Eye Pressure Test (Tonometry)
Tonometry measures the pressure inside your child’s eyes (intraocular pressure, or IOP).
An eye pressure test may be done during your child’s diagnostic office exam, during EUAs and at follow up office exams.
Measuring eye pressure is important in retinoblastoma. High pressure (glaucoma) may indicate cancer fills the front of the eye. Cancer in this area has high risk of spreading outside the eye through blood vessels.
A tonometer measures intraocular pressure by recording resistance of the cornea to indentation. The force required to flatten a small area of the cornea is measured in millimeters of mercury, (mm Hg). Normal pressure ranges from 10 – 21 mm Hg.
Goldman tonometry and the air puff test may be used with older children who can sit at the slit lamp microscope. The air puff test is commonly used with children because it does not involve touching the eye.
During the Procedure
The ophthalmologist will put anaesthetic drops and a drop of fluorescein yellow dye in your child’s eye. A blue light on the slit lamp illuminates the dye so the doctor can see the surface of the eye.
A small, fine cone-shaped probe with a flat tip is gently pressed onto the eye. Alternatively, a gentle puff of air is used to flatten the cornea.
When children are too young to sit at the slit lamp, a small handheld device is gently applied to the cornea. This looks a little like a pen. 3-4 readings will usually be taken to gain an accurate measurement. Using a comfort position will help reduce your child’s anxiety.
The anaesthetic drops may sting for a few seconds, but this fades quickly as the eye becomes numb. The eye will not hurt during the test as it is numbed. However, your child will feel a little pressure from the probe or air. She may cry or resist if not prepared for this sensation.
Practice some fun games or action songs in which you and your child take turns gently touching around the eye area, or blowing softly into each other’s faces to familiarize her with the sensations she may feel during this test.