Background
The impact of ophthalmic diseases on quality of life (QoL) has been documented in a series of studies
The NEI-VFQ 25 (National Eye Institute visual function questionnaire) is a widely used vision-specific instrument for the assessment of VS-QoL. The instrument was originally developed by the National Eye Institute mainly for the English-speaking North American populations
The aim of our study was the evaluation of the reliability and validity of NEI-VFQ 25 in a sample of native Greek subjects with a series of common ophthalmic diseases.
Methods
Instrument development
The study adhered to the tenets of the Declaration of Helsinki and approval was granted by the Bioethics Committee of the University of Thessaly. All participants provided written informed consent.
For this study we developed a Greek version of the NEI-VFQ 25. The original NEI-VFQ 25 is a VS-QoL instrument that has been used in numerous studies. The concepts investigated by the items have been extensively analyzed both during the development of the original version and during the validation of the instrument in other languages. Forward translation was done by native Greek ophthalmologists with solid command of the English language. Two independent bilingual speakers performed the backward translation. Proper adaptation of the questionnaire to the experience of Greek patients mandated slight modification of three questions. Thus, item "13" [How much difficulty do you have visiting people at their homes, at parties, or in restaurants?] was translated as: [How much difficulty do you have visiting people at their homes or outdoors, to restaurants, cafes, or in church?]. Accordingly, item "A7" [Because of your eyesight, how much difficulty do you have taking part in active sports or other outdoor activities that you enjoy (like golf, bowling, jogging, or walking)?] was translated as: [Because of your eyesight, how much difficulty do you have taking part in active sports or other outdoor activities that you enjoy (going long walks or jogging)?]. On the other hand, item "9" [Because of your eyesight, how much difficulty do you have going down steps, stairs, or curbs in dim light or at night?] was modified as follows: [Because of your eyesight, how much difficulty do you have going down stairs, or curbs in dim light or at night?], since the Greek words for "stairs" and "steps" are almost identical. The Greek version of the instrument was pilot-tested in a sample of ten ophthalmic patients who visited the outpatient service of our clinic for their annual check-up. The results of the pilot-testing indicated that the instrument was well accepted, since it was short in duration (about 10 minutes) and all items were easy to understand.
It should be mentioned that the NEI-VFQ 25 has already been translated into Greek (Laboratory of Experimental Ophthalmology of Aristotle University, Thessaloniki, Greece, 2000)
Study Design
Evaluation of the reliability and validity of the Greek version of the NEI-VFQ 25 questionnaire was conducted by the University Eye clinic, Larissa, Greece, between August and November 2006. The University Hospital of Larissa is an 800-bed General Hospital, located at the center of mainland Greece, offering tertiary healthcare to more than one million beneficiaries. The University Eye Clinic provides integrated ophthalmic services to patients from four counties in mainland Greece and one on the islands. Two hundred fifty patients were recruited for the study. Of them, 186 successfully responded to the questionnaire, including the test-retest module (response rate: 74.4%). The patients were randomly selected from the local national health system hospitals of the corresponding counties.
Subject groups
Subject group 1 consisted of a random sample of 84 known glaucoma patients (38 males/46 females). All subjects had been diagnosed with primary open angle glaucoma (POAG), pseudoexfoliation glaucoma (PXG), pigment glaucoma (PG) or normal tension glaucoma (NTG) at least two years prior to the study, and demonstrated adequate compliance. Glaucoma patients had bilateral typical glaucomatous visual field defects on Humphrey 24-2 tests, untreated intraocular pressure higher than 22 mmHg (except for the NTG patients) and either retinal nerve fibre layer defects compatible with glaucoma on OCT, or optic nerve heads with a typical glaucomatous appearance. Subject group 2 consisted of a random sample of 30 age-related macular degeneration (ARMD) patients (14 males/16 females). To be eligible for the ARMD group, each subject should have variable bilateral involvement presenting either with geographic atrophy involving the fovea, choroidal neovascular membrane, or pigment epithelium defects. Subject group 3 consisted of a random sample of 25 patients (1 male/24 females) diagnosed with dry-eye syndrome. These had been diagnosed according to the European classification criteria
Data collection
Subjects responded to the self-administered Greek version of the NEI-VFQ 25 in the presence of an independent researcher who had no direct involvement in the provision of care. All questionnaires were completed prior to the clinical examination. Clinical and demographic data regarding the participants was retrieved from their medical records. Proxy responses (i.e. from family members) were excluded.
Descriptive analysis and item analysis
Data from the different subject groups were used for the item analysis. Missing values were estimated for each item. Large ceiling or floor effects were evaluated as well.
Reliability
Reliability analysis was done by Cronbach's alpha estimation as an index of internal consistency for each subscale
Construct validity
Construct validity was evaluated by means of multi-trait analysis according to Campbell and Fiske
Rasch analysis
Besides the traditional methods, the psychometric properties of the Greek NEI-VFQ 25 were also evaluated by Rasch analysis. The item response theory has been described in earlier studies
The tests of construct validity measure the fit of the person measures to the model, and the correlations of person- and item parameter values with other variables, compared with expected correlations. The tests of content validity measure the fit of individual items to the model, the estimation errors of item parameter values, and the spacing and range of item parameter values, relative to the distribution of person parameter values.
Statistical analysis
Statistical analyses were performed with SPSS® version 13 for Windows (SPSS Inc, Chicago, IL). Rasch analysis was performed with the Winsteps programme (Linacre, 2007).
Results
Regarding glaucoma subjects, 43 patients had primary open angle glaucoma (POAG), 10 had pseudoexfoliation glaucoma (PXG), 16 had normal tension glaucoma (NTG) and 15 subjects had ocular hypertension (OH). The MD ranged from -1.9 dB to -7.1 dB in Humphrey 24-2 threshold testing (mean: -3.2 dB). Regarding ARMD subjects, 28 patients presented variable degrees of bilateral geographical atrophy, while 2 patients presented exudative changes in one eye. Regarding cataract subjects, mean LOCS III score for nuclear opalescence was 3.1 and LOCS III score for nuclear color was 3.3. Regarding the dry-eye syndrome group, all subjects were treated with artificial tears, 13 subjects reported that artificial tears treatment was effective, while 17 subjects demonstrated combined fluorescein score > 0.5. Demographics and clinical data for the participants are presented in Table
Demographics and clinical data
Glaucoma
ARMD
Cataract
Dry Eye
Control
Mean ± SD age (years)
60.9 ± 11.7
65 ± 4.4
63 ± 7.3
59.1 ± 8.7
56 ± 8.9
males/females
38/46
14/16
5/13
1/24
6/23
mean BCVA best (range)
0.63 (0.5 to 0.8)
0.4 (0.67 to 0.32)
0.5 (0.63 to 0.32)
0.8 (0.67 to 1.0)
1
mean BCVA worse (range)
0.4 (0.33 to 0.63)
0.33 (0.25 to 0.40)
0.29 (0.16 to 0.4)
0.67 (0.5 to 0.8)
0.8 (1 to 0.67)
VF MD (dB) (range)
-3.2 (-7.1 to-1.9)
-
-
-
-
0 medical comorbitities
8
4
6
4
13
1 medical comorbitities
47
8
5
15
8
≥2 medical comorbitities
29
18
7
6
8
Mean subscale and overall NEI-VFQ scores for the different groups of subjects are presented in Table
Index and subscale scores
Subject Group
NEI-VFQ 25 subscales
Glaucoma
ARMD
Dry-eye
Cataract
Control
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
General health
55.3
20.3
57.6
17.1
45.9
17.2
57.8
19.7
80.3
12.2
General vision
69.6
15.5
56.6
10.9
75.1
15.2
60
17.4
90.7
12.9
Ocular pain
69.9
23.1
94.2
16
60.5
18.9
84
20.5
89.7
12.1
Near activities
78.7
18.7
58.6
23
86.2
16.3
65.6
26.9
96.1
9.7
Distance activities
82.2
19
74.4
17.7
90.2
13.9
74.7
18.5
96
7
Vision specific social functioning
89.2
19.4
89.1
12.8
94.1
9.7
84.3
22.9
99.4
3.1
Vision specific mental health
69.7
21.6
63.3
22.4
80.8
19.3
67.8
24.5
89.7
10.4
Vision specific role difficulties
74.3
21.7
59.8
24.4
86.5
18.7
68
29.3
94.8
12.1
Vision specific dependency
82.5
25.1
70.3
22.5
91.3
19.8
79.6
26.4
97.7
7
Driving
81.1
16.9
61.1
26.4
90
11.5
75
35.4
93.8
8
Color vision
88.3
19
86.7
23.4
89.3
22.1
86.1
17.6
100
0
Peripheral vision
82.4
21.4
79.2
25.5
89.6
15.4
79.4
28.3
95.7
11.7
Overall Score
76.9
20.2
70.9
20.2
81.6
16.5
73.5
24
93.7
8.9
Item analysis is presented in Table
Item analysis
Item
Missing responses
Floor responses
Ceiling responses
Number
%
Number
%
Number
%
1. General Health: 5-level health rating
1
0.5
14
8.9
6
3.8
2. General Vision: 6-level general vision
1
0.5
1
0.6
6
3.8
3. Mental Health: Amount true: worry
2
1.3
21
13.4
11
7.0
4. Ocular Pain: Amount pain
2
1.3
1
0.6
55
35.0
5. Near Vision: Reading normal newsprint
4
2.5
21
13.4
38
24.2
6. Near Vision: See well up-close
1
0.5
1
0.6
46
29.3
7. Near Vision: Finding objects on crowded shelf
1
0.5
5
3.2
88
56.1
8. Distance Vision: Reading street signs
2
1.3
6
3.8
64
40.8
9. Distance Vision: Going down stairs at night
2
1.3
2
1.3
61
38.9
10. Peripheral Vision: Seeing objects off to side
2
1.3
1
0.6
82
52.2
11. Social Function: Seeing how people react
2
1.3
2
1.3
99
63.1
12. Color Vision: Difficulty matching clothes
1
0.5
1
0.6
101
64.3
13. Social Function: Visiting others
1
0.5
4
2.5
114
72.6
14. Distance Vision: Going out to movies/plays
6
3.8
56
35.7
56
35.7
15. Driving: Daylight familiar places
21
13.4
84
53.5
52
33.1
16. Driving: At night
50
68.2
1
0.6
12
7.6
17. Role Limitation: Accomplish less
8
5.1
6
3.8
53
33.8
18. Role Limitation: Limited in endurance
10
6.4
6
3.8
53
33.8
19. Ocular Pain: Amount time: pain
8
5.1
1
0.6
73
46.5
20. Dependency: Stay home most of time
6
3.8
14
8.9
80
51.0
21. Mental Health: Amount true: frustrated
9
5.7
11
7.0
76
48.4
22. Mental Health: Amount true: no control
12
7.6
6
3.8
84
53.5
23. Dependency: Rely too much on other's word
12
7.6
4
2.5
92
58.6
24. Dependency: Need much help from others
10
6.4
6
3.8
89
56.7
25. Mental Health: Amount true: embarrassment
9
5.7
8
5.1
100
63.7
Evaluation of the reliability of the Greek version of the NEI-VFQ 25 is presented in Table
Reliability and validity analysis
Subscale
Number of items
Intraclass correlation coefficients
Cronbach's alpha
Range of item-scale correlations
Convergent validity
Discriminant validity
General Health
1
0.841
NA
NA
NA
NA
General Vision
1
0.889
NA
NA
NA
NA
Ocular pain
2
0.803
0.851
0.893 – 0.903
100
100
Near activities
3
0.901
0.734
0.719 – 0.875
100
100
Distance activities
3
0.908
0.686
0.752 – 0.892
100
100
Vision specific social functioning
2
0.91
0.678
0.887 – 0.889
100
100
Vision specific mental health
4
0.823
0.786
0.596 – 0.837
100
100
Vision specific role difficulties
2
0.888
0.926
0.902 – 0.907
100
100
Vision specific dependency
3
0.826
0.848
0.835 – 0.899
100
100
Driving
3
0.871
0.757
0.575 – 0.953
100
100
Color vision
1
0.717
NA
NA
NA
NA
Peripheral vision
1
0.84
NA
NA
NA
NA
N.A.: Not applicable (needs two or more items).
Evaluation of the validity of the Greek version of NEI-VFQ 25 is presented in the multitrait-multimethod matrix (see Additional file
Multitrait-multimethod matrix. Matrix of correlation for the assessment of construct validity of sets of measures. Instead of "1" along the diagonal (as in a typical correlation matrix) we have substituted an estimate of the test-retest reliability of each measure.
Click here for file
The impact of visual acuity and visual field deficits on vision-specific quality of life is presented in Table
Pearson correlations of NEI VFQ 25 subscales with visual acuity and visual fields
BCVA worse
BCVA better
VF worse
VF better
General Health
Pearson Correlation
-0.145
-0.078
-0.175
-0.145
Sig. (2-tailed)
0.231
0.521
0.153
0.238
General Vision
Pearson Correlation
-0.279(*)
-0.251(*)
-0.444(**)
-0.407(**)
Sig. (2-tailed)
0.019
0.035
0
0.001
Ocular Pain
Pearson Correlation
-0.082
-0.065
-0.1
-0.216
Sig. (2-tailed)
0.499
0.589
0.415
0.075
Near Activities
Pearson Correlation
-0.331(**)
-0.337(**)
-0.361(**)
-0.411(**)
Sig. (2-tailed)
0.005
0.004
0.002
0
Distant Activities
Pearson Correlation
-0.440(**)
-0.159
-0.260(*)
-0.346(**)
Sig. (2-tailed)
0
0.186
0.031
0.004
Social Functioning
Pearson Correlation
-0.369(**)
-0.159
-0.227
-0.295(*)
Sig. (2-tailed)
0.002
0.184
0.061
0.014
Mental Health
Pearson Correlation
-0.236(*)
-0.172
-0.021
-0.083
Sig. (2-tailed)
0.047
0.15
0.862
0.498
Role Difficulties
Pearson Correlation
-0.218
-0.199
-0.204
-0.242
Sig. (2-tailed)
0.074
0.103
0.1
0.05
Dependency
Pearson Correlation
-0.475(**)
-0.242
-0.174
-0.292(*)
Sig. (2-tailed)
0
0.065
0.196
0.028
N
59
59
57
57
Driving
Pearson Correlation
-0.239
-0.134
-0.371(*)
-0.041
Sig. (2-tailed)
0.187
0.466
0.04
0.826
N
32
32
31
31
Color vision
Pearson Correlation
-0.405(**)
-0.345(**)
-0.231
-0.288(*)
Sig. (2-tailed)
0.001
0.004
0.062
0.019
Peripheral vision
Pearson Correlation
-0.22
-0.087
-0.334(**)
-0.336(**)
Sig. (2-tailed)
0.07
0.478
0.006
0.005
**: Correlation is significant at the 0.01 level (2-tailed).
*: Correlation is significant at the 0.05 level (2-tailed).
Regarding Rasch analysis, the normalized item fit statistics are presented in Table
Estimates of item measures and fit statistics from Rasch analysis
Item
Item Number
Standard Error
Infit zstd
Outfit zstd
Matching clothes
12
-1.07
0.14
0.00
-0.20
Finding something
7
-0.92
0.13
0.10
-0.30
See reaction
11
-0.92
0.13
2.20
2.00
Visit people
13
-0.82
0.12
-0.70
-1.30
Noticing objects
10
-0.7
0.11
-0.70
-0.90
Eye pain
4
-0.42
0.10
-2.30
-3.00
Going down steps
9
-0.41
0.10
-1.80
-2.10
Reading signs
8
-0.4
0.10
-0.20
-0.50
See up close
6
-0.29
0.09
0.30
-0.20
Overall eyesight
2
-0.1
0.09
-6.90
-6.60
Reading print
5
-0.03
0.09
2.70
2.60
Overall health
1
0.15
0.08
5.80
5.40
Worry about eyesight
3
0.2
0.09
-1.20
-0.90
See movies
14
0.24
0.09
6.90
6.80
Limited
18
0.32
0.09
1.30
1.60
Accomplish less
17
0.32
0.09
-0.40
0.30
Stay home
20
0.44
0.09
1.10
1.40
Feel frustrated
21
0.48
0.09
1.20
0.90
Less control
22
0.69
0.10
0.00
0.40
Need help
24
0.71
0.10
-2.90
-1.60
Eye discomfort
19
0.72
0.10
-0.70
-0.10
Rely too much
23
0.88
0.11
0.60
0.60
Embarrass myself
25
0.94
0.11
-0.60
0.00
Infit and outfit values for the list of items
Infit and outfit values for the list of items.
Infit and outfit values for the list of items – "agreement" items removed from model
Infit and outfit values for the list of items – "agreement" items removed from model.
Estimates of item measures and fit statistics from Rasch analysis (difficulty items only)
Item
Item number
Standard Error
Infit zstd
Outfit zstd
Matching clothes
12
-0.77
0.16
-0.70
-2.50
Finding something
7
-0.58
0.15
1.90
1.30
See reaction
11
-0.58
0.15
-0.10
0.50
Visit people
13
-0.43
0.14
-1.30
0.40
Noticing objects
10
-0.27
0.13
1.90
1.00
Going down steps
9
0.16
0.12
2.80
1.70
Reading signs
8
0.18
0.12
-0.10
-0.20
See up-close
6
0.34
0.11
0.90
-0.20
Reading print
5
0.74
0.11
-1.10
-0.80
See movies
14
1.2
0.11
-3.30
-1.70
Figure
Distribution of visual ability measures
Distribution of visual ability measures.
Distribution of the infit and outfit statistics for the estimates of visual ability
Distribution of the infit and outfit statistics for the estimates of visual ability.
Discussion
The primary objective of our study was the evaluation of the reliability and construct validity of the NEI-VFQ 25 in native Greek populations with a series of common ophthalmic diseases. Proper adaptation of the instrument to the Greek norms mandated slight modification of some items and a thorough revision of the translation process that had already been performed by previous investigators. Minor modifications of some items were considered necessary during the translation and validation of the NEI-VFQ 25 in other populations, too
Contrary to the original validation studies in North American populations, relatively high missing rates were encountered in some subscales. However, these missing rates were comparably lower than the ones encountered during the translation and validation of the instrument in other populations
The subscales of the Greek version of NEI-VFQ 25 presented variable but adequate internal consistencies indicating high reliability of the instrument in the population studied. The lowest values of Cronbach's alpha were detected in "Social Functioning" (0.678) and "Distance Activities" (0.686) subscales, while the rest of the subscales presented significantly higher values. On the other hand, the time-window of three weeks between test and retest visits, ensured that no significant changes in the vision-related and/or systemic functional status of the subjects would take place. In fact, solid test-retest reliability was indicated by the high values of the intraclass correlation coefficients.
Regarding the construct validation of the questionnaire, none of the items failed either the convergent or the discriminant tests.
Strong correlations were detected between visual acuity of the subjects and the "general vision", "distant activities" and "near activities" subscales suggesting that the corresponding subscales were actually associated with central vision. Similar correlations between visual acuity and NEI-VFQ subscales have been detected by previous investigators during the validation of the instrument in other languages as well
On the other hand, item response analysis revealed potential weaknesses of the questionnaire that should be taken into consideration prior to the interpretation of results. These potential weaknesses are associated with the assumptions of the Rasch model. Among these assumptions are: a) only one variable is measured by the instrument, b) subjects' responses to the items depend only on visual ability, c) subjects' responses are probabilistic and conditional on the subjects' visual ability required to perform that activity with ease, d) the odds of performing an activity with ease increase monotonically with the difference between the subject's ability and the ability required to perform the activity with ease. The results of the study indicate that