Driving with Eye Disease

Anatomy of the Eye

The eye is one of the most important organs that has a lot of working parts with each part playing a complex role in helping us to see.

The eye is small being on average around 2.5 cm in diameter.

The various important structures of the eye are outlined below by the Fred Hollows Foundation. (1)

Cornea; This is the clear front “window” of the eye .It continues backwards to form the tough outer fibrous coat of the eyeball. Visible at the white part of the eye and this coat is called the sclera.

Iris: The Iris acts as the gatekeeper that controls the amount of light that enters the eye. The iris also gives the eye its attractive colour.

Lens: This is a clear specialised protein structure that helps focus images by adjusting the eye’s focussing power according to how near or far way an object is.

Vitreous gel; This is the clear, firmly jelly which forms the main bulk of the eye between the lens and the retina, and helps to support its internal structure.

Ciliary body: This is a muscle that changes the shape of the lens to allow for focusing. A watery fluid is produced by this gland that is known as the aqueous humor. The balance between the production and drainage of this fluid is one of the key factors that creates the pressure to which the eye is “pumped up”.

Retina: The retina is a delicate and consists of finely layered nerve cells which line the inside of the eye. It receives light (similar to the film in analog cameras) and converts it into electrical signals for transmission to the brain.

Macula: This is the area that contains the greatest concentration of light-sensitive cells, the photo receptors that allows us to see things in great detail as well as to receive colour signals.

Optic Nerve: This nerve is formed from all the fine nerve fibres that originate from the photoreceptors in the retina. The fibres gather into a cable-like bundle and exit the back of the eye through small openings in its tough outer coat.

The head of this optic nerve is viewed through the pupil as a structure known as the optic disc.

How do Eyes Work?

The eye is like a tiny camera that processes the light reflected off surfaces to create images that we see.

There is a muscle that acts like a lens called the iris that controls the size of the pupil (similar to an aperture).

When the light entering our eye is too bright, the iris reduces the size of the pupil but when it is dark, the iris in the pupil is enlarged or dilated to maximise the amount of light entering the eye.

After the retina receives the correctly focused light, the role of the retina is to analyse colour, intensity and form to transmit these electric impulses to the brain

The various parts of our brain are connected by the optic nerve to ensure that our emotions, experiences and visual impulses are combined together as an image that we do not just see, but actually perceive.

The actual image from the retina is actually upside down and our brains flip the image around to prevent confusion.

The cornea and the lens work together to bring the light into focus on the retina (the back of the eye) and this is dependent on how far away the object is that we are looking at.

The lens is much more dynamic, especially in young people and changes shape (thickness and curvature) to assist us to shift focus.

If the light from an image isn’t perfectly focused, this can often be corrected with the assistance of appropriate glasses or contact lenses.

Eye Problems and Eye Diseases

There are a host of medical conditions that can affect the eye and an individual should seek medical attention as soon as possible if they have a problem with the eye.

These may include conditions such as Blepharitis(inflammation of the eyelids associated with chronic eye irritation, watery eyes, foreign body sensation, sensitivity to light and crusty debris at the base of the eyelashes) and diabetic retinopathy ( a condition where the retina of the eye is damaged due to diabetes).

A more comprehensive outline of various eye diseases and eye problems are outlined by Gary Heiting (2).

Visual Standards to hold a UK Driver’s License

In the United Kingdom, the visual standard to hold a UK driver's license since 2012 includes visual acuity (VA) measured indoors and the ability to read a car numberplate outdoors (3)

When individuals possess reduced contrast sensitivity, they may have greater visual difficulties outdoors.

Consequently Rae and colleagues investigated the agreement between the 2 tests in the presence of combined reduction in contrast sensitivity and Visual acuity.

Simulation glasses (“sim-specs”) were used to reduce both high-contrast VA and contrast sensitivity (CS).

After evaluation of the influence of sim-specs on VA and CS, levels 2 to 4 were chosen to give a range of VAs on either side of the driving standard of 6/12.

62 participants wearing sim-specs then had VA tested with Snellen and ETDRS charts indoors, and ability to read a number plate assessed outdoors as per DVLA regulations.

Sim-specs reduced VA and CS by ~0.10 logMAR VA per 0.10 logCS.

The sensitivity of test chart VA <6/12 to correctly predict failure on the numberplate was 61% for Snellen and 56% for ETDRS.

False-negative and -positive rates were higher than in a previous study with uncorrected refractive error only.

Reduced CS increased the lack of agreement between the 2 driving vision standards, which likely occurs as the VA test is performed indoors and the numberplate test outdoors.

The increased likelihood of failing the numberplate test even though VA is 6/12 or better needs to be considered when advising patients on fitness to drive who have ocular disease such as cataract.

Very interestingly, B E Dougherty and colleagues conducted a retrospective study of patients who received a vision examination and subsequently obtained bioptic licensure. (4)

They obtained driving records from the Ohio Bureau of Motor Vehicles in order to determine motor vision collisions (MVC) involvement.

They investigated the relationships among vision, age, sex, previous experience, and MVC’s using time-to event analysis and the Cox proportional hazards regression model.

More than 40 states in the US allow for some form of bioptic driving licensure for people with decreased central vision where bioptic telescopic spectacles (BTS) consist of a small telescope(s) mounted high in a pair of spectacle lenses.

The purpose of their study was to determine significant associations among previous driving experience, vision, and MVs for bioptic drivers in Ohio.

The authors found that Visual acuity and contrast sensitivity were not significant predictors of MVC in a study of 237 (65% were males) bioptic drivers.

Furthermore the age at initial exam ranged from 16 to 81 years and mean visual acuity was approximately 20/120.

The number of MVCs per driver ranged from 0-11 with 124 (52%) of drivers having at least 1 MVC.

Visual acuity and contrast sensitivity were not significant predictors of MVC.

Drivers without previous driving experience were significantly more likely to have been involved in an MVC (P < 0.001), and this association remained significant after adjusting for age and sex (P = 0.01).

Thereafter the rate of MVC per year decreased steadily over a 10-year period for drivers without previous experience.

The authors concluded that previous nonbioptic driving experience, but not visual acuity or contrast sensitivity, was associated with yearly MVC rate in bioptic drivers.

What about the effects of Different Levels of Refractive Blur on Nighttime Pedestrian Visibility?

Wood and colleagues investigated the effects of different levels of refractive blur and driver age on night-time pedestrian recognition and also whether clothing that has been shown to improve pedestrian conspicuity is robust to the effects of blur. (5)

They studied Night-time pedestrian recognition for 24 visually normal participants (12 younger mean=24.99 ±4.5 years and 12 older adults mean=77.66 ± 5.7 years) for 3 levels of binocular blur (+0.50 diopter [D], +1.00 D, +2.00 D) compared with baseline (optimal refractive correction).

Pedestrians walked in place on a closed road circuit and wore one of 3 clothing conditions: everyday clothing, a retro-reflective vest, and retro-reflective tape positioned on the extremities in a configuration that conveyed biological motion (known as "biomotion"); the order of conditions was randomized among participants.

Pedestrian recognition distances were recorded for each blur and pedestrian clothing combination while participants drove an instrumented vehicle around a closed road course.

The investigators found that recognition distances for pedestrians were significantly reduced (P < 0.05) by all levels of blur compared with baseline.

Furthermore, pedestrians wearing biomotion clothing were recognized at significantly longer distances than for the other clothing configurations in all blur conditions.

However, these effects were smaller for the older adults, who had much shorter recognition distances for all conditions tested.

The very interesting conclusion was that even small amounts of blur had a significant detrimental effect on night-time pedestrian recognition.

Biomotion retro-reflective clothing was effective, even under moderately degraded visibility conditions for both young and older drivers.

How Does Obesity Impact on Driving Safety?

E Demird??en ?etino?lu and fellow researchers examined the relationship between obesity, risk of obstructive sleep apnoea, daytime sleepiness, history of road traffic accident and performance on a driving simulator among commercial drivers.

They found that obese drivers failed in the peripheral vision test when compared with non-obese (p=0.02) (6)

How to Improve Your Eyesight

A diet that is high in fruits and vegetables and low in sugar and fatty foods will greatly assist you to maintain healthy eyes. (7)

It is important to have Vitamin A, C and E, along with minerals like copper and zinc in your daily diet.

These vitamins are essential for good vision and protection against diseases.

Strawberries, salmon, mackerel, eggs, oranges and almonds are an excellent source of vitamins with oysters, turkey and crabs ideal for minerals.

Beta-carotene, lutein and zeaxanthin are antioxidants that help protect your eyes from getting sun damage.

They are commonly found in dark leafy vegetables, pumpkins, sweet potatoes and carrots.

It is important to protect the lens of your eyes from forming cataracts.

Garlic, caper and onions provide sulphur, cysteine and lecithin that are a good food source to protect the lens of your eyes.

Vision can also be improved by eating grapes, blueberries and goji that possess anti-inflammatory properties such as anthocyanin.

By taking around 1,000 mg of omega-3 fatty acids per day can also help to prevent macular degeneration and dry eyes.

Herring, flaxseeds, mackerel, salmon and walnuts are high in omega=3 fatty acids.

Exercise your eyes daily can also assist you to maintain healthy eyes and optimum vision. (8)

It is very important to also rest and relax your eyes by taking breaks throughout the day and to obtain enough sleep every night to fully repair, and recover your vision.

Lack of sleep will weaken your vision health (9)

It is essential to visit an optometrist regularly to check for visual impairments or diseases that may harm your overall eye health.

Symptoms such as blurred vision, near-sightedness, or farsightedness may require corrective eyewear or surgery. (10)

To improve your vision if you have either near-sightedness or farsightedness you may need to wear glasses.

Corrective lenses will either counteract the increased or decreased curvature of your cornea or the length of your eye. (11, 12)

If surgery is utilised instead of corrective lenses, a doctor uses a laser to reshape the cornea. (13.14)

It is also wise to keep the room you are in softly lit.

Fluorescent lighting is generally considered bad for the eyes because they give off the wrong light frequencies of colour and emit radiation that makes you drowsy all day long.

Where possible avoid watching television or the computer in the dark. (15)

To prevent dry eye that is caused by a lack of lubrication and moisture on the surface of your eye it is important to improve air quality. (16)

This will assist to prevent problems such as minor irritation to serious inflammation of the tissues of the eye.

It is essential to invest in the correct glasses or contact lenses for your specific situation.

The optometrist can tailor the prescription for the most likely environment where you will be wearing your glasses. (17)

Wherever possible, limit your computer usage. They are a major source of eye strain for most people.

Limit your screen time b routinely taking breaks, exercising your eyes, and keeping them hydrated. (18, 19)

References

(1) The Fred Hollows Foundation. https://www.hollows.org/au/eye-health/the-eye

(2) Gary Heiting, OD. Eye Problems and Diseases. https://www.allaboutvision.com/conditions/

(3)  Rae S, Latham K, Katsou MF. Meeting the UK driving vision standards with reduced contrast sensitivity. Eye (Lond). 2016 Jan; 30 (1):89-94 doi: 10.1038/eye.2015.188. Epub 2015 Oct 16.

(4)  Dougherty BE, Flom RE, Bullimore MA, Raasch TW. Previous Driving Experience, but Not Vision, Is Associated With Motor Vehicle Collision Rate in Bioptic Drivers. Invest Ophthalmol Vis Sci. 2015. Oct; 56(11):6326-32. doi: 10.1167/iovs.15-16882.

(5)  Wood JM, Marszalek R, Carberry T, Lacherez P, Collins MJ. Effects of Different Levels of Refractive Blur on Nighttime Pedestrian Visibility. Invest Ophthalmol Vis Sci.2015.Jul; 56(8):4480-5. doi: 10.1167/iovs.14-16096.

(6)  Demird??en ?etino?lu E, G?rek Dilektasli A ,Demir NA, ?zkaya G, Acet NA, Durmus E, Ursavas A, Karada? M, Ege E. The relationship between driving simulation performance and obstructive sleep apnoea risk, daytime sleepiness, obesity and road traffic accident history of commercial drivers in Turkey. Sleep Breath 2015 Sep:19 (3):865-72.doi:10.1007/s11325-014-1114-6.Epub 2015.Jan 22.

(7)  ↑https://www.allaboutvision.com/nutrition/nutrition_summary.htm

(8)  ↑ https://www.allaboutvision.com/buysmart/see_clearly.htm

(9)  ↑ https://www.labnol.org/software/computer-eye-exercise/14069/

(10) ↑ https://www.mayoclinic.org/tests-procedures/eye-exam/basics/what-you-can-expect/prc-20014417

(11)↑ https://www.mayoclinic.org/diseases-conditions/farsightedness/basics/treatment/con-20027486

(12)↑ https://www.mayoclinic.org/diseases-conditions/nearsightedness/basics/treatment/con-20027548

(13)↑ https://www.mayoclinic.org/diseases-conditions/farsightedness/basics/treatment/con-20027486

(14)↑ https://www.mayoclinic.org/diseases-conditions/nearsightedness/basics/treatment/con-20027548

(15)↑ https://www.consumerhealth.org/articles/display.cfm?ID=20000102232127

(16)↑ https://www.allaboutvision.com/conditions/dryeye.htm

(17)↑ https://www.skincancer.org/prevention/sun-protection/for-your-eyes/how-sunlight-damages-the-eyes

(18)↑ https://www.mayoclinic.org/diseases-conditions/eyestrain/basics/lifestyle-home-remedies/con-20032649

(19)How to Improve Your Eyesight. https://www.wikihow.com/Improve-Your-Eyesight