A vision test which measures the capability to differentiate between fineness of light and dark contrast is referred to as Contrast Sensitivity Test. The examination is different than other common visual acuity tests we usually undergo during a routine eye exam that is recognising alphabets and fonts on a standard eye chart.
Contrast sensitivity is imperative for measuring visual functions, especially when exposed to dim-lit surroundings, fog or extreme glare. This is when contrasting effect between the actual objects and their background flickers and reduces. Night time driving is one of the finest examples which require adequate contrast sensitivity for safety.
Even individuals with visual acuity of 20/20 may suffer from particular health anomalies that diminish the contrast sensitivity thus compromising the ability to see things clearly.
Low contrast sensitivity is sure to raise problems with nighttime driving as well as to see pedestrians walking under dim street lights. Another symptom of reduced or compromised contrast sensitivity is frequent tiring of the eyes when engaged in activities that require visual focus like watching television, reading or using a digital device.
All this increases a person’s risk of fall from stairs, especially when walking on likewise coloured steps and footpaths. The low contrast sensitivity itself can be an onset of underlying eye anomalies such as glaucoma, diabetic retinopathy, and cataracts. Various refractive surgeries including PRK and LASIK can also change an individual’s contrast sensitivity.
Test & diagnosis
It’s unlikely of a routine eye exam to include contrast sensitivity testing but not impossible and it also depends on the eye care facility’s rules and regulations. An eye specialist in Dubai would conduct the test due to patient’s particular visual complaints and doctor’s expertise. He can correctly diagnose the condition that compromises the ability to discriminate the contrast effect.
The Pelli Robson Contrast Sensitivity Chart is the widely used device to test and diagnose the anomaly. It has capital letter imprinted horizontally much like the standard Snellen visual acuity chart. One difference, however, is the change of color contrast against each letter/alphabet rather than the smaller fonts.
Then there’re many other advanced devices to test and diagnose the contrast sensitivity. Most of these devices use targets known as sine-wave gratings containing various parallel, fuzzy bars in light and dark, varying in width as well as contrast. This allows for a more thorough evaluation of your eye sensitivity towards contrast difference.
The test is conducted without the patient removing the eyeglasses or contact lenses especially when vision correction is required.
Contrast Sensitivity Function (CSF)
Detailed measurements of contrast sensitivity include both sizes (spatial frequency) and contrast which helps in plotting the CSF. It’s basically charting the curve which defines the lowest contrast level a person can detect per each spatial frequency tested.
The test results would help the doctor determine if an individual’s having vision errors like higher-order aberrations or any other that may require eye surgery or a special eyewear for correction. Corrective lenses with yellow tint/filter are mostly preferred by an eye specialist in Dubai and others for the treatment of low contrast sensitivity.
Premium-grade Intraocular Lenses (IOLs) that are tailored with wavefront technology can help overcome higher-order aberrations as well as improves the sensitivity to contrast post cataract surgery.