Tono 2 Flashcards
How to align probe tip if corneal cyl is greater than 3D
Align probe with steeper K axis.
How does WTR and ATR astigmatism over 4D affect reading?
error= 1 mmHg for every 4D cyl
Under estimates WTR
Over estimates ATR
3 components of goldmann tone
Application probe
Probe arm mounted into spring loaded control box
Measuring drum
Formaula application tono uses
Force = pressure x area
Imbert Fick Principle and 3 assumptions
When a flat surface with a defined area is pressed against the surface of a sphere (applanation) with a given internal pressure. Equilibrium occurs when the force exerted is balanced by the internal pressure
Assumptions:
- Sphere should be dry, thin, perfectly elastic
- Displaced volume during application should be small in relation to total volume of sphere.
- Corneal thickness = 520 microns
Forces when taking pressure
Surface tension of tear film
Corneal Rigidity
Force + surface tension = (pressure x area) + corneal rigidity
Thick mires ___estimate IOP
Thin mires ___estimate IOP
Thick over
Thin under
Serial tonometry
Multiple measurements of IOP on the same day in a patient
Useful for diurnal variation determination
Recommended by some professionals to be performed on every glaucoma suspect/patient
Normal difference in tono readings between eyes
4mmHg
If IOP is less than 7, what is the patient at risk for?
Retinal detachment
Uveitis
Wound leak
Corneal penetration
If IOP is greater than 21, what is patient at risk for?
Ocular HTN if high IOP and no other signs
Glaucoma
Contraindications to using Tono
Eye infection
Allergy to drops
Corneal scar
Ocular trauma
Normal corneal thickness: 545
Thinner than normal cornea __ estimates IOP
Thicker than normal cornea ___ estimates IOP
thinner- under estimates. add 4 to reading.
Thicker- over estimates. Subtract 4 from reading.
