Medical Surveillance 

Programs for Aircraft 

Maintenance Personnel 

Performing Nondestructive 

Inspection and Testing

Van B. Nakagawara

Ronald W. Montgomery

Civil Aerospace Medical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

Gregory W. Good

College of Optometry

The Ohio State University

Columbus, OH 43210

November 2005

Final Report

DOT/FAA/AM-05/21

Offi ce of Aerospace Medicine

Washington, DC 20591
NOTICE

This document is disseminated under the sponsorship of

the U.S. Department of Transportation in the interest of

information exchange. The United States Government

assumes no liability for the contents thereof.
i

Technical Report Documentation Page 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

DOT/FAA/AM-05/21 

4. Title and Subtitle 5. Report Date

 

November 2005 

6. Performing Organization Code 

Medical Surveillance Programs for Aircraft Maintenance

Personnel Performing Nondestructive Inspection and Testing 

 7. Author(s) 8. Performing Organization Report No. 

Nakagawara VB,1 Montgomery RW,1 Good GW2

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) 

11. Contract or Grant No. 

1

FAA Civil Aerospace Medical Institute 

P.O. Box 25082 

Oklahoma City, OK 73125 

2

The Ohio State University 

Columbus, OH 43210 

12. Sponsoring Agency name and Address 13. Type of Report and Period Covered 

14. Sponsoring Agency Code 

Office of Aerospace Medicine 

Federal Aviation Administration 

800 Independence Ave, S.W. 

Washington, DC 20591 

15. Supplemental Notes 

16. Abstract 

INTRODUCTION: Visual inspection and nondestructive inspection and testing (NDI/NDT) are performed routinely to 

ensure that aircraft are maintained in safe operating condition. Inspectors must make critical judgments about the condition 

of aircraft and aircraft components using their eyes, basic visual aids (magnifiers, mirrors, and flashlights), and complicated

NDI/NDT techniques to detect anomalies. Failure to detect observable defects has been implicated in several aviation 

accidents. This study examines the medical surveillance programs employed by aircraft maintenance facilities in the United 

States, including specific vision standards and tests used for inspection personnel. METHODS: We interviewed medical 

surveillance program personnel from nine major aircraft maintenance facilities and repair stations by phone or in person. The 

current vision standards for inspectors at each of the facilities surveyed were extracted from internal facility documents. 

Additionally, we reviewed the vision screening tests used for medical surveillance of inspection personnel. RESULTS: There 

were differences in the vision standards for near vision (Snellen 20/20 and 20/25, Jaeger #1 and #2, Ortho Rater #8) distant 

vision (20/25, 20/30, none), color vision (distinguish and differentiate contrast among colors, colors in the methods, normal 

color vision), and test intervals (annual, 2-year) at the facilities surveyed. Vision screening tests used in the medical 

surveillance programs at these facilities were equally diverse, including choice of vision screening instruments (Stereo Optical,

Titmus), wall charts, reading cards, and pseudoisochromatic plate color vision screening tests. CONCLUSION: Medical 

surveillance programs for the aircraft maintenance facilities we surveyed differed considerably for both vision standards and 

screening tests used to evaluate vision performance of inspectors. The use of uniform vision standards and test methods 

would provide quality control and facilitate a more accurate evaluation of the visual capabilities for inspection personnel. 

17. Key Words 18. Distribution Statement 

Nondestructive Inspection; Nondestructive Testing; 

Visual Inspection; Aircraft Maintenance; Medical 

Surveillance 

Document is available to the public through the 

Defense Technical Information Center, Ft. 

Belvior, VA 22060; and the National Technical 

Information Service, Springfield, VA 22161

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price 

Unclassified Unclassified 14 

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized 

1

MEDICAL SURVEILLANCE PROGRAMS FOR AIRCRAFT MAINTENANCE PERSONNEL

PERFORMING NONDESTRUCTIVE INSPECTION AND TESTING

INTRODUCTION 

Recurring visual and nondestructive inspection and 

testing (NDI/NDT) is crucial for ensuring that aircraft 

are maintained in safe operating condition. A recent FAA 

report, entitled “Analysis of Airworthiness Directives 

1995 to 1999,” indicated that 57% of all Airworthiness 

Directives issued during this period mandated some type 

of inspection. The report further states that 62% of these 

directives require visual inspection. In addition, a Federal 

Aviation Administration (FAA) Advisory Circular (AC 

43-204), entitled “Visual Inspection for Aircraft,” dated 

August 1997, states that over 80% of the inspections on 

large transport category aircraft are visual inspections. 

For smaller commuter transport and privately owned 

general aviation aircraft, this percentage is even greater. 

These statistics suggest that the visual performance of 

aircraft maintenance personnel has a great infl uence on 

aviation safety.

Visual inspection tasks are performed by qualifi ed 

professionals who gain their expertise through rigorous 

training programs and often years of on-the-job experience in aircraft maintenance work. Visual inspectors 

must make judgments about the condition of aircraft and 

aircraft components, frequently using only their vision and 

basic visual aids (magnifi ers, mirrors, and fl ashlights) to 

detect anomalies. NDI/NDT specialists are trained and 

often certifi ed to use sophisticated imaging devices and 

techniques (fl uorescent penetrant and magnetic particle 

inspections, ultrasonic scans, eddy current imaging, Xrays, etc.) to perform a variety of procedures developed 

to increase the probability of detecting subtle defects in 

aircraft parts and assemblies. While visual aids, imaging 

devices, and technical procedures can enhance their ability 

to identify defects, it is essential that these individuals 

possess good visual skills in order to carry out inspection 

tasks effectively.

In some aircraft maintenance facilities, visual inspectors 

and NDI/NDT specialists are considered separate and 

independent groups with differing skills and job qualifi cations. Other facilities, however, do not formally distinguish between these groups, as there is often considerable 

overlap in both the tasks they perform and the expertise 

required. The major difference between these workers is 

that visual inspectors normally inspect the assembled or 

partially assembled aircraft, while NDI/NDT specialists 

tend to focus on the aircraft’s individual components. 

(NOTE: Except when it is appropriate to do otherwise, this 

document will refer to visual inspectors and NDI/NDT 

specialists collectively as NDI/NDT personnel.)

Statistics show that about 50% of adults in the United 

States have diffi culty seeing clearly at far distances, and 

about 60% have diffi culty seeing at near distances when 

no corrective lenses are worn. Research with subjects 

using their usual refractive corrections has indicated 

that the prevalence of impaired distant and near vision 

can be as high as 30% and 40%, respectively (1). When 

optimal manifest refraction is performed and best-corrected visual acuity (BCVA) is provided, these numbers 

can be substantially reduced. This result underscores 

the importance of frequent vision examinations and the 

use of best possible refractive correction by NDI/NDT 

personnel. In the absence of a properly administered vision-screening program, it is possible that a substantial 

percentage of the NDI/NDT workforce would perform 

their duties with less than optimal vision.

Nondestructive testing frequently requires precise 

visual inspection under a variety of conditions. For example, penetrant inspections involve the use of visible 

red or fl uorescent dye to highlight surface imperfections or defective aircraft parts. The intensities of visible 

background light and excitation ultraviolet radiation are 

verifi ed with calibrated light meters to ensure viewing 

conditions are optimal. Magnetic particle inspection also 

uses visible and fl uorescent inspection techniques, while 

radiography relies on the individual’s ability to detect 

subtle differences in contrast either on fi lm images or on 

a video monitor. Additionally, when direct observation 

is impossible it may be necessary to use remote viewing 

techniques such as mirrors, telescopes, borescopes, or 

fi ber-optic cameras attached to video monitors. Lighting 

conditions can also infl uence the effectiveness of a visual 

inspection of a part. Normal visual inspection is typically 

performed in the range of 50 to 100 ft-candles, which is 

equivalent to normal offi ce lighting while inspection of 

fi ne detail may require up to 200 ft-candles. Under such 

varied conditions, inadequate vision can reduce a worker’s 

effectiveness, resulting in poorly executed inspections that 

could compromise aviation safety.
2

Unfortunately, there have been several instances 

where the failure to identify visually detectable corrosion, cracks, or inclusions were found to be the probable cause or a contributing factor in aviation accidents. 

The National Safety Transportation Board (NTSB; 

NTSB/AAR-98/01)(2) reported that on July 6, 1998, in 

Pensacola, Florida, two passengers died on Delta Flight 

1288 during an aborted take-off attempt as a result of 

an uncontained engine failure. The cause was linked to 

a fl awed maintenance inspection that failed to identify 

a detectable crack in the engine hub. Other reports that 

questioned the effectiveness of NDI/NDT inspections 

include the United Airlines crash at Sioux City, Iowa, 

on July 17, 1989 (NTBS/AAR-90/06)(3), and a rapid 

decompression event on Aloha Airlines Flight 243, near 

Maui, Hawaii, in April of 1988 (NTBS/AAR-89/03)(4). 

These accidents resulted in passenger and fl ight crew 

fatalities, as well as the loss of millions of dollars due 

to legal actions and lost revenue due to reduced public 

confi dence in these airlines. Whether or not the poor 

visual performance of inspectors was specifi cally to blame 

in these instances may never be determined beyond a 

reasonable doubt; however, these events emphasize the 

importance of an effective medical surveillance program 

for NDI/NDT personnel that includes a suitably rigorous 

vision-screening process to keep their visual performance 

at optimal levels.

Although most aircraft maintenance personnel must 

meet minimum qualifi cation standards upon initial 

employment and to become certifi ed1

 for performing 

specifi c NDI/NDT procedures, the vision performance 

requirements observed at private, military, and commercial aircraft maintenance facilities lack standardization. 

Furthermore, there is currently no federal regulation that 

identifi es specifi c occupation-based vision standards for 

these individuals. On September 26, 2001, in recognition of this general lack of national policy concerning 

qualifi cation requirements for NDI/NDT personnel, 

the FAA’s Production and Airworthiness Division (AIR200) prepared a memorandum to address the issue (5). 

The memorandum recommended adopting minimum 

qualifi cation and certifi cation standards originally developed by several national and international organizations 

for NDI/NDT personnel. The standards identifi ed in 

this memorandum were those found acceptable by the 

FAA for assuring that only qualifi ed individuals perform 

NDI/NDT procedures (Table 1).

The FAA Aircraft Maintenance Division (AFS-300) 

and the Airworthiness TCRG (Technical Committee 

Research Group) recently recommended that the minimum vision performance standards adopted by industry 

be reviewed to determine if they are adequate for all tasks 

performed by NDI/NDT personnel and, if necessary, 

research be performed to aid in the development of a 

task-based vision standard. In support of this research 

effort, multiple studies were performed to analyze the 

demographic characteristics (6) and vision-task requirements of NDI/NDT and visual inspectors (7). The results 

of these studies will be provided in separate reports. The 

present report identifi es the medical surveillance programs 

utilized at selected aircraft maintenance facilities in the 

United States and determines how these facilities currently 

perform the vision testing necessary to verify the ocular 

status of their employees.

METHODS

A research protocol was developed to assess the visual 

performance demands placed on workers performing 

maintenance inspections. Due to resource limitations, this 

initial investigation identifi ed the visual performance requirements of three specifi c inspection procedures. These 

procedures included fl uorescent penetrant, borescope, 

and visual inspection. Personnel and facility surveys were 

conducted, visual-task data were collected, and reviews of 

medical surveillance programs for inspection personnel 

were performed at fi ve commercial airline maintenance 

facilities, two private aircraft repair stations, and one 

military aircraft repair facility. We analyzed the vision 

standards currently applied to NDI/NDT personnel 

and the vision screening tests used at these facilities to 

confi rm that workers meet the level of vision performance 

required by these standards.

RESULTS

The vision standards at the maintenance facilities 

surveyed are presented in Table 2, including near vision, 

distant vision, color vision requirements, and the interval 

for testing used by each facility. (Note: The names of 

the maintenance facilities are withheld for the sake of 

anonymity and letter identifi ers were assigned.)

Table 3 summarizes the actual vision tests used for 

medical surveillance of NDI/NDT personnel at the 

facilities surveyed. 1

American Society of Nondestructive Testing, Inc. (ASNT), 

Recommended Practice No. SNT-TC-1A, defi nes qualifi ed as 

“demonstrated skill, demonstrated knowledge, documented training 

and documented experience required for personnel to properly perform 

the duties of a specifi c job”; certifi ed is defi ned as: “written testimony 

of qualifi cation.”
3

Table 1: FAA Recommended Vision Standard for NDI/NDT Personnel

VISION 

STANDARD NEAR VISION DISTANCE VISION COLOR INTERVAL 

MIL-STD-401E 

Jaeger #1 at not less 

than 12” or equivalent 

with one eye, either 

natural or corrected. 

None.

Distinguish and 

differentiate between 

colors used in the 

method for which 

certification is sought 

(Practical alternative). 

Annual

ATA Specification 105 

Snellen 20/25 or Jaeger 

#2 in at least one eye. 

Vision required from 

both eyes. 

Snellen 20/50 in at least 

one eye. Vision required 

from both eyes. 

Distinguish and 

differentiate between 

colors used in the 

method.

Not to exceed two years. 

AIA NAS 410 (May 

1996)

Jaeger #1 test chart at 

not less than 12” or 

equivalent as 

determined by medical 

personnel with one eye, 

either natural or 

corrected. 

None.

Distinguish and 

differentiate between 

colors used in the 

method for which 

certification is sought. 

Near vision annually and 

color perception tests 

shall be administered 

prior to certification or 

recertification 

ISO 9712 (1999-05-01) 

Reading a minimum of 

Jaeger #1 or Time 

Roman N4.5 or 

equivalent letters at not 

less than 30cm with one 

or both eyes, either 

corrected or 

uncorrected.

None.

The candidate can 

distinguish and 

differentiate contrast 

between the colours 

used in the NDT method 

concerned as specified 

by the employer. 

Annual
4

Table 2. Vision Standards at Selected Maintenance Facilities

Facility Near Vision Distant Vision Color Interval

(A)

Near Vision, of at least one eye, either 

corrected or uncorrected, must be such 

that the employee can read SNELLEN 

equivalent of 20/25 (Jaeger #2 or OrthoRater #8). 

Distant vision, of at least one eye, either 

corrected or uncorrected, must be equal 

to or better than SNELLEN equivalent of 

20/30

Color perception will be measured by the 

HRR Pseudo-Isochromatic Screening 

series or Ishihara Color Vision Tests. Any 

deficiencies are subject to approval of the 

Medical and NDT departments. 

2 years 

(B)

Near Vision of at least one eye, either 

corrected or uncorrected, must be such 

that the inspector can read Snellen 

equivalent of 20/25 (Jaeger #2 or Orthorater #8). 

Distant vision of at least one eye, either 

corrected or uncorrected, must be equal 

to or better than Snellen equivalent 20/30

Color vision shall be considered along 

with any physical requirements for 

inspection personnel at facility B. 

2 years 

(C)

The applicant must be capable of reading 

a minimum of Jaeger Number 2 letters at 

a distance of 12” on the standard Jaeger 

Test Chart, or equivalent, in at least one 

eye, either corrected or uncorrected. 

Must be such that the employee can read 

SNELLEN equivalent of 20/25. 

Distant Vision, of at least one eye, to 

better than SNELLEN equivalent of 

20/30. 

Color vision will be checked to determine 

any deficiencies that applicant has when 

performing MT or PT. 

2 years 

(D)

Near vision of at least one eye, either 

corrected or uncorrected, must be such 

that the individual can read Snellen 

equivalent of 20/25 or Ortho-Rater #8 

(Jaeger #1 @ 12” for NDI Inspectors) 

(Jaeger 2 @ 12 inches for visual 

inspectors)

Distant Vision of at least one eye, either 

corrected or uncorrected, must be equal 

to or better than Snellen equivalent of 

20/30. 

Color contrast differentiation - capable of 

distinguishing and differentiating contrast 

among colors. 

Yearly 

(E)

Near Vision – An annual examination by 

a medical technician using Snellen 

equivalent of 20/25 or Jaeger #1 @ 12 “ 

or equivalent, may be corrected 

None

Color perception – Shall be given to all 

NDI technicians at the same time as 

vision examination. Must be able to 

distinguish and differentiate between 

colors using the method for certification 

sought

Annual

(F)

Near Vision - Jaeger #1 test chart at not 

less than 12 “ or equivalent in with one 

eye, either natural or corrected. 

None

Color Perception: Distinguish and 

differentiate between the colors used the 

method for which certification sought 

Annual

(G)

Natural or corrected near distant such that 

the individual is capable of reading with 

at least one eye, the Snellen equivalent of 

20/25. (Ability to perceive Ortho-Rater 

minimum of eight or similar test pattern 

is also acceptable) 

None

Individual shall be capable of 

distinguishing contrast between colors 

using Ishihara color plates or another 

method which gives equivalent results. 

2 years 

(H)

Visual acuity (natural or corrected vision 

required to the following standard in at 

least one eye) Near Vision 20/20 Snellen 

equivalent required. 

Visual acuity (natural or corrected vision 

required to the following standard in at 

least one eye) Near Vision 20/25 Snellen 

required standard. 

Color Perception - Normal color vision is 

required for inspection personnel assigned 

to an inspection process in which color 

differentiation is essential. 

2 years 
5

DISCUSSION

Administrative differences in medical surveillance 

programs and the latitude allowed by the recommended 

vision standards resulted in considerable variation in vision screening methodology among the facilities surveyed. 

For example, larger maintenance facilities are more likely 

to have on-site clinics with medical personnel on staff 

to provide emergency and routine medical support for a 

substantial number of workers. Repair stations employ a 

considerably smaller workforce and may provide a medical professional (full or part-time), arrange periodic visits 

from local occupational healthcare providers, or contract 

their medical surveillance needs with off-site clinics.

An aircraft maintenance worker’s job classifi cation and 

vision performance requirements can vary within certain 

limits, and oversight is dependent on the administrative 

policy of the employer. At some facilities, NDI/NDT 

operations are kept independent of visual inspection activities, allowing for clearly defi ned job titles, responsibilities, 

and vision performance requirements between NDI/

NDT specialists and visual inspectors. In these facilities, 

NDI/NDT specialists may be allowed to perform most 

visual inspection tasks, but not all visual inspectors are 

qualifi ed to perform certain NDI/NDT procedures due 

to training and certifi cation requirements associated with 

these tasks. In other maintenance facilities, NDI/NDT 

specialists and visual inspectors were combined into a 

single department under a common administrative staff 

with identical medical surveillance practices. When this 

structure is applied, vision performance requirements must 

logically default to the most stringent standard required 

for any inspection task performed at the facility. However, 

even when two facilities perform similar maintenance 

tasks and apply similar administration policies, minimum 

vision performance requirements and vision screening 

tests can vary, depending on the particular recommended 

standard adopted by the facilities.

Work-related specifi cations often dictate the type of 

inspection or test required for a particular aircraft and/or 

aircraft component. These specifi cations also impact 

the qualifi cation and certifi cation requirements of the 

individual performing the work. The certifi cation process often requires the worker to meet a specifi c vision 

standard. In other words, depending on the type of work 

being performed, an employee’s vision requirements are 

more closely associated with the individual’s qualifi cation 

and certifi cation requirements than his specifi c job title 

(NDI/NDT specialist or visual inspector).

Table 3: Vision Screening Methods Used by Selected Maintenance Facilities

Facility Near Vision Test Used Distant Vision 

Test Used Color Test Used Test Performed By 

(A) Stereo Optical Vision Tester Stereo Optical Vision 

Tester

Stereo Optical Vision Tester 

and/or 

Ishihara PIP 

On-site Medical Personnel 

(B) Stereo Optical Vision Tester Stereo Optical Vision 

Tester Stereo Optical Vision Tester On-site Medical Personnel 

(C) EPSDT near Snellen card Snellen Wall Chart Ishihara (Concise Ed.) On-site Non-medical 

Personnel 

(D) Site 1 

Titmus Vision Tester 

and/or 

Western Optical Reading Card 

Titmus Vision Tester 

Titmus Vision Tester 

and/or 

Good-Lite PIP 

(D) Site 2 Western Optical Reading Card Snellen Wall Chart Good-Lite PIP 

On-site Medical Personnel 

(E) Titmus Vision Tester N/A Dvorine PIP Off-site Occupational 

Medicine Personnel 

(F) Graham-Field Jaeger Reading Card N/A Richmond International 

Pseudoisochromatic Plate Test 

On-site Occupational 

Medicine Personnel 

(G) Titmus Vision Tester N/A Titmus Vision Tester On-site Occupational 

Medicine Personnel 

(H) Stereo Optical Vision Tester Stereo Optical Vision 

Tester

Stereo Optical Vision Tester 

and/or 

Ishihara PIP 

On-site Medical Personnel 
6

Vision screening is further complicated due to multiple 

specifi cations for minimum visual acuity requirements 

used to certify NDI/NDT specialists who perform particular procedures. For example:

NAS 410 (1996) recommends: “Near Vision - Jaeger 

#1 test chart at not less than 12 inches or equivalent visual 

examination as determined by medical personnel.”

SNT-TC-1A recommends: “Jaeger Number 2 or 

equivalent type and size letter at the distance designated 

on the chart but not less than 12 inches (30.5 cm) on a 

standard Jaeger test chart.” 

Jaeger or similar test cards are used mainly to determine 

whether an individual has adequate accommodative ability or whether the near addition in spectacles (i.e., the 

bifocal addition) is suffi cient for older individuals (Figure 

1). The earliest reading test cards to attain widespread 

popularity were introduced by Jaeger in 1854 and are 

still in use. Print sizes are numbered for reference with 

the prefi x J (i.e., Jaeger number), the smallest size being 

J1. Each progressively larger text is noted with an increase 

in the J number. In some references, J1 is reportedly 

equivalent to 20/15 optotype and J2 to 20/20 optotype. 

However, tests are often implemented inconsistently 

with different cards and no specifi ed test distance (8). 

Originally, the “Jaeger number” simply referred to the 

number on the boxes in the print shop from where 

Jaeger selected his type; therefore, the number had no 

corresponding biological or optical foundation (8). Jaeger 

values have undergone a number of revisions over the 

years, but the “Revised Jaeger Standard” was adopted 

in the late 1950s (9). The Revised Jaeger Standard recommends that all near testing be kept at 14 inches. At 

this distance, J1 is equivalent to 20/20 Snellen visual 

acuity (10). Moving a chart closer or further away than 

the recommended testing distances changes the visual 

angle of the optotypes, resulting in changes to the visual 

acuity required to read the chart. If the Revised Jaeger 

Standard is used but the testing distance is changed, 

as has been recommended in some of the NDI/NDT 

vision standards, the actual visual acuity measured will 

vary. For instance, when the Revised Jaeger Standard is 

used, for J1 to be equivalent to 20/15 and J2 equivalent 

to 20/20, the test must be performed at a distance of 

17.5 inches. For someone with presbyopia, reading a 

near vision chart is easier at greater distances because 

there is less accommodative demand.

Figure 1. Jaeger Near Vision Card
7

Unfortunately, the actual visual acuity measured 

with Jaeger cards can vary even when the recommended 

14-inch test distance is maintained. Depending on the 

manufacturer, the size of print (point size) on Jaeger 

cards may vary by half a point. Therefore, J1 can be 3 to 

4 point, or 20/20 to 20/25 Snellen acuity at a 14-inch 

(35 cm) test distance, while J2 can be 4 to 5 point, or 

20/25 to 20/32 Snellen acuity at the same test distance 

(8). As a result of this inconsistency, it is suggested that 

reduced Snellen visual acuity charts be adopted for near 

vision tests should modifi cations be made to the current 

recommended vision standards.

In addition to differences in the devices used to conduct vision screening, the way they were administered 

also varied among facilities. Vision standards at most 

of the surveyed facilities required that inspectors meet 

the minimum acuity requirement in at least one eye 

(corrected or uncorrected). Only Facility D tested all 

inspectors’ binocular vision function as well as each eye 

independently. Eyecare practitioners routinely measure 

visual acuity in each eye, separately, as this practice can 

detect small changes in refractive error and may indicate 

functional changes in the visual pathway that can result 

from a pathological condition. However, if a person 

is monocular (i.e., < 20/200 in poorer eye), binocular 

acuity will be equal to that of the eye with better vision. 

For a binocular person, the binocular measurement is 

usually one-half to two lines of optotype better than 

that of the eye with better vision. Since most workers 

are binocular, a binocular measurement of visual acuity 

may better predict a person’s functional capability in the 

workplace. However, measurement of monocular acuities 

should also be encouraged to better detect pathological 

and functional changes in vision.

As this study shows, a number of tests are currently 

used to measure visual acuity at near distances. Jaeger 

cards were the most commonly used testing device for 

near vision by the facilities surveyed. As previously 

mentioned, depending on the manufacturer, Jaeger 

cards may vary in print size. The Rosenbaum near vision testing card is another widely used card, but some 

versions have been shown to be inaccurate because the 

optotypes are not properly scaled to the Snellen system 

(i.e., Rosenbaum optotype is 38-62% larger) (11,12). 

Other testing methods included reduced Snellen charts 

and vision screeners such as the Stereo Optical and Titmus units. While all of these test methods are considered 

acceptable when properly administered, problems can 

arise when one method is used for near vision tests and 

another is used for distance. When testing a presbyopic 

person, the test card is often kept at the distance where 

the person’s corrective lenses make the image clearest, 

not at the specifi c distance required for proper test chart 

calibration. Automated vision testers, such as the Titmus 

or Stereo Optical vision testers (Figure 2), should be 

carefully maintained (e.g., optics and slides kept clean, 

change bulb periodically) and require some degree of 

training to be used effectively. Inaccurate fi ndings may 

result when using these instruments if the person administering the test has not had adequate training and 

does not perform testing correctly (13,14). Vision testers 

are designed to be tabletop instruments that optically 

simulate a test distance of 14 inches for near tests and 20 

feet for distant tests. The actual nearness of the test slides, 

however, can stimulate an unintentional convergence of 

the eyes by the observer (proximal convergence) leading 

to less reliable fi ndings (15).

Figure 2. Stereo Optical (L) and Titmus (R) Vision Testers 
8

As a result of these diffi culties, use of a reduced Snellen 

visual acuity card (Figure 3), similar to the Near Vision 

Acuity chart (FAA Form 8500-1) used by the Federal 

Aviation Administration, should be encouraged. The 

card should be held at 16” (40 cm) from the eyes, at 

right angles to the line of sight, and illuminated with not 

less than 10 nor more than 25 ft-candles of light. The 

automated vision testers, such as the Titmus or Stereo 

Optical vision testers, are acceptable alternatives as long 

as testing is performed as instructed by the manufacturer 

and by properly trained personnel.

Observations of inspectors on-the-job have found that 

a substantial percentage of time is dedicated to work at 

intermediate distances (20-30”) (7) and the average age of 

the workforce is 45 years (6). Because an inspection item 

may not be accessible at the inspector’s prescribed best-corrected near visual acuity distance, an intermediate vision 

test may be necessary to assess a presbyopic individual’s 

visual performance capabilities more accurately. The 

current FAA aeromedical standard for fi rst- and secondclass pilots 50-years of age or older is 20/40 at 32” (16). 

A similar age-specifi c intermediate vision standard may 

be appropriate for NDI/NDT personnel (7).

Distant visual acuity is not required by all the standards 

recommended by the FAA. However, when distance acuity 

is included as a requirement at a particular maintenance 

facility, the required visual acuity ranged from 20/20 to 

20/50 (5). Visual acuity at distance is most often measured 

with high contrast letter charts, and there are numerous charts available that can be used at different testing 

Figure 3. Near Vision Acuity Chart (FAA Form 8500-1)
9

distances. The present international recommendation 

for distance visual acuity testing is based on a measurement of 4 m (13 ft), because a 6 m (20 ft) distance is not 

always possible in some examining rooms. In addition, 

to be comparable with the distance visual acuity, it is 

more desirable to measure near visual acuity with the 

same test symbols or optotypes as used for visual acuity 

at distance. Finally, the luminance level use for the test 

affects visual acuity values and, therefore, standardization 

is important. For standardization of test results, a Snellen 

20-foot eye chart or equivalent vision-screening device 

is recommended for testing NDI/NDT personnel. The 

chart should be placed 20 feet from the applicant’s eyes 

and the 20/20 line should be placed at approximately eye 

level. The eye chart should be illuminated by a 100-watt 

incandescent lamp placed 4 feet in front of and slightly 

above the chart. Care should be taken to prevent direct or 

refl ected glare from interfering with the applicant’s view 

of the chart. The examination room should be darkened, 

with the exception of the illuminated chart.

The color vision standards recommended for aircraft 

maintenance personnel often only require the ability to 

distinguish and differentiate colors used in specifi c testing 

or inspection tasks. Some facilities surveyed used sophisticated color vision tests, while others used modifi ed versions 

of these tests. It is often stipulated that practical tests be 

employed should an individual fail the initial color vision 

test. The myriad of possible variations in practical color 

vision tests effectively eliminates the potential for any 

standardization. However, when optimal color perception 

is required, the most commonly used color vision screening 

tests in optometric clinics are the American Optical (AO) 

or the Ishihara pseudoisochromatic plates with numbers. 

Many different tests have been produced containing similar 

designs to the Ishihara plates; however, the color quality 

often varies and none are superior to Ishihara for color 

vision screening (17). At some facilities, the “Ishihara 

Concise Edition,” introduced in 1989, was being used. 

However, it has been reported to be less accurate than the 

Ishihara 24- or 38-plate series (17). The Concise Edition’s 

14 test plates differ from the other Ishihara test plates 

in that they are printed on white background instead of 

individual white cards interleaved onto a black surround, 

as illustrated in Figure 4 (18). Additionally, the size of 

the color difference step determines the level of diffi culty 

for the test. If this is inappropriate, either false positives 

or false negatives will result. If the color difference step is 

too small, someone who has normal color vision may be 

incorrectly diagnosed as color defi cient, or if the color step 

is too large, some color defi cient observers may be incorrectly classifi ed as normal trichromats (18). Individuals 

who fail the pseudoisochromatic plate test may need to 

Figure 4. Ishihara Color Vision Tests

Concise Edition (14 plate) Sample

38-Plate Unlettered Sample

24-Plate Sample
10

be quantitatively assessed by using a functional test such 

as the Farnsworth Panel D-15 test (Figure 5). In this test, 

the person arranges colored caps in order starting with a 

blue “pilot” cap so that the next cap is closest in color with 

the previous. The advantage of this test is that the patient 

cannot memorize the test, as the caps are mixed, making 

each test situation new. The test reveals both the axis of 

the color defi ciency, whether red-green or blue-yellow, and 

the severity of the defi ciency.

Regardless of the color vision test used, testing conditions are critical for the validity of the tests. When nonstandard illumination is used, those with color defi ciencies 

may pass tests they would ordinarily fail, and those with 

normal color vision may fail tests they would ordinarily 

pass (19). Illumination should closely approximate northern skylight in natural daylight (19). It is recommended 

that all measurements of color vision be done under a day 

light lamp with a color temperature close to 6774K, the 

Commission Illumination de E’ Clairage (CIE) standard 

illuminant. Currently, the Richmond True Daylight HRR 

Illuminator with an easel stand meets CIE illumination 

standards for color vision testing.

In summary, it is evident from this review that the 

vision standards and medical surveillance practices vary 

greatly at different aircraft maintenance facilities. Even 

when the vision standard used had similar performance 

requirements (near and distance acuity, color vision), the 

method of application (who is tested) and administration 

(who performs the tests) differed, as did the method used 

for validation (vision screening test performed). Other 

differences included the time interval between examinations, the location for testing, and whether the tests 

are performed binocularly or monocularly. A review of 

the existing vision screening tests at other maintenance 

facilities may be necessary so that a meaningful spectrum of tests can be recommended that will effectively 

 characterize an inspector’s vision as adequate for the tasks 

performed. Use of standardized tests would also provide 

better quality control and a more accurate evaluation 

of visual capabilities for inspection personnel. Practical 

application of vision testing can improve the reliability 

and effectiveness of many inspection tasks and enhance 

aviation safety.

REFERENCES

1. Kleinstein RN. “Occupational optometry and 

primary care.” In: Pitts DG, Kleinstein RN, eds. 

Environmental vision: Interactions of the eye, vision and 

the environment. Butterworth-Heinemann, Boston, 

MA, 1993.

2. National Transportation Safety Board. Uncontained 

engine failure. Delta Air Lines fl ight 1288. McDonnell Douglas MD-88, N927DA, Pensacola Regional 

Airport, Pensacola, Jul. 6, 1996. NTSB/AAR-98/01. 

1998.

3. National Transportation Safety Board. Aircraft Accident Report. United Airlines Flight 232, McDonnell 

Douglas DC-10-10, Sioux Gateway Airport, Sioux 

City, Jul. 19, 1989. NTSB/AAR-90/06. 1990.

4. National Transportation Safety Board. Aircraft Accident Report. Aloha Airlines, Flight 243. Boeing 

737-200, N73711, near Maui, Hawaii, Apr. 28, 

1988. NTSB/AAR-89/03. 1989.

5. Paskiewicz FP. Qualifi cation Standards for Nondestructive Testing (NDT) Inspection/Evaluation 

Personnel. FAA Memorandum. Production and 

Airworthiness Division, AIR-200. 26 Sep. 2001.

6. Nakagawara VB, Montgomery RW, Good GW, and 

Nichols JJ. A demographic profi le of nondestructive 

inspection and testing (NDI/NDT) personnel: a 

preliminary report. Krebs WK (ed.) Proceedings of 

the Offi ce of the Chief Scientist for Human Factors’ 

FY03 Aviation Maintenance, General Aviation, and 

Vertical Flight Program Review. CD-ROM. Sep. 

10-11, 2003. Reno, NV.

7. Good GW, Nichols JJ, Subbaram MV, Nakagawara 

VB, and Montgomery RW. An analysis of the visual 

demands associated with aviation maintenance inspectors. Krebs WK (ed.) Proceedings of the Offi ce of 

the Chief Scientist for Human Factors’ FY04 Aviation 

Maintenance, General Aviation, and Vertical Flight 

Program Review. Nov. 16-17, 2004. Washington, 

DC. Retrieved Dec. 8, 2004 from Web site: www.

hf.faa.gov/FY04Program.htm. 

Figure 5. Farnsworth D-15 
11

8. Kniestedt C, Stamper RL. Visual acuity and its measurement. Ophthalmol Clin North Am. Jun. 2003; 

16(2):155-70.

9. Keeney AH, Durerson HL Jr. Collated near-vision 

test card. Am J Ophthalmol. 1958; 46:592-4.

10. Physicians’ Desk Reference for Ophthalmology. 

28th Edition. 2002; p. 64. Medical Economics 

Company.

11. Romano PE. Optotype distortion on the Rosenbaum 

Pocket Vision Screener. Ann Ophthalmol. Oct. 1989; 

21(10):362-3.

12. Horton JC, Jones MR. Warning on the inaccurate 

Rosenbaum cards for near testing near vision. Surv 

Ophthalmol. Sep.-Oct. 1997; 42(2):169-74.

13. Stereo Optec 2000 Vision Tester Reference and training Manual. Chicago, IL. Stereo Optical Company. 

1990.

14. Titmus Vision Tester Reference Manual, Petersburg, 

VA. Titmus Optical Company, Inc. 1970.

15. McAlister WH, Peters JK. The validity of Titmus Vision testing results. Mil Med. Sep. 1990; 

155(9):396-400.

16. U. S. Department of Transportation/Federal Aviation Administration: Guide for aviation medical 

examiners. Washington, DC: Sep. 2003; FAA Offi ce 

of Aerospace Medicine. Retrieved Dec. 8, 2005, 

from Web site: www.faa.gov/about/offi ce_org/ 

headquarters_offi ces/avs/offi ces/aam/ame/guide/

17. Birch J. Tests for defective colour vision. In: Birch 

J. Diagnosis of defective colour vision. 2nd Ed. Butterworth Heinemann, Boston, MA. 2001.

18. Birch J. Tests for defective colour vision. In: Birch J. 

Diagnosis of Defective Colour Vision. Oxford Medical 

Publication. Oxford, UK. 1993.

19. Swanson WH, Cohen JM. Color vision. Ophthalmol 

Clin N Am. Jun. 2003; 16(2):179-203.