Medical Contact Lens Practice

166 Pages·2005·12.62 MB·English

by  Elisabeth AW Millis, MD DO MRCOphth (Auth.)

© 2005, Elsevier Limited. All rights reserved.
First published 2005
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ISBN 0 7506 4327 7
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Note
Knowledge and best practice in this field are constantly changing. As new
research and experience broaden our knowledge, changes in practice,
treatment and drug therapy may become necessary or appropriate.
Readers are advised to check the most current information provided (i) on
procedures featured or (ii) by the manufacturer of each product to be
administered, to verify the recommended dose or formula, the method and
duration of administration, and contraindications. It is the responsibility
of the practitioner, relying on their own experience and knowledge of the
patient, to make diagnoses, to determine dosages and the best treatment
for each individual patient, and to take all appropriate safety precautions.
To the fullest extent of the law, neither the Publisher nor the Author
assumes any liability for any injury and/or damage.
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vii
Foreword
The field of medical contact lenses spans a and any condition can have a variety of secondary
potential gap between the disciplines of ocular effects. The early chapters outline the skills in
surface medicine and refractive contact lens fit- clinical history-taking and examination technique
ting. Contact lenses can be used as medical needed to unravel the presenting symptoms and
devices to treat ocular surface disease. In con- signs and identify the problem. The later chapters
trast, contact lenses worn for refractive purposes describe how contact lenses can be used to treat
can cause medical problems. In addition, there ocular surface disease and complex refractive
are patients with eye problems such as allergy errors. There are discussions of some of the newer
who would like to wear contact lenses for refrac- techniques and materials, such as digital photo-
tive purposes, but may be exposing themselves graphy, projection-based topography and silicone
to a greater risk of medical problems. hydrogel lenses.
The fields of ocular surface medicine and Dr Millis has selected for coverage in greater
refractive contact lens fitting commonly come detail some of the areas causing particular diffi-
under the care of two different professions – culty in the clinic. She highlights the differences
ophthalmologists for the former and optometrists in the normal ocular surface and refractive status
for the latter. This book will help individuals of older patients, the importance of changes to
from either profession to bridge this gap. Contact the ocular surface physiology when the eye
lens fitters will gain the medical knowledge is closed, and the use of topical medications in
needed to diagnose pre-existing conditions and contact lens wearers.
complications, apply simple medical care and The frequent subheadings, tables and boxes
decide when to refer the patient. Similarly, doc- make the text easy to read and assimilate, and
tors in the emergency room or receiving referrals the ample clinical photographs contribute to it
will learn about contact lenses and how they may being a valuable handbook for trouble-shooting
have caused a problem. In addition those from in the clinical setting. It is easy to follow-up
either profession will benefit from the knowledge points of particular interest due to the extensive
of how to use therapeutic contact lenses to treat bibliography in each chapter.
medical conditions. I therefore congratulate Elisabeth on giving us
Elisabeth Millis has a background in ophthal- a book which draws together experience from
mology, but her work with gurus in medical both the medical ocular surface and contact lens
contact lenses, and then as a well-recognized fields. I highly recommend it to ophthalmolo-
expert in her own right, has given her a wealth of gists and optometrists alike, and even those spe-
experience on which to draw when writing this cialising in the field will find valuable tips from
book. The practical tips she is able to pass on will which to learn.
facilitate the care of the trickiest clinical condi-
London, 2005 Melanie Corbett
tions and the most difficult of contact lens fits.
The ocular surface is a complex environment.
Any clinical picture can be multifactorial in origin,
ix
Preface
As an ophthalmologist who has specialized in and therapeutics. The advent of silicone hydrogel
fitting contact lenses both in hospital and private lenses has improved the prospects for extended
practice, I have been particularly concerned with wear, and their use in cases of corneal vascular-
those who have medical indications for such ization is discussed. Ashort chapter on keeping
lenses. This book assumes a basic knowledge and maintaining clinical records has been
of contact lens fitting, although some sugges- included. It is hoped that greater understanding
tions are made for fitting in particular circum- of these factors will help the practitioner to safely
stances. Instead emphasis is placed on aspects and successfully fit lenses to a wide range of
such as inflammation and hypersensitivity, the patients.
evaluation of the older patient, the changes
occurring in the closed eye, and pharmacology London, 2005 Elisabeth Millis
xi
Acknowledgements
My grateful thanks to Jonathan Walker for his Jack Kanski for Figs 2.4, 3.1, 3.2, 3.3, 3.4, 9.1, 9.2,
advice, and to Melanie Corbett for all the helpful 9.6, 9.9 and 9.10
advice she has given me throughout the prepara- Michael Loughnan for Fig. 2.3
tion of the manuscript and who willingly agreed Ian Mackie for Figs 7.6 and 7.7
to write the foreword. To Anita O’Sullivan, my Michael Wilson for Figs 2.1, 7.1, 7.3 and 7.4
secretary, for her tireless help with all the adminis- Steve Lennox of SCL Contact Lenses for Figs
tration and to my husband Tom for all his support 12.2 and 12.3
when the going got tough. Karl Southern of The Western Eye Hospital,
I would also like to thank the following for pro- London for Figs 5.1, 6.1, 6.2, 6.3, 6.6, 6.8, 8.3, 8.5,
viding many of the illustrations: 9.3, 9.8, 10.4, 11.4, 12.1, 12.4, 12.5, 12.6 and 13.2.
John Dart for Figs 6.5 and 6.7 Finally, my gratitude to the two people without
Andrew Gasson for Figs 2.2, 2.5, 2.7, 4.1, 5.3, 5.4, whom this book would not have been completed –
5.5, 5.8, 5.9, 5.11, 5.12, 5.15, 5.16, 5.18, 7.1, 7.5, 9.5 my editors Caroline Makepeace and Kim Benson,
and 11.2 for their expertise and patience.
Kathy Dumbleton for Fig. 5.10
1
1
Chapter
Examination of the external eye
HISTORY AND EXAMINATION
CHAPTER CONTENTS
Initial visit
History and examination 1
Examination 2 All potential and current contact lens wearers
Fitting contact lenses with should undergo a full ophthalmic history and
videokeratoscopy 8 examination (Tables 1.1 and 1.2) at their first visit to:
Photography of the anterior eye 12
● exclude any conditions that may contraindicate
Teaching appointment 14
lens wear
Follow-up examination 14
● record any abnormalities
References 15
● identify and treat conditions such as blepharitis
Further reading 15
before lens wear.
Many excellent texts describe the routine exam-
ination of the eye, and the indications and con-
traindications for lens wear. This chapter outlines
these points, and looks in greater detail at the part
Table 1.1 Initial patient examination
Patient history
General medical history
Family history
Contact lens history
Visual acuity
General examination, including hands and fingernails
Full slit-lamp examination including intraocular pressure
measurement
Keratometry and topography
Refraction
Ophthalmoscopy
Assessment tear film
Eversion upper lid
Corneal sensitivity
2 MEDICAL CONTACT LENS PRACTICE
past history of topical or systemic use may be
Table 1.2 Factors affecting choice of lens and
complicated by cataract formation or glaucoma.
mode of wear
Patients do not always volunteer this information
Ocular condition, including refraction and should be asked directly if they take any
Type of employment tablets or other medication.
Sports and hobbies Specific questioning may also be needed to
Environmental conditions elicit the use of preparations not prescribed by a
Special visual needs medical doctor because many patients do not
think to include homeopathic, herbal or home
remedies as “treatment”.
played by modern technology in both the exami-
Family history
nation and the recording of the findings.
Any family history of systemic or ocular disease,
or atopy should be recorded.
History of the present condition
The contact lens history will cover the present
Contact lens history
symptoms and signs as described by the patient.
The information should not be “interpreted” by If the patient is a new lens wearer the reason for
the examiner, but recorded as described by the wanting contact lenses should be determined
patient. In the event of the notes or the diagnosis because this may influence the type of lens selec-
being reviewed, the patient’s description may be ted. If the patient has worn lenses previously, the
more informative than a clinician’s opinion of lens type or types, the wearing regime, and any
what was said. problems arising either from the lenses or the
The duration of the symptoms and signs will solutions used must be documented.
determine whether the condition is acute or
chronic. Details of previous similar episodes, the
EXAMINATION
degree of resolution, and whether it is sponta-
neous or the result of medication, may all suggest Observation of patients begins as they enter the
the nature of the condition. Alens-related problem room. Conditions such as arthritis, rosacea, red
is likely if there is improvement when the lens is eye, heterochromia, or lid and pupil anomalies
removed from the eye and the problem recurs (Fig. 1.1) may affect lens wear and are often best
when the lens is reinserted. viewed from a distance in a good light, when the
two eyes are more easily compared.
Patients who are normally contact lens wearers
Medical history
who attend the consultation wearing spectacles
Details of the patient’s general health, including should be asked why. Have they been told to
allergies, asthma, eczema, hay fever, diabetes and attend without having worn lenses for a period of
other general medical conditions, and any med- time? Are they having difficulty with lens wear?
ication must be sought: Have they lost a lens or run out of supplies of dis-
posable lenses?
● dry eyes and contact lens discoloration may be
This is an opportunity to observe the patient’s
due to systemic medicines
hands and fingernails. Is there any condition that
● drugs such as amiodarone and tamoxifen may
might make lens handling difficult? Are the nails
cause corneal deposits
clean and reasonably short? Some patients wear
● tricyclic antidepressants may result in blurred
artificial nails and these are more prone to causing
vision and raised intraocular pressure.
soft lens damage.
Current use of topical corticosteroids would The visual acuity for each eye separately and
normally contraindicate contact lens wear and a for near and distance is recorded at each visit.
Examination of the external eye 3
With modern rigid, gas-permeable and soft
lenses refraction can usually be undertaken on
removal of the patient’s lenses. For those few still
wearing polymethylmethacrylate (PMMA) lenses,
removal should precede refraction by 3 or more
days. If the patient cannot manage without lenses,
for example in cases of keratoconus, it may be pos-
sible for the patient to manage with one lens for a
few days and to refract one eye at one visit and the
other a week or so later.
The fit, parameters and general condition of
any lenses worn by the patient should be assessed
Figure 1.1 Soft contact lens wear in a patient with lens and entered in the records.
opacities and coloboma.
Corneal topography
A careful note should be made of whether the
visual acuity was measured unaided, with glasses, It is essential to measure corneal curvature when
or lenses. Failure to record visual acuity may lead fitting any type of lens. This is most important in
to medicolegal problems. the fitting of rigid lenses. For fitting soft lenses
A complete, systematic ophthalmic examin- measuring corneal curvature is useful as a base-
ation is carried out, including an assessment of line record, for comparison in the future, and as a
corneal sensation and eversion of the upper lids, guide to selection of the trial lens, and should be
which is often best achieved by grasping the lid carried out when soft lenses are fitted.
margin and rolling the lid over a cotton bud. It is
important that the lid margins are examined care-
Keratometry
fully on the slit lamp to exclude meibomian gland
disease and blepharitis, and that the tear film is The most commonly used method of measuring
examined before installation of fluorescein or corneal curvature is the keratometer based on
other drops (see Ch. 2). Helmholz’s assumption that the central cornea is
The clinician identifies and records all abnor- spherocylindrical. It has been used as the standard
malities. Acomparison of the two eyes may yield with which all other methods are compared.
vital information. The full range of slit-lamp mag- The corneal surface acts as a convex mirror,
nification and beam width is used to examine any which creates a virtual image behind the cornea.
lesion, and a detailed description of the findings The keratometer measures an area of 2.8–4.0mm
including size, color and situation is made and centrally, depending on the corneal curvature and
recorded by drawing, or by photographic or image type of instrument. The size of the image is deter-
capturing techniques (see below). mined by the anterior corneal surface – a steep
Grading scales such as those by Efron1and the cornea results in a small image and a flat cornea
Cornea and Contact Lens Research Unit (CCLRU)2 a large image.
may be used to monitor any change and may be The keratometer measures the radius of curva-
useful if examination is undertaken by different ture of the cornea in millimeters. The same cornea
clinicians. may provide different readings, depending on the
Initially it is more important to have an accu- instrument used. Different types of keratometer use
rate description of a condition than to identify it. different mire separations, so the area of reflection
All abnormalities whether pathologic or non- is different, or may use different refractive indices
pathologic must be recorded because patients tend so the same radius gives differing surface powers.
to examine their eyes more closely when wearing If a lens support is used it is possible to use the
contact lenses and may think that a problem pres- keratometer to measure the back optic zone radius
ent before lens wear has been caused by the lens. (BOZR) of a rigid lens.
4 MEDICAL CONTACT LENS PRACTICE
Automated keratometry the findings. Measuring the diameter of each ring
allows the shape factor to be calculated.
Automated keratometers measure different areas
of cornea (Canon 3.8mm diameter, Humphrey
2.6–3.24mm) and use different algorithms for their
Videokeratoscopy
calculations. Accuracy and repeatability of measure-
ments is high for test spheres and normal corneas.3,4 Reflection-based systems Videokeratoscopy
Rapid, accurate measurements are obtainable in (VKS) has superseded photokeratoscopy, but most
most cases, but the manual keratometer may be able systems in clinical use are still based on Placido’s
to record data over a wider range (e.g. in cases of disc. Data are gathered over a wider area of cornea
corneal irregularity and high astigmatism, and in (8–9mm) and curvature or power is calculated for
those with blepharospasm or head tremor, when thousands of points. Images are captured by one
results are not obtainable with the automated or more video cameras and a frame grabber; they
instrument). are then digitized and analysed by computer soft-
Handheld autokeratometers are now available ware. Algorithms construct a three-dimensional
and are useful in the operating theater or as part of shape from the two-dimensional image and this
a domiciliary ophthalmologic examination, and shape is then displayed on the monitor, most com-
may appear less frightening for children. monly as color-coded maps, but also as wire-mesh
or solid models, depending on the instrument.5
Videokeratoscopes are used to examine and
Photokeratoscopy
monitor corneal shape (Fig. 1.2). They are particu-
The photokeratoscope uses the principle of larly useful in showing the site of the cone in kera-
Placido’s disc to produce a photographic record of toconus, and in identifying irregular astigmatism,
the reflection of a series of black and white illumi- which is essential to select the most appropriate
nated concentric rings. Qualitative information is contact lens design.
obtained from a Polaroid photograph as the mires Videokeratoscopy monitors shape changes
appear distorted if there is irregular astigmatism. following surgery or contact lens fitting, assists in
Narrowing of the space between mires suggests the identification of corneal warpage, whether as a
steepening of the cornea and widening suggests result of lens decentration or orthokeratology, and
flattening, but tear film abnormalities and epithelial may make some corneal pathology more apparent
irregularities may cause difficulties in interpreting than on clinical examination.
Figure 1.2 Topography map showing central corneal steepening greater in the left eye than the right. The left cornea
is more astigmatic.
Examination of the external eye 5
Videokeratoscopes have software programs that above a reference plane; the contours on the map
create stylish graphics and allow rapid data analy- follow lines of equal height rather than slope. The
sis. The limitations of Placido’s disc to measure an image needs to be intensified to be visible. Fluor-
aspheric surface still apply and certain assump- escein has been used for this, but may interfere
tions are made in the calculations. There may be with the tear film.
mechanical problems in capturing the image and Projection-based systems do, however, have a
although the area of cornea measured is greater number of advantages. They can record results
than in keratometry it is still limited to 8–9mm in from irregular and nonreflecting surfaces from
diameter. the total corneal area, and are as accurate at the
Quantitative results are not perfect with current periphery as at the center of the cornea. They have
instruments, but they do provide additional help- only recently entered into routine clinical use
ful information. because they require costly computers to rapidly
The cornea reflects the concentric black and analyse the large amounts of data generated.
white mires and the virtual image behind the Rasterstereography projects a lighted grid onto
cornea is detected by the video cameras. The the cornea that is rendered opaque with sodium
patient fixes on an illuminated target, but in cur- fluorescein and viewed obliquely from a known
rent systems the head may need to be turned angle. It makes direct point-to-point measurement
slightly to achieve correct alignment. Failure to of the surface elevation using a stereotriangulation
align with the line of sight can lead to errors in the technique. The advantages of the grid are that:
calculations determining the topography.
● it covers the entire cornea and will extend onto
Some instruments have an image subtraction and
the sclera
enhancement program to locate the pupil, which is
● it does not need an intact epithelium nor pre-
critical for centration in cases of refractive surgery.
cise spatial alignment for accurate imaging
Clinical factors that affect the use of the instru-
● it is less affected by irregular corneas.
ments include the ability of the patient to maintain
fixation and the need to blink frequently to main- The distortion of the projected grid is converted
tain corneal wetting because the image is reflected into true elevation measurements from which cur-
from the tear film. This may make rapid changes of vature values can be calculated. Pooling of fluo-
curvature difficult to detect and it may not be pos- rescein may result in an artificial distortion of the
sible to obtain accurate maps in some postsurgical image.
eyes. The presence of tear film debris, particularly More recently the same principle has been used
make-up particles, can make capturing an image with a scanning slit beam in which 40 slit sections
more difficult. Brow or lid obstruction may cause are captured across the cornea.8This also provides
difficulties, and problems may arise from center- information about the posterior corneal shape and
ing the image and focusing the instrument, which corneal thickness.
require the subjective judgement of the examiner The KM-1000 CLAS Corneal Topography Unit
with some instruments. Poor alignment can cause (Keratometrics Inc.) uses laser holography to
pattern distortions that may mimic keratoconus.6 image the corneal surface and fringe detection to
Szczotka and Thomas7 found axial and instan- assess topographic change.
taneous (tangential) maps differ significantly in
apical position and apex curvature in kerato-
Color maps
conus. Although the tangential radius may repre-
sent corneal shape better, they found that axial Most current VKS instruments present data as
curvatures are better to predict base curves for color-coded maps where red represents steepness
rigid gas-permeable (RGP) lenses in these cases. and blue flatness. Each color is assigned a dioptric-
step value, and the larger the step the greater the
Projection-based systems In projection-based range of corneal power display, but the less the
systems an image is projected onto the tear film detail. The pattern displayed therefore depends
and measurements are made in terms of elevation on the range of the scale used and the step size