Section ONE Preliminaries
5.2 Indications and contraindications
5.2.1 Advantages and disadvantages of contact lenses compared with spectacles
Advantages
•More natural vision.
•Wider field of view.
•Better for refractive anisometropia.
•Retinal image size almost normal with refractive ametropia (e.g. with aphakia, high minus).
•No unwanted prismatic effects with eye movements.
•Less convergence required by hyperopes for near vision.
•Avoid surface reflections.
•Minimal oblique or other aberrations.
•Cosmetically superior.
•More practical for sports.
•Avoid weather problems (rain, snow, fogging up).
•Provide good acuity for irregular corneas (keratoconus, trauma, grafts and subsequent to refractive surgery).
•Therapeutic uses.
•Vocational uses.
Disadvantages
•Time required for fitting and adaptation.
•Handling skills required by patient.
•Hygienic procedures and lens disinfection necessary.
•Wearing time may be limited.
•Range of useful tints limited, especially with complex lenses.
•For binocular problems, only limited vertical prism possible.
•Greater convergence required by myopes for near vision.
•Lenses can be lost or broken or disposable supplies run out.
•Problems with foreign bodies.
•Peripheral flare (especially at night).
•Conventional lenses deteriorate with use and age.
•Retinal image size disparity in axial anisometropia.
•Lens supply and maintenance costs.
•Greater overall expense.
•Administrative procedures for disposable lens supplies.
60
Preliminary considerations and examination 5 Chapter 
5.2.2 Indications and contraindications
Indications
There are many patients for whom contact lenses are not merely a matter of cosmetic choice, but the best means of providing a satisfactory visual correction.
Visual
•Anisometropia.
•High myopia.
•Aphakia.
•Irregular corneas, scarring, keratoconus, grafts.
•Failures with refractive surgery.
Occupational
•Film, theatre and other stage performers.
•Armed forces.
•Professional sports.
Cosmetic
•To avoid spectacles.
•Change eye colour.
•Prosthetic lenses or shells.
Medical
•Therapeutic.
•Bandage.
Psychological
• Where the patient cannot accept wearing spectacles.
Other
•Sports.
•Physical inability to wear spectacles (e.g. allergy to frame materials, nasal problems).
Contraindications
There are a great many factors that may be considered as contraindications. Few of them are absolute, but all must be carefully assessed prior to fitting.
Visual
•Low refractive errors (e.g. +1.00/−0.75, −0.25/−0.50).
•Correction required only for near vision.
•Acuity with lenses may be worse than with spectacles.
•Prism required horizontally or >3 vertically.
61
Section ONE Preliminaries
Occupational
• Where legal constraints apply (e.g. commercial pilots, fire brigade).
Cosmetic
•Where spectacles are better with a large-angle squint.
•Where spectacles hide facial disfigurement.
•Where a patient has previously been reconciled to a long-standing unsightly eye (e.g. scar, mature cataract).
Medical
•Active infection or pathology.
•Recurrent corneal erosions (where a bandage lens is inappropriate).
•Severe sinus or catarrhal problems.
•Allergies.
•Vernal catarrh.
•Diabetes (fragile epithelium).
•Blepharitis
•Anatomical (e.g. misshapen lid).
•Smoking.
Dryness
•Poor volume or quality of tears.
•Poor blinking.
•Dry environment.
•Drug-induced (e.g. antihistamine).
•Work-induced (e.g. VDUs).
•Susequent to cosmetic lid surgery.
Psychological
•Cannot accept the idea of a lens on the eye.
•Cannot tolerate any level of discomfort.
•Unable to cope with insertion and removal.
•Total perfectionist.
Sensitivity
•Cornea too sensitive.
•Lids or lid margins too sensitive.
Environment
•Dust.
•Fumes.
•Dryness (central heating, air conditioning, aeroplanes).
•Altitude (low EOP).
62
Preliminary considerations and examination 5 Chapter 
Other factors
There are other factors which may not necessarily be contraindications but should be carefully considered:
Age
There are many patients, such as aphakics, who have been successfully fitted at an advanced age, but the elderly1 should be carefully assessed for the following:
•The ability to handle lenses.
•Visual requirements.
•Reduced pupil size.
•Reduced lid tonus – entropion, ectropion.
•Tendency to ptosis and reduced palpebral aperture.
•Reduced tear flow.
•Meibomian gland dysfunction.
Complexion
Patients with fair skin and blue eyes may well have more sensitive corneas and find adaptation more difficult.
Motivation
Patients must be sufficiently motivated to be successful with contact lenses. For example, those who are fitted as a present by a friend or relative often do less well if they do not really wish to wear lenses.
Compliance
It is obvious from the outset that some patients are unlikely to be compliant with instructions. It is better not to commence fitting unless the practitioner is certain that they will follow advice in respect of:
•Lens cleaning and disinfection.
•Correct use of disposable lens supplies.
•General hygiene.
5.3 Advantages and disadvantages of lens types
5.3.1 Hydrogel lenses
Advantages
•Good initial comfort.
•Ease of adaptation.
•Natural facial expression and head posture.
•Long wearing times.
•Low incidence of oedema.
63
Section ONE Preliminaries
•Rare occurrence of overwear syndrome.
•Absence of spectacle blur.
•Maintenance of corneal sensitivity.
•Good for intermittent wear.
•Low incidence of photophobia and lacrimation.
•Low incidence of flare, even with large pupils.
•Few problems with foreign bodies.
•Low risk of loss.
•Good for sports.
Disadvantages
•Astigmatism not corrected with spherical lenses.
•Variable vision.
•Near vision problems.
•Lens dehydration.
•Liable to damage.
•Deposits and ageing with conventional lenses.
•Disinfection and hygiene essential.
•Solutions allergies.
•Lens cleaning more difficult.
•Lens contamination.
•Limited life span.
•No modifications possible.
•Difficult to check.
•Corneal vascularization with thicker or low water content lenses.
•Contact lens-induced papillary conjunctivitis (CLIPC).
•Expensive to maintain or replace regularly.
5.3.2 Silicone hydrogel lenses
Most of the above points also apply to silicone hydrogel lenses. Their advanced characteristics, however, present the following differences which are gradually making them the lenses of first choice:
Advantages
•Extremely high oxygen permeabilities.
•Virtually no risk of vascularization.
•Suitable for extended wear.
•Less dehydration because of lower water content.
Disadvantages
•Not tolerated by a minority of patients
•Limited range of powers.
64
Preliminary considerations and examination 5 Chapter 
•Limited availability of complex lenses (torics, bifocals).
•Greater incidence of arcuate staining.
•More liable to lipid deposits.
•More expensive.
5.3.3 Rigid gas-permeable lenses
Advantages
•Excellent visual acuity.
•Correct corneal astigmatism.
•Variety of complex designs available.
•Ease of maintenance.
•Few solutions allergies.
•Minimal deposits with proper cleaning.
•High oxygen permeabilities (Dks).
•Do not cover the entire cornea.
•Tears pump on blinking.
•Good long-term ocular response.
•Easy to check.
•Modifications possible.
•Lenses available in a range of tints.
Disadvantages
•Initial discomfort.
•Precise fitting required.
•Stringent regulations concerning the use and disinfection of diagnostic lenses.
•Foreign bodies.
•Risk of loss.
•Flare.
•3 and 9 o’clock staining.
•Lens adhesion.
•Breakage and scratching.
•Greasing with some patients.
•Instability of some materials.
5.3.4 Polymethyl methacrylate (PMMA) lenses
PMMA lenses, despite their historical importance, are now almost never used either for fitting or refitting. They may be regarded as a small subgroup within the general category of rigid lenses being worn only by a declining number of long-standing patients.
65