OPTOM 345B Flashcards
Cornea Structure
Fat-Water-Fat
Forms that drugs exist in
Non-ionised, Fat and water soluble, Water insoluble and ionised, and fat insoluble
How do drugs enter through the cornea
Fat soluble form penetrates epithelium, penetrates stroma in ionised form, fatsoluble form goes through endothelium and then re-equilibriates as both forms. Then ionised form diffuses through AH to the tissues
When to use cycloplegics
Strabismic px, High plus, accommodative esotropia, Low AoA, Impaired BV and children under 3
What to check for before cycloplegia
Px sensitivity to drugs, general health and family hx of glaucoma.
Also do full refraction before cycloplega
Why check glaucoma history with cycloplegics
Cycloplegics are mydriatics so should check if anterior chamber angle is open or not
How to cycloplegics work
Competitive antagonists of PSNS so it blocks mach in ciliary body and sphincter pupillae smooth muscle
What are the main muscarinic receptor types in human ciliary muscles
Mostly M3 and M2
Name all the cycloplegic drugs
Cyclopentolate + Tropicamide + Atropine sulphate + Hyoscine + Homatropine
Cyclopentolate
Fast onset in minutes w 24H recovery for cycloplegia. Mydriatic effect last up to several days
1% on children and 0.5% if over 16
What affects onset and recovery rates for cyclopentolate
Iris pigment density
What works better with darker irises
Combination of 1% cyclopentolate and tropicamide
Toxic reactions to cyclopentolate
Stings but reduced w anaesthetic. Lacrimaution and mucous discharge seen. Toxic reactions depend on dose and CNS side effects
Early signs of toxicity is ataxia, incoherent speech and drowsiness
Tropicamide
Onset within minutes with cyclo recovery in 3H and mydriasis recovery in 6-8H.
No adverse reactions
When to use tropicamide
Children over 12 years of age
Atropine sulphate
Use 3 days prior in infants. Recovery ( 2 weeks ) for cyclo and mydriasis.
When else to use atropine sulphate
Adult has anterior chamber inflammation, amblyopia and for myopia control
Hyoscine
Potent and long lasting cycloplegia w similar side effects to atropine.
Derived from Belladonna or Jimsonweed
What is Hyoscine also used for
Motion sickness, prevents posterior synechiae in inflammatory disease.
But produces retrograde amnesia
Homatropine
10% potency of atropine. It is less of a cycloplegic than cyclopentolate but has prolonged mydriatic effect
Has toxic reactions like atropine
What is Homatropine also used for
Inflammatory disease to prevent posterior synechiae and relieve painful spasms of ciliary muscle
Precautions with cycloplegics
Use minimum dose and occlude the punch. Caution with blonde chilren and prepare for ADRs. Dont use if past allergies and use in cool room temperatures.
Cycloplegic refraction procedure
Measure AoA 20-30 mins post drug check drug effect. Observe reflex with ret and use distance fixation with tropicamide.
Can use autorefraction with cycloplegia. Pupil size is not an indication of level of cycloplegia
Refracting Children Methods
- Spray administration of cycloplegia ( 0.5% cyclypentolate and tropicamide w 2.5% phenylephrine )
- Photorefraction ( Need cycloplegia for accuracy in high Rx error )
- Mohindra’s near retinoscopy technique which is useful but inaccurate on young high hyperopes and squinters
