages.

•Monovision still has a higher success rate than multifocals.

•Do not fit patients with very small pupils of 3 mm or less. They are unable to use the area beyond the central power.

PRACTICAL ADVICE

•Always use a trial frame for subjective examination as a phoropter may influence the pupil size.

•It is also easier to obtain the reading addition under normal viewing conditions for near vision.

References

1.Evans BJW. Monovision: a review of the scientific literature. Ophthalmic and Physiological Optics 2007;27:417–39.

2.Bennett E, Luk B. Rigid gas permeable bifocal contact lenses: an update. Optometry Today June 2001;15:26–8.

3.Morris J. Contact lenses for the over 40’s. Optometry Today 2009;31 July:30–7.

4.de Carle JT. The de Carle bifocal contact lens. Contacto 1959;3:5–9.

5.Freeman MH, Stone J. A new diffractive bifocal contact lens. Transactions of the British Contact Lens Association Annual Clinical Conference 1987;4:15–22.

6.Ruston DM. How to fit alternating vision RGP bifocals: the Tangent Streak bifocal

– Part 1. Optometry Today 1995;23 October:24–30.

7.Christie C, Beerton R. The correction of presbyopia with contact lenses. Optometry in Practice 2007;8(1):19–28.

8.Ezekiel D. A ‘genuinely’ new bifocal lens design. Optometry Today 2002;17 May:34–5.

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25.1 Lens identification

25.1.1 Rigid gas-permeable lenses

•A single dot engraved on the right lens used to be the standard recommendation.

•‘R’ and ‘L’ engravings. Sometimes only the ‘R’ is used.

•Partial or complete lens specification is engraved by some manufacturers (e.g. CIBAVision). This is intended for practitioner rather than patient information.

•Location of cylinder axis or prism base, usually with a dot.

•Position of segment to assist bifocal fitting.

•Hypermetropes, aphakics and other patients with poor unaided near vision sometimes find it useful to have right and left lenses made in different tints. Usually the Right is gRey and Left bLue.

•A black dot is easier to see on high powered minus lenses than an engraving which merges into the lenticulation.

25.1.2 Soft lenses

Modern laser techniques have largely eliminated earlier problems with mechanical engravings which could either develop fractures or attract deposits. Information can also be imprinted onto the lens photographically and the same method was once used by the practitioner to mark ‘R’ and ‘L’.

©2010 Elsevier Ltd, Inc, BV

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

Section FOUR Complex lenses

•Numerical (123) markings to ensure the lens is not inside out.

•A manufacturer’s logo.

•‘R’ and ‘L’ engravings.

•‘R’ and ‘L’ photographic markings.

•A code, serial or lot number.

•Details of partial or complete lens specification.

•Location of cylinder axis or prism base.

•Position of segment to assist bifocal fitting.

25.2 Tinted, cosmetic and prosthetic lenses

Lenses are tinted for a variety of reasons:

•To reduce adaptive photophobia.

•To assist handling.

•To enhance or change the natural eye colour.

•To reduce photophobia in albinism and aphakia.

•For identification.

•To improve colour vision (see Section 25.2.5).

The potential disadvantages of tinted lenses are:

•Change in colour values (e.g. for artists).

•Possible difficulties with night vision, particularly driving.

•Reduced comfort if there is an increase in thickness.

Tinted lenses are sometimes referred to as enhancer tints where they accentuate rather than change the natural eye colour.

Cosmetic lenses, in this context, may be defined as those used to change the colour of the eyes, whereas prosthetic lenses are used to conceal unsightly scarring or abnormalities of the iris.

25.2.1 Rigid gas-permeable lenses

Most modern lenses are available in a fairly restricted range of tints. Many materials are made only in pale blue and do not give the option of clear lenses. Grey and sometimes brown are usually possible. Green is not available in several widely used materials and, in addition, the colour reproducibility tends to be unreliable. There is often poor consistency of colour between different batches of material and patients should be advised of possible variation with replacement lenses.

Several rigid gas-permeable materials also include a UV inhibitor (see Section 25.2.4). Photochromatic lenses have also been produced but problems occur with dimensional stability and the speed of reversal from dark to light.

Hand-painted cosmetic and prosthetic lenses are limited to stable, very low Dk materials such as XL20.

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25.2.2 PMMA lenses

PMMA lenses, in contrast, have been available in a wide range of stable, consistently reproducible colours. The most commonly used tints were:

912 Light grey (the most common).

512 Medium grey.

1077-1 Light blue.

2240-2 Light green.

2285-1 Light brown.

Cosmetic and prosthetic lenses

Cosmetic and prosthetic corneal lenses are available with painted laminated inserts (e.g. Cantor + Nissel). These are colour-matched from photographs or sets of sample iris buttons and are usually painted by hand with the appropriate clear or black pupil. Although they give excellent cosmetic results, there are several difficulties associated with the use of corrective lenses:

•They are necessarily thick with large total diameters (about 11.50 mm) to give good corneal coverage and appearance.

•Comfort is often poor, with limited wearing time.

•There is a high risk of corneal oedema and long-term vascularization.

•The artificial pupils often give visual disturbance on blinking.

•There is a tunnel vision effect, with restricted field of view.

•It is not possible to assess the fitting of opaque lenses with fluorescein.

Some of these problems are overcome with the use of scleral lenses.

25.2.3 Soft lenses

There is much less clinical need for tinted soft lenses because of the low incidence of adaptive photophobia. There are, however, various enhancer tints for mainly cosmetic reasons. Opaque and semi-opaque lenses are also available for cosmetic and prosthetic fitting. The most common variations are shown in Figure 25.1:

A B C D

Figure 25.1  Variations possible with soft lens tints: (A) tinted iris with clear peripheral annulus; (B) tinted iris with clear peripheral annulus and clear pupil; (C) black (opaque) pupil on clear lens; (D) tinted iris with clear peripheral annulus and black (opaque) pupil

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Section FOUR Complex lenses

(a)Tinted iris with clear peripheral annulus. The iris diameter is usually standardized at 11.50 mm, with a clear periphery to give a natural appearance on the eye. Some laboratories (e.g. CooperVision and Ultravision International) offer both a range of tints and colour densities. Very pale handling tints are also possible (e.g. Omniflex, Durasoft 3 Lite Tint).

(b)Tinted iris with clear pupil and clear peripheral annulus. The clear pupil partially avoids problems with changed colour values and light reduction at night. The cosmetic appearance is not as satisfactory for many patients as a completely tinted iris.

(c)Clear lens with black pupil. Used for occlusion or prosthetic reasons.

(d)Tinted iris with black pupil and clear peripheral annulus. Used for occlusion or prosthetic reasons.

Soft lenses are also produced with inhibitors, specifically to eliminate the ultraviolet part of the spectrum (e.g. Precision UV, Acuvue) and ‘sun filters’.

GENERAL ADVICE

•Unless there is a particular reason, order all rigid gas-permeable lenses with a light tint to assist handling and reduce adaptive photophobia.

•Do not fit tinted soft lenses just for the sake of it. Unless a specific cosmetic effect is required or the lens type is made with a standard handling tint, the advantages may be outweighed by practical difficulties of colour matching, time delays, colour fading and the constraints of which solution systems can be used.

•Avoid tints where colour values are important (e.g. artists).

•Care is required with the choice of solutions for tinted and cosmetic soft lenses. Oxidizing systems, especially those based on chlorine, can cause colour fading or laminates to peel apart. Take advice from the laboratory as peroxide systems can be better than multipurpose solutions.

•It is difficult to persuade many patients, particularly emmetropes, that tinted and cosmetic lenses are more than just a fashion accessory. Careful explanation is necessary that they must be fitted with the same skill and accuracy as conventional lenses and that proper care and maintenance are essential to avoid the risk of infection.

•The effect of a tinted lens cannot be judged unless placed on the eye. The final result is a combination of lens tint, iris colour and ambient lighting.

•To enhance eye colour, do not use a tint that is too saturated. The most pleasing cosmetic effect is usually achieved with a subtle colour change.

•Dark brown eyes are virtually unaffected by purely tinted lenses. Use opaque or dot matrix soft lenses to give a cosmetic colour change.

•Grey eyes respond well to blue and green tints.

•Light and medium brown eyes may sometimes respond to green tints.

•Brown eyes can sometimes be lightened with a yellow tint.

•Blue eyes may become brown with an orange tint.

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Opaque painted and printed lenses

For cosmetic, prosthetic and theatrical purposes, it is also possible to manufacture soft lenses with an opaque laminated backing or insert. They may be either painted or printed with clear or black pupils. Depending upon the laboratory, a limitless range of colours and cosmetic effects is possible, but the additional lens thickness and rigidity can cause problems with comfort and oedema. Despite their greater stability on the eye compared with rigid lenses, opaque corrective soft lenses with a clear pupil can also give visual disturbance on blinking and a reduced field of view.

Very large lenses with total diameter of up to 18.00 mm can be stabilized with prism ballast. By painting a decentred iris, they can be used cosmetically to correct squints.

Dot matrix lenses

Another successful cosmetic approach is the manufacture of lenses with coloured dot matrix patterns (e.g. CIBAVision, Freshlook; CooperVision, Frequency Colours). These avoid most of the visual disturbance that occurs with opaque lenses, although comfort is sometimes a problem. A further refinement of design to overcome the restricted field of view is to have the patterns more widely spaced towards the pupil area.

25.2.4 UV inhibitors

Several varieties of soft lens are now available with a UV inhibitor (e.g. Acuvue, Johnson & Johnson; Precision UV, CIBAVision). This provides a degree of ocular protection and considerably helps glare with some patients. The inclusion of the inhibitor, however, can adversely affect the Dk value. Precision UV, for example, uses a chromophore known as UVAM and the Dk of the material is reduced from 43 to 38 × 10−11 Fatt units.

25.2.5 Lenses to enhance colour vision

The X-chrom lens

A specialized application of tinting is the monocular use of the dark red X-chrom lens (Cantor + Nissel). Its particular transmission characteristics are reported to enhance colour discrimination in patients with red–green deficiency.1 Lenses are also available in soft lens form.

Chromagen

The Chromagen system (Cantor + Nissel) also claims to achieve enhancement to colour vision. The system consists of coloured filters that are available in a range of hues and densities. The lens is usually fitted monocularly to the nondominant eye. To obtain the optimal result, a multicoloured display is viewed through the selection of filters and any change in the number, brightness or

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