Stereopsis is the process through which a person can perceive their surroundings in 3-D, experience the sensation of depth, closeness, or distance of each of the objects in a scene. It occurs due to a mechanism known as retinal disparity or binocular disparity. The retina is the spot on the inner lining of the back wall of the eye, which recognizes light and images. Each of the retinas transmit slightly different pictures of a scene, and the brain combines both images to create a three-dimensional (3D) vision. The somewhat different images of a view are because of different positions of the eyes on the head. The brain uses the information provided by both retinas to calculate depth in the scene. It provides a significant basis for depth perception.
Therefore, stereopsis is linked to a compelling perception of 3-dimensionality or solidity, i.e., a phenomenal impression of realism and a distinct sense of space between objects. It is fundamental in daily life. One needs a stereoscopic vision to perform everyday tasks such as driving. Bad stereopsis can affect a person's daily work, particularly in professions that require a good close up, like surgeons, footballers, sportspeople, precision machines operators, and operators of equipment that can cause hand or bodily injuries. Estimates indicate that more than 5% of the American population has challenges with relief or depth vision and diagnosing them is vital to optimal visual health.
Also Known As
- Binocular vision
- Stereoscopic vision
- Binocular depth perception
- Stereoscopic depth perception
The stereopsis test can be conducted at the doctor’s office, eye clinic, or hospital by:
- A technician
- An optometrist
- An ophthalmologist
The slightly different perspective of the eyes is because images fall on different points on the retina of each eye. This retinal disparity is the critical aspect assessed in a stereopsis test, which is also known as a stereo test. Tests of near stereoacuity can help the doctor in the management of amblyopia and strabismus. Distance stereoacuity can provide important information that helps the doctor in the management of distance fixation strabismus.
Stereoscopic vision needs the coordination of both eyes. It also requires that both eyes have excellent sight and are correctly aligned. Patients with certain anomalies that affect the visual capacity of the eye or ocular alignment can have their stereopsis compromised. Frequently, it occurs in patients with:
- Squints – The disorders happen when there is a variation in the position of the patient’s eyes, causing their gaze to be aimed at different points when focusing.
- Amblyopia (lazy eye) – It arises due to the underdevelopment of the visual function of one of the eyes. The condition is linked to strabismus but can also occur due to other causes.
Any other disorder, such as brain trauma, eye injury, cataract, etc., that affects the ability of the eyes to see correctly can affect the patient’s stereoscopic vision and impact their ability to judge the distance of objects or depth vision.
Preparation & Expectation
The stereopsis test is a simple test that doesn’t require preparation, and there is no discomfort.
Type of Examination
The standard tests for stereopsis and stereo acuity fall under two categories:
- Random dot stereo tests
The tests use images of stereo pictures imprinted on a background of random dots.
- Contour stereo tests.
The tests use images in which the figures targeting each eye are separated horizontally.
Stereopsis consists of two main components - gross or coarse stereopsis, which is vital for significant depth levels, and fine stereopsis, essential for minor depth levels. Most stereo tests measure both components.
There are various methods to examine stereopsis, both in adults and children. Somewhat different images are presented to each eye in a way that a patient with stereovision will perceive a three dimensional (3-D) image. It may be done using:
- Head-mounted display technology
- Anaglyphs - visible with red-green glasses
- Lenticular lenses - evident with the naked eye
- Vectographs - visible through polarized glasses
The changes from one eye to the other can vary according to the degree of stereo acuity the doctor wants to detect. Therefore, a stereo acuity test is a series of stereo tests for selected degrees.
- Random dot stereo tests
The doctor may test the patient’s stereopsis ability using random dot stereo targets viewed through polaroid glasses. Many testing methods fall under this category. For example, the Random test requires the patient to identify hidden geometric figures from a series of images. It uses single plates and has several levels. In the Test E method, the patient is shown a series of letter E images and has to identify the side to which each letter is facing.
- Contour stereo tests.
Titmus stereo tests are the most frequently used in this category. The patient will put on 3-D glasses to view a target and identify the 3-D image in it. The typical examples are the test of the fly, animal test and the test of the circles.
Modern digital instruments (stereoscopes) are used for dynamic vision to examine drivers and professionals such as athletes.
In normal results, the patient will be able to see objects in 3-D and have a proper perception of depth and distance. Abnormal results may indicate a partial defect or a stereoblindness, which is a complete deficiency in stereopsis. The causes of the stereopsis deficiency include strabismus, amblyopia and blindness in one of the patient’s eyes.
The doctor may recommend vision rehabilitation therapy which might enhance the patient’s stereoscopic vision through a series of exercises that may help to strengthen and improve eye movement. The doctor may also recommend eye surgery, such as cataract or refractive surgery to treat amblyopia. Furthermore, some treatments can stimulate brain cells and activate the retinal disparity signals and help the patient to recover the stereoscopic vision.
Risks & Complications
Stereopsis and stereo acuity tests are simple and straightforward. They present no risks or complications.