Perception – Vision (Visual Acuity)

Perception – Vision (Visual Acuity)

LASA filenames:
LASA191
LASA192

Constructs: VAS score right/left eye, stenopeic VAS score right/left eye, Snellen visual acuity right/left eye, stenopeic Snellen visual acuity right/left eye, vision related quality of life.

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. Visual acuity is the eye’s ability to see details at near and distance. A visual field is the entire area a person can see when their gaze is fixed in one direction. Contrast sensitivity refers to the ability to distinguish an object from its background. Color vision is the ability to distinguish colors. 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 visual acuity and visual field. The WHO defines low vision as a visual acuity of less than 6/18, but equal to or better than 3/60, and/or a visual field loss less than 20 degrees around the central fixation point in the better eye with the best possible correction1. Blindness is defined as a visual acuity of less than 3/60, a visual field loss to less than 10 degrees in the better eye with the best possible correction.1 More background information can be found under vision (self-report).

Measurement instruments in LASA – VAS and Snellen visual acuity (LASA*191)
Visual acuity was measured during the medical interview, using the Colenbrander 1-meter chart. This chart follows the Early Treatment Diabetic Retinopathy Study (ETDRS) layout, which includes Sloan letters, proportional spacing and the sizes of the letters progress systematically in logarithmic progression. It requires 1 dioptrie (dpt) over the distance correction and has a cord attached to accurately maintain the viewing distance.2 The participants were tested at a distance of one meter, and both eyes were tested separately using an occluder to cover the other eye. Participants were asked to sit on a chair in front of the chart which was fixed on a music stand and adjusted to the participant’s height. The interviewer made sure there was enough light and no inappropriate reflection of light on the chart. Glasses or contact lenses, with a correction for the distance, were worn if necessary. Participants with multifocal glasses were asked to look straight through the correction for distance and not through the reading addition. Furthermore, the visual acuity of both eyes was measured with the use of pinholes if the participant did not reach the maximum visual acuity, again the eyes were tested separately. With the use of pinholes it is possible to measure the visual acuity of the eye that can be attained by lenses to correct for refraction errors or, in some cases, to measure and estimate the visual acuity of the eye after a cataract surgery of a person with cataract. Interviewers were trained according to a strict protocol. The interviewers pointed out the letters on the chart and started with the letters on the 2m line. The participant had to tell the interviewer which letter he/she was pointing to. Measurements were recorded on audiotape and a random selection was checked to examine whether the measurements were conducted correctly. The ETDRS chart has shown to be accurate and has high reliability, with similar precision for varying of levels visual acuity.3,4,5

The administration of the Colenbrander 1-meter chart yields two measures of visual acuity.

  1. VAS score. This score is calculated by summing the scores corresponding to each of the letters read correctly by the respondent. The lowest possible score is 10 (reading zero letters correctly). Each letter that is read correctly yields one additional point, except for the letters in the top two lines. For the upper line, each letter read correctly yields 1.67 points. For the second line, each letter read correctly yields 1.25 points. The highest possible score is 100.
  2. Snellen visual acuity.

For each of the visual acuity measurements, reasons for not or partly running the test were documented. The VAS or Snellen visual acuity can be converted into a logMAR visual acuity.

Measurement instruments in LASA – VCM1 questionnaire (LASA*192)
The Vision-related quality of life Core Measure (VCM1 questionnaire) contains 10 questions, primarily concerned with feelings associated with vision loss. The Dutch version that was used can be found here. Each question has six response options, ranging from ‘not at all’ (0) to ‘all the time’ (5). The total score is the summed score of the 10 questions, divided by ten (range 0-50). The VCM1 has a high reliability (Cronbach’s alpha=0.93) and validity.5 Besides the 10 questions of the VCM1, two additional questions were asked prior to the administration of the VCM1 questionnaire:

The interviewer reads out loud the following instructions to the respondent:

“The following questions are about possible changes in your vision during the past month. If you wear glasses or lenses or use magnifying devices such as magnifiers for some activities, please answer the questions as if you would use them.

1. Did you have an eye operation or eye/visual acuity measurement during the past month? yes / no

2. Did you receive different glasses or contact lenses during the past month, or did your vision suddenly change during the past month? yes / no”

Below are the questions of the VCM1 questionnaire:

“By answering the following questions, think about how your vision has affected your feelings during the past month, and give the answer that best suits you. You can choose from: never (0), seldom (1), sometimes (2), reasonably often (3), often (4) very often (5).

  1. Have you felt embarrassed because of your eyesight?
  2. Have you felt frustrated or annoyed because of your eyesight ?
  3. Have you felt lonely or isolated because of your eyesight ?
  4. Have you felt sad or low because of your eyesight ?
  5. How often have you worried about your eyesight getting worse?

How often has your eyesight made you concerned or worried concerning the following items, during the past month.

  1. Your general safety at home?
  2. Your general safety outside of your home?
  3. Coping witheveryday life?
  4. How often has your eyesight stopped you from doing the things you want to do?
  5. How much has your eyesight interfered with your life in general? “


Questionnaires
LASAE191 / LASAF191 / LASAG191 / LASAH191 / LAS3B191 (medical interview, in Dutch);
LASAE192 / LASAF192 / LASAG192 / LASAH192 (medical interview, in Dutch)

Variable information
LASAE191 / LASAF191 / LASAG191 / LASAH191 / LAS3B191
(pdf);
LASAE192 / LASAF192 / LASAG192 / LASAH192
(pdf)

Availability of information per wave ¹

BCDE
2B*		FGH

3B*		MB*IJK
VAS score

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Snellen visual acuity

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VCM1 questionnaire

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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
Van Nispen et al. (2010) assessed the psychometric quality of the VCM1 and the feasibility in a community-based sample:

Van der Aa (2015) used the VAS score and the Snellen visual acuity score to select LASA-respondents with normal vision (to compare with visually impaired older adults originating from outpatient low vision rehabilitation centers).

Other:

  • Rooth V. Association between vision and people’s investment in independence. Masterthesis VU: 2014 (supervisors: DJH Deeg, RMA van Nispen).


References

  1. World Health Organization. International statistical classification of diseases, injuries and causes of death, tenth revision. Geneva: WHO; 1993.
  2. Colenbrander A. Measuring vision and vision loss. In: Duane TD, Tasman W, Edward A. Duane’s Clinical Ophthalmology. Vol 5. Philadelphia: Lippincott Williams & Wilkins; 2001:chap 51.
  3. Beck RW, Maguire MG, Bressler NM, Glassman AR, Lindblad AS, Ferris FL. Visual acuity as an outcome measure in clinical trials of retinal diseases. Ophthalmology. 2007 Oct;114(10):1804–1809.
  4. Elliott DB, Sheridan M. The use of accurate visual acuity measurements in clinical anti-cataract formulation trials. Ophthalmic Physiol Opt. 1988; 8(4):397-401.
  5. Schulze-Bonsel K, Feltgen N, Burau H, Hansen L, Bach M. Visual acuities “hand motion” and “counting fingers” can be quantified with the freiburg visual acuity test. Invest Ophthalmol Vis Sci. 2006 Mar; 47(3):1236-40.
  6. Frost NA, Sparrow JM, Durant JS, Donovan JL, Peters TJ, Brookes ST. Development of a questionnaire for measurement of vision-related quality of life. Ophthalmic Epidemiol. 1998;5:185-210.


Date of last update: March 14, 2018 (LS)