Week 1.10 Cycloplegic Refraction Flashcards
When would you use cyclo
When px cannot relax accomodation sufficiently for the absolute refractive error to be measured
- latent hyperopia - can cause eye strain, headaches
- pseudomyopia - emmetrope who accommodates so too much plus power
- unstable ret reflex
- when high hyperopia or anisometropia suspected
- amblyopia investigation
What age is cyclo most used on
4-11 year old
What are some signs that indicate the need for cyclo
- sphere found on ret sig higher than sphere on subjective
- variable ret reflex or fixation
- poor VA
- strabismus
- FH of strab, hyperopia, anisometropia, amblyopia
- abnormal AoA for age of px
- double vision
- headache following near work
- blue after intense bear work
Advantages of cyclo refraction
- keeps accomodation response at one level
- more reliable ret
- No fluctuation
- makes latent hyperopia manifest - can find total refractive error
- dilates the pupils makes fundus exam easier
Disadvantages of cyclo
- Photophobia
- Confusing ret reflex due to aberrations
- Need to consider modification of refractive findings to make them compatible with normal accommodation
- Effect on near vision for the rest of day - school work
- Adverse reactions
- Discomfort - loss of trust in optom
What type of drug are all cyclos
Antimuscarinic
Relaxes ciliary muscle and prevents activation of receptor by acetylcholine
Cycloplegic drugs available?
Cyclopentolate hydrochloride
Tropicamide
Atropine - level 2
Homatropine hydropbromide - level 2
Cyclopentolate hydrochloride
0.5% and 1.0% conc
PH will sting ~5
Onset time: One drop 1% (or 2 drops of 0.5% separated by 5 mins)
Max cycloplegia in 30-40 minutes
Max mydriasis occurs earlier 15-20 mins
What’s the recovery time for 0.5% cyclo and 1% cyclo
0.5% - 4-12hrs ——> mydriasis 24hrs
1.0% - 16-24hrs ——> mydriasis 48hrs
Dark irides and cyclo
Drug binds to melanin
Onset time & mydriasis may be increased
Depth of cyclo may be reduced
Melanin acts as slow release ‘reservoir’ for the drug therefore increasing duration of effect
Cyclopentolate side effects
Ocular: stinging, blurred vision, photophobia, conj redness/ oedema, raised IOP
Systemic: drowsiness, restlessness, hallucinations, dry mouth, tachycardia, skin flushing, urinary sxs
Tropicamide as a cylco
- weak cycloplegic
- useful in young adults when deep cyclo not required and rapid recovery necessary
- 2 drops of 1% solution, separates by 5 minutes, gives useful cycloplegia
- max cyclo 20-30 mins after instillation
- duration 2-6hrs
Atropine sulphate
Less commonly used for cycloplegic refraction
Observe in:
- orthoptics clinics
- myopia control
Useful in treating amblyopia - parents give drops to child’s good eye forcing child to use their other eye
What is the onset and duration of atropine
1 drop (1%) twice per day 1-3 days before refraction
Onset: 36hrs
Duration: 7hrs
Homatropine
POM
1%
Max cyclo: 30-60 minutes
Duration 1-2 days
Can be used in tx of ant uveitis
What are alternatives to cycloplegia
- binocular refraction useful to relax out latent hyperopia in older children
- mohindra technique: ret at 0.5m WD in a very dark room
Child fixates retinoscope light during procedure - should not stimulate accomodation: resting tonic position
Subtract +1.25DS from the lenses giving neutral reflexes. - represents difference between 2D WD and the -0.75D allowance for tonic accomodation
