Eye Gaze Essentials | Sight test essentials

April 1, 2020


Lisa Donaldson, Head of Eyecare and Lead Clinical Optometrist at SeeAbility details sight test essentials, the things Optometrists test and look out for during a sight test with someone who has complex needs.

Level of detail

The classic one that we all think about straight away is the level of detail that you can see. For many of us, this would be how far down the letter chart you can read.

There are lots of other way of measuring this for people with complex needs. For example, using pictures charts or watching balls or beads.

Level of contrast

A second sight test essential is how much you can determine contrast.

For example, shades of gray against a background. You may be able to see quite fine detail but really struggle to pick it out against a background that’s not very in high contrast. 

Eye movement control

Optometrists look to understand eye control movements.

They will assess if you can make accurate movements from one object to another.  Whether you can smoothly follow a target with your eyes or whether the eye movement is quite jerky.

Field of vision

Assessing whether someone has full field of vision and can see in all four quadrants. 

It is quite common, particularly in Cerebral Palsy, if there is hemiplegia there may be hemianopia there won’t be vision down the middle of each eye. This is because that area of vision originates in the brain.

This can be more disabling that not being able to see out of one eye.

Are the eyes healthy?

When assessing the health of the eyes, optometrists are looking to see that the front
of the eye structures are healthy. The cornea and eye lens are checked for cataracts.

A glimpse of the retina to check that the eye and optic nerve are healthy.

Eye focus

Last, but not least, will be a measure to understand how the eyes are focusing.

For many, that would be typically be choosing between lens 1 or 2. When assessing the eye focus of people with complex needs a torch can be used to look at the red reflect shining off the back of the eye. This allows an accurate prescription for glasses based on those measurements.

So, glasses can be prescribed just by shining the torch at arm’s length.

Zoom function

Many of the special school population don’t have a zoom function. This is the ability to focus between things that are far, to close.

A lot of the children need bifocals, varifocals, two pairs of glasses or just reading glasses. In the general public these typically aren’t needed until the mid-40s. Many of the special school population can’t shift focus, so need more than one prescription for different tasks.

Sight test essentials

  • What level of detail can an individual see?
  • What differing level of contrast can they detect?
  • What level of eye movement control do they have?
  • How wide is their field of vision?
  • Are the eyes healthy?
  • How is the eye focusing?
  • Do they have zoom function?

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