NCT

What is NCT

non-contact tonometry

an instrument used to measure intraocular eye pressure

What is tomometry

the measurement of intraocular eye pressure

What is applanation

flattening of the cornea

What uses applanation

NCT

Goldmann

Perkins

Tonopen

What uses indentation

Schoitz

What uses rebound

Icare tonometer

What is the basic principle of NCT

uses a puff of air to flatten a portion of the cornea

the time it takes to flatten the specific area is measured and converted to IOP

What is the alignment system

optically aligns the patient’s cornea with the instrument

What is the transmitter

directs light beam to cornea vertex

What is the receiver/detector

accepts parallel rays reflected from the cornea

once the cornea is flattened

What is the pneumatic system

generates the puff of air, air pulse force increases as a function of time

light is reflected from the flattened cornea and received by the detector

How much of the corneal diameter does NCT applanate

3.6 mm

1.4 gms of force/ 10mmHg

How much does Goldmann applanate

3.06 mm

1gm/ 10mmHg

What can affect NCT accuracy

Ocular pulse, blinking, misalignment, irregular corneas

What corresponds with ocular pulse

NCT takes 1-3msec, may not correlate with ocular pulse

may get variable readings, average 3 measurements

How does blink affect accuracy

falsely high IOP if applanated during start of blink

How does misalignment affect accuracy

increased force needed to applanate cornea, falsely high IOP

Why do we test IOP

Screening, primary care exam, children, glaucoma

When do we retest with Goldmann

Glaucoma suspect

IOP is elevated with NCT, greater than 21mmHg

asymetric IOP, greater than a difference of 4mmHg

The blind spot is, optic nerve is

temporal; nasal

Which reading on the printout do we use

IOPg

When do we repeat testing

asterisk or orange data, low confidence

low score

greater than 21

difference greater than 4

glaucoma