Intraocular pressure (IOP)
- = fluid pressure of the eye
- IOP = (F/C) + P where
- F = aqueous flow rate
- C = aqueous outflow
- P = episcleral venous pressure
Normal IOP = 11-21mmHg
- Important in glaucoma, uveitis, retinal detachment
- Acute ↑IOP → retinal ischaemia
- Chronic ↑IOP → 1° open-angle glaucoma (POAG)
- ↓IOP (globe rupture) →retinal detachment
Anatomy
- Aqueous is produced by the ciliary epithelium of iris ciliary body in post. chamber
- It then flows through the pupil into the Ant. chamber via:
- Most via trabecular meshwork at the angle of the anterior chamber → Schlemm canal → episcleral veins
- Some into venous circ. via ciliary body, choroid, & sclera
- Via iris back into the posterior chamber
- Sympathetic Βeta-2 ↑ secretion of aqueous
- Sympathetic Αlpha-2 ↓ secretion
- Prolonged ↑ IOP → glaucomatous optic neuropathy
iCare200 use
- Press the Select or Measure btn to turn tonometer on
- Open the probe tube by removing the cap and tip the probe into the probe base – it will magnetically hold
- Ensure the forehead support is fully extended by turning the adjustment wheel
- Bring the tonometer in front of the eye until the support touches the forehead. Keep the probe horizontal and pointing perpendicularly to the central cornea
- Adjust the probe-cornea distance by turning the forehead support wheel; the distance should be about 5 mm
- IOP can be measured in the supine or upright positions
- Probe will contact the eye during measurements
- Press and hold the Measure button to collect 6 measurements in a row. The grey segments of a circle on the display screen will turn blue one by one:
- LONG BEEP = six good measurements: IOP shown
- SHORT BEEP = correct single measurement
- DOUBLE BEEP = incorrect single measurement
- Normal IOP: 11 - 21 mmHg
- Discard the probe into a sharps bin
- Replace tonometer into its metal case & lock back inside its safe. Tonometer (iCare200) is kept locked in a safe above the VBG machines opposite Procedure Room 3. Yellow key for safe is kept with resus drug keys
Practical
The IC200 can be used in 200 degrees measurement angle; the patient can be upright, supine or lateral recumbent or any position in between.
Tonometry CUH
- Tonometer (iCare200) is in a metal case in the CDU DD drug cupboard
- Used by EM Consultant, ANP, Reg
- Use (video) for IOP measurement in:
- Suspicious headache
- Eye trauma
- Suspected acute glaucoma