National Health and Nutrition Examination Survey

2005-2006 Data Documentation, Codebook, and Frequencies

Vision (VIX_D)

Data File: VIX_D.xpt

First Published: April 2008

Last Revised: NA

Component Description

The NHANES Vision Examination data will be used to:

measure the prevalence of visual acuity impairment (visual acuity worse than 20/40) in the U.S. population;
measure the distribution of refractive error in the U.S. population; and
evaluate functional impairment related to vision.

The NHANES 2005–2006 Vision Examination consisted of three parts:

Eye Glasses Prescription Determination – For persons 12 years of age and older, eye glass prescriptions are measured when eye glasses for viewing distant objects are available.
Distance Visual Acuity and Objective Refraction/Keratometric Evaluation – For all persons 12 years and older, distance vision is assessed regardless of whether they wear eyeglasses or contacts; the refraction test measures the person’s refractive error and corneal curvature.
Vision Near Card Test – For persons 50 years and over, visual acuity at near was assessed.

Eligible Sample

All sample persons aged 12 years and older are eligible to participate in (1) automated determination of prescription for eye glasses used to view distant objects, (2) distance visual acuity assessment and (3) automated objective refraction/keratometric evaluation. Sample persons aged 50 years and older are also eligible for the Near Card visual acuity test.

Participants were excluded from the Vision Exam if they were determined to be completely blind or unable to see in both eyes based on the following question asked in the Sample Person Household Interview: “With both eyes open, can you see light?” Participants were also excluded from the exam if they had a severe eye infection (i.e., purulent discharge with redness and inflammation) in one or both eyes. A participant wearing an eye patch would not be excluded; however, the exam would not be conducted on the affected eye.

Protocol and Procedure

The vision exam included measurements of:

eyeglass prescription for glasses used to view distant objects;
presenting visual acuity with current correction;
visual acuity incorporating objective refraction; and
near-vision acuity.

Health technicians completed screening questions that involved observation of the subject to determine if the medical exclusion criteria applied. The sample person was then asked additional screening questions (e.g. do they wear any distance correction) to determine which measurements in the examination protocol were relevant.

If the sample person wore eyeglasses to see distant objects, their current eyeglass prescription was determined by using the Nidek Auto Lensmeter Model LM-990A. The Nidek Auto Refractor Model ARK-760 instrument was used to assess visual acuity. Presenting visual acuity was tested with whatever distance correction the participant usually wears, if any. If the participant’s visual acuity with their usual correction was 20/30 or worse, visual acuity was further assessed using the objective refraction measurements as the “correction factor” for the participant.

For sample persons aged 50 years and older, near vision was tested with a near vision card, and usual reading distance was recorded prior to measuring their presenting distance visual acuity.

The Nidek Auto Lensmeter Model LM-990A and the Nidek Auto Refractor Model ARK-760 instruments have been used since 1999.

The Vision Examination Protocol is discussed in detail in the NHANES Vision Procedures Manual.

Quality Assurance & Quality Control

A variety of quality control procedures were used to ensure the accurate and reliable collection of these data. Calibrations of the lensmeter and the autorefractor were performed prior to conducting examinations at each survey location, and weekly thereafter. At regular intervals, NCHS and contractor staff observed vision examinations conducted in the MEC to evaluate whether appropriate procedures and techniques were being followed. Retraining sessions were conducted with all MEC health technicians to review data collection procedures.

The MEC health technicians conducted the vision examination. These technicians received 8 weeks of training initially, and subsequently underwent updates and remedial training as needed.

Technicians referred to the Vision Procedures Manual for specific instructions for the administration of this component.

For details on the QA/QC process for this component, please refer to the NHANES Vision Procedures Manual.

Data Processing and Editing

Automated data collection procedures for the survey were used to collect the vision data. Eyeglass prescription data were captured electronically by the lensmeter, and the objective refraction and visual acuity data were captured by the autorefractor. Both sets of data were then transferred to the survey database system. Visual acuity data values were also captured manually by the technician and entered directly into the database.

During the editing process, all data were examined for logical inconsistencies and technician or equipment errors. Back-end edits of the data were performed when errors were detected.

Variable-Specific Editing:

VIDLVA and VIDRVA – Presenting visual acuity variables

These variables provide the participant’s presenting visual acuity, tested with the autorefractor, while wearing whatever distance correction the participant usually wears, if any. The values were automatically captured from the autorefractor and also manually recorded by the technician. In cases of disagreement between the automatic and technician-recorded values, the values recorded by the technician were used (unless they were missing, in which case the machine-captured data were used).

VIDLOVA and VIDROVA – Visual acuity with objective refraction variables (measured only for eyes with presenting visual acuity of 20/30 or worse).

These variables provide the participant’s visual acuity, measured after incorporating information from the objective refraction measurements. The values were automatically captured from the autorefractor and also manually recorded by the technician. In cases of disagreement between the automatic and technician-recorded values, the values recorded by the technician were used (unless they were missing, in which case the machine-captured data were used).

Analytic Notes

Users are encouraged to note carefully the English instructions describing the various variables in the codebook documentation.

This dataset only contains data for the vision examination conducted in the MEC. There is another dataset containing household interview responses to the vision section (VIQ) of the Sample Person Questionnaire. Data from the two datasets can be combined and analyzed using the guidelines provided by NCHS. Note that not all of the same persons appear in the household interview and MEC examination datasets.

Please refer to the Analytic Guidelines for further details on the use of sample weights and other analytic issues. The Analytic Guidelines are available on the NHANES website.

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:: SEQN
SAS Label:: Respondent sequence number
English Text:: Respondent sequence number
Target:: Both males and females 12 YEARS - 150 YEARS

VIQ110 - SP has a severe eye infection?

Variable Name:: VIQ110
SAS Label:: SP has a severe eye infection?
English Text:: Does SP appear to have a severe eye infection in one or both eyes?
English Instructions:: The examiner observes the examinee's eyes for possible infection. If either eye has a sign of infection, the examinee is excluded from the vision component.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
1	Yes	0	0
2	No	6558	6558	VIQ130
.	Missing	422	6980

VIQ121 - Which eye(s) infected?

Variable Name:: VIQ121
SAS Label:: Which eye(s) infected?
English Text:: if VIQ110 = "Yes" record which eye(s) is/are affected.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
1	Right	0	0	End of Section
2	Left	0	0	End of Section
3	Both	0	0	End of Section
.	Missing	6980	6980

VIQ130 - Is SP wearing an eye patch?

Variable Name:: VIQ130
SAS Label:: Is SP wearing an eye patch?
English Text:: Is SP wearing an eye patch?
English Instructions:: Although the SP is not excluded from the vision examination because he/she wears an eye patch, the examiner will not conduct the examination on the affected eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
1	Yes	1	1
2	No	6557	6558	VIQ150
.	Missing	422	6980

VIQ141 - Which eye has eye patch?

Variable Name:: VIQ141
SAS Label:: Which eye has eye patch?
English Text:: If VIQ130 = "Yes" record which eye(s) is/are affected.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
1	Right	1	1
2	Left	0	1
3	Both	0	1
.	Missing	6979	6980

VIQ150 - Glasses/contact lenses for near work?

Variable Name:: VIQ150
SAS Label:: Glasses/contact lenses for near work?
English Text:: Do you wear glasses or contact lenses for reading or near work?
Target:: Both males and females 50 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
1	Yes	1696	1696
2	No	302	1998	VIXNC1
9	Don't know	0	1998
.	Missing	4982	6980

VIQ160 - Glasses/contact lenses available?

Variable Name:: VIQ160
SAS Label:: Glasses/contact lenses available?
English Text:: If VIQ150 = "Yes", record if the examinee brought their near work glasses, contacts, or a combination of glasses and/or contacts to the testing facility.
Target:: Both males and females 50 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
1	Yes	1515	1515
2	No	181	1696	VIXNC1
.	Missing	5284	6980

VIQ170 - Glasses or contacts worn for near test?

Variable Name:: VIQ170
SAS Label:: Glasses or contacts worn for near test?
English Text:: If VIQ160 = "Yes", record whether the examinee wore glasses, contacts, or a combination of glasses and/or contacts for test of near vision.
Target:: Both males and females 50 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
1	Glasses	1483	1483
2	Contacts	31	1514
3	Both glasses and contact lenses	1	1515
.	Missing	5465	6980

VIXNC1 - Line read on near card

Variable Name:: VIXNC1
SAS Label:: Line read on near card
English Text:: The number of the last line the examinee read with one or fewer misses, that is the number of the last line where the examinee read at least four out of the five characters correctly. Line 1 has the largest print: line 5 has the smallest print.
Target:: Both males and females 50 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0 to 5	Range of Values	1994	1994
8	Could not obtain	4	1998
.	Missing	4982	6980

VIXNC2 - Testing distance of near card

Variable Name:: VIXNC2
SAS Label:: Testing distance of near card
English Text:: Record to the nearest inch the distance from the center of the card to the examinee's brow.
English Instructions:: A measuring tape is used to determine the distance. (Rounding rule: Numbers less than 0.5, round down (example 16 1/4 = 16) and numbers equal to or greater than 0.5, round up (13 1/2 = 14, 21 3/4 = 22).)
Target:: Both males and females 50 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
1 to 35	Range of Values	1994	1994
88	Could not obtain	4	1998
.	Missing	4982	6980

VIQ180 - Eye surgery for near sightedness?

Variable Name:: VIQ180
SAS Label:: Eye surgery for near sightedness?
English Text:: Have you ever had eye surgery to treat or prevent nearsightedness or myopia?
English Instructions:: The interest is in laser or radial keratotomy (RK) surgeries used to improve nearsightedness. Some other terms to describe this surgery include: PRK, RK, Lasik, Eximer, or Refractive Surgery.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
1	Yes	94	94
2	No	6443	6537	VIQ200
9	Don't know	10	6547	VIQ200
.	Missing	433	6980

VIQ191 - Which eye(s) surgery - near-sightedness?

Variable Name:: VIQ191
SAS Label:: Which eye(s) surgery - near-sightedness?
English Text:: If VIQ180 = "Yes", record which eye(s) was/were operated on.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
1	Right	7	7
2	Left	4	11
3	Both	82	93
9	Don't know	1	94
.	Missing	6886	6980

VIQ200 - Eye surgery for cataracts?

Variable Name:: VIQ200
SAS Label:: Eye surgery for cataracts?
English Text:: Have you ever had eye surgery to treat cataracts?
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
1	Yes	350	350
2	No	6194	6544	VIQ220
9	Don't know	3	6547	VIQ220
.	Missing	433	6980

VIQ211 - Which eye(s) cataract surgery?

Variable Name:: VIQ211
SAS Label:: Which eye(s) cataract surgery?
English Text:: if VIQ200 = "Yes", record which eye(s) was/were operated on for cataracts.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
1	Right	62	62
2	Left	36	98
3	Both	247	345
9	Don't know	5	350
.	Missing	6630	6980

VIQ220 - Glasses/contact lenses worn for distance

Variable Name:: VIQ220
SAS Label:: Glasses/contact lenses worn for distance
English Text:: Do you wear glasses or contact lenses for distance vision, such as when you watch television?
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
1	Yes	2765	2765
2	No	3780	6545	VIXOCMT
9	Don't know	2	6547
.	Missing	433	6980

VIQ230 - Is distance correction available?

Variable Name:: VIQ230
SAS Label:: Is distance correction available?
English Text:: If VIQ220 = "Yes", record if examinee brought their distance correction to the testing center.
English Instructions:: The SP could be wearing the correction or brought it with them.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
1	Yes	2380	2380
2	No	385	2765
.	Missing	4215	6980

VIQ240 - Which type? Glasses or contacts?

Variable Name:: VIQ240
SAS Label:: Which type? Glasses or contacts?
English Text:: If VIQ230 = "Yes", record the type of correction (glasses, contacts, or a combination of glasses and contacts) the SP has with them.
English Instructions:: This specifies the type of correction worn by the SP for the presenting VA tests (VIDRVA and VIDLVA).
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
1	Glasses	1949	1949
2	Contacts	383	2332	VIXOCMT
3	Both glasses and contact lenses	48	2380
.	Missing	4600	6980

VIQ250 - Was prescription obtained?

Variable Name:: VIQ250
SAS Label:: Was prescription obtained?
English Text:: Did the examiner capture the prescription of the examinee's lens?
English Instructions:: This pertains to the lens prescription used for viewing distant objects.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
1	Yes	1991	1991
2	No	6	1997
.	Missing	4983	6980

VIXPRS - Prescription, right sphere

Variable Name:: VIXPRS
SAS Label:: Prescription, right sphere
English Text:: The prescription of the sphere in the right lens used for distance correction.
English Instructions:: For distance eyeglasses only.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
-14.25 to 11.75	Range of Values	1947	1947
88	Could not obtain	45	1992
.	Missing	4988	6980

VIXPRC - Prescription, right cylinder

Variable Name:: VIXPRC
SAS Label:: Prescription, right cylinder
English Text:: Prescription of the cylinder in the right lens used for distance correction
English Instructions:: For distance eyeglasses only
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0 to 8.25	Range of Values	1946	1946
88	Could not obtain	45	1991
.	Missing	4989	6980

VIXPRA - Prescription, right axis

Variable Name:: VIXPRA
SAS Label:: Prescription, right axis
English Text:: Prescription of the axis in the right lens used for distance correction
English Instructions:: For distance eyeglasses only.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0 to 180	Range of Values	1947	1947
888	Could not obtain	45	1992
.	Missing	4988	6980

VIXPLS - Prescription, left sphere

Variable Name:: VIXPLS
SAS Label:: Prescription, left sphere
English Text:: Prescription of the sphere in the left lens used for distance correction.
English Instructions:: For distance eyeglasses only.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
-14.5 to 11.5	Range of Values	1947	1947
88	Could not obtain	45	1992
.	Missing	4988	6980

VIXPLC - Prescription, left cylinder

Variable Name:: VIXPLC
SAS Label:: Prescription, left cylinder
English Text:: Prescription of the cylinder in the left lens used for distance correction.
English Instructions:: For distance eyeglasses only.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0 to 7	Range of Values	1948	1948
88	Could not obtain	44	1992
.	Missing	4988	6980

VIXPLA - Prescription, left axis

Variable Name:: VIXPLA
SAS Label:: Prescription, left axis
English Text:: Prescription of the axis in the left lens used for distance correction.
English Instructions:: For distance eyeglasses only
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0 to 180	Range of Values	1948	1948
888	Could not obtain	44	1992
.	Missing	4988	6980

VIXOCMT - Visual Acuity Comments

Variable Name:: VIXOCMT
SAS Label:: Visual Acuity Comments
English Text:: The examiner can note special circumstances related to a visual acuity test.
English Instructions:: These apply to distance vision tests.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
1	Monovision glasses/contacts worn for visual acuity	11	11
2	Cataract contact lenses worn for objective refraction	3	14
3	Contacts worn for objective refraction	17	31
4	Artificial eye	6	37
5	Monovision contacts worn for objective refraction	2	39
6	Contact in right eye only for presenting visual acuity	1	40
7	Contact in left eye only for presenting visual acuity	3	43
.	Missing	6937	6980

VIXORSM - OR right sphere, median

Variable Name:: VIXORSM
SAS Label:: OR right sphere, median
English Text:: Spherical dioptric power (median value of three objective refractions) of the examinee's right eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
-20 to 9.25	Range of Values	6324	6324
88	Could not obtain	203	6527
.	Missing	453	6980

VIXORCM - OR right cylinder, median

Variable Name:: VIXORCM
SAS Label:: OR right cylinder, median
English Text:: Cylindrical dioptric power (median value of three objective refractions) of the examinee's right eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0 to 8	Range of Values	6321	6321
88	Could not obtain	203	6524
.	Missing	456	6980

VIXORAM - OR right axis, median

Variable Name:: VIXORAM
SAS Label:: OR right axis, median
English Text:: Axis of refractive astigmatism (median value of three objective refractions) of the examinee's right eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0 to 180	Range of Values	6324	6324
888	Could not obtain	203	6527
.	Missing	453	6980

VIDORFM - OR right confidence level reading

Variable Name:: VIDORFM
SAS Label:: OR right confidence level reading
English Text:: The confidence level of the objective refraction reading for the right eye (mean of three measures).
English Instructions:: Lower values equate to less confidence in the objective refraction values.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
5 to 9	Range of Values	6363	6363
.	Missing	617	6980

VIXOLSM - OR left sphere, median

Variable Name:: VIXOLSM
SAS Label:: OR left sphere, median
English Text:: Spherical dioptric power (median value of three objective refractions) of the examinee's left eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
-21.5 to 11.25	Range of Values	6309	6309
88	Could not obtain	218	6527
.	Missing	453	6980

VIXOLCM - OR left cylinder, median

Variable Name:: VIXOLCM
SAS Label:: OR left cylinder, median
English Text:: Cylindrical dioptric power (median value of three objective refractions) of the examinee's left eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0 to 8	Range of Values	6306	6306
88	Could not obtain	218	6524
.	Missing	456	6980

VIXOLAM - OR left axis, median

Variable Name:: VIXOLAM
SAS Label:: OR left axis, median
English Text:: Axis of refractive astigmatism (median value of three objective refractions) of the examinee's left eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0 to 180	Range of Values	6309	6309
888	Could not obtain	218	6527
.	Missing	453	6980

VIDOLFM - OR left confidence level reading

Variable Name:: VIDOLFM
SAS Label:: OR left confidence level reading
English Text:: The confidence level of the objective refraction reading of the left eye (mean of three measures).
English Instructions:: Lower values equate to less confidence in the objective refraction values.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
5 to 9	Range of Values	6384	6384
.	Missing	596	6980

VIXKRM1 - Right keratometry radius flat curve (mm)

Variable Name:: VIXKRM1
SAS Label:: Right keratometry radius flat curve (mm)
English Text:: Keratometric measure. Radius of corneal curvature (in mm) in the least power meridian of the examinee's right eye (median of three measures).
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
6.74 to 9.77	Range of Values	6429	6429
88	Could not obtain	98	6527
.	Missing	453	6980

VIXKRD1 - Right keratometry power flat curve (D)

Variable Name:: VIXKRD1
SAS Label:: Right keratometry power flat curve (D)
English Text:: Keratometric measure. Dioptric power in the least power meridian of the cornea in the examinee's right eye (median of three measures).
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
34.5 to 50	Range of Values	6429	6429
88	Could not obtain	98	6527
.	Missing	453	6980

VIXKRG1 - Right keratometry axis flat curve (deg)

Variable Name:: VIXKRG1
SAS Label:: Right keratometry axis flat curve (deg)
English Text:: Keratometric measure. Axis of corneal astigmatism (in degrees) in the least power meridian of the examinee's right eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0 to 180	Range of Values	6429	6429
888	Could not obtain	98	6527
.	Missing	453	6980

VIXKRM2 - Right keratometry radius steep curve(mm)

Variable Name:: VIXKRM2
SAS Label:: Right keratometry radius steep curve(mm)
English Text:: Keratometric measure. Radius of corneal curvature (in mm) in the greatest power meridian of the examinee's right eye (median of three measures).
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
4.96 to 9.39	Range of Values	6429	6429
88	Could not obtain	98	6527
.	Missing	453	6980

VIXKRD2 - Right keratometry power steep curve (D)

Variable Name:: VIXKRD2
SAS Label:: Right keratometry power steep curve (D)
English Text:: Keratometric measure. Dioptric power in the meridian of the cornea with the greatest power in the examinee's right eye (median of three measures).
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
36 to 68	Range of Values	6429	6429
88	Could not obtain	98	6527
.	Missing	453	6980

VIXKRG2 - Right keratometry axis steep curve (deg)

Variable Name:: VIXKRG2
SAS Label:: Right keratometry axis steep curve (deg)
English Text:: Keratometric measure. Axis of corneal astigmatism (in degrees) in the greatest power meridian of the examinee's right eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0 to 179	Range of Values	6429	6429
888	Could not obtain	98	6527
.	Missing	453	6980

VIXKRMM - Right keratometry radius, average (mm)

Variable Name:: VIXKRMM
SAS Label:: Right keratometry radius, average (mm)
English Text:: Keratometric measure. Radius of corneal curvature (in mm) averaged across meridians in the examinee's right eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
6.39 to 9.45	Range of Values	6429	6429
88	Could not obtain	98	6527
.	Missing	453	6980

VIXKRDM - Right keratometry power, average (D)

Variable Name:: VIXKRDM
SAS Label:: Right keratometry power, average (D)
English Text:: Keratometric measure. Dioptric power of the cornea averaged across meridians in the examinee's right eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
35.75 to 52.75	Range of Values	6429	6429
88	Could not obtain	98	6527
.	Missing	453	6980

VIXKRCD - Right keratometry cylinder

Variable Name:: VIXKRCD
SAS Label:: Right keratometry cylinder
English Text:: Keratometric measure. Difference in dioptric power between meridians of the cornea in the examinee's right eye
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
-5.75 to 24.75	Range of Values	6429	6429
88	Could not obtain	98	6527
.	Missing	453	6980

VIXKRCG - Right keratometry axis (deg)

Variable Name:: VIXKRCG
SAS Label:: Right keratometry axis (deg)
English Text:: Keratometric measure. Axis of corneal astigmatism (in degrees) in the steepest meridian of the cornea in the examinee's right eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0 to 179	Range of Values	6429	6429
888	Could not obtain	98	6527
.	Missing	453	6980

VIXKLM1 - Left keratometry radius flat curve (mm)

Variable Name:: VIXKLM1
SAS Label:: Left keratometry radius flat curve (mm)
English Text:: Keratometric measure. Radius of corneal curvature (in mm) in the least power meridian of the examinee's left eye (median of three measures).
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
6.36 to 9.72	Range of Values	6460	6460
88	Could not obtain	67	6527
.	Missing	453	6980

VIXKLD1 - Left keratometry power flat curve (D)

Variable Name:: VIXKLD1
SAS Label:: Left keratometry power flat curve (D)
English Text:: Keratometric measure. Dioptric power in the least power meridian of the cornea in the examinee's left eye (median of three measures).
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
34.75 to 53	Range of Values	6460	6460
88	Could not obtain	67	6527
.	Missing	453	6980

VIXKLG1 - Left keratometry axis flat curve (deg)

Variable Name:: VIXKLG1
SAS Label:: Left keratometry axis flat curve (deg)
English Text:: Keratometric measure. Axis of corneal astigmatism (in degrees) in the least power median of the examinee's left eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0 to 180	Range of Values	6460	6460
888	Could not obtain	67	6527
.	Missing	453	6980

VIXKLM2 - Left keratometry radius steep curve (mm)

Variable Name:: VIXKLM2
SAS Label:: Left keratometry radius steep curve (mm)
English Text:: Keratometric measure. Radius of corneal curvature (in mm) in the greatest power meridian of the examinee's left eye (median of three measures).
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
5.15 to 9.23	Range of Values	6460	6460
88	Could not obtain	67	6527
.	Missing	453	6980

VIXKLD2 - Left keratometry power steep curve (D)

Variable Name:: VIXKLD2
SAS Label:: Left keratometry power steep curve (D)
English Text:: Keratometric measure. Dioptric power in the meridian of the cornea with the greatest power in the examinee's left eye (median of three measures).
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
36.5 to 65.5	Range of Values	6460	6460
88	Could not obtain	67	6527
.	Missing	453	6980

VIXKLG2 - Left keratometry axis steep curve (deg)

Variable Name:: VIXKLG2
SAS Label:: Left keratometry axis steep curve (deg)
English Text:: Keratometric measure. Axis of corneal astigmatism (in degrees) in the greatest power meridian of the examinee's left eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0 to 179	Range of Values	6460	6460
888	Could not obtain	67	6527
.	Missing	453	6980

VIXKLMM - Left keratometry radius, average (mm)

Variable Name:: VIXKLMM
SAS Label:: Left keratometry radius, average (mm)
English Text:: Keratometric measure. Radius of corneal curvature (in mm) averaged across meridians in the examinee's left eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
5.8 to 9.34	Range of Values	6460	6460
88	Could not obtain	67	6527
.	Missing	453	6980

VIXKLDM - Left keratometry power, average (D)

Variable Name:: VIXKLDM
SAS Label:: Left keratometry power, average (D)
English Text:: Keratometric measure. Dioptric power of the cornea averaged across meridians in the examinee's right eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
36.25 to 58.25	Range of Values	6460	6460
88	Could not obtain	67	6527
.	Missing	453	6980

VIXKLCD - Left keratometry cylinder

Variable Name:: VIXKLCD
SAS Label:: Left keratometry cylinder
English Text:: Keratometric measure. Difference in dioptric power between meridians of the cornea in the examinee's left eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
-5.5 to 24.75	Range of Values	6460	6460
88	Could not obtain	67	6527
.	Missing	453	6980

VIXKLCG - Left keratometry axis (deg)

Variable Name:: VIXKLCG
SAS Label:: Left keratometry axis (deg)
English Text:: Keratometric measure. Axis of corneal astigmatism (in degrees) in the steepest meridian of the cornea in the examinee's left eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0 to 179	Range of Values	6460	6460
888	Could not obtain	67	6527
.	Missing	453	6980

VIDRVA - Right visual acuity, presenting

Variable Name:: VIDRVA
SAS Label:: Right visual acuity, presenting
English Text:: The presenting visual acuity of the right eye with usual correction.
English Instructions:: Usual correction could be: eyeglasses, contacts, eyeglasses and contacts, or no correction depending on what the SP wore (or brought with them) to view distant objects on the day they visited the MEC (see VIQ230 and VIQ240).
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
20	20/20	2885	2885
25	20/25	1632	4517
30	20/30	621	5138
40	20/40	281	5419
50	20/50	623	6042
60	20/60	87	6129
80	20/80	121	6250
200	20/200	164	6414
666	20/200+	72	6486
.	Missing	494	6980

VIDLVA - Left visual acuity, presenting

Variable Name:: VIDLVA
SAS Label:: Left visual acuity, presenting
English Text:: The presenting visual acuity of the left eye with usual correction.
English Instructions:: Usual correction could be: eyeglasses, contacts, eyeglasses and contacts, or no correction depending on what the SP wore (or brought with them) to view distant objects on the day they visited the MEC (see VIQ230 and VIQ240).
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
20	20/20	2930	2930
25	20/25	1610	4540
30	20/30	630	5170
40	20/40	258	5428
50	20/50	611	6039
60	20/60	88	6127
80	20/80	104	6231
200	20/200	173	6404
666	20/200+	74	6478
.	Missing	502	6980

VIDROVA - Right visual acuity, w/ obj. refraction

Variable Name:: VIDROVA
SAS Label:: Right visual acuity, w/ obj. refraction
English Text:: The visual acuity with objective refraction of the right eye.
English Instructions:: This is the visual acuity reported by the SP after the autorefractor inserted what it deemed, based on the objective refraction, to be the most appropriate lens (if any) to allow the eye to see 20/25 or better. This test was only performed on eyes whose presenting visual acuity was 20/30 or worse.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
25	20/25	1357	1357
30	20/30	125	1482
40	20/40	80	1562
50	20/50	193	1755
60	20/60	13	1768
80	20/80	27	1795
200	20/200	42	1837
666	20/200+	33	1870
.	Missing	5110	6980

VIDLOVA - Left visual acuity, w/ obj. refraction

Variable Name:: VIDLOVA
SAS Label:: Left visual acuity, w/ obj. refraction
English Text:: The visual acuity with objective refraction of the left eye.
English Instructions:: This is the visual acuity reported by the SP after the autorefractor inserted what it deemed, based on the objective refraction, to be the most appropriate lens (if any) to allow the eye to see 20/25 or better. This test was only performed on eyes whose presenting visual acuity was 20/30 or worse.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
25	20/25	1343	1343
30	20/30	129	1472
40	20/40	84	1556
50	20/50	186	1742
60	20/60	18	1760
80	20/80	24	1784
200	20/200	34	1818
666	20/200+	34	1852
.	Missing	5128	6980

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