Metropsis Visual Function Assessment

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Precise tests of acuity, spatial and temporal contrast, colour and stereo vision

Metropsis is a complete test suite suitable for clinical, pre-clinical research, applied vision research, drug trials, screening, sports science and human factors research. The tests have been developed to investigate diseases of the eye and the brain, as well as changes in visual functions as a secondary effect of systemic disorders, such as cardiovascular diseases or neurological dysfunctions.

Guide Price: £13250

SKU: M0400

Achromatic spatial contrast sensitivity function

Measurements of spatial luminance contrast sensitivity functions are obtained using standard psychophysical procedures and stimuli.

Metropsis provides accurate measurements of the observer's ability to see low contrast spatial patterns, making it very suitable for assessing and monitoring eye diseases, such as age-related macular degeneration and glaucoma, or to evaluate visual functions of systemic disorders, such as cardiovascular or neurodegenerative diseases, and diabetes.

The system is automated and runs on an iMac computer. Default test protocols are preset and locked for quick and easy testing; however, the psychophysical and stimulus parameters are highly configurable, and can be unlocked for advanced users.

For advice on setting up your own protocols, please contact our Staff Scientist.

The Limitations of Standard Eye Charts

Images in the ‘real world’ include objects of various sizes (spatial frequencies) and contrast.

Although eye charts can provide a quick assessment of spatial resolution, they are limited to one level of contrast, to a high spatial frequency content, and only test the central visual field. For this reason, they often miss significant losses in contrast sensitivity caused by retinal dysfunctions occurring in the peripheral visual field, or due to more general ophthalmological or neurological disorders.

For example, it has been reported that some patients with multiple sclerosis show a significant loss in the medium range of the contrast sensitivity function (CSF), which is not reflected by measurements of visual acuity obtained with standard visual acuity charts [Regan et al, Brain, 1981 (2), 333-50].

Similar discrepancies between visual acuity measurements and contrast sensitivity for low and medium spatial frequencies have been reported also for patients affected by amblyopia, astigmatic error, cataract, diabetes, glaucoma, keratoconus, ocular hypertension, optic neuritis, and papilloedema. Conventional visual acuity tests are also rarely related to functions such as mobility, sports, face recognition, or driving [for a comprehensive review, see: Russell et al., 1995, Clinical and Experimental Optometry (78), 43-57].

Thus, for a more detailed assessment of spatial visual capability, contrast letter charts and measurements of contrast sensitivity are more informative.

 

Contrast Sensitivity - EDTRS Chart (based on the Pelli-Robson Chart)

John Robson, co-founder of Cambridge Research Systems

Professor John Robson FRS, co-inventor of the original printed Pelli-Robson chart, was one of Cambridge Research Systems' founders. We're pleased to offer this updated and automated test, which measures contrast sensitivity using letters with customised spatial frequencies.

Our computerised letter-contrast test offers many advantages over printed contrast sensitivity charts:

  • user-defined set of spatial frequencies
  • finer contrast range
  • very low contrast levels
  • different light levels can be used
  • easy, quick and efficient to score

Automated Pelli Robson Chart

References

Contrast sensitivity is a measure of the amount of contrast required to detect or discriminate an object. This ability has traditionally been measured using sinusoidal gratings of different spatial frequencies. However, it has been suggested [Pelli et al., 1988, Clin. Vision Sci. (2),3,187-199], that the measurement of two or three well-chosen spatial frequencies tuned around the human contrast sensitivity peak, can adequately describe the contrast sensitivity function. The authors also claim that the standard letter-based acuity chart offers a satisfactory method for determining a subject’s high contrast acuity.

 

Achromatic Contrast Sensitivity Function (aCSF)

The aCSF protocol measures contrast sensitivity using achromatic Gabor patches which consist of sinusoidal gratings convolved with a cosine Gaussian function.

Contrast sensitivity is measured across 7 spatial frequencies which are randomly interleaved during the test. For each spatial frequency, the test measures the minimum amount of contrast required to discriminate the grating from the homogeneous grey surround.

In each trial, the Gabor patch may be presented with either vertical or horizontal orientation.

 

The observer’s task consists in discriminating the grating’s orientation by pressing the right button of the response box if the orientation is horizontal, or the top button if the orientation is vertical.

When the experiment is complete, the data are plotted and fit as a graph of contrast sensitivity function.

 

 

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