IOP Flashcards
Normal IOP range
10-21mmHg
- diurnal variations (higher in the AM)
- > 2mmHg difference suspicious
Factors affecting IOP
- genetics
- environment
- physiology
- ethnicity
- refractive error
- diurnal and postural variation
- exertional influences
- eyelid and eye movement
- intraocular conditions
- systemic conditions
Genetics and IOP
- twin studies: IOP highly correlated between monozygotic than dizygotic twins
- some studies show a gene that contributes to variances in IOP
- blue mounts eye, beaver dam
Environment and decreased IOP
- cold air: due to decreased EVP
- general anesthesia: high concentration in infants and hcildren and ocular trauma with ruptured globe
- heroine and MJ
- acute doses of alcohol: due to possible inhibition of aqueous secretion
- nutritional diet: fruits, vegetables, omega-3 FA; also possible reduced risk of glaucoma
Environment and increased IOP
- reduced gravity: due to cephalad shifts in intravascualr and extravascular body fluids
- tobacco smoking: immediately after smoking; due to vasconstriction and elevated EVP
- LSD
- corticosteroids
- caffeine
Why do anticholinergics, antihistamines, decongestants, and psychiatric medications contraindicated in patients with glaucoma
Due to risk of pupillary block glaucoma or acute angle closure glaucoma in pateitns with anatomically narrow angles
Scopolamine dermal patches and glaucoma
Assocaited with acute angle closure glaucoma, but no direct effect on IOP
Dietary supplements and increased IOP
Research still needed
Gender and IOP
- no major effect in 20-40 yo
- >40 yo: increase in mean IOP with increasing age is greater in women than men. Coincides with onset of menopause
Age and IOP
- generally IOP increases with age
- children have lower IOPs than adults (does ability to take IOPs factor in?)
- aging effects: reduced faciltiy of aqueous outflow and uveoscleral outflow with decrease in aqueous production, episcleral venous pressure has no change
Ethnicity and IOP
- increased risk of POAG in AA (thinner corneas, greates CD and higher IOP)
- increased angle closure in Asian
Refractive errors and IOP
Infants
-increased IOP: axial myopia, seen in bupthalmos
Older children: positive correlation between IOP and axial length of globe and increasing degrees of myopia
Adutls
-conflicting studies if myopia is a risk factors
Diurnal and postural variation of IOP
- highest during daytime
- IOP elevation at nighttime (supine position)
- whole-body- head-down tilt position leads to increase in IOP (increase EVP)
- in office can take multiple IOP pressures: every 2 hours from AM to evening, and stimulate nighttime by placing patient in supine position
Exertional influences and decreased IOP
Exercise
- helpful in patients with and without glaucoma
- watch patients with pigment dispersion syndrome/glaucoma: exercise can induce AC pigment dispersion-increase in IOP; consider low dose pilocarpine before exercise to cause miosis to minimize contact between midperipheral iris and zonules
Exertional influences and increased IOP
- straining
- valsalva maneuver
- electroshock therapy
- playing a high resistance musical instrument
- overweight patients in Goldman
- possible mechanism: elevated EVP, uveal engorgement, increased orbicualris tone
Eyelid and eye movement and IOP
- blinking can increase IOP by 10mmHg
- hard eyelid squeeze can increase IOP to 90mmHg
- voluntary eyelid figure widening can increased IOP by 2mmHg
- up gaze and during strab surgery can increase IOP
Intraocular conditions: decreased IOP
- anterior uveitis without angle abnormalities: due to decrease in aqueous production and increase uveoscleral
- rhegmatogenous RD: due to reduced aqueous flow and shunting of aqueous from posterior chamber through vitreous and retinal hole into subretinal space and across RPE
HTN and glaucoma
- increases risk for glaucoma
- positive correlation between HTN and IOP in Latinos, Japanese, angling menm presents of mixed African decent blue mountains eye study cohort, whites in beaver dam eye study
Types of tonometer
Indentation
Applanation
Noncontact
Rebound
Indentation of tonometry
Shiotz
Indentation shape on cornea
Types of indentation tonometry
Goldman and Perkins
NCT
Puff of air
Rebound tonometry
Icare
- no anesthetic
- good for children
- good for special needs
- easy
- accuracy similar to tonopen
Factors effecting tonometry
-thinner corneas underestimate ( <555)
-thicker corneas overestimates
(>588)
-effected by refractive surgery, corneal disease
