What are the 2 separate vascular systems of the eye?
- Uveal blood vessels
- Retinal vessels
Purpose of cornea
- Transparent protective membrane (must remain transparent, allows light rays to reach the retina)
- Avascular (corneal epithelium, stroma, and endothelium)
Purpose of lens
- Avascular and transparent
- Focus, accommodation
What effect can chlorpromazine have on the eye?
- Pigmentation ranging from white to yellow to tan (5 stages)
- Begins on anterior surface of the lens
- Cornea is involved when lenticular pigmentation reaches grade 3
What determines the effect of chlorpromazine on the eye?
- Dependent on cumulative dose
- Unlikely to show if total dose < 500g
- 90% of px w/ total cumulative dose > 2500g show ocular changes
- Px on high doses or on long-term low-dose regimens w/ chlorpromazine should have eyes checked annually
What effect can corticosteroids have on the eye?
- Systemic, topical, nasal, inhaled steroids cause posterior subcapsular cataracts (PSC)
- MOA –> altered lens epithelium electrolyte balance and binding to protein of lens
- Generally reversible
What determines the effect of corticosteroids on the eye?
- Unlikely in px who receive < 10 mg prednisone (or treated for < 1 year)
- Px on long-term oral steroid therapy should have eyes examined q6months
What effect can quetiapine have on the eye?
- Manufacturer recommends eye exam at baseline and q6months throughout therapy
- Cataract development observed in dog model
- Some px have developed lens changes but no cataracts
Aqueous humour is equivalent to ____
CSF
Where is the aqueous humour found?
Flows between posterior surface of iris and anterior lens surface
Normal intraocular pressure?
10-22 mmHg
What can intraocular pressure > 28-30 mmHg cause?
Ischemic damage of the optic nerve causing glaucoma
Sx of open-angle glaucoma
- Absence of pain
- Slow loss of peripheral visual field
- Often unnoticed by pt
Causes of closed-angle glaucoma
- Happens to individuals that are genetically susceptible
- Narrow anterior chamber angle
- Caused by anything that dilates the pupil
Which drugs affect intraocular pressure?
- Corticosteroids
- Phenothiazines (chlorpromazine)
- TCAs
Affect of corticosteroids on IOP?
- Increased resistance to aqueous humour outflow
- Topical ophthalmic agents more likely than oral agents to increase IOP
- Prolonged continuous use (1600 mg beclomethasone or budesonide/day for 3 months or longer)
Which drugs increase tear production?
- Cholinergics (pilocarpine)
- Adrenergic agonist (ephedrine)
Which drugs are excreted in tears?
Oral erythromycin and rifampin (orange coloured tears)
What is the uvea?
Iris, ciliary body, and choroid
Sx of anterior uveitis
- Eye pain
- Conjunctival redness
- Photophobia and blurred vision
- Pupil small and responds sluggishly to light
Which drugs are associated w/ anterior uveitis?
- Rifabutin
- Bisphosphonates
Chloroquine and hydroxychloroquine effect on retina
- Accumulation in the choroid, RPE (retina pigment epithelium), ciliary body and iris
- Irreversible retinopathy
- Doses < 400 mg/day of hydroxychloroquine appear safe even after prolonged therapy
Digoxin and digitoxin effect on retina
- Visual sx -> dyschromatopsia, flickering or flashes of light, coloured spots surrounded by coronas, snowy vision, hazy or blurred vision, glare sensitivity
- Vision disturbances can also occur at therapeutic doses of digoxin
- Inhibition of Na+K+ATPase (cone receptor function)
- Reversible w/in few weeks after dose reduction or discontinuation
Which drugs affect the retina?
- Chloroquine and hydroxychloroquine
- Digoxin
- Indomethacin
- Tamoxifen
- Retinoids
- Quinine
Indomethacin effect on retina
- Chronic administration of 50-200 mg/day for 1-2 years produces corneal opacities, paramacular depigmentation, decreased visual acuity, altered visual fields, blue-yellow colour deficits, and increased threshold for dark adaptation
- MOA of retinotoxicity unknown
- Colour disturbances return to normal after d/c
Tamoxifen effect on retina
- Chronic high-dose therapy (180-240 mg/day for 3 years) = axonal degeneration in the macular and perimacular areas
- Permanent decrease in visual acuity and abnormal visual fields
- Crystallizes in the retina
Retinoids effect on retina
- Poor night vision
- Glare sensitivity
- Problems w/ colour detection
Quinine effect on retina
- Neurotoxic injury to retinal ganglion cells (permanent loss) and optic nerve
- Retinal vasoconstriction
- Blurred vision, central and peripheral scotomata, and complete blindness
- Sudden visual loss can occur as late as 14 h after OD
Purpose of optic nerve
Carries visual info from retina to several distinct areas of the CNS
Ethambutol effect on optic nerve
- Decreased contrast sensitivity and colour vision
- Dose-related alterations = blue-yellow and green-red dyschromatopsia
- Optical neuropathy (central scotoma, visual field loss, decreased visual acuity)
- 10% of px receiving 25-50 mg/kg/day show loss of vision between 1-7 months; reversible upon discontinuation
What is a normal pupil size?
- 3-4 mm
- Equal to each other
What causes pupil constriction (miosis)?
- Cholinergic agents
- Opiates
- Phenothiazines
- Sedative hypnotics
What causes pupil dilation (mydriasis)?
- Anticholinergics
- Anti-depressants
- Sympathomimetics
Which drug causes jerk nystagmus?
Phenytoin
What is the most common nystagmus?
Jerk nystagmus
Which drugs can cause vertical nystagmus?
- Ketamine
- Dextromethorphan
- Phencyclidine
What are some ocular complications of drug abuse?
- Quinine amblyopia (IV use of quinine-containing heroin)
- Talc retinopathy
- Infectious complications -> fungal & bacterial endophthalmitis
- HIV-related retinitis
- Cocaine -> diffuse vasospasm = retinal ischemia and blindness
- “Crack eye” (corneal defects)