All day measurements of eye pressure

This page is for people having all-day measurements of eye pressure. It explains what will happen during this procedure, answering frequently asked questions some patients may have.

What is eye pressure?

The eyeball contains a fluid called aqueous humour, which is constantly produced by the eye. Usually any excess fluid drains out of the eyeball through small internal drainage tubes, whichallow the maintenance of normal fluid pressure (or intraocular pressure) inside the eye. The normal pressure in the eye is approximately between 10 and 21 millimetres of mercury(mmHg). However, if for any reason the fluid is blocked and cannot get out, the pressure can rise.

What is all-day measurement of eye pressure?

Eye pressure can vary by as much as 6mmHg during the day and this can be more common in glaucoma patients. During a regular appointment, a single pressure measurement of eye pressure is taken. Typically, measurements are higher in the early morning although this is not always the case. Therefore, your consultant ophthalmologist has arranged for you to have the pressure in your eyes assessed every two hours over an eight-hour period. This is called day phasing.

What are the benefits of day phasing?

This assessment helps us diagnose and monitor your eye condition and is useful if:

  • Your eye pressure is borderline with or without eye treatment.
  • You are showing symptoms of normal eye pressure glaucoma and treatment is being considered.
  • Your glaucoma is progressing even though you have normal eye pressure measurements.
  • You have recently started treatment for eye pressure and your consultant wants to see if your eye pressure has lowered sufficiently during the day.

What happens during the procedure?

A phasing nurse or technician will measure your eye pressure every two hours. The nurse/technician will put anaesthetic drops (a painkilling medication) into your eye. A yellow/orange dye may also be put into your eyes to temporarily stain the tears. Your vision will not be affected by the drops.

The phasing will take place in the eye clinic every two hours from 8:30am- 4.30pm. You are welcome to leave the clinic in between measurements or you can stay in our waiting area. It can be a long day so you may wish to bring someone with you or bring something to read or do while waiting. If you would like something to eat or drink during our appointment, you can bring in your own refreshments. There are also several places to buy food and drink within the hospital and in the local area.

When will I get my results?

You can ask the nurse/technician for your results during your appointment. You will not be reviewed by a doctor on that day, unless the results show very high intraocular pressures, which require urgent attention. A clinic appointment will be arranged at a time interval that has been requested by your treating clinician.


Author: Eleni Nikita 

Review date: March 2023

Some of the content from this page has been reproduced with the permission of The Dudley Group NHS Foundation Trust.