• The following are the requirements for the medical certification of aircrew, including guidance material issued by the UK CAA Medical Department in relation to the visual system

    Implementing Rules

    Acceptable Means of Compliance

    Guidance Material

    MED.B.070 Visual System

    Visual System  

    Refer to Eye Conditions for certificatory guidance on common eye conditions. 

    Refer to Isotretinoin policy for guidance, where appropriate. 

    Refer to guidance on Retinal Arterial Disorders and Retinal Vein Occlusion.

    Refer to Aviation laser exposure self-assessment (Alesa) (PDF)
    Medical reports - Ophthalmic (PDF)


    (a) Examination     
     
    1) For a class 1 medical certificate:

    (i) a comprehensive eye examination shall form part of the initial examination and shall be undertaken when clinically indicated and periodically, depending on the refraction and the functional performance of the eye.
     
    (ii) a routine eye examination shall form part of all revalidation and renewal examinations.  
     
    CLASS 1 - AMC1 MED.B.070

    (a) Eye examination 

     (1) At each aero-medical examination, an assessment of the visual fitness should be undertaken and the eyes should be examined with regard to possible pathology.

     (2) All abnormal and doubtful cases should be referred to an ophthalmologist. Conditions which indicate ophthalmological examination include but are not limited to a substantial decrease in the uncorrected visual acuity, any decrease in best corrected visual acuity and/or the occurrence of eye disease, eye injury, or eye surgery.

    (3) Where specialist ophthalmological examinations are required for any significant reason, this should be imposed as a limitation on the medical certificate.
      

    (4) The possible cumulative effect of more than one eye condition should be evaluated by an ophthalmologist.     
                                                                                 




     

    Eye examination 

    Refer to Ophthalmology Examination report (PDF) and guidance on completion. 

    A routine eye examination that forms part of all revalidation and renewal examinations shall include: history; visual acuity, near and distant vision (uncorrected and with best optical correction if needed), examination of the external eye, anatomy, media, fundoscopy and further examination on clinical indication.

    For conditions where deterioration in visual function may pose a significant risk to flight safety, then a Medical Assessor should impose a RXO limitation



     
     CLASS 1 - AMC1 MED.B.070

    (b) Comprehensive eye examination
                    
    A comprehensive eye examination by an eye specialist is required at the initial examination. All abnormal and doubtful cases should be referred to an ophthalmologist.
          
    The examination should include:
    (1) history;          
    (2) visual acuities - near, intermediate and distant vision (uncorrected and with best optical correction if needed);
    (3) examination of the external eye, anatomy, media (slit lamp) and fundoscopy;    
    (4) ocular motility; 
    (5) binocular vision; 
    (6) visual fields;
    (7) tonometry on clinical indication
    (8) objective refraction: hyperopic initial applicants with a hyperopia of more than +2 dioptres and under the age of 25 should undergo objective refraction in cycloplegia;      
    (9) assessment of mesopic contrast sensitivity; and
    (10) colour vision                                                                                                               

    CLASS 1 - AMC1 MED.B.070

     (c)  Routine eye examination  
      
    A Routine eye examination may be performed by an AME and should include:

    (1) history;
    (2) visual acuities – near, intermediate and distant vision (uncorrected and with best optical correction if needed);
    examination of the external eye, anatomy, media and fundoscopy; and further examination on clinical indication.

     

    Comprehensive eye examination

    Eye specialist refers to an ophthalmologist or an optometrist qualified in optometry and trained to recognise pathological conditions.

     

    2) For a class 2 medical certificate:
     
    (i) a routine eye examination shall form part of the initial and all revalidation and renewal examinations. 

    (ii) a comprehensive eye examination shall be undertaken when clinically indicated.     
                                                                                        
     

    CLASS 2 - AMC2 MED.B.070   


    (a) Eye examination

    (1) At each aero-medical revalidation examination an assessment of the visual fitness of the applicant should be undertaken and the eyes should be examined with regard to possible pathology. Conditions which indicate further ophthalmological examination include but are not limited to a substantial decrease in the uncorrected visual acuity, any decrease in best corrected visual acuity and/or the occurrence of eye disease, eye injury, or eye surgery.




    Eye examination 


    Refer to Ophthalmology Examination report (PDF) for information for AMEs on completion of the Ophthalmology form.





     
     (2) At the initial assessment, the examination should include:


    (i) history;
    (ii) visual acuities - near, intermediate and distant vision (uncorrected and with best optical correction if needed);
    (iii) examination of the external eye, anatomy, media and fundoscopy;
    (iv) ocular motility; 
    (v) binocular vision;
    (vi) visual fields;
    (vii) colour vision;
    (viii) further examination on clinical indication.
    (3) At the initial assessment the applicant should submit a copy of the recent spectacle prescription if visual correction is required to meet the visual requirements.

     

    At the initial assessment

    All initial applicants who use optical correction should submit the result of a recent spectacle prescription.
     
     CLASS 2 - AMC2 MED.B.070 

    (b)  Routine eye examination

    A routine eye examination should include:

    (1) history;
    (2) visual acuities - near, intermediate and distant vision (uncorrected and with best optical correction if needed);
    (3) examination of the external eye, anatomy, media and fundoscopy;
    (4) further examination on clinical indication.

     
    Routine eye examination

    Refer to  Visual Acuity conversion chart (PDF) for guidance on alternative notation used to record visual acuity measurements
     
    Refer to Visual Acuity revalidation/renewal for guidance on vision and visual acuity measurement at routine eye examinations.


     
    (b) Visual acuity

    (1) For a class 1 medical certificate:

    (i) Distant visual acuity, with or without correction, shall be 6/9 (0,7) or better in each eye separately and visual acuity with both eyes shall be 6/6 (1,0) or better.

     
    CLASS 1 - AMC1 MED.B.075

    (e) Uncorrected visual acuity 

    No limits apply to uncorrected visual acuity.

     
     
    (ii) At the initial examination, applicants with substandard vision in one eye shall be assessed as unfit.

    (iii) At revalidation and renewal examinations, notwithstanding point (b)(1)(i), applicants with acquired substandard vision in one eye or acquired monocularity shall be referred to the medical assessor of the licensing authority and may be assessed as fit subject to a satisfactory ophthalmological evaluation. 

     


    CLASS 1 - AMC1 MED.B.075

    (f) Visual acuity
     
    (1) Reduced vision in one eye or monocularity: Applicants for revalidation or renewal with reduced central vision or acquired loss of vision in one eye may be assessed as fit with an OML if:

    (i) The binocular visual field or, in the case of monocularity, the monocular visual field is acceptable;
    (ii) In the case of monocularity, a period of adaptation time has passed from the known point of visual loss, during which the applicant should be assessed as unfit;
    (iii) The unaffected eye achieves distant visual acuity of 6/6 (1,0) corrected or uncorrected;
    (iv) The unaffected eye achieves intermediate visual acuity of N14 and N5 for near;
    (v) The underlying pathology is acceptable according to ophthalmological assessment and there is no significant ocular pathology in the unaffected eye; and
    (vi) A medical flight test is satisfactory.

     

    Substandard vision 


    Local ophthalmologist reports and an assessment with a consultant aviation ophthalmologist will be required before a fit assessment can be made.

    Class 1 applicants with substandard vision should be referred to a Medical Assessor for further advice about the type of Medical Flight Test to be undertaken.

     
    (2) For a class 2 medical certificate:

    (i) Distant visual acuity, with or without correction, shall be 6/12 (0,5) or better in each eye separately and visual acuity with both eyes shall be 6/9 (0,7) or better.

    (ii) Notwithstanding point (b)(2)(i), applicants with substandard vision in one eye or monocularity may be assessed as fit, in consultation with the medical assessor of the licensing authority and subject to a satisfactory ophthalmological evaluation.

     
    CLASS 2 - AMC2 MED B.075   

    (c) Visual acuity

    Reduced vision in one eye or monocularity: Applicants with reduced vision or loss of vision in one eye may be assessed as fit if:

    (1) the binocular visual field or, in the case of monocularity, the monocular visual field is acceptable;
    (2) in the case of monocularity, a period of adaptation time has passed from the known point of visual loss, during which the applicant should be assessed as unfit;
    (3) the unaffected eye achieves distant visual acuity of 6/6 (1,0), corrected or uncorrected;
    (4) the unaffected eye achieves intermediate visual acuity of N14 or equivalent and N5 or equivalent for near (Refer to GM1 MED.B.070);
    (5) there is no significant ocular pathology in the unaffected eye; and
    (6) a medical flight test is satisfactory.

     

    Substandard vision 

    Class 2 - UK CAA Sub-standard vision (PDF) flow chart 
    Medical Flight Test (PDF) - Substandard Vision in one Eye

     

    (3) Applicants shall be able to read an N5 chart or equivalent at 30-50 cm and an N14 chart or equivalent at 100 cm, if necessary with correction.   
    (c) Refractive error and anisometropia 

    (1) Applicants with refractive errors or anisometropia may be assessed as fit subject to a satisfactory ophthalmological evaluation.

    (2) Notwithstanding point (c)(1), applicants for a class 1 medical certificate with any of the following medical conditions shall be referred to the medical assessor of the licensing authority and may be assessed as fit subject to a satisfactory ophthalmological evaluation:

    (i) Myopia exceeding -6.0 dioptres;

    (ii) astigmatism exceeding 2.0 dioptres;

    (iii) anisometropia exceeding 2.0 dioptres

    (3) Notwithstanding point (c)(1), applicants for a class 1 medical certificate with hypermetropia exceeding +5.0 dioptres shall be referred to the medical assessor of the licensing authority and may be assessed as fit subject to a satisfactory ophthalmological evaluation, provided that there are adequate fusional reserves, normal intraocular pressures and anterior angles and no significant pathology has been demonstrated. Notwithstanding point (b)(1)(i), corrected visual acuity in each eye shall be 6/6 or better.


     
    CLASS 1 - AMC1 MED.B.070

     (d) Refractive error and anisometropia

    (1) Applicants with the following conditions may be assessed as fit subject to satisfactory ophthalmic evaluation and provided that optimal correction has been considered and no significant pathology is demonstrated:

    (i) hypermetropia not exceeding +5.0 dioptres; 

    (ii) myopia not exceeding -6.0 dioptres;

    (iii) astigmatism not exceeding 2.0 dioptres; 

    (iv) anisometropia not exceeding not exceeding 2.0 dioptres.


    (2) Applicants should wear contact lenses if:

    (i) hypermetropia exceeds +5.0 dioptres;

    (ii) anisometropia exceeds 3.0 dioptres

     

    Refractive Error 


    Refer to SpecCalc (Excel) for guidance.

    Applicants for a class 1 medical certificate with any of the following medical conditions shall be referred to the medical assessor of the licensing authority and may be assessed as fit subject to a satisfactory ophthalmological evaluation:

    (i) Myopia exceeding -6.0 dioptres;

    (ii) astigmatism exceeding 2.0 dioptres;

    (iii) anisometropia exceeding 2.0 dioptres

    Assessment should be conducted by, or under the supervision of, an ophthalmologist and ensure that there is no underlying pathology or other ocular abnormalities.  Monocular visual acuities shall be 6/6 or better.  Assessment shall include: 

       1) Dilated, binocular, indirect ophthalmoscopy in cases of myopia exceeding –6.00 dioptres 

       2) Corneal topography at initial assessment (and at renewal where there is significant change in refraction) in cases of astigmatism exceeding 2.00 dioptres

    Applicants with excess hypermetropia exceeding +5.0 dioptres should be assessed by a consultant aviation ophthalmologist and referred to a medical assessor.  Monocular visual acuities shall be 6/6 or better. 

    Assessment shall include: 

    1) Intraocular pressures and anterior angle assessment, with gonioscopy where clinically indicated, to assess the risk of closed angle glaucoma attack 

    2) Fusional reserve testing to ensure there are no adverse prism effects from spectacles 

    3) Exclusion of underlying pathology or other ocular abnormalities

    Where hypermetropia exceeds +5.0 dioptres or anisometropia exceeds 3.00 dioptres and the applicant does not meet the usual standard with spectacles, a pilot who does not wear contact lenses should be referred to a local contact lens practitioner for suitability assessment.  A report should be provided after contact lens trial to either confirm successful wearing times and visual acuities or to specify why contact lens wear was not successful.



     

     
     (3) An evaluation by an eye specialist should be undertaken 5-yearly if:

    (i) the retractive error is between -3.0 and -6.0 dioptres or +3 and +5 dioptres;

    (ii) astigmatism or anisometropia is between 2.0 and 3.0 dioptres.

    (4) An evaluation by an eye specialist should be undertaken 2-yearly if:

    (i) the refractive error is greater than -6.0 dioptres or +5.0 dioptres;

    (ii) astigmatism or anisometropia exceeds 3.0 dioptres.

     
     
    (4) Applicants with a clinical diagnosis of keratoconus may be assessed as fit subject to a satisfactory examination by an ophthalmologist. Such applicants for a class 1 medical certificate shall be referred to the medical assessor of the licensing authority.
     
    CLASS 1 - AMC1 MED.B.075
     
    (g) Keratoconus 

    Applicants with keratoconus may be assessed as fit if the visual requirements are met with the use of corrective lenses and periodic evaluation is undertaken by an ophthalmologist.

     

    Keratoconus 

    A CCL limitation - correction by means of contact lenses - should be applied in cases of keratoconus where the visual requirements are met only with contact lenses, rather than spectacles.

    Refer to Eye Surgery for guidance following collagen cross-linking for keratoconus. 
    Medical reports - Ophthalmic (PDF)

     

    (d) Binocular function
     
    (1) Applicants for a class 1 medical certificate shall be assessed as unfit, where they do not have normal binocular function and that medical condition is likely to jeopardise the safe exercise of the privileges of the license, taking account of any appropriate corrective measures where relevant.

    (2) Applicants with diplopia shall be assessed as unfit.
     
    CLASS 1 - AMC1 MED.B.070

    (h) Binocular function

    Applicants with heterophoria (imbalance of the ocular muscles) exceeding:

    (1) at 6 metres:

    2.0 prism dioptres in hyperphoria,

    10.0 prism dioptres in esophoria,

    8.0 prism dioptres in exophoria

    and

    (2) at 33 centimetres:

    1.0 prism dioptre in hyperphoria,

    8.0 prism dioptres in esophoria,

    12.0 prism dioptres in exophoria

    should be assessed as unfit. A fit assessment may be considered if an orthoptic evaluation demonstrates that the fusional reserves are sufficient to prevent asthenopia and diplopia. 


    CLASS 2 - AMC2 MED.B.070 

    (d) Binocular function

    Reduced stereopsis, abnormal convergence not interfering with near vision and ocular misalignment where the fusional reserves are sufficient to prevent asthenopia and diplopia may be acceptable.


     
    Applicants for a class 1 medical certificate shall be required to have normal fields of vision and normal binocular function 


    Refer to Visual fields and binocular function policy for guidance on normal fields of vision and binocular function. 

     

    e) Visual fields

    Applicants for a class 1 medical certificate shall be assessed as unfit, where they do not have normal fields of vision and that medical condition is likely to jeopardise the safe exercise of the privileges of the license, taking account of any appropriate corrective measures where relevant.

     
    CLASS 1 - AMC1 MED.B.070 (f)
    (2) Visual Fields

    Applicants with a visual field defect, who do not have reduced central vision or acquired loss of vision in one eye, may be assessed as fit if the binocular visual field is normal.

     
     
      Eye surgery 
    Refer to Eye Surgery for guidance 
    Medical reports - Ophthalmic (PDF)
     
    (f) Eye surgery

    Applicants who have undergone eye surgery shall be assessed as unfit. However, they may be assessed as fit after full recovery of their visual function and subject to satisfactory ophthalmological evaluation. 

     
    CLASS 1 - AMC1 MED.B.075

    (i) Eye surgery

    The assessment after eye surgery should include an ophthalmological examination. 

    (1) After refractive surgery, a fit assessment may be considered, provided that:

    (i) stability of refraction of less than 0.75 dioptres variation diurnally has been achieved;

    (ii) examination of the eye shows no post-operative complications;

    (iii) glare sensitivity is within normal standards;

    (iv) mesopic contrast sensitivity is not impaired;

    (v) an evaluation is undertaken by an eye specialist.

    (2) Following intraocular lens surgery, including cataract surgery, a fit assessment may be considered once recovery is complete and the visual requirements are met with or without correction. Intraocular lenses should be monofocal and should not impair colour vision and night vision. 

    (3) Retinal surgery entails unfitness. A fit assessment may be considered 6 months after surgery, or earlier if recovery is complete. A fit assessment may also be considered earlier after retinal laser therapy. Regular follow up by an ophthalmologist should be carried out.

    (4) Glaucoma surgery entails unfitness. A fit assessment may be considered 6 months after surgery or earlier if recovery is complete. Regular follow-up by an ophthalmologist should be carried out. 



     
    Eye surgery 


    Refer to Eye Surgery for guidance

    Medical reports - Ophthalmic (PDF)
     

     CLASS 2 - AMC2 MED B.075   

    (e) Eye surgery

    (1) The assessment after eye surgery should include an ophthalmological examination.

    (2) After refractive surgery a fit assessment may be considered provided that there is satisfactory stability of refraction, there are no post-operative complications and no increase in glare sensitivity.

    (3) After cataract, retinal or glaucoma surgery a fit assessment may be considered once recovery is complete and the visual requirements are met with or without correction.
     

    Eye surgery 


    Refer to Eye Surgery for guidance

    Medical reports - Ophthalmic (PDF)
     

     
    (g) Spectacles and contact lenses 

    (1) If satisfactory visual function is achieved only with the use of correction, the spectacles or contact lenses shall provide optimal visual function, be well-tolerated and suitable for aviation purposes.

    (2) No more than one pair of spectacles shall be used to meet the visual requirements when exercising the privileges of the applicable licence(s).

    (3) For distant vision, spectacles or contact lenses shall be worn when exercising the privileges of the acceptable licence(s).

    (4) For near vision, a pair of spectacles shall be kept available when exercising the privileges of the applicable licence(s).

    (5) A spare set of similarly correcting spectacles, for distant or near vision as applicable, shall be readily available for immediate use when exercising the privileges of the applicable licence(s).

    (6) If contact lenses are worn when exercising the privileges of the applicable licence(s), they shall be for distant vision, monofocal, and non-tinted and well-tolerated.

    (7) Applicants with a large refractive error shall use contact lenses or high-index spectacle lenses.

    (8) Orthokeratological lenses shall not be used. 

     
    CLASS 1 - AMC1 MED.B.075

    (j)          Visual correction

    Correcting lenses should permit the licence holder to meet the visual requirements at all distances.

    CLASS 2 - AMC2 MED B.075   


    (f) Visual correction

    Correcting lenses should permit the licence holder to meet the visual requirements at all distances.

     

    Class 1 & 2 - Correcting lenses 

    Refer to  Guidance on presbyopic correction 

    Refer to guidance for the use of Contact lenses

    Refer to Guidance on pilot spectacle frame and lens choice

    Refer to Guidance on use of sunglasses by pilots

     

    MED.B.075          Colour vision Colour Vision  
    (a) Applicants shall be assessed as unfit, where they cannot demonstrate their ability to readily perceive the colour that are necessary for the safe exercise of the privileges of the license. CLASS 1 and 2 - UK Alternative AMC1 and AMC2 to MED B.075 Colour vision 

    (a) At revalidation and renewal examinations colour vision should be tested on clinical indication.
     
     
    (b) Examination and assessment

    (1) Applicants shall be subjected to the Ishihara test for the initial issue of a medical certificate. Applicants who pass that test may be assessed as fit.

    (2) For a class 1 medical certificate:

    (i) Applicants who do not pass the Ishihara test shall be referred to the medical assessor of the licensing authority and shall undergo further colour perception testing to establish whether they are colour safe.

    (ii) Applicants shall be normal trichromats or shall be colour safe.

    (iii) Applicants who fail further colour perception testing shall be assessed as unfit.

    (3) For a class 2 medical certificate:

    (i) Applicants who do not pass the Ishihara test shall undergo further colour perception testing to establish whether they are colour safe.

    (ii) Applicants who do not have satisfactory perception of colours shall be limited to exercising the privileges of the applicable licence in daytime only.




     
    (b) The Ishihara test (24 plate version) is considered passed if the first 15 plates, presented in a random order, are identified without error.

    (c) Those failing the Ishihara test should be examined by:

    (1) Anomaloscopy (Nagel or equivalent). This test is considered passed if the colour match shows normal trichromacy, i.e. a matching midpoint of 38-42 scale units and the matching range is 4 scale units or less; or if the anomalous quotient is acceptable; or by
     
    (2) Colour Assessment and Diagnosis (CAD) Test. This is considered passed if the threshold is less than 6 SU for deutan deficiency, or less than 12 SU for protan deficiency. A threshold greater than 2SU for tritan deficiency indicates an acquired cause which should be investigated.

     

    The Ishihara test is to be conducted as per manufacturer’s instructions: test distance 75cm with plane of plates at right angles to line of vision under daylight or daylight simulated light (usually colour temperature around 6500K) allowing 3 seconds per plate for response. The plates should be presented to the applicant in a random order. Ishihara plates should be updated periodically or if showing any signs of fading.

    The Alternative Means of Compliance submitted by the UK CAA can be accessed below this table.


    The UK CAA does not accept lantern testing as evidence of being colour safe.


    Anomaloscopy (Nagel or equivalent) may be considered provided the full protocol used for testing is enclosed with the result.  This test is only considered passed if the colour match shows normal trichromacy, i.e. a matching midpoint of 38-42 scale units and the matching range is 4 scale units or less. Tests that have not been performed in the UK must have been conducted by an Aeromedical Centre in another Competent Authority. Applicants failing the Anomaloscope test may undergo the CAD test.
     
    All applicants in the UK for advanced colour vision testing should be tested using the CAD test conducted under CAA protocols (available on request).


    The CAD test will only pass as colour safe, those individuals who perform as well as individuals with colour vision in the normal range on the most difficult aviation colour vision tasks. See CAA papers:


    CAA Paper 2006/04 Part 1 Minimum Colour Vision Requirements for Flight Crew: The Use of Colour Signals and the Assessment of Colour Vision Requirements in Aviation

    CAA Paper 2006/04 Part 2 Minimum Colour Vision requirements for Professional Flight Crew: Task Analysis

    CAA Paper 2009/04 Minimum Colour Vision Requirements for Professional Flight Crew: Recommendations for new colour vision standards.
    For further additional reading, see CAP 1429 Analysis of European colour vision certification requirements for air traffic control officers.


     

  • There is a wide diversity of colour testing methods employed and standards used for the assessment of flight crew minimum colour vision requirements throughout the world, including amongst European States.

    Ishihara (IH) tests

    Colour vision requirements and assessment of 'colour safety' based on Ishihara (IH) tests have the following problems:

    1. Inconsistent application of the manufacturers' instructions / CIE protocols for the conduct of the tests by the test operator/institution. 

    2. Variation in the lighting conditions used to view the test plates (illuminant spectral power distribution and illuminance level).

    3. Use of different test plate editions that are by no means identical, and the current availability of very inexpensive 'Ishihara' test plates sets on the web that may not be genuine.

    4. The possible use of other cues such as the recognition of vertically and/or horizontally arranged dot patterns, or the learning of the order of plates when the presentation sequence is not randomised.

    5. A large proportion of normal trichromats fail the IH plates (various editions) when the protocol requires zero errors for a Pass.  

    6. A large proportion of applicants with congenital colour deficiency (some with severe loss of RG colour vision) that pass with 3 or fewer errors on the 38 plates edition. There is little or no correlation between the applicant's severity of colour vision loss and the number of failed IH test plates. 

    7. When more than three errors are allowed as a pass, some applicants with congenital colour deficiency that pass can have severe loss of colour vision. For example, having a pass standard (e.g. for LAPL) that requires fewer plates to be correctly identified (LAPL 9 of the 15 plates) allows applicants with severe colour deficiency to pass. 

    Lantern Tests

    Colour vision requirements and assessment of 'colour safety' based on lantern tests have the following problems.

    1. Inconsistent application of the manufacturers' instructions for the conduct of the tests by the test operator/institution.

    2. Maintenance and calibration is usually not carried out. Old lanterns are difficult to service and many types are no longer manufactured. 

    3. Applicants can learn the order of the lights presented and use other cues to correctly name the lights, particularly if the starting point and order of presentation are not varied.

    4. The variability in outcome on repeated lantern test protocols is high which results in many false positives and negatives.

    5. Lanterns do not diagnose or quantify either the type or the severity of colour vision loss.

    6. A significant proportion of deutan subjects (in particular) pass lantern tests based on red, green and white lights without guaranteeing minimum colour deficiency.
       
    7. Different organisations/states performing the tests and interpreting the results have different definitions of what constitutes a pass.

    8. Many lanterns were not specifically designed for aviation purposes so the colour of the lights used and the intensity do not necessarily represent a proper representation of the coloured signals/ lights used in aviation.

    Anomaloscope Tests

    Colour vision requirements and assessment of 'colour safety' based on anomaloscope tests (i.e., dichromatic, RG colour matching tests) have the following problems.

    1. Inconsistent application of the manufacturers' instructions for the conduct of the tests by the test operator/institution.

    2. Calibration and proper maintenance cannot be demonstrated and 'normal' match parameters are usually needed when the light source is replaced, etc.

    3. There can be substantial differences in testing between anomaloscope type and models,  such as the use of white, interstimulus adapting fields.

    4. Although anomaloscopes (which employ a dichromatic Rayleigh match) distinguish between the type of RG colour deficiency (e.g., protan- vs deutan-like deficiency) the severity of colour vision loss and whether the applicant is 'colour safe' cannot be demonstrated.

    5. Different organisations/states performing the tests and interpreting the results have different definitions of what constitutes a pass. This particularly relates to interpretation of the matching midpoint and the size of the matching range. Applicants with a 'normal' matching mid-point as tested might have a large range, and those with a very abnormal midpoint might have a small matching range, often well within the mean matching range measured in normal trichromats.

    6. Some subjects exhibit 'extreme' anomalous matches that spread over the midpoint measured in normal trichromats. These subjects cannot therefore be diagnosed as either deutan- or protan-like.

    7. A small proportion of subjects exhibit normal Rayleigh matches, but demonstrate significant loss of RG chromatic sensitivity in other tests. The opposite is also the case when subjects with heavily abnormal anomaloscope midpoints exhibit completely normal RG chromatic sensitivity.

    8. Anomaloscopes were designed for clinical diagnostic reasons and not specifically designed for use in aviation to determine whether an individual is colour safe of not. They can determine whether subjects are normal trichromats with a normal matching mid-point and  normal matching range.

    The Colour Assessment and Diagnosis (CAD) Test

    The Colour Assessment and Diagnosis (CAD) Test provides an accurate and reproducible assessment of an applicant's class of colour vision and severity of RG and YB colour vison loss. The latter can be used to set Pass / Fail limits that do not discriminate against applicants with mild to moderate RG colour deficiency who have been shown to carry out the safety-critical, colour related tasks as well as normal trichromats.  

    The CAD test cannot be learnt and there are no cues the applicant could use to pass it. The results reflect only the RG and the YB sensitivity of the eye.  The results are expressed in Standard Normal CAD units (i.e., RG = 1.0 and YB = 1.0) which represent the median RG and YB colour signal strengths for young, healthy normal trichromats. A threshold of 6 units means that the applicant requires 6 times greater colour signal strength than the standard CAD observer. 

    Upper limits that describe the binocular and the monocular performance of normal trichromats as a function of age (~ 8 to 85 yrs of age) are incorporated in the test. These are used to screen reliably for normal trichromatic colour vision and also make it possible to detect the presence of retinal or / and systemic diseases that affect vision.  The CAD test can also detect acquired deficiencies, even when acquired loss is present in applicants with congenital RG colour deficiency.

    Reference Material

    1. CAA Paper 2006/04 Part 1 : Minimum Colour Vision Requirements for Flight Crew: The Use of Colour Signals and the Assessment of Colour Vision Requirements in Aviation.

    2. CAA Paper 2006/04 Part 2: Minimum Colour Vision requirements for Professional Flight Crew: Task Analysis

    3. CAA Paper 2009/04: Minimum Colour Vision Requirements for Professional Flight Crew. Recommendations for new colour vision standard 

    4. Barbur JL, Rodriguez-Carmona M, Harlow JA, Mancuso K, Neitz J, Neitz M. A study of unusual Rayleigh matches in deutan deficiency. Vis Neurosci. 2008 May-Jun;25(3):507-16.

    5. Squire TJ, Rodriguez-Carmona M, Evans Adb, Barbur Jl. Color Vision Tests For Aviation: Comparison Of The Anomaloscope And Three Lantern Types. . Aviat Space Environ Med 2005; 76:421-9.

    6. Detailed Interpretation Of The Nagel Anomaloscope.     

    7. Cole BL, Vingrys AJ. Who fails lantern tests? Doc Ophthalmol. 1983 May 1;55(3):157-75.

    8. Watson DB. Lack of international uniformity in assessing color vision deficiency in professional pilots. Aviat Space Environ Med. 2014 Feb;85(2):148-59.

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