Contrast sensitivity testing

If you are looking for a laser eye clinic in London, then the London Vision Clinic should be on your shortlist.  

That may seem like a strong statement, but the London Vision Clinic emphasises that, in expert hands, laser eye surgery can be an extremely safe, life enhancing experience. More than 100,000 laser eye surgery procedures will be done in the UK this year. Read the guide to Laser Eye Surgery to help make the right choice for your eyesight.

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What is it for?

Measuring your ability to see gray-on-gray, or your ability to distinguish objects in low contrast situations.

When is this done?

Initial screening and during aftercare appointments.

What actually happens?

Following the refraction you will be shown images of gray stripes or letters of reducing size and contrast. You will be challenged to recognize the stripes and letters as the contrast decreases until it is so faint that you can no longer recognize that there are stripes or what the letters are. You will be asked to do this over 1 to 4 different sized stripes or letters depending on the test.

How does it feel?

You feel nothing.

What does it do?

Using this test, the optometrist can assess your ability to see contrast between images in low lighting conditions. This provides an important measure of visual function at night. It gives your surgeon an understanding of how you see things in the real world as opposed to just black-on-white (100% contrast) letters on a chart. Occasionally people complain of poor vision, particularly in dim lighting conditions yet they have normal or very near normal (black-on-white) visual acuity. This is often because they have reduced contrast vision.

How does it benefit you?

With any but the most advanced laser systems (those using aspheric treatment profiles) night vision disturbances may be induced by laser eye surgery, particularly if the refractive error corrected is high and the pupil size is large.

Measuring your contrast sensitivity provides your surgeon with another measure of how well you already see at night, giving him an indication of how to best plan your treatment in order to avoid night vision disturbances.

Many laser systems, even the latest versions still do not use aspheric treatment profiles.

Not all aspheric treatment profiles are the same, but in general lasers using these will be safer with respect to changing night vision. Some systems are so well designed that they can even improve your contrast  sensitivity and night vision.