National Health and Nutrition Examination Survey

2007-2008 Data Documentation, Codebook, and Frequencies

Vision (VIX_E)

Data File: VIX_E.xpt

First Published: September 2009

Last Revised: NA

Component Description

The NHANES Vision Examination data will be used to: 1) measure the prevalence of visual acuity impairment (visual acuity worse than 20/40) in the U.S. population; 2) measure the distribution of refractive error in the U.S. population; and 3) evaluate functional impairment related to vision.

The NHANES Vision Examination consisted of three parts:

Eye Glasses Prescription Determination – For persons 12 years of age and older, eye glass prescriptions were measured when eye glasses for viewing distant objects were available.

Distance Visual Acuity and Objective Refraction/Keratometric Evaluation – For all persons 12 years and older, distance vision was assessed regardless of whether they wore eyeglasses or contacts; the refraction test measured 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 were 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 were 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: 1) eyeglass prescription for glasses used to view distant objects; 2) presenting visual acuity with current correction; 3) visual acuity incorporating objective refraction; and 4) 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.

Exam sample weights should be used for analyses. 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	5	5
2	No	6543	6548	VIQ130
.	Missing	369	6917

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	1	1	End of Section
2	Left	3	4	End of Section
3	Both	1	5	End of Section
.	Missing	6912	6917

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	0	0
2	No	6543	6543	VIQ150
.	Missing	374	6917

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	0	0
2	Left	0	0
3	Both	0	0
.	Missing	6917	6917

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	2387	2387
2	No	398	2785	VIXNC1
9	Don't know	3	2788
.	Missing	4129	6917

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	2048	2048
2	No	339	2387	VIXNC1
.	Missing	4530	6917

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	2011	2011
2	Contacts	31	2042
3	Both glasses and contact lenses	6	2048
.	Missing	4869	6917

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	2775	2775
8	Could not obtain	13	2788
.	Missing	4129	6917

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
4 to 31	Range of Values	2775	2775
88	Could not obtain	13	2788
.	Missing	4129	6917

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	98	98
2	No	6409	6507	VIQ200
9	Don't know	20	6527	VIQ200
.	Missing	390	6917

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	8	8
2	Left	8	16
3	Both	80	96
9	Don't know	2	98
.	Missing	6819	6917

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	534	534
2	No	5982	6516	VIQ220
9	Don't know	11	6527	VIQ220
.	Missing	390	6917

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	75	75
2	Left	71	146
3	Both	384	530
9	Don't know	4	534
.	Missing	6383	6917

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	2976	2976
2	No	3548	6524	VIXOCMT
9	Don't know	3	6527
.	Missing	390	6917

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	2582	2582
2	No	394	2976
.	Missing	3941	6917

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	2214	2214
2	Contacts	351	2565	VIXOCMT
3	Both glasses and contact lenses	17	2582
.	Missing	4335	6917

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	2220	2220
2	No	11	2231
.	Missing	4686	6917

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
-15 to 9.25	Range of Values	2154	2154
88	Could not obtain	70	2224
.	Missing	4693	6917

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
-1.75 to 6.25	Range of Values	2154	2154
88	Could not obtain	70	2224
.	Missing	4693	6917

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	2154	2154
888	Could not obtain	70	2224
.	Missing	4693	6917

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
-14.25 to 9.25	Range of Values	2155	2155
88	Could not obtain	69	2224
.	Missing	4693	6917

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
-0.25 to 6	Range of Values	2155	2155
88	Could not obtain	69	2224
.	Missing	4693	6917

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	2155	2155
888	Could not obtain	69	2224
.	Missing	4693	6917

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	9	9
2	Cataract contact lenses worn for objective refraction	3	12
3	Contacts worn for objective refraction	12	24
4	Artificial eye	5	29
5	Monovision contacts worn for objective refraction	3	32
6	Contact in right eye only for presenting visual acuity	2	34
7	Contact in left eye only for presenting visual acuity	3	37
.	Missing	6880	6917

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
-18 to 12	Range of Values	6239	6239
88	Could not obtain	267	6506
.	Missing	411	6917

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 7.75	Range of Values	6238	6238
88	Could not obtain	267	6505
.	Missing	412	6917

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	6239	6239
888	Could not obtain	267	6506
.	Missing	411	6917

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	6291	6291
.	Missing	626	6917

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
-22 to 9.5	Range of Values	6169	6169
88	Could not obtain	337	6506
.	Missing	411	6917

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 7.75	Range of Values	6168	6168
88	Could not obtain	337	6505
.	Missing	412	6917

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	6169	6169
888	Could not obtain	337	6506
.	Missing	411	6917

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	6295	6295
.	Missing	622	6917

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
6.79 to 9.95	Range of Values	6432	6432
88	Could not obtain	72	6504
.	Missing	413	6917

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 to 49.75	Range of Values	6432	6432
88	Could not obtain	72	6504
.	Missing	413	6917

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	6432	6432
888	Could not obtain	72	6504
.	Missing	413	6917

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
4.91 to 9.25	Range of Values	6432	6432
88	Could not obtain	72	6504
.	Missing	413	6917

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
36.5 to 68.75	Range of Values	6432	6432
88	Could not obtain	72	6504
.	Missing	413	6917

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	6432	6432
888	Could not obtain	72	6504
.	Missing	413	6917

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
6.04 to 9.46	Range of Values	6432	6432
88	Could not obtain	72	6504
.	Missing	413	6917

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 56	Range of Values	6432	6432
88	Could not obtain	72	6504
.	Missing	413	6917

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
0 to 24.75	Range of Values	6432	6432
88	Could not obtain	72	6504
.	Missing	413	6917

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	6432	6432
888	Could not obtain	72	6504
.	Missing	413	6917

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
6.43 to 9.56	Range of Values	6441	6441
88	Could not obtain	63	6504
.	Missing	413	6917

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
35.25 to 52.5	Range of Values	6441	6441
88	Could not obtain	63	6504
.	Missing	413	6917

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	6441	6441
888	Could not obtain	63	6504
.	Missing	413	6917

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
4.95 to 9.22	Range of Values	6441	6441
88	Could not obtain	63	6504
.	Missing	413	6917

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 68.25	Range of Values	6441	6441
88	Could not obtain	63	6504
.	Missing	413	6917

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	6441	6441
888	Could not obtain	63	6504
.	Missing	413	6917

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
6.22 to 9.37	Range of Values	6441	6441
88	Could not obtain	63	6504
.	Missing	413	6917

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 left eye.
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
36 to 54.25	Range of Values	6441	6441
88	Could not obtain	63	6504
.	Missing	413	6917

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
0 to 25.25	Range of Values	6441	6441
88	Could not obtain	63	6504
.	Missing	413	6917

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	6441	6441
888	Could not obtain	63	6504
.	Missing	413	6917

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	2583	2583
25	20/25	1730	4313
30	20/30	656	4969
40	20/40	319	5288
50	20/50	704	5992
60	20/60	89	6081
80	20/80	115	6196
200	20/200	188	6384
666	20/200+	57	6441
.	Missing	476	6917

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	2549	2549
25	20/25	1718	4267
30	20/30	704	4971
40	20/40	308	5279
50	20/50	705	5984
60	20/60	117	6101
80	20/80	121	6222
200	20/200	168	6390
666	20/200+	62	6452
.	Missing	465	6917

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	1396	1396
30	20/30	154	1550
40	20/40	103	1653
50	20/50	226	1879
60	20/60	21	1900
80	20/80	31	1931
200	20/200	59	1990
666	20/200+	21	2011
.	Missing	4906	6917

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	1430	1430
30	20/30	142	1572
40	20/40	95	1667
50	20/50	253	1920
60	20/60	17	1937
80	20/80	31	1968
200	20/200	59	2027
666	20/200+	24	2051
.	Missing	4866	6917

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