PC - Posterior Segment Examination - Week 1 Flashcards
What is the purpose of dilation?
Allows improved view of the retina.
List 13 indications for dilation.
- New patient
- Routine for all every 2 years
- Flashes/floaters
- Unexplained vision reduction/loss
- Progressive retinal diseases
- Systemic conditions
- Hx of head/ocular trauma
- Hx of chronic uveitis
- Hx of peripheral retinal degenerations or holes
- Yearly for hx of ocular sx
- Biennially for moderate to high myopia, annually for 8D-
- Limited or no view of the posterior pole (cataracts)
- Hyperopes, anisometropes,, <6yo
List 13 contraindications for dilation.
- Angle closure glaucoma
- Pilocarpine use for glaucoma tx
- Dislocation of crystalline or intraocular lens
- Iris fixed or anterior chamber intraocular lens
- Hypaemia
- Acute corneal diseases
- Hypersensitivity to mydriatic drops
- Pregnancy/lactation
- Narrow anterior chamber angle
- Recent ocular injury
- Petite/anorexic individuals
- Children = liver enzyme activity
- Sick/febrile
Consider the following types of patients that require dilation:
Petite/anorexic
Children
Sick/febrile
What can be done to minimise systemic absorption, and what percentage reduction in absorption does this result in? What must be monitored?
Dont have them open their eyes, and digital occlusion.
Reduces absoprtion by 70%.
Monitor pulse rate.
Do drugs targetting the dilator muscles result in more or less dilation? Why?
Less, because the dilator muscle is weaker.
Do dilator drugs targetting the dilator muscles result in cycloplegia? Why?
No, because the muscles are innervated by the sympathetic nervous system, which only accounts for 1% of accommodation.
Define sympathomimetics.
Drugs that target the dilator muscles to mydriasis (agonists).
Name a common sympathomimetic targetting the sympathetic nervous system.
Phenylephrine.
How long does phenylephrine take to have effect, and how long does it last for?
Takes 10 mins, and lasts for 5-7 hours.
What effect does eye colour have on phenylephrine action?
Is less effective on higher pigmented eyes.
Do drugs targetting the sphincter muscles result in more or less dilation? Why?
More, because it is the stronger muscle.
Do dilator drugs targetting the sphincter muscles result in cycloplegia? Why?
Yes, because the sphincter muscle is innervated by the parsympathetic nervous system, which also accounts for 99% of accommodation.
Name 4 dilator drugs that target the parasympathetic nervous system.
Tropicamide
Cyclopentolate
Atropine
Homatropine
What is the dilator drug of choice and why? Describe is onset and duration.
Tropicamide - highly safe to use, has a quick onset and short duration.
What percentage concentrations of tropicamide is used for DFE and cycloplegia?
0.5% - DFE
1% - cycloplegia
