Perception – Vision (Contrast Sensitivity)

Perception – Vision (Contrast Sensitivity)

LASA filenames:
LASA157

Constructs: contrast sensitivity values, self-reported contrast sensitivity

Contact: Ruth van Nispen

Background
Several aspects of vision can be measured. Among these aspects are visual acuity, visual field, contrast sensitivity, color vision and depth perception. The visual acuity is the eye’s ability to see details nearby and at distance. The visual field is the total area a person can see when the gaze is fixed to one direction. Contrast sensitivity refers to the ability to distinguish an object from its background. Color vision is the ability to distinguish colors. Finally, depth perception is the ability to see in three dimensions. These aspects of vision can be measured using various tests.

Most definitions of visual impairment, which includes both low vision and blindness, only base their definition on the visual acuity and the visual field. For instance, the World Health Organization (WHO) defines low vision as a visual acuity of less than 6/18, but equal to or better than 3/60, or a corresponding visual field loss of less than 20 degrees in the better eye with the best possible correction. Blindness is defined as a visual acuity of less than 3/60, or a corresponding visual field loss of less than 10 degrees in the better eye with the best possible correction.1 Additional background information can be found under vision (self-report).

Measurement instruments in LASA – Contrast sensitivity values
Contrast sensitivity was assessed during the medical interview using the VCTS-6000-1 chart for near vision (Vistech Consultants, Dayton, OH, USA), which was placed at 30-40cm of the respondent’s face. Contrast sensitivity was measured at five different spatial frequencies (1.5, 3, 6, 12, and 18 cycles per degree). The chart consists of eight circles with lines, with decreasing contrast per spatial frequency. The respondent was asked to state whether the lines were oriented to the left, to the right, or upwards.

The reliability of the VCTS charts for distant contrast sensitivity is moderate to good (ICC=0.60 for test retest and ICC=0.63-0.83 for the inter observer reliability),2,3 and the criterion validity good.4 The reliability and validity of the VCST-6000-1 and the VCST-6500 can be regarded as similar, given the statistically non-significant difference between the average results of both charts.5

Contrast sensitivity was scored using the method described by Cornelissen et al.6 First, the scores on the contrast sensitivity chart were expressed in real contrast sensitivity values using table 1 (see below). Second, using the syntax presented below under ‘syntaxes’, the real contrast sensitivity variables were calculated. They were named seeoda, seeodb, [….], seeodf, where OD stands for right eye, and OS stands for left eye (the syntax displays the variables for LASA wave C, but the ‘c’ in the syntax can be replaced by a different LASA cycle).

After that, the area under the contrast sensitivity curve was calculated. In consultation with Professor Aart Kooiman (RUG), we chose to set the right-hand border of this curve at 24 cycles per degree. The calculation of the area under the curve results in a total score for the right eye and the left eye. The scores are used to calculate the contrast sensitivity of the best eye. As especially the low spatial frequencies are associated with reading7 and mobility8 difficulties, it might be informative to calculate a score for these frequencies separately. The following variables can be used when performing an analysis with contrast sensitivity:

  • seetotbe: this is the area under curve of the best eye.
  • seetotd1: this is seetotbe dichotomized, with the persons with the lowest 5% of the values vs. the remaining persons.
  • seeabe: this is the real contrast sensitivity score on the lowest spatial frequency (1,5 c/d) of the best eye.
  • seebbe: this is the real contrast sensitivity score on the second lowest spatial frequency (3 c/d) of the best eye.
  • seetotlf: this is the mean score of seeabe and seebbe.

A syntax is given for the calculation of these variables.

Table 1 : calculating the real contrast sensitivity values (between parentheses the new variable names).

Old values 1 2 3 4 5 6 7 8
Variable
*mvar112 (mctrey1)
/mvar117 (mctley1)		 3 7 12 20 35 70 120 170
*mvar113 (mctrey2)
/mvar118 (mctley2)		 4 9 15 24 44 85 170 220
*mvar114 (mctrey3)
/mvar119 (mctley3)		 5 11 21 45 70 125 185 260
*mvar115 (mctrey4)
/mvar120 (mctley4)		 5 8 15 32 55 88 125 170
*mvar116 (mctrey5)
/mvar121 (mctley5)		 4 7 10 15 26 40 65 90


Measurement instruments in LASA – Self-reported contrast sensitivity
The six questions below (freely translated from Dutch to English) were asked during the medical interview to assess the self-reported contrast sensitivity. The original Dutch version used in LASA can be found here.

The interviewer introduced the questions as follows:

“The following section concerns your vision in everyday situations. The questions can be answered with: almost never, sometimes, often, or almost always.

  1. Can you see better in cloudy weather as compared to in sunny weather?
  2. Do you suffer from glare under clear skies?
  3. Do you suffer from glare when you go from indoors to outdoors during the day?
  4. Do you see cars and cyclists approaching on the street?
  5. Do you notice that you regularly do not see doors, chairs etc., because you for example hit against them?
  6. Do you notice that you regularly do not see doorsteps, low tables or other things lying on the floor, because you for example hit against them?”

During the B-wave and C-wave, only the first three questions were asked.

Questionnaires
LASAB157 / LASAC157 / LASAD157 / LASAE157 / LAS2B157 / LASAF157 (medical interview, in Dutch)

Variable information
LASAB157 / LASAC157 / LASAD157 / LASAE157 / LAS2B157 / LASAF157
(pdf)

Availability of information per wave 1

BCDE
2B*		FGH

3B*		MB*IJK
Contrast sensitivity

MeMeMe----------
Self-reported contrast sensitivity

MeMeMeMeMeMe-------

1 More information about the LASA data collection waves is available here.

* 2B=baseline second cohort;
3B=baseline third cohort;
MB=migrants: baseline first cohort

Me=data collected in medical interview

Previous use in LASA
The contrast sensitivity was used in the study of de Boer et al. (2004), in order to examine whether impairments in near contrast sensitivity and other aspects of vision are associated with falls and fractures.


References

  1. World Health Organization. International statistical classification of diseases, injuries and causes of death, tenth revision. Geneva: WHO; 1993.
  2. Rubin GS. Reliability and sensitivity of clinical contrast sensitivity tests. Clinical Vision Science. 1988;2:169-77.
  3. Harper R, Doorduyn K, Reeves B, Slater L. Evaluating the outcomes of low vision rehabilitation. Ophthalmic Physiol Opt. 1999;19:3-11.
  4. Leat SJ, Woo GC. The validity of current clinical tests of contrast sensitivity and their ability to predict reading speed in low vision. Eye. 1997;11(Pt6):893-9.
  5. Woo GC, Bohnsack H. Comparison of the Distance and NearVistech Vision Contrast Test Systems (VCTS). Canadian Journal of Optometry. 1986;48:12-5.
  6. Cornelissen FW, Bootsma A, Kooijman AC. Object perception by visually impaired people at different light levels. Vision Res. 1995;35:161-8.
  7. Rubin, GS & Legge, GE (1989). Psychophysics of reading – V1. The role of contrast in low vision. Vision Research, 29, 79-91.
  8. Marron, JA & Bailey, IL (1982). Visual factors and orientation mobility performance. Journal of Optometry and Physiological Optics. 59. 413-426.


Date of last update: June 2016 (Vera Rooth, Ruth van Nispen, Marieke Pronk)