Eyes and Vision
Appendix A: Eye Issues
Important principles to consider when dealing with eye issues in a LEO:
- Obtain a thorough exam by an eye professional, especially one familiar with the eye issue in question.
- Refer for further treatment if needed; for example, if the issue is poor visual acuity due to a cataract, have it removed and have an IOL placed.
- When the LEO is optimized, make the fitness-for-duty decision.
- If the condition is progressive, for example diabetic retinopathy, realize that periodic re-examinations are necessary as deterioration is likely to occur.
The best corrected visual acuity is a consensus recommendation of the Task Group. The Federal Motor Carrier Safety Administration requires corrected visual acuity of 20/40 in each eye (e.g., two eyes required) to operate a commercial motor vehicle.1 The Task Group believes driving in emergency response conditions is more visually demanding than driving a commercial vehicle. The literature describes performance decrements of important police functions (shoot/no shoot decisions, recognizing faces, identifying license plates, and weapons vs. non-weapons) as visual acuity worsens.2-6
California’s POST vision guidelines provide a detailed review of this literature.7 LEOs with vision worse than 20/20 appear to make significantly more errors in these situations, especially in dim light when more critical decisions are more likely to occur. For example, in dim light, correct identification of a potential weapon less than 6 feet away in officers with 20/20 vision was found to be less than 80%; with 20/60 vision it dropped to less than 40%.4 Similarly, LEOs with distant vision better than 20/20 made less than 10% errors in shoot/no shoot scenarios – in the 20/20 to 20/25 range, the error rate was less than 15%; in the 20/32 to 20/40 range, it was more than 20%; and at less than 20/60 was about 30%.3
Regarding uncorrected visual acuity, LEOs who wear glasses for correction of distant visual acuity are at risk for dislodgement of those glasses during critical and other important law enforcement activities.8 Should that occur, LEOs with uncorrected distant visual acuity of worse than 20/100 (binocularly – measured with both eyes open) are at a greater risk of being unable to perform job functions. When distant vision was worse than 20/100,9 there was a significant decrement in performance in two tasks: 1) discriminating between non-weapons and weapons; and 2) finding lost spectacles. Although soft contact lens wearers may risk dislodgement in critical situations, this is less likely. Bilateral loss is even more unlikely and is not nearly as likely as loss of glasses.8 Therefore, there is no uncorrected distant visual acuity recommendation for soft contact wearers. This recommendation is based on the presumption that the LEO is wearing soft contact lenses. If the LEO is not wearing soft contact lenses, the appropriate guidance should apply (e.g., spectacles or hard contact lenses).
The agency should consider what visual performance level it considers necessary. An agency may have unique job functions, needs, or issues related to operational risk management that requires a particular performance level.
Regarding near vision, LEOs should have corrected near visual acuity in the better eye of no less than 20/40; if either eye cannot be corrected to 20/40, both medical and functional evaluations should be conducted. The medical evaluation should be done to evaluate for eye diseases, especially those amenable to treatment. The functional test could include a demonstration of the ability to read and write documents or interpret computer/video images; this should be tailored to the demands of the job.
The military has extensive experience with refractive surgery for soldiers and airmen in operational settings with good outcomes.10,11 As a point of reference to assist the department’s physician in reviewing this opinion, U.S. military ophthalmologists usually clear personnel for deployment by 4 weeks post-operatively for laser-assisted in-situ keratomileusis (LASIK), and 12 weeks post-operatively for PRK or LASEK.12
Photorefractive keratectomy (PRK) and laser assisted sub-epithelial keratomileusis (LASEK) patients may return to work when approved by their surgeon, but should have a refraction at about 12 weeks and 6 months post-operatively to insure stability. In addition, those receiving “touch-up” surgeries should resubmit all information in these recommendations.
Post-operatively, the LEO should present a stable refraction (no more than ½ diopter of change between documented refractions at least 2 weeks apart). In addition, for unrestricted duty, the LEO should not have any of the following:
- use of steroid eye drops;
- significant haze (+2 or less is acceptable);
- glare, halos, starbursts, and ghosting (monocular diplopia);
- microstriae that affect vision;
- dryness that affects vision; and
- loose epithelium, diffuse lamellar keratitis (DLK), and/or active infection.
Every post-operative course after refractive surgery varies. The treating ophthalmologist should provide the previously described report (see Appendix B) that includes her or his opinion as to when the LEO is able to return to unrestricted duty. The department’s physician should review this opinion.12
LEOs who are status post-refractive surgery should have an annual refraction or visual acuity measurement to assess for possible deterioration; this is even more critical for LEOs who originally presented with greater refractive errors (e.g., >7 diopters).
Exposure to physical confrontation or pepper spray is allowable after return to unrestricted duty following any refractive surgery. Officers should consider ballistic eye wear in situations where these events are likely to occur (e.g., in-service or police academy training).
Radial keratotomy (RK) is an archaic procedure. Nearly every RK patient will be many years post-surgery. RK patients are very prone to progressive hyperopia or regressive changes with time. These patients must have an ophthalmologist exam and an annual refraction (which should include diurnal measurements showing no more than ½ diopter of variation), which should be reviewed by the agency’s physician. Due to the much higher risk of globe rupture from incidental trauma, these individuals should wear ballistic eye wear when in training or on patrol.
Orthokeratology is a method to improve visual acuity by wearing specifically shaped hard contact lenses to reshape the cornea so that when the lens is removed, the newly shaped cornea leads to improved visual acuity. Although this method can be effective, it wears off quickly (hours to days) and the lenses have to be worn again to “reshape” the cornea. This method leads to inconsistent visual acuity and therefore is not recommended as a suitable answer for visual acuity problems.
LEOs who have had cataract surgery usually receive an intraocular lens (IOL). These individuals should be tested for visual acuity at the intermediate range (16 inches to infinity), since this is the distance where weapons are encountered as well as the distance at which computer displays are used. Some (particularly older) IOLs do not cover this range, which may require the use of glasses to obtain a 20/20 binocular distant visual acuity. Many newer IOL correct for a full range of distances and make the use of glasses unnecessary. In all cases, testing should be done to ensure compliance with the guidance.
Color vision is critical in a number of areas, including identification of vehicles and suspects, identifying evidence, and recognizing license plates, buildings, and containers.7,17 Color vision is also important in recognizing the status of brake and traffic lights, critical for pursuit driving.17 There is evidence that drivers who are color vision deficient have more accidents related to interpretation of traffic signals and recognition of brake lights.18 Also, those with defective color vision also have problems identifying items in visual searches when color recognition is important.19 LEOs with mild color vision deficiency still may be able to identify colors correctly.20,21 However, more severe impairment (e.g., failing the Farnsworth D-15 test) is well correlated to difficulties in color recognition.22 LEOs with moderate to severe color impairment will require restrictions.
Color vision can be impaired due to issues with red, green, or blue cones. Ideally, the LEO should be evaluated by methods that test for: 1) red-green deficits (protan – weak red function, or deutan – weak green function); and 2) blue-yellow deficits (tritan – weak blue function). Because congenital tritan deficits are rare (1 in 10,000), the value of screening for them is limited. However, screening for tritan deficits can detect other acquired retinopathies (e.g., diabetic, hypertensive). In LEOs with any color vision impairment, it is critical to qualify the severity (mild, moderate, severe).23
Table 1 lists some of the commonly used color vision tests and their ability to test for different types of color vision deficits. Other than the Ishihara, the Farnsworth D-15 or the HRR, these tests are uncommon in routine clinical practice in the U.S.
Detects Protan or Deutan
Measures Degree of Impairment
|HRR, 4th Edition||Yes||Yes||Yes|
|Farnsworth D-15||Yes||Yes||Yes (mild vs. moderate-severe)|
|City U. London||Yes||Yes||No|
|SPP2||Yes (to some degree)||Yes||No|
|Lanthony 15 Desat||Yes||Yes||Mild only|
*Adopted from Richmond Products (now Good-Lite Co.) color vision chart.
The Task Group consensus is that the HRR and D-15 are more comprehensive tests since they cover tritan deficiencies and can describe the degree of impairment. Nevertheless, due to the rarity of tritan deficiently and the ubiquity of the Ishihara pseudoisochromatic plates, the Ishihara PIP test using plates 1-11 is a reasonable screening tool (additional plates can be used, but the Ishihara manual defines normal color vision as correct identification of plates 2-11).
The Hardy Rand and Ritter (HRR) 4th edition pseudoisochromatic plates test represents a good choice for color screening for LEO candidates as it is fast, covers both red-green and blue-yellow deficits, provides a gradation of defects, is inexpensive and is readily available for purchase. The Ishihara pseudoisochromatic plates (PIP), commonly found in many physician offices are also good for rapid screening of candidates. When a candidate fails to pass on either set of isochromatic plates (Ishihara or HRR), it is recommended to use a more functional test to evaluate color vision performance. That next test commonly used is the Farnsworth D-15. Alternatively, instead of using isochromatic plates, a clinic could just use a Farnsworth D-15 as their screening tool; the only drawback is a slightly longer administration time (about 1 minute for isochromatic plates versus 3 minutes for the D-15.) For the Farnsworth D-15, the Task Force opinion was that to avoid clearing persons with moderate (not mild) defects, a passing score requires no (zero) major (i.e., diametrical) crossings.24 If the physician has access to an anomaloscope or a Cone Contrast Testing machine, these items can be used as well to measure the degree of color impairment, although they are rare outside academic or military institutions.25 The use of traffic light simulators, lanterns, threads, yarns, or wire insulation to assess color vision is not appropriate.
Color vision testing must be done with the appropriate illumination (i.e., correct wavelength and intensity). Failure to do so can result in erroneous data and conclusions.24
The use of tinted lenses (e.g., “X-chrom”) to pass the test is not an acceptable accommodation. Use of tinted contact lenses to pass a pseudoisochromatic plate test has been associated with poor color identification (especially greens) and poorer depth perception.26,27 LEOs who have blue-yellow deficits (tritans) should be referred to an ophthalmologist for evaluation for other eye pathology as a tritan defect can be a sign of other eye pathology such as retinal diseases or cataracts.
Binocular visual field deficiencies have been associated with increased errors in operating motor vehicles.28,29,30 LEOs with glaucoma should receive formal visual field testing annually, since they generally deteriorate. Formal visual field testing should be done on all individuals with a history of eye disease and in those who cannot be corrected to 20/20 in either eye.
LEOs should have binocular vision for adequate visual performance. Although the literature regarding monocularity and accident risk is mixed, adaptive factors need consideration. In addition to scanning (turning head or eyes side to side to enhance the visual field), monocular drivers often slow down their vehicle speed, especially in non-familiar areas. This is in direct contrast to the essential function of pursuit driving which requires high-speed driving in a variety of areas. LEOs also need binocular vision for appropriate situational awareness.31,32,33
While anisometropia itself is not always a problematic factor, it often indicates that the LEO has a condition that may be a problem and that needs treatment or correction. Anisometropia occurs when the two eyes have unequal (significantly different) refractive power. Anisometropia is particularly significant when the LEO cannot be corrected to 20/20 in each individual eye. In these cases, the LEO should be referred to an optometrist or an ophthalmologist for a thorough evaluation to rule out more significant eye pathology including measurement of phorias and tropias.
It is not recommended that LEOs undergo surgically induced anisometropia or “monovision.” The American Academy of Ophthalmology and the federal government both note numerous side effects from surgically induced anisometropia (i.e., monovision), including blur or fog, glare/halos (especially at night), reduced night-time vision (especially with driving), reduced depth perception, and transient double vision. Visually demanding tasks (e.g., law enforcement) usually require the wearing of corrective lenses.34
LEOs who have undergone monovision correction via Lasik or other surgeries need to have a distance-corrected visual acuity of 20/20 binocularly, with at least 20/40 in each eye. Uncorrected distant visual acuity should be as previously defined in the section on Uncorrected Distant Visual Acuity. The near visual acuity in the better eye should be at least 20/40 with or without corrective lenses. Corrective lenses will typically have to be worn.
Nyctalopia (Night Vision Impairment)
Nyctalopia is the inability to see well at night or in poor light. It is not a disease in itself, but rather a symptom of a possible underlying disease, such as cataracts, glaucoma, vitamin A deficiency or retinitis pigmentosa. In the absence of such diseases, there is controversy about the magnitude of impairment of individuals with this complaint.15
Night myopia is probably the most common cause for the complaint of nyctalopia and is due to accommodation shift at low light levels. Chromatic and spherical aberrations are minor effects. Diagnoses of night myopia are usually managed with negative corrective lenses. Other diagnoses should be addressed as possible.
Stereopsis or the ability to perceive depth by the fusion of visual images of two eyes is only one of a number of methods that humans assess depth. Stereopsis is particularly useful for small targets that are close at hand (<1m), and may be useful for LEOs. It is less useful with larger targets and longer distances. Stereopsis is only one of a number of items used to determine a perception of depth. Humans also use parallax, size, shading, interposition, perspective, and relative distance to complete their perception of depth.35 Stereopsis does not play a major role in high-speed driving. It has not been found to be critical in other tasks such as backing of a tractor trailer, lift truck operations or stock picking. A 2011 Canadian Tribunal decision (Lauzon v. Ontario Provincial Police) judged that a lack of stereopsis was not sufficient to exclude training for a stereopsis-deficient candidate.36
Although not disqualifying in itself, the consensus recommendation of the Task Group is that individuals who have less than 100 seconds of arc in stereopsis should be referred for further evaluation as LEOs with this level of visual performance may have other conditions such as amblyopia, a phoria, or tropia that should be addressed to optimize their visual performance.
Standard visual acuity testing uses black and white letters in a well illuminated area. However, LEO work rarely takes place in black and white and/or well-illuminated areas. Contrast sensitivity testing is useful in evaluating the quality of vision in areas with poor illumination, glare, fog, and haze, and in workers with retinal and other non-spherical eye disease. Contrast sensitivity testing measures two variables, size and contrast, while acuity measures only size. Decreased contrast sensitivity is a strong predictor of inferior driving performance.
Routine contrast sensitivity screening is not indicated for most LEOs as it is most likely to be normal in persons without eye disease. However, LEOs with complaints of glare issues or with retinal diseases, diabetic retinopathy, cataracts, optic neuritis, corneal aberration, or irregular (higher order) astigmatism should have their conditions optimized as much as medical or surgical interventions allow. When those interventions have been done, contrast sensitivity testing should be performed. LEOs with a Pelli Robson score of ≥1.50 in the worse eye are unlikely to be impaired. LEOs with a Pelli Robson score of <1.25 in the worse eye are unlikely to be able to perform the essential job functions of a LEO. Those with scores between 1.50 and 1.25 should be monitored annually for deterioration of function. Discussion with an optometrist, ophthalmologist, vision scientist, or physician experienced in these issues would be important in making decisions regarding surveillance and restrictions for workers with scores between those values. The agency may wish to create a job simulation scenario to verify adequate performance.16