Fields maybe green and grassy but optometrists are interested in your Fields of Vision.
Arthur Schopenhauer may have said “Every man takes the limits of his own field of vision for the limits of the world.” Optometry recognises that there are diverse fields of vision and is not just interested in their limits but in changes to them. By measuring their limits, depths or changes we can build a greater understanding of the health and efficiency of the visual system.
In the consulting room we are mainly interested in;
- Central Visual Fields and Peripheral Visual Fields.
- If we are screening for disease then each eye has to be tested on its own, i.e. looking at the monocular fields, with the eye not being tested occluded or covered up.
- If we are screening for safe driving then it is the binocular field that matters. Both eyes are used together. This type of field test can assess your Useful Field of View (UFoV).
Poor central fields makes it difficult to recognise people’s faces or to read but has less effect on mobility. Some very Simple central field tests are –
- An Amsler chart. This is a grid of lines and you will be asked to judge if any lines appear distorted or if any squares look bigger or smaller than the rest. This is usually used to assess macular function when there may be concerns about the onset of AMD.
- Reading Letter Charts. This gives a measure of your central visual acuity. This is a recordable measurement of how well you can see small details in your Central Field of Vision as opposed to your Peripheral Field of Vision. The letter chart may be at 6 metres or at your preferred reading (or working ) distance, it depends on what we want to measure.
Poor Peripheral Fields relate to your ability to see movement and/or changes on the periphery of your vision, movement out of the corner of your eye. Reading vision and social skills are less affected but people are more likely to trip over and bump into things. Some Simple tests Peripheral Field tests are-
- The simplest peripheral field test is a confrontation test. Your optometrist may get you to look at his nose whilst he ‘waggles’ his fingers at the side of your head and asks if you can see them, or he may bring a pen from behind your head (outside your peripheral field of view) and ask you to say when you first see the pen.
- Visual Field Analyser or Screener. there are many different types but essentially it is a machine that flashes small lights at you. You either have to say how many you see or whether you see one or not.
Field tests may not be carried out routinely at every Sight Test. Your optometrist will use her/his experience to decide whether or not they are necessary. Changes in your visual fields can indicate disease within the eye or disease within the brain.
Various instruments can be used to measure both central and peripheral fields and especially mid-peripheral fields. Different practices will have different instruments, but they all give a permanent record of your field of vision so your optometrist can see whether there are any changes as you get old.