What is the Mesopic Contrast Test? In Which Situations is it Applied?
Do you have difficulty distinguishing objects while driving at night? The mesopic contrast test is a specialized examination method that evaluates your vision ability, especially under low light conditions. This test measures your contrast sensitivity, determining your capacity to perceive differences in minimal increases of light compared to darkness. It plays a crucial role in the early detection of eye diseases such as cataracts, glaucoma, or diabetic retinopathy. In this article, you will find answers to questions about what the mesopic contrast test is, in which situations it is applied, and how it is performed.
What is the mesopic contrast test?
The concept of contrast sensitivity
The mesopic contrast test is based on the measurement of contrast sensitivity used to evaluate visual function. Contrast sensitivity is defined as the ability to detect the lowest illumination difference between an object and its background. Unlike visual acuity measured in standard eye examinations, this test assesses your ability to distinguish objects under varying light conditions.
Even if your visual acuity is at 20/20, your contrast sensitivity may be low. Therefore, contrast sensitivity tests are used to detect visual losses that cannot be identified in the Snellen test. This measurement, which is one of the fundamental conditions for good vision, varies according to age, refraction, and pupil size.
It reveals the amount of vision loss more accurately, especially in cataracts, corneal edema, neuro-ophthalmological diseases, and certain retinal diseases. Thus, a decrease in contrast sensitivity is observed in glaucoma, amblyopia, keratoconus, macular diseases, and diabetic retinopathy.
Mesopic vision conditions
In mesopic lighting conditions, the cone and rod cells in your visual system work together. Since the visual environment during night driving is significantly within the mesopic glare region, road lighting is one of the most prominent applications of mesopic vision.
The average road surface glare levels provided in road lighting standards range from 0.3 cd/m² to 2 cd/m². However, there are also glows in the photopic vision range, such as headlights of other vehicles and light-emitting surfaces of fixtures outside the driver’s field of vision. Similarly, dark areas outside the road and nearby surroundings, such as the sky, also contain glows in the scotopic region.
Measurements of contrast sensitivity in mesopic conditions have been found to be higher than in photopic conditions. This is due to the increased ability to distinguish between the ground and the object with the dimming of ambient light.
The importance of glare and the mesopic contrast test
Glare refers to the visual discomfort caused by bright light sources, such as oncoming vehicle headlights. Some devices used in the mesopic contrast test contain bright light sources that can be directed to your eyes during the test to simulate glare conditions like oncoming vehicle headlights during night driving.
The connection between reaction time and driving performance is significant. Road accidents increase at low lighting levels where visibility decreases and reaction time increases. If your contrast sensitivity is low, you may have difficulty seeing pedestrians walking in poorly lit streets.
Many factors affect visual performance, such as static and dynamic visual acuity, contrast sensitivity, color vision, and motion detection. The mesopic contrast test provides detailed information about your night vision quality by evaluating these factors together.
Differences Between Photopic and Mesopic Contrast
Contrast measurement in bright environments (photopic)
The photopic contrast sensitivity test is conducted at high light levels simulating daytime lighting conditions. The lighting level used during the test is set at 85 cd/m². This value creates an environment close to normal daylight conditions.
It has been determined that your age does not affect your contrast sensitivity in measurements made under photopic conditions. Results obtained in bright environments are also independent of your pupil size. This indicates that your daytime visual performance is less affected by age-related changes.
In a photopic test environment, pupils naturally constrict. A high-light test environment may reduce your contrast sensitivity. However, under standard conditions, no differences in contrast sensitivity among age groups have been detected in bright environments.
Contrast measurement in dark environments (mesopic)
Mesopic and scotopic contrast tests are performed at low light levels. Scotopic contrast sensitivity is measured at 0.032 ± 0.003 cd/m², while mesopic contrast sensitivity with glare is evaluated at 0.10 ± 0.01 cd/m².
In dark environments, a decrease in contrast sensitivity values measured at high frequencies is observed as age increases. Especially, your contrast sensitivity values at high spatial frequencies decrease with age. Therefore, your night vision problems may increase as you age.
In dark environments, as your pupil size increases, your contrast sensitivity values also increase. Thus, your pupil size directly affects your visual performance in mesopic conditions. Pupil size measurements in myopic individuals are found to be wider than in hyperopic individuals across all lighting environments.
Comparison of test results
Your high contrast sensitivity in bright environments decreases in dark environments. Contrast sensitivity measurements obtained in dark environments are found to be higher than those in bright environments across all spatial frequencies. This result indicates that your ability to distinguish between the ground and the object increases in dark environments.
Your binocular contrast sensitivity measurements are higher in every test environment and at every spatial frequency than monocular measurements. Tests performed with both eyes yield better results than those performed with one eye.
In both pseudophakic and phakic eyes, a decrease in scotopic contrast sensitivity and mesopic contrast sensitivity with glare is observed with age. Both photopic contrast sensitivity and scotopic contrast sensitivity decrease with age. However, this decrease is more pronounced under mesopic conditions.
No significant difference has been found between eyes that have undergone cataract surgery and normal eyes in terms of photopic contrast sensitivity, scotopic contrast sensitivity, and mesopic contrast sensitivity with glare. However, differences arise in evaluations within age groups under mesopic conditions.
In Which Situations is the Mesopic Contrast Test Applied?
The application areas of the mesopic contrast test are quite broad. This test is applied in many situations, from pre-operative evaluations in eye surgery to driver’s license examinations.
Pre-operative and post-operative evaluation for cataract surgery
The success of cataract surgery is directly related to accurate and reliable measurements taken before the operation. In a detailed examination to be performed before the surgery, the transparency of the cornea, the structure of the cataract, the position of the lens, and the width of the pupil are evaluated. The mesopic contrast test is an important part of these evaluations.
Sensitivity to light is a common side effect after surgery, especially seen more frequently in patients with light-colored irises. Low contrast sensitivity in eyes that have undergone cataract surgery is one of the factors affecting post-operative visual quality. In most cases, patients notice significant improvement in both visual acuity and contrast sensitivity after surgery.
LASIK and refractive surgery control
Some patients may experience visual irregularities, blurriness, or night vision problems after refractive surgery. Irregular astigmatism reduces visual quality due to irregularities on the corneal surface. When the pupil enlarges after surgery, light may scatter and halos may form.
Contrast sensitivity and night vision can be optimized again with personalized planning. The mesopic contrast test provides evaluations that will help you see better in low light after surgery, improve your vision while driving, and reduce halo symptoms and glare during night driving. Special or wavefront LASIK can reduce high-order aberrations and improve contrast sensitivity.
Night vision problems
Night blindness is the inability to see well at night or under low light conditions. It may stem from a problem in the ability of the cells in the retina to provide vision in dim light. The night blindness test checks the pigment cells in the patient’s retina. Additionally, vision is assessed in dim light during the test.
Since eye pressure affects peripheral vision, visual problems become particularly pronounced in the dark and when driving. Cataracts can cause difficulty in driving, especially due to discomfort from the headlights of oncoming vehicles at night. Night driving is an activity that requires good contrast sensitivity for safety.
Diagnosis of eye diseases
Low contrast sensitivity may be a sign of certain eye diseases. In particular, contrast sensitivity decreases in diseases such as cataracts, glaucoma, or diabetic retinopathy. One of the most common symptoms of diabetic retinopathy is weakness in night vision.
The contrast sensitivity test helps determine whether you have visual errors known as higher-order aberrations or other issues that can be corrected with special glasses or eye surgery. If a diagnosis of poor contrast sensitivity is made, you may be advised to wear yellow-filter corrective lenses to improve your contrast discrimination ability.
Driver’s license examinations
The mesopic contrast test may be part of the evaluation process in eye examinations for driver’s licenses. Those with night blindness can drive from one hour after sunrise until one hour before sunset. In cataract disease, driver’s licenses are issued provided that minimum standards are met for each group.
How is the Mesopic Contrast Test Performed?
The test follows a standard procedure. Your eye specialist will explain how the test will be conducted and complete the necessary preparations.
Preparation before the test
The test is usually performed while wearing glasses or contact lenses. You do not need to remove your corrective lenses. Additionally, the test can be applied separately to each eye or with both eyes open. Your doctor will decide which method is appropriate based on your condition.
Your pupil sizes are measured before the test. This measurement is performed in the same environment as the lighting level during the test. This step is important because your pupil size can affect the test results.
Routine checks such as anterior and posterior segment examination, intraocular pressure measurement, and refraction measurement are completed. These evaluations are necessary for the test to be performed accurately.
Devices used during the test
The most commonly used device in the mesopic contrast test is the Mesotest II. This device is specifically designed to measure mesopic vision and glare sensitivity. It is a standard unit approved by the German Ophthalmology Society and meets the requirements of Section 7 of DIN 58220 Standard.
The device uses LED lighting and the size of the Landolt ring is equivalent to VA 0.1 = 6/60. Contrast levels are set at 1:23, 1:5, 1:2.7, and 1:2. The test sequence is programmed, ensuring reliable operation.
Free-field tests are conducted under normal vision conditions, without device adaptation. The unit is sized so that it will not be affected by patients from different pupil distances. Since it is a closed viewer, measurements can be made even in bright rooms.
Pelli Robson charts or sinusoidal wave lines can also be used. These methods involve targets consisting of blurred, parallel open and dark bars. Some devices contain bright light sources to simulate glare conditions like oncoming vehicle headlights during night driving.
Spatial frequency measurements
During the test, measurements are made at different spatial frequencies. Evaluations are conducted at spatial frequencies of 0.5, 1.5, 3.0, 6.0, 12.0, and 24.0 cycles/degree. These frequencies represent different levels of visual detail.
In the contrast sensitivity test, spatial frequencies between 0.5-1.5 cycles/degree are defined as low, between 3.0-6.0 cycles/degree as medium, and between 12.0-24.0 cycles/degree as high spatial frequency. In the system where each black and white bar is first presented at low contrast, the contrast is then automatically increased by the device.
The first moment you notice the lines is recorded. Four contrast levels are tested without reflection at an ambient light of 0.032 cd/m², while four contrast levels with reflection are evaluated at an ambient light of 0.10 cd/m².
Things to consider during the test
You are asked to sit in a comfortable position throughout the test. Keep your eyes naturally open and focus on the targets shown. Inform your doctor as soon as you clearly see the lines or rings.
The device can be controlled by a manual control unit or a computer. Your test results are printed and stored for data management purposes. The compact unit weighs only 7.8 kg and is portable, allowing it to be used in different environments.
Frequently Asked Questions
Many patients ask similar questions about the mesopic contrast test. Here are the most frequently asked topics about this test and their answers.
Is the test painful?
The mesopic contrast test is a completely painless examination. It does not involve any physical contact or intervention in the eye. During the test, you are only asked to look at the screen from a certain distance.
Visual tests are generally non-invasive procedures. Although light sources are directed to your eyes, this does not cause discomfort. You will sit in a comfortable position throughout the test and focus naturally on the targets shown.
Some patients may experience slight discomfort due to bright light sources. However, this is a temporary condition inherent to the nature of the test. Once the test is completed, your eyes quickly return to normal.
When are test results obtained?
Your test results are usually evaluated on the same day. Your eye specialist immediately reviews the measurements taken during the test and informs you. Therefore, you will not experience a long waiting period.
In cases requiring detailed reporting, the analysis of results may take a bit longer. Especially in pre-operative evaluations or the diagnosis of complex eye diseases, your specialist reviews all data comprehensively. This process may take a few days.
Test results are printed and added to your medical file. Thanks to digital record systems, your data is securely stored and can be compared in future examinations. However, results are evaluated immediately in emergencies.
Who is required to take the mesopic contrast test?
Individuals with complaints of night blindness must undergo this test. Especially if you have difficulty driving in the dark, it is necessary to measure your contrast sensitivity. This evaluation is vital for night driving safety.
For patients planning refractive surgery, the mesopic contrast test is one of the mandatory pre-evaluation tests. Your visual quality in low light must be measured before surgeries such as LASIK or similar. The results of this test serve as a reference point to determine your expectations after surgery.
Patients who will undergo cataract surgery also undergo this test. Monitoring the changes in your contrast sensitivity before and after surgery indicates the success of the treatment. Similarly, this test may be a requirement for pilots and professional driver candidates.
The mesopic contrast test is also regularly performed in the follow-up of certain eye diseases. Individuals with glaucoma, diabetic retinopathy, or macular diseases should periodically repeat contrast sensitivity measurements. This way, the progression of the disease is evaluated objectively.
Should glasses be removed before the test?
If you wear glasses or contact lenses, it is recommended to wear them during the test. Your corrective lenses do not affect the accuracy of the test results. In fact, it is more accurate to conduct the test with your glasses to evaluate your level of vision in daily life.
Your eye specialist first measures your corrected vision. That is, the test is conducted with your glasses or lenses. Then, if necessary, an uncorrected measurement can also be taken. This comparison helps to identify the source of your vision problems.
Your glasses are a medical tool and do not need to be removed during the examination. Unless your doctor gives you special instructions, continue wearing your lenses. It is important for your eyes to be comfortable and reflect your natural vision state during the test.
The mesopic contrast test is an important examination method that objectively evaluates your vision quality, especially while driving at night. If you have difficulty distinguishing objects in low light, this test provides you with clear answers. Therefore, you obtain vital information regarding your night driving safety.
The test is completely painless, and you will learn your results on the same day. Knowing your contrast sensitivity is crucial for the success of treatments such as cataract surgery, LASIK, or monitoring diseases like glaucoma and diabetic retinopathy.
Do not ignore your night vision problems. Consult your eye health specialist immediately and have your mesopic contrast test done. Make an appointment to contact us here.
