Lecture 22 - Myopia and its management

Question 1

What are the four classifications of myopia?

Answer 1

• Pre-myopia- combination of risk factors and pattern of eye growth indicate high risk of myopia onset
• Secondary myopia-arising from a single specified cause which is not a recognised risk factor for myopia e.g. drugs, corneal disease
• Axial myopia- arising from excessive axial elongation
• Refractive myopia- arising from a cornea and/or lens which is too powerful

Question 2

Quantitative classifications of myopia

Answer 2

• Low myopia (SER≤-0.50D)
• High myopia (SER≤-6.00D)

Question 3

Myopic growth: Axial myopia

Answer 3

• Primarily occurs due to excessive axial elongation
• Axial length is measured from the anterior cornea to the anterior retina
• Measuring axial length is the gold standard method of monitoring myopia progression

Question 4

Measuring axial length:

Answer 4

• It is measured using A-scan ultrasonography
• Non-invasive, quick and simple to measure
• 5 readings are taken from each eye and the average used

Question 5

SER Vs AL?
( Spherical equivalent refraction vs Axial length)

Answer 5

• AL measurement with IOL master 95% CI: +0.06mm
• A significant change in an individual px is therefore 0. 12mm or over
0.1mm AL change = 0.25D change in SER2
Rule of thumb only

• Using rule of thumb, IOL master can detect 95% Cl: to $0.15D (‡0.0
• This means it detects a change equivalent to 0.30D between 2 indiv measures

AL is a more sensitive measure than SER

Question 6

Surrogate measures of axial length:

Answer 6

• i.e calculating axial length from cyclo SER and K readings
• Useful as a predictor and establishing initial risk (variability 3%)
• For comparison, biometers have variability of 0.25% or less (12x less variable)
• Not appropriate to use in myopia management as this degree of variability means treatment effects will not be detected

Question 7

Theories of refractive development

Answer 7

Emmetropization
• Passive emmetropization (proportional enlargement of the eye )
• Active emmetropization (axial elongation involving visual feedback)

Question 8

Passive emmetropisation:

Answer 8

• Optical components compensate for each other to produce an emmetropic eye

Question 9

Active emmetropisation;

Answer 9

Eye growth is locally controlled: Influenced by the visual environment
• Eyes must grow towards an emmetropic state (axial elongation)
• A negative feedback system may drive this process
- We are born hyperopic at birth (+2.00DS), suggests that hyperopic defocus may drive ocular growth in active emmetropisation

Question 10

Other changes within myopic eye:

Answer 10

Anterior chamber depth (ACD)
• deepens due to eye growth and lens thinning
• Small contribution to axial elongation

Crystalline lens
• Lens becomes thinner

Vitreous chamber depth (VCD)
• Deepens due to eye growth
• Contributes most significantly to axial elongation in myopia

• Other structures affected by stretching: Sclera, choroid and retina

Question 11

Expected axial length increase values for myopes: Axial length growth curves

Answer 11

• Useful in:
Assessing risk of myopia onset
Assessing risk of myopia progression

• Two growth curves which relate to axial length data in children of largely European ethnicities:
1. Generation R
2 Northern Ireland Childhood Errors of Refraction (NICER) study

Question 12

Im emmetropia;

Answer 12

• AL increases up until 14 years of age. This is largely due to deepening of the VCD
• Lens thickness decreases with age= reduction in power
• Corneal power decreases during infancy but does not change significantly after 4 years of age

Question 13

In myopia:

Answer 13

• Myopia occurs due to excessive axial elongation
• ACD and LT do not significantly contribute to axial elongation
• VCD contributes most significantly to axial elongation
• Other structures such as the sclera, choroid and retina are also affected by excessive elongation
• Axial elongation occurs, on average, until late teenage years

Question 14

Myopic growth theory: Hyperopic blur and myopia:

Answer 14

1. Prolate shaped eye
2. Image shell from SV correction
   Both create peripheral hyperopic defocus

Question 15

Myopic growth theory: Other theories

Answer 15

Biochemical theories:
• Sclera: Decreased collagen synthesis and increased collagen degradation»
Decreased strength and tissue loss
• RPE: Increased permeability, secretion of growth factors
• Choroid: Thinning» decreased barrier to growth, secretion of growth factor

Question 16

Change in prevalence of myopia in UK

Answer 16

• 1960s: 10% of children (10-16yrs) were myopic
• 2006-2008: 23% of children (12-13yrs) were myopic
• The prevalence of myopia has doubled over the past 5 decades

Question 17

Pathologies associated with myopia:

Answer 17

• Greater risk of:
- Primary Open Angle Glaucoma
- Cataract
- Myopic maculopathy
- Retinal detachment

• Leading to….
- Increased number of adults with visual impairment
- Increased strain on NHS eye care services

Question 18

Risk factors from history and symptoms

Answer 18

Modifiable
• Behavioural
- <2hrs/day outdoors
- <30cm working distance
- Breaks>30mins
- Hobbies

Non-modifiable
• Genetics
- At least one parent with myopia
- Amount of parental myopia
• Ethnicity

Question 19

Ways of evaluating risk:

Answer 19

1. Predicting myopia onset and progression (PreMO)
2. Brien Holden myopia calculator
3. Myopia clinic at GCU:
   - H+S
   - Current/previous Rx
   - Current/previous axial length

Question 20

Greater time spent outdoors associated with near work:

Answer 20

• Less peripheral
• retinal
• hyperopic
• defocus
(Decreased near work)

Question 21

Myopia management: three categories

Answer 21

• Optical: Spectacles and contact lenses
• Pharmacological: Eye drops (not available in UK)
• Behavioural: Time outdoors, near work habits

Question 22

Myopia management: Delaying onset

Answer 22

• Can we prevent onset?
- Unlikely
• Can we delay onset to a later age?
- Possibly.
- Shorter period of time for myopia to progress and smaller amount of myopia by adulthood

Question 23

How can we delay myopia onset: Behavioural

Answer 23

• Identify children most at risk of becoming myopic and provide behavioural advice:
• At least one parent with myopia
• Spending <2hrs/day outdoors
• Reading at a close WD (<30cm) for prolonged time (>30mins)

Question 24

How can we delay myopia onset: Cyclo SER

Answer 24

Identify children most at risk of becoming myopic
Using cycloplegic SER ‘cut off’ values

Aged 6 years= SER<+ 0.75D
Aged 7-8 years= SER<+0.50D
Aged 9-10 years= SER <+0.25D

Question 25

Can we stop, reverse or slow down progression of myopia:

Answer 25

• Can we stop progression? For most children, no
• Can we reverse myopia? No
• Can we slow down progression? Yes
Slowing down the rate of progression decreases the amount of myopia reached by adulthood

Question 26

What risk factors can be identified from H+S

Answer 26

• Parental myopia: 1 or 2 myopic parents, high myopia
• Ethnicity: East asian
• Gender: Female
• Age: <10 years
• Age of onset: < 7 years
• Refraction: High myopia (more than -6.00DS)
• Time outdoors: Not significant
• Near work: Inconsistent evidence

Question 27

Myopia management options:

Answer 27

• Distance under-correction
- Not effective, some studies report greater myopic progression with this method
- Some studies report no change, some report a slowing of progression
- No strong evidence to support this as a treatment option

• Bifocal and multifocal spectacles
Reduces accommodative lag=reduces hyperopic defocus
No clinically significant reduction in progression

Question 28

Note on licensing options treating myopia

Answer 28

• The ONLY licensed myopia management option is MiSight contact lens in children aged 8-12 years
• Reflection: Would you be happy to offer other options knowing they aren’t licensed and why/why not?

Question 29

What is atropine?

Answer 29

• Anti-muscarinic
• Inhibits activation of acetylcholine in parasympathetic nervous system

Question 30

Atropine eye drops: Ocular side effects

Answer 30

• Rebound
• Pupil dilation
• Photophobia
• Reduced accommodation
• Blurred near vision

Question 31

Atropine eye drops: systemic side effects

Answer 31

• Dry mouth
• Flushing
• Tachycardia
• Palpitations
• Arrhythmias
• Urinary urgency, retention and constipation
• Reduced bronchial secretions

Question 32

Atropine mechanism: Biochemical response

Answer 32

1. Promotes choroidal thickening in LIM in chicks
2. Thickening of scleral fibrous layer (chicks)
3. May module expression of growth factors/dopamine

Question 33

Low dose atropine for myopia progression
LAMP studies (Hong Kong)

Answer 33

• Randomized, placebo-controlled, double-masked trial.
• Phase 1: Atropine: 0.05%, 0.025%, and 0.01% and placebo
• Phase 2: Treatment continued for 1 more year, Placebo group started with 0.05% atropine
• Phase 3: Effect of atropine, ‘washout’/rebound

Question 34

Low dose atropine for myopia progression
LAMP studies (Hong Kong)
Phase 1 results

Answer 34

• 0.05%: AL: 0.20mm
• 0.025%: AL: 0.29mm
• 0.01%: AL: 0.36mm
• Placebo: AL: 0.41mm

> Accommodation and pupil size changes: dose dependent
Near vision and distance vision not significantly affected
No difference in vision related quality of life

Question 35

The Western Australian atropine for the Treatment of Myopia (WE-ATOM) trial:

Answer 35

• 0.01%: SER -0.64D, AL 0.34mm
• Placebo: SER -0.78D, AL 0.38mm
(Not statistically significant)

Need to consider:
• Placebo group: (1 year older and started wearing spx when older)
• 22 withdrawals (10 atropine, 12 placebo) had significant progression
• Those who remained on trial had minimal progression (placebo and atropine)

Question 36

College Optometrists advice:

Answer 36

• You must obtain explicit consent
• “Axial length monitoring is the preferred method to assess stabilisation or progression of myopia’, especially in orthokeratology. “
• “If this is not available, you should undertake cycloplegic autorefraction and keratometry to provide an estimate of axial length”

Question 37

Warning from calculating axial length from cyclo SER and K readings…

Answer 37

• Useful as a predictor and establishing initial risk (variability 3%)
• For comparison, biometers have variability of 0.25% or less (12x less variable)
• Not appropriate to use in myopia management as this degree of variability means treatment effects will not be detected

Question 38

Strengths of mean efficacy method:

Answer 38

AL growth after treatment Vs AL growth before treatment is calculated

Strengths
• Robust estimation of treatment success
• Meets College’s guidelines of measuring treatment success using AL
• not too conservative or liberal

Limitations
• Need to measure AL, which many optoms currently do not have access to
• Majority of research on treatment effectiveness is in East Asian children
• Patient characteristics (age, SER) should be similar to clinical data