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Contact Lens Practice E-Book

Contact Lens Practice E-Book

Nathan Efron

(2010)

Additional Information

Book Details

Abstract

Thoroughly revised and updated, this popular book provides a comprehensive yet easy to read guide to modern contact lens practice. Beautifully re-designed in a clean, contemporary layout, this second edition presents relevant and up-to-date information in a systematic manner, with a logical flow of subject matter from front to back.

This book wonderfully captures the ‘middle ground’ in the contact lens field … somewhere between a dense research-based tome and a basic fitting guide. As such, it is ideally suited for both students and general eye care practitioners who require a practical, accessible and uncluttered account of the contact lens field.

  • Outlines a rational clinical approach to modern contact lens fitting - practical advice for the clinic and the classroom 
  • Logical structure and systematic layout, with relevant chapters grouped into coherent sections for easy reference 
  • Up-to-date for accurate information 
  • Chapters are contextualised through cross-referencing - helping to reflect the relative importance of different topics 
  • Provides an 'historical time line' of contact lens development and explains the current global situation 
  • Explains how contact lenses are fabricated, designed, manufactured and measured 
  • Reviews the scientific principles that underpin the clinical application of contact lenses
  • New chapter on daily disposable contact lenses.
  • Contributing authors comprising optometrists, ophthalmologists, dispensing opticians, industry experts, researchers and clinicians – all of whom are true international leaders in their sub-specialty areas.
  • Many new line diagrams and clinical photographs to illustrate, inform and explain the concepts outlined in the text.
  • Special consideration is given to the most popular lens replacement systems – daily, two-weekly and monthly.
  • Extensive appendices to assist chair-side decision making in everyday practice.
  • Efron Grading Scales for Contact Lens Complications.
  • Evidence-based approach with numerous up-to-date references at the end of each chapter.

Table of Contents

Section Title Page Action Price
Front cover cover
Half title page i
Contact Lens Practice iii
Copyright page iv
Table of Contents v
Contributing authors ix
Preface to the Second Edition xi
Acknowledgements xiii
I Introduction 1
1 Historical perspective 3
Introduction 3
Early theories (1508–1887) 3
Glass scleral lenses (1888) 4
Plastic scleral lenses (1936) 5
Plastic corneal lenses (1948) 5
Silicone elastomer lenses (1965) 5
Soft lenses (1972) 6
Rigid gas-permeable lenses (1974) 6
Disposable lenses (1988) 6
Daily disposable lenses (1994) 7
Silicone hydrogel lenses (1998) 7
The future 7
References 8
2 The anterior eye 10
Introduction 10
The cornea 10
Corneal anatomy 10
Gross anatomy 10
Microscopic anatomy 10
Epithelium 10
Basal lamina and Bowman’s layer 11
Stroma 12
Descemet’s membrane 13
Endothelium 13
Corneal innervation 14
Source and distribution of corneal nerves 14
Functional considerations 14
Corneal metabolism 15
Source of oxygen and nutrients 15
Oxidative metabolism 15
Corneal transparency 16
Stromal organization 16
Hydration control 16
Response to oedema 17
Corneal epithelial wound healing 17
The ocular adnexa 17
Eyelids 17
Gross anatomy 17
Muscles of the eyelids 18
Orbicularis oculi 18
Levator palpebrae superioris 18
Superior and inferior tarsal muscles (of Müller) 19
Control of eyelid movements 19
Microscopic anatomy 19
Glands of the eyelids 20
Meibomian glands 20
Glands of Zeis and Moll 20
Blood and nerve supply 20
Nerves of the eyelids 20
Blood and lymphatic supply to the eyelids 20
The conjunctiva 20
Gross anatomy 20
Microscopic anatomy 21
Epithelium 21
Goblet and other secretory cells 22
Conjunctival stroma 22
Innervation and blood supply 22
Nerves 22
Blood vessels and lymphatics 23
Functional considerations 23
Lacrimal system 23
Lacrimal gland 23
Gross anatomy 23
Microscopic anatomy 23
Blood and nerve supply 24
Accessory lacrimal glands 24
Functional considerations 24
Lacrimal drainage system 24
The preocular tear film 25
Function and properties of the preocular tear film 25
Tear production 25
Sources and composition 26
Electrolytes 26
Proteins 26
Mucins 26
Lipids 27
Models of tear film structure 27
Conclusions 28
References 28
3 Visual optics 30
Introduction 30
The basic optics of the eye and ametropia 30
General optical characteristics 30
Model eyes and ametropia 30
Accommodation and the precision of ocular focus 31
Corneal topography 32
Pupil diameter and retinal blur circles 33
Effects of diffraction and aberration 34
Diffraction 34
Monochromatic aberrations 35
Chromatic aberration 37
Overall optical performance of the eye in white light 38
Ocular depth of focus 38
Correction of higher-order ocular aberration 39
Effectivity, spectacle magnification, accommodation and convergence effects with contact lens and spectacle corrections 40
Effectivity 41
Spectacle magnification 41
Accommodation demand 42
Convergence demand 43
Other optical effects 43
Fields of view and fixation 43
Apparent size of the eyes 44
Summary 44
References 44
4 Clinical instruments 47
Introduction 47
Observation of the eye 47
Burton lamp 47
Non-invasive examination of the tear film 47
Tear morphology 47
Tear break-up 47
Osmometry 48
Tear meniscus height 48
Slit-lamp biomicroscopy 49
Illumination system 50
The microscope 51
High-powered microscopy 51
Specular microscopy 51
Confocal microscopy 52
Tandem scanning confocal microscopy 52
Slit scanning confocal microscopy 52
Confocal microscopy through focusing 52
Rostock cornea module on HRT II 54
Measurement of corneal sensitivity 54
Contact aesthesiometry 54
Non-contact aesthesiometry 54
Assessment of corneal shape 55
Keratometry 55
Corneal topographic analysis 55
Reflective devices 56
Qualitative assessment 56
Quantitative assessment 56
Slit-scanning devices 57
Determination of corneal thickness 58
Pachymetry 58
Optical pachymetry 58
Ultrasonic pachymetry 59
Optical coherence tomography 59
Confocal microscopy 61
Orbscan 61
Conclusions 61
Acknowledgements 61
References 61
II Soft contact lenses 65
5 Soft lens materials 67
Introduction 67
Polymers 67
The structure of polymers 68
Polymerization 69
Chain polymerization 69
Initiation 69
Propagation 70
Termination 70
Properties of hydrogel materials 70
Optical transparency 70
Mechanical properties 70
Surface properties 72
Water content 73
Oxygen permeability 73
Fluid and ion permeability 74
Refractive index 74
Swell factor and dimensional stability 74
Hydrogel materials 75
Conventional hydrogel materials 75
Silicone hydrogel materials 77
Classification of soft lens materials 82
Conclusion 82
Acknowledgements 82
References 82
Appendix 5.1 Classification of soft lens materials 84
Food and Drug Administration (FDA) classification system 84
Association of Contact Lens Manufacturers (ACLM) classification system 84
BS EN ISO 18369-1: 2006 84
Example 85
6 Soft lens manufacture 86
Introduction 86
Methods of manufacture 86
Lathe cutting 86
Spin casting 88
Cast moulding 88
Reproducibility and quality of mass-produced lenses 90
Edge defects 90
Non-edge (body) defects 90
Conclusion 92
References 92
7 Soft lens optics 93
Introduction 93
On-eye power changes 93
Aberration 94
Conclusion 97
References 97
8 Soft lens measurement 100
Introduction 100
Back optic zone radius 100
Keratometry 100
Radiuscopy 101
Profile matching 101
The ‘sag’ method 101
Interferometry 102
Optical interferometry 102
Geometric interferometry 102
Overall diameter, optic zones, edge profile and surface quality 103
Back vertex power 104
Water content 105
Thickness 106
Surface wettability 107
Conclusion 107
References 108
9 Soft lens design and fitting 109
Introduction 109
Ocular measurement 109
Basic principles 109
Forces acting on a soft lens 109
Ideal soft lens fit 110
Soft lens design 110
Lens material and water content 110
Method of manufacture 111
Back optic zone radius 111
Total diameter 111
Back vertex power 111
Centre and edge thickness 111
Soft lens fitting options 112
Trial lens fitting 112
Initial lens selection 112
Soft lens insertion 112
Soft lens removal 113
Settling time 113
Lens fit characteristics 113
Optimum soft lens fit 113
Tight soft lens fit 114
Loose soft lens fit 114
Assessment of fit 114
Comfort 114
Centration 114
Movement 114
Tightness on push-up 115
Peripheral fit 115
Vision 116
Other methods of fit assessment 116
Soft lens fitting problems 116
Discomfort 116
Inappropriate diameter 116
Too large 116
Too small 117
Inappropriate fit 117
Too loose 117
Too tight 117
Poor vision 117
Variable vision 117
Conclusions 117
References 117
10 Soft toric lens design and fitting 119
Introduction 119
Criteria for use of soft toric lenses 119
Degree of astigmatism 119
Cylinder axis 119
Ocular dominance 119
Viability of other alternatives 119
Visual needs of the patient 119
Design of soft toric lenses 120
Surface optics 120
Stabilization techniques 120
Toroidal back surface 120
Prism ballast 120
Peri-ballast 120
Truncation 120
Dynamic stabilization 121
Principles of correction 122
Fitting 122
Back vertex power determination 122
Effect of lens rotation 122
Predicting lens rotation 122
Lid anatomy 122
Lens–eye relationship 122
Lens thickness profile 123
Allowing for lens rotation 123
Measurement of lens rotation 123
Determining lens misalignment 124
Planned replacement of soft toric lenses 125
Limitations of toric soft lenses 126
Low spherical components 126
Oblique cylinders 126
Large cylindrical components 126
Irregular astigmatism 126
Physiological considerations 126
Conclusions 126
References 126
11 Soft lens care systems 128
Introduction 128
A rationale for disinfecting contact lenses 128
A rationale for cleaning contact lenses 128
The evolution of soft lens care systems 129
Lens care systems 129
Physical methods 129
Chlorhexidine and thiomersal preserved systems 130
Chlorine 131
Hydrogen peroxide 131
Lens cleaning 133
Multipurpose solutions 134
Polyhexanide-based MPS 134
Polyquaternium-1-based MPS 134
Multipurpose solutions and silicone hydrogel lenses 135
Rewetting solutions 136
Saline solutions 137
Relative performance measures 137
The lens storage case 139
Conclusions 139
References 139
III Rigid contact lenses 143
12 Rigid lens materials 145
Introduction 145
Poly(methyl methacrylate) 145
The need for oxygen 145
The problem of hydrophobic surfaces 146
The search for better materials 146
Hybrid rigid gas-permeable materials 146
The Gaylord patents – harnessing silicon 147
Commercial rigid materials and their properties 149
Oxygen permeability 149
Mechanical properties 152
Flexure 152
Hardness 152
Surface properties 152
Refractive index 153
Conclusions 153
References 153
13 Rigid lens manufacture 154
Introduction 154
Rigid lens manufacture 154
Raw materials 154
Generating the lens back surface 155
Generating the lens front surface 155
Engraving, marking and fenestration 155
Edge polishing and final inspection 157
Specialty rigid lens manufacture 159
Toric rigid lens manufacture 159
Aspheric rigid lens manufacture 160
Reverse-geometry lens manufacture 160
Industry regulation 160
Conclusions 160
Acknowledgements 160
References 161
14 Rigid lens optics 162
Introduction 162
Basic tear lens properties 162
The tear lens during trial lens fits 162
Required BVP when the lens to be ordered has a different BOZR from the trial lens used 163
Calculation of required surface radii from a trial lens fit 164
Neutralization of corneal astigmatism by a rigid lens of spherical power 164
Aberrations of rigid contact lenses 165
Other rigid lens effects 166
Prismatic effects due to decentred or tilted lenses 166
Flexure effects with rigid corneal lenses 166
Visually disturbing effects with rigid lenses 166
Conclusion 167
References 167
15 Rigid lens measurement 168
Introduction 168
Surface radius 168
Radiuscope 168
Keratometer 169
Diameter 170
Back vertex power 170
Thickness 171
Lens edge 172
Profile 172
Edge lift 172
Lens surface 173
Surface quality 173
Surface wetting 173
Flexibility 173
Material 174
Refractive index 174
Specific gravity 174
Tint 174
Conclusion 174
References 175
16 Rigid lens design and fitting 176
Introduction 176
Ocular topography 176
Cornea 176
Lids 177
Ethnic variations in ocular dimensions 177
Forces acting on the rigid lens 177
Rigid lens design 177
Back optic zone diameter 177
Front optic zone diameter 178
Centre thickness 178
Edge lift and edge clearance 178
Edge form 179
Spherical versus aspheric designs 179
Spherical designs 179
Aspheric designs 180
PMMA versus RGP lens design 180
Trial fitting options 180
Trial fitting set 180
Empirical fitting 180
Videokeratoscopic fitting 181
Selection of initial lenses 181
Trial fitting set 181
Empirical fitting 181
Lens insertion, removal and settling 182
Lens insertion 182
Lens removal 182
Settling time 183
Lens fit characteristics 183
Optimum lens fit 183
Satisfactory lens fit 183
Assessment of lens fit 184
White light assessment of fit 184
Diameter 184
Centration 184
Movement 184
Peripheral fit 185
Fluorescein assessment of fit 185
Interpretation of fluorescence 185
Fluorescein instillation 185
Central fit 185
Mid peripheral fit 186
Edge fit 186
Overrefraction 186
Rigid lens fitting problems 186
Decentration 186
Peripheral corneal desiccation 187
Peripheral corneal mechanical trauma 187
Discomfort 188
Poor or unstable vision 188
Lens loss 188
Conclusion 188
References 188
17 Rigid toric lens design and fitting 190
Introduction 190
Forms of toric lens 190
Criteria for use 190
Design considerations 191
Optical considerations 192
Refraction 192
Residual astigmatism 193
Induced astigmatism 193
Spherical power equivalent (‘compensated’) bitoric lenses 194
Cylindrical power equivalent toric lenses 194
Alignment bitoric lenses 194
Back surface toric lenses 194
Front surface toric lenses 195
Oblique bitoric lenses 195
Effect of lens rotation 195
Conclusions 196
References 196
18 Rigid lens care systems 197
Introduction 197
Disinfection and wetting solutions 197
Cleaning solutions 197
Protein removal solutions 197
Disinfection of trial lens sets 198
Conclusions 199
References 199
IV Lens replacement modalities 201
19 Unplanned lens replacement 203
Introduction 203
Long-term changes in lenses that are not replaced on a planned basis 203
Lens deposits 203
Irreversible water loss 205
Surface damage and crazing 206
Storage contamination 206
Ocular ramifications of non-planned lens replacement 207
Discomfort 207
Reduced vision 207
Ocular surface pathology 207
Conclusions 208
References 208
20 Daily soft lens replacement 209
Introduction 209
Patterns of wear 209
Clinical benefits 210
Advantages from the perspective of practitioners 211
Advantages from the perspective of lens wearers 212
Disadvantages 212
Comfort enhancement strategies 212
Manufacturing reliability 213
Environmental impact 214
Limitations to more general acceptance 214
Corneal infiltrative events and keratitis 214
Conclusions 215
Acknowledgements 215
References 215
21 Planned soft lens replacement 217
Introduction 217
Advantages of planned replacement 217
Use of higher-water-content hydrogel materials 218
Use of silicone hydrogel materials 218
Simple lens care regimes 218
Ready availability of replacement lenses 219
Enhanced compliance with aftercare schedules 219
Single-use trial lenses 219
Trial lens fitting with accurate prescription 220
Lens parameters easy to change 220
Potential disadvantages of planned replacement 220
Patient non-compliance 220
Quality and reproducibility issues 220
Determining the appropriate lens replacement frequency 221
Practice management issues relating to planned soft lens replacement 221
Lens delivery systems 221
Manufacturer-driven systems 221
Practice-driven systems 221
Lenses available for planned replacement 222
Practice logistics 222
Cost to the patient 223
Financial management 223
Alternative supply routes 223
Conclusions 224
Acknowledgements 224
References 224
22 Planned rigid lens replacement 225
Introduction 225
Life expectancy of rigid contact lenses 225
Regular replacement of rigid lenses 226
Advantages of regular replacement of rigid lenses 226
Daily wear 226
Extended wear 227
Lens binding 228
Optimum replacement schedule 228
Clinical data 228
Theoretical model 228
Planned replacement schemes available 228
Conclusions 229
References 229
V Special lenses and fitting considerations 231
23 Scleral lenses 233
Introduction 233
Advantages and disadvantages of scleral lenses 233
Indications for scleral lenses 233
Fitting principles 234
Non-ventilated preformed scleral lenses 234
The scleral zone 235
Optic zone sagittal depth and optic zone projection 235
Non-coaxial scleral lenses 238
Toroidal lenses 238
Impression moulding 238
Fenestrated lenses 238
Modification 238
Ordering scleral lenses 238
Lens hygiene and maintenance 239
Storage 239
Cleaning and conditioning 239
Saline for filling non-ventilated RGP scleral lenses 239
Rewetting 239
Problems and complications with scleral lens wear 239
Discomfort 239
Bubbles 239
Accumulation of mucus 240
Conjunctival blanching and hyperaemia 240
Conjunctival displacement over the limbus 240
Degradation of the surface 240
Infection 240
Giant papillary conjunctivitis 240
Hypoxia 240
Neovascularization 240
Neovascularization in keratoconus 241
Conclusion 241
Acknowledgement 241
References 241
24 Tinted lenses 243
Introduction 243
Basic options 243
Tinted lens designs and applications 243
Handling tints 243
Cosmetic tinted lenses 244
Prosthetic tinted lenses 244
Therapeutic tinted lenses 244
Performance-enhancing tinted lenses 245
Colour vision 245
Dyslexia 245
Sport 245
Prophylactic tints 246
Theatric tinted lenses 246
Identification tints 247
Manufacture 247
Translucent tints 247
Dye dispersion tinting 247
Vat dye tinting 247
Chemical bond tinting 248
Printing 248
Opaque tints 248
Dot matrix printing 248
Laminate constructions 248
Opaque backing 249
Clinical considerations 249
Tint distribution 249
Lens fitting 250
Lens maintenance 250
Oxygen transmissibility 250
Visual effects 250
Replacement frequency 250
Care of multiple pairs 250
Lens deposits 250
Discomfort and dryness 250
Conclusions 250
References 250
25 Presbyopia 252
Introduction 252
Patient selection 252
Patient expectations 253
Initial measurements 254
Monovision 254
General principles of monovision fitting 255
Partial monovision 255
Enhanced monovision 255
Modified monovision 255
Bifocal and multifocal contact lenses 255
Simultaneous-vision designs 256
Biconcentric designs 257
Multizone concentric designs 257
Modified monovision multizone concentric designs 258
Diffractive designs 258
Aspheric designs 259
Back surface aspheric designs 259
Front surface aspheric designs 259
Zonal aspheric design 259
Lens fitting 259
Lens adjustments 260
Alternating (translating)-vision designs 261
General principles of lens designs 261
Solid design 261
Fused design 262
Lens fitting 262
Conclusions 263
Acknowledgements 265
References 265
26 Continuous wear 266
Introduction 266
Experiences with extended wear 266
Conventional soft extended wear 266
Non-hydrophilic materials 267
Disposable soft lenses 267
Silicone-containing hydrogel contact lenses 268
Mechanisms of adverse effects in extended wear 268
Acute physiological effects 268
The role of hypoxia 270
Chronic physiological changes 272
Mechanical effects 274
Non-infectious inflammatory events 275
Infectious corneal ulceration 276
Clinical extended-wear practice 276
Is extended wear safe? 276
Application of continuous wear in practice 277
Managing extended-wear complications 277
Acute responses 278
Chronic physiological stress 278
Microbial keratitis 278
Papillary conjunctivitis 279
Superior epithelial arcuate lesions 279
Conclusions 279
References 279
27 Sport 281
Introduction 281
Deciding on the best form of correction 281
Refractive surgery 281
Do contact lenses enhance sporting performance? 281
Environmental and physical constraints 282
Environmental conditions 282
Cold 282
Altitude 282
Dirt and dust 283
Aquatic environments 283
Subaquatic environments 284
Ultraviolet light 284
Physical conditions 284
Extreme body movements 284
Body contact 284
Airflow 284
Gravitational forces 285
General considerations 285
Conclusions 285
References 286
28 Keratoconus 287
Introduction 287
Demographics of keratoconus 287
Management options 287
Spectacle correction 287
Soft lenses 288
Hybrid lenses 289
Rigid contact lens correction 289
Scleral lenses 289
Surgical management 289
Most suitable rigid lens types 290
Fitting philosophies and fluorescein patterns 291
Apical touch versus apical clearance 291
Lens fitting protocols 292
Rigid lens fitting procedure 293
Keratometry 293
Refraction 293
Trial lens fitting 293
Fluorescein pattern analysis 293
CLEK study fitting protocol 294
Criteria for referral for evaluation for keratoplasty 294
Conclusion 296
Reference 296
29 High ametropia 298
Introduction 298
Lens materials for high ametropia 298
Silicone elastomer 298
Silicone hydrogel 298
Principles of high-power lens design 299
High-plus 299
Aphakia 299
High-minus 300
High astigmatism 300
Fitting challenges 301
Low vision 301
Conclusions 301
References 302
30 Paediatric fitting 303
Introduction 303
Indications 303
Aphakia 303
Pseudophakia 303
Myopia 304
Ocular motility disorders 305
Irregular astigmatism 305
Tinted and prosthetic lenses 305
Therapeutic lenses 305
Ocular response to lens wear 305
Examination techniques 305
Anterior-segment examination 305
Keratometry 306
Refraction 306
Biometry 306
Lens selection 306
Hydrogel lenses 306
Silicone hydrogel lenses 306
Silicone rubber lenses 307
Rigid lenses 307
Handling of lenses 307
Common aftercare problems 307
Acknowledgement 308
References 308
31 Therapeutic applications 310
Introduction 310
Indications 310
Unusual or distorted corneal shape 310
Relief of pain 310
Recurrent erosion syndrome 310
Corneal dystrophies involving the epithelium 310
Filamentary keratitis 311
Corneal degenerations involving the epithelium 311
Chemical injuries 311
Cicatricial conjunctivitis 312
Tear deficiency 312
Protection from lids and environment 312
Maintenance of a precorneal tear reservoir 313
Following trauma or surgery 313
Following spontaneous perforation 313
Lens types 313
Soft hydrogel and silicone hydrogel lenses 313
Rigid lenses 314
Scleral lenses 314
Concurrent medication 315
Drug delivery 315
Complications 315
Conclusions 316
References 316
32 Post-refractive surgery 317
Introduction 317
Types of refractive surgery 317
Contact lens fitting following radial keratotomy 317
Corneal topography 317
Rigid lenses 317
Soft lenses 318
Contact lens fitting following photorefractive procedures 318
Tissue ablation and corneal topography 319
Rigid lens designs 319
Reverse-geometry rigid lens designs 320
Soft lenses 320
Comparative performance of rigid versus soft lenses 321
Decentred ablations 321
Conclusions 321
References 321
33 Post-keratoplasty 322
Introduction 322
Indications 322
Types of corneal graft 322
Corneal topography following PKP 324
Suture techniques for PKP 324
Indications and contraindications for contact lens wear post corneal grafts 325
General concerns 326
Lens fitting techniques 326
Continuing care and complications 327
Graft rejection and failure 328
Epithelial rejection 328
Stromal rejection 328
Endothelial rejection 328
Graft failure 328
Other management issues 328
Contact lens results 329
Conclusions 329
Acknowledgement 329
References 329
34 Orthokeratology 332
Introduction 332
Outcomes of earlier techniques 332
Independent studies 332
Modern orthokeratology 333
Reverse-geometry lenses 333
Indications and contraindications 333
Outcomes of accelerated orthokeratology 334
Efficacy 334
Regression 335
Safety 335
How orthokeratology works 336
Determinants of success 336
Correction of hyperopia 337
Control of myopia progression in children 337
Correlations 337
Conclusions 337
Is orthokeratology effective in modifying refractive errors? 337
Is orthokeratology safe? 337
Is orthokeratology clinically efficacious? 337
Acknowledgement 338
References 338
35 Diabetes 339
Introduction 339
The anterior eye 339
Orbit 339
Eyelids 339
Tear film 339
Conjunctiva 339
Iris 339
Pupil 340
Cornea 340
Epithelium 340
Corneal nerves 340
Endothelium 341
Corneal hydration control 341
Microbial keratitis 341
Panretinal photocoagulation 341
Ocular response to contact lenses 341
Special considerations 342
Prescribing contact lenses 342
Compliance 342
Contact lens wear in patients with other systemic disease 342
Corneal scarring or thinning 342
Keratoconjunctivitis sicca 342
Handling problems 342
Ocular side-effects of therapy 343
Conclusion 343
References 343
VI Patient examination and management 345
36 History taking 347
Introduction 347
Indications and contraindications for contact lens wear 347
Anatomical 347
Ocular health 347
General health 348
Allergies 348
Chronic infection 348
Metabolic disorders 348
Pregnancy 348
Systemic medication 348
Psychological factors including motivation 348
Lifestyle/occupational issues 349
Financial considerations 349
The case history 349
Non-lens wearers 349
Previous lens wearer 350
Patient education, risk/benefit analysis and informed consent 350
Record keeping 350
Conclusions 351
References 351
37 Preliminary examination 352
Introduction 352
Measurement of vision 352
Retinoscopy and subjective refraction 352
Anatomical measurements 352
Keratometry 353
Corneal topography 353
Slit-lamp biomicroscopy 354
Diffuse wide beam 355
Direct focal illumination 355
Parallelepiped 356
Optic section 356
Oblique illumination 356
Specular reflection 356
Indirect illumination 357
Sclerotic scatter 357
Retroillumination 358
Fluorescein staining 358
Tear film evaluation 358
Ophthalmoscopy 359
Binocular vision assessment 359
Supplementary tests 359
Corneal sensitivity 359
Visual fields 359
Tonometry 359
Stereopsis 359
Colour vision testing 359
Conclusions 359
References 360
38 Patient education 361
Introduction 361
Objectives 361
Timing 361
Creating the optimum teaching environment 361
The teaching area 361
Accoutrements 362
Patient instruction 362
Hand grooming and hygiene 362
Lid manipulation 362
Lens inspection 362
Lens application 363
Tips on comfort and lens recentring 364
Lens removal 365
The blink technique 365
The two-handed technique 365
Suction holders 366
Care products 366
Cosmetics 366
Wearing schedules 366
Soft lenses 367
Rigid lenses 367
Recognizing an emergency 367
Patient discharge 367
Informed consent 367
Conclusion 368
References 368
39 Aftercare 369
Introduction 369
Recommended visit schedules 369
Preparing for the aftercare visit 370
Aftercare procedures while lenses are worn 370
History taking 370
Visual acuity 371
Overrefraction 371
Overkeratometry 371
External examination 371
Slit-lamp biomicroscopy 371
Lens surface assessment 371
Lens fitting characteristics 373
Lens–eye interactions 373
Aftercare procedures following lens removal 374
Uncorrected vision 374
Refraction 374
Keratometry and corneal topography 374
Oblate shape 375
Inferior steepening 375
Impression arcs 375
Posterior corneal elevation 376
Slit-lamp biomicroscopy 377
Lens inspection and verification 377
Additional procedures 377
Pachymetry 378
Corneal endothelial analysis 378
Other tests as required 378
Discussion with patient 378
Grading scales 378
Grading scale design 378
Image size 379
How to grade 379
How to record grading 379
Interpretation of grading 379
Determinants of grading performance 379
General approaches to solving problems 380
Eye redness 381
Characterizing eye redness 381
Strategies for diagnosing and solving eye redness 381
Discomfort 382
Characterizing symptoms of discomfort 382
Strategies for solving symptoms relating to discomfort 383
Poor vision 384
Characterizing symptoms of poor vision 384
Strategies for solving symptoms relating to poor vision 385
Conclusions 386
References 386
40 Complications 388
Introduction 388
Eyelids 388
Blinking 388
Ptosis 389
Meibomian gland dysfunction 389
Eyelash disorders 390
Tear film 391
Dry eye 391
Mucin balls 392
Conjunctiva 393
Conjunctival staining 394
Conjunctival redness 394
Papillary conjunctivitis 395
Limbus 396
Limbal redness 396
Vascularized limbal keratitis 397
Superior limbic keratoconjunctivitis 398
Corneal epithelium 399
Epithelial staining 399
Microcysts 400
Vacuoles 401
Wrinkling 401
Corneal stroma 403
Oedema 403
Thinning 404
Deep stromal opacities 404
Neovascularization 406
Keratitis 407
Warpage 408
Corneal endothelium 409
Bedewing 409
Blebs 410
Polymegethism 411
Conclusions 412
References 412
41 Digital imaging 416
Introduction 416
Previous imaging methods 416
Principles of digital imaging 416
Benefits of digital imaging for contact lens practice 417
Examples of digital imaging in contact lens practice 418
Limbal neovascularization 418
Rigid lens fitting 418
Refractive surgery on disposable contact lens wearer 418
Illumination methods for slit-lamp digital imaging 418
Commercial digital imaging systems 419
‘Build-your-own’ digital imaging system 419
Video slit-lamp imaging system 421
Digital video camera and beam splitter 421
Computer and video digitizer 422
Software for still images 422
Recording digital movies 422
File back-up 422
Printer 423
Digital still camera slit-lamp imaging system 423
Fundus camera 423
OCT anterior segment 423
Other instruments 423
Image editing 425
Conclusion 425
References 425
42 Compliance 427
Introduction 427
Consequences of non-compliance 427
Extent and pattern of non-compliance 427
Duration of the prescription 427
Erroneous contact lens procedures 427
Compliance with the incorrect prescription 428
Compliance with the correct prescription 428
Investigation of strategies for compliance enhancement 428
Improving initial patient education 429
Periodic self-review 429
Reducing cost 429
Predicting non-compliance 430
A compliance enhancement model 430
The clinic and practitioner 430
The patient 430
The advice 431
The contact lens industry 431
Conclusion 431
References 431
43 Practice management 433
Introduction 433
Practice location and accommodation 433
Layout 434
Reception area and front desk 434
Waiting area 434
Consulting room 434
Spectacle dispensary 434
Contact lens dispensary 434
Personnel at the practice 434
Recruitment and selection 434
Contract of employment 435
Discipline and dismissal 435
Training staff 435
Products and services provided 436
Pricing – fees and charges 436
Speciality–commodity continuum 436
Professional model 437
Promotional issues 437
Internal 437
External 437
Processes 437
Managing patients 438
Contracts, service agreements and informed consent 438
Patient scheduling 438
Patient education 438
Records on patient web pages 439
Managing contact lens products 439
Managing money 439
Lens ordering 439
Professional regulation 439
Conclusions 441
References 441
Appendices 443
Appendix A Contact lens design and specifications 444
Appendix B Contact lens tolerances 445
Appendix C Vertex distance correction 446
Appendix D Corneal curvature – corneal power conversion 448
Appendix E Extended keratometer range conversion 450
Appendix F Soft lens average thickness 452
Appendix G Soft lens oxygen performance 453
Appendix H Constant edge clearance rigid lens designs 455
Appendix I Soft toric lens misalignment demonstrator 456
Appendix J Dry-eye questionnaire 457
Appendix K Efron grading scales for contact lens complications 459
Index 463