introduction to diagnostic drugs Flashcards
what are mydriatic drugs?
mydriatics are used to dilate (open up) the pupil
why is there an increased use of mydriatics in optometric practice?
- expansion of co-management (shared care) schemes
e. g. gluacoma schemes for primary open angle glaucoma - increase in professional negligence cases
e. g. missed retinal detachment - better appreciation of the benefits of dilation
when to dilate ?
- conditions e.g. diabetes, uveitis, pigmented fundus lension, suspected glaucoma, peripheral retinal degeneration, hypertension (high blood pressure), cataract, age-related macular degeneration, history of retinal detachment, history of metastatic cancer
- symptoms e.g. flashes and floaters, new distortion, unexplained loss of vision , recent blunt force trauma
- relevant family ocular history
- small pupils, nystagmus, unsteady fixation
- where stereoscopic view of retina is necessary
- systemic medications with potential side effects
- to get good fundus photograph
explain the benefits of pupil dilation?
- ability of ophthalmoscopy to grade correctly diabetic retinopathy is more than 50% higher through a dilated pupil than through an undilated pupil
what are the mydriatics used by optometrists?
- Tropicamide 0.5%
- Tropicamide 1.0%
- phenylephrine 2.5%
. all available in minims - single use plastic files
what the college of optometrists guidelines when using a drug?
- optometrists should record the batch number and expiry date of drugs that are used in their professional practice
- also record drug name, concentration and time instilled
- this will facilitate verification that:
. drug is in date
. in the case of a drug recall- makes it easier to trace all patients who may have been affected
what are the 4Ds when it comes to drugs?
drug
dosage
date( expiry )
disposal
what are precautions to take before mydriasis ?
- explanation to patient
. why dilating, effects and duration - previous experience of dilation
- medical history
. phenylephrine: caution in patients with cardiovascular disease, hypertension - current medication
- measurement of IOP
- assessment of risk of angle closure
the impact of mydriatic drugs on IOP?
- small risk of increasing IOP and inducing angle closure gluacoma when using mydriatic drugs?
why is there a small risk of increasing IOP and inducing angle closure gluacoma when using mydriatic drugs?
- angle closure gluacoma occurs when angle of drainage becomes blocked
- when dilating the pupil, there is a risk of blocking the drainage angle
- the region around the black arrowhead shows the front surface of the iris that has come into contact with the trabecular meshwork
what is the risk of mydriasis provoking an acute ACG attack?
1 - Baltimore eye survey ( cross sectional study) dilated approx 5000 subjects
. used 1% tropicamide / 2.5% phenylephrine
. No ACG episodes
. later gonioscopy( more detailed way of assessing the anterior chamber angle) judged 20 of theses to be at high risk
2- another study - systematic review
. tropicamide used alone( 0.5% or 1.0%)
. zero cases in 3972 dilations
. all other dilating agents
- 33 cases in about 600,00 dilations
- or 1 in 18,020
. dilating patients with primary open angle gluacoma
- zero cases in over 1000 patients
what are other points to note regarding the risk of mydriasis provoking an acute ACG attack?
- dilation facilitates evaluation of disc in cases of possible open angle glaucoma i.e. is useful to dilate these patients
- if someone has a very narrow ( potentially occludable) angle, should refer anyway as at high risk attack of ACG at any time
- if patient has suspect retinal detachment, wet AMD and you cannot obtain sufficient view, must either dilate, or refer on worst case scenario
what are different ways to assess risk of angle closure?
- Van herick
- flashlight test
- smith’s slit-length method
- methods using pachymeters
- gonioscopy
what to advice patients regrading mydriasis ?
1- loss of acuity
because
. depth of focus worsen when dilate pupil
. drugs relax accommodation
2- glare problems
. patient may benefit from wearing sunglasses
. patient may wish to bring sunglasses with them to the examination
3- driving difficulties
4- recognition of symptoms of an acute ACG attack
5- give information sheet
what is the advice regarding driving after dilation?
- patients should be given an information sheet, and recommended not to drive for the rest of the day
- college of optometrists information sheet says that ‘ it is recommended that driving should be avoided whilst your vision is affected
what is topicamide ?
- an anti-muscarinic drug which causes mydriasis by relaxing the sphincter muscle of the iris and cycloplegia by relaxing the ciliary muscle
- blocks the parasympathetic nervous system
- onset action = approx 10 to 30 minutes
- maximum effect=within approx 20 to 40 minutes
- recovery to normal= approx
4-9 hours
how likely is an allergic reaction after tropicamide?
- very few allergic reactions
- only isolated adverse systemic reactions reported
. CNS effects can occur with cyclopentolate - risk of ACG in predisposed eye
- be careful of possible interactions with other anti-muscarinics
what is phenylephrine ?
- a sympathomimetic drug which causes mydriasis by stimulating the dilator muscle of the iris
- mydriasis is not complete
- light reflex is not abolished
- may be used in combination with tropicamide in patients who are difficult to dilate
- onset of action= approx 10 to 30 minutes
- maximum effect= within approx 30 to 90 minutes
- recovery to normal = approx 5 to 12 hours
what are cycloplegics ?
- drug used to produce ‘cycloplegia’
. paralysis or partial paralysis of ciliary muscle i.e. accommodation is disabled
when is cycloplegics mostly used?
- used if there are indications of fluctuating or excessive accommodation during refraction
- used mainly in children when their accommodation is unstable, making retinoscopy unreliable
- young latent hypermetropes
- tropicamide and cyclopentolate are both cyclopegic agents, but cyclopentolate is more effective at disabling accommodation young people
what is cyclopentolate?
- an anti-muscarinic drug ( like tropicamide ) which causes cycloplegia by relaxing the ciliary muscle ( and mydriasis by relaxing the sphincter muscle of the iris)
- used widely for cycloplegia , not as a mydriatic
- consider iris colour
. onset of action = approx 10 to 30 minutes
. maximum effect = within approx 20 to 60 minutes
. recovery to normal = within 24 hours
what is cyclopentolate available in ?
- available in minims 0.5% and 1.0%
- tend to use 1% minims in under 12s and 0.5% in children aged 12 and over
what are side effect of cyclopentolate?
- more likely to get CNS effect with cyclopentolate than with tropicamide
what are the effects of iris colour ( applies to all mydriatics and cycloplegics) ?
- drug binds with melanin on the iris and is slowly released
- in dark irides contain more melanin this leads to
. slower onset of action
. lower duration of action - this applies to all mydriatics
