IOP Flashcards
IOP
IOP - fluid pressure inside eye
determined by tonometry
important in glaucoma – routine screening when the pressure is too high for the eye
patient explanation to measure IOP
fluid is being made and fluid is being drained in the eye everyday. In glaucoma there is either too much fluid made or drainage is blocked. Extra fluid causes pressure within eye that presses on retina/optic nerve and damages it
aqueous humor
secreted by ciliary epithelium lining the ciliary processes.
enters posterior chamber - flows around the lens - through the pupil into AC - then through the trabecular meshwork to Schlemm’s canal to episcleral veins
why measure IOP - decisions
tonometry: contributes to diagnosis of glaucoma
usefule in making decision to treat patients: IOP > 30 usually treated
useful evaluation of tx/pt management
Review: normal IOP?
upper limit of normal = 21 mmHg
(5-7% of population >21 mmHg)
4 mmHg or more of IOP asymmetry suggests pathology
what influences IOP
long-term influences: genetics and family history, age, gender, races, refractive error, seasonal variation
short term influences: heartbeat, breathing, diurnal variation, systemic conditions, intraocular conditions, postural variation, eyelid movement, doctor technique, exertion, episcleral venous pressure
long term influences - genetics and fmaily history
polygenic, multifactorial role
phenotype determined by greater than 1, and possibly many genes together with environmental factors, heritability estimates for IOP range from 0.29 - 0.36
long term influences - age
IOP increase with age, mostly accounted for increase in BP with age
7 glaucoma-related traits
central corneal thickness (CCT)
IOPcc (mmHg)
IOPg (mmHg)
Corneal hysteresis (mmHg)
IOPp (mmHg)
Pulsatility of blood velocity (kH2)
Pulsatility of blood flow (H2U)
Long term influences - gender
IOP of female is slightly higher than males
older females have greater increase in mean IOP with age
Long term influences - race
mean IOP in blacks greater than that for whites
long term influences - refractive error
increase in IOP with increasing axial length
increase in IOP with increasing myopia
long term influences - seasonal variation
mean IOP highest in winter, lowest in summer
small variation
short term influences - heart beat (ocular pulse)
influx of blood into eye with cardiac cycle
associated with arterial pulse
mean ocular pulse ~3 mmHg
short term influences - breathing
due to change in systemic BP with respiration
~ 1-2 mmHg variation
short term influences - diurnal variation
mean in normals: ~ 5mmHg
diurnal variation > 10 mmHg -> pathology
glaucoma patients have mean 13 mmHg (can be > 30 mm Hg)
peak classically morning
24 hr rhythm IOP in NTG
short term influences - systemic conditions
increased IOP in:
- systemic htn
- diabetes
- obesity
- inc. pulse rate
- hypothyroidism
- hypoosmotic state
- acromegaly
- hyperthermia
- inc. Hb
- certain meds
short term influences - sytemic conditions
decrease iop:
- acute hypoglycemia
- hyperthyroidism
- myotonic dystrophy
- ipsilateral cartoid artery disease
- hyperosmotic states
- horner’s syndrome
- HIV infections
- pregnancy
- certain meds
short term influence s- intraocular conditions
increased IOP: ocular trauma, neovascularization, lens (phacolytic)
decreased IOP: anterior uveitis, rhegmatogenous retinal detachment
short term influences - postural variation
supine position increase IOP (0.3 - 6 mmHg)
short term influence - total body inversion
increased IOP
5 min can 16 mmHg increase
short term influences - lid/eye movement
voluntary blink can 10 mmHg increase
hard lid squeece - 50 mmHg increase
voluntary lid fissure widening - 2 mmHg increase
horizontal gaze can produce slight increase
short term influence - pressure on globe can raise IOP by variable amounts
can raise iop variable amount
short term influences - exertion
iop may increase or decrease depending on type of exertion
prolonged running/bicycling can produce decrease
straining can cause increase in IOP