Functional vision is the physical and interpretive ability of the visual system to produce images. According to the channel model, the eyes use several different methods (channels) to interpret and process various kinds of visual information and create a cohesive image. Functional vision is the simultaneous composite of all the information from the different vision channels. Testing and evaluating patients' functional vision is the key to understanding how well they see in the real world. Demonstrating functional vision can help produce meaningful corrective outcomes for patients.
Comparing Functional Vision Testing with Other Methods
Nearly all eye care patients are familiar with the Snellen 20/20 Visual Acuity scale, in which one reads a series of black letters on a white background. While this method establishes a standard, it is limited in what it evaluates regarding the quantity of vision. Acuity testing is not effective in providing a complete picture of how well the patient's vision functions in daily life. A greater understanding of a patient’s vision in various conditions is crucial when making decisions that could affect surgical outcomes. Determining functional vision has become the major factor in everything from providing the best spectacle correction and contact lens fit, to surgical decisions and predicted outcomes in cataract and refractive surgery.
For an example of how 20/20 testing does not provide a conclusive visual diagnosis, consider the case of a patient who can see the smallest letters on the eye chart, yet still complains of glare. Although the patient has 20/20 vision, they have difficulty seeing clearly at night or in a dimly-lit room. In this situation, a 20/20 rating does not equate to perfect vision in all circumstances. To obtain a complete understanding of how well the patient's vision system performs in the wide variety of situations found in everyday life, other methods of testing are needed.
Analyzing Functional Vision
The essence of functional vision is the ability to see in both high-light and low light situations. Relying heavily on contrast sensitivity studies, functional vision analysis grants the ability to assess or quantify the patient's vision under varying environmental conditions during the functional vision exam.
Functional vision analysis is performed using the contrast sensitivity methodology of linear sine wave gratings in five different spatial frequencies (1.5, 3,6,12, an 18 cycles per degree). Testing is performed under precisely calibrated simulations of photopic (day) and mesopic (night) conditions, both with and without glare. The points at which the patient is no longer able to distinguish these images are plotted onto the standardized contrast sensitivity graph. The curve of the patient's graph provides an accurate assessment of how well his vision functions in everyday life. Functional vision analysis, as measured with contrast sensitivity testing, is a comprehensive and accurate way to understand the health and performance of all channels of the vision system in their function together as a whole.
Functional Vision Analysis with Stereo Optical
Stereo Optical has introduced to the clinical research market the only functional vision analysis device meeting ANSI standards. The Functional Vision Analyzer™ is self-calibrating instrument incorporating the F.A.C.T.® contrast sensitivity test. Combined with EyeView® software, the Functional Vision Analyzer™ system is a powerful and practical solution for refractive, cataract, and General Ophthalmologists to test and demonstrate functional vision under precisely controlled variable conditions. For more details about the Functional Vision Analyzer™ and EyeView®, click here.
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