Practical assessments

Describe GAT procedure

1) Explain procedure to patient

2) Standard hygiene procedures with slit lamp- wipe down chin rest

3) Replace probe with new disposable probe / use a reusable probe that has been prepared correctly

4) Anaesthetic and fluorescein

4) Set up tonometer and illumination

•Cobalt blue light – position illumination system 40 to 60 degrees to one side

•Turn dial to put some weight into the probe

5) 10x to 16x magnification

•Illumination set to 45-60 degrees

•Set tonometer scale to 1.6 grams (16 mmHg)

6) Align probe with centre of cornea

7) Ask patient to blink a few times

•Stare straight ahead

8) Advance probe towards patient’s cornea

9) Watch as the probe touches the cornea

•Advance the probe  a little further to applanate the cornea

•Probe arm will be seen to move backwards slightly

10) Look through the eyepieces

•Adjust weight setting by turning dial on tonometer body until mires are correctly aligned

11) Remove probe from cornea & repeat procedure for fellow eye

12) Record result and time of measurement

13) Remove tonometer

14) Check cornea for staining

15) Clean probe if reusable type

•Dispose of probe appropriately if ‘disposable’ type

(See IOP starred flashcards for more information)

Describe the Van Herrick procedure

Set angle of 60 degrees between illumination and observation system of slit lamp

•16x magnification

Optic section: bright, thin beam

Assess relative width of anterior chamber against width of cornea when light just enters anterior chamber

Abduct eye when assessing nasal angle:

•Illumination system locked 60 degrees to the nasal side of the observation system

•Rotate whole system temporally

•Ask patient to look into observation system (eye being measured has to abduct to do this; prevents nose from blocking the slit beam)

(see anterior segment starred flashcards for more information)

Describe the US procedure

Compact handheld ultrasound pachymetry

Procedure:

•Explain procedure to patient

•Topical anaesthetic

•Apply probe tip to to the centre of the patient’s cornea

•Obtain readings according to the manufacturer’s instructions

•Check cornea with slit lamp and fluorescein

(See pachymetry starred flashcards for more information)

Describe how to calibrate GAT

Place tonometer on slit lamp, with probe in place

Insert calibration rod into socket on side of GAT housing

Set rod to the 2 gram setting

•Increase the weight setting on the dial and watch for the probe to rock forwards

•Read off scale to check calibration accuracy

•Decrease weight and watch for probe rocking backwards

Repeat the above, with the rod set to 0 grams and 6 grams

Absolute calibration error and any change in the error between the weight settings should be noted

(See IOP starred flashcards for more information)

ONH description:

Case scenario case history: