Occupational Eye Disease

Dr. Alireza Safaeian

Occupational Medicine Specialist

Assistant Professor of Isfahan University of Medical Sciences

Visual Assessment

Visual Acuity

• Definition

• Visual acuity is a measurement of central

vision only

• Assessment of total visual system from

cornea to occipital cortex

Normal Vision

Normal vision relies on the following:

• Both eyes in alignment (extraocular muscles

functioning)

• Clear cornea

• Clear lens of the eye

• Clear ocular media (aqueous and vitreous)

• Intact retina, optic nerve, visual pathway

• •Each eye needs to be tested separately •Use an occluder to cover the eye that is not being tested •If glasses are worn, the occluder goes over the top of the glasses •If occluder is not available use the patient’s cupped hand or a patch •Avoid pressure on the eye and be aware of patients peeking through their fingers

The Snellen Chart

•Place patient 3 or 6 metres from chart (depending on the chart) •Use adequate illumination •Cover left eye with occluder / pad or cupped hand •Ask patient to read from the top letter •Keep going until they cannot read the line clearly and start to make multiple errors. The previous line is the line you document.

The Snellen Chart

•Encourage patient to keep going as some give up easily •Encourage patient to relax and blink regularly •If the 6/6 line is not reached, use pinholes to see if vision improves •If yes, continue testing vision until the patient is unable to clearly identify further letters/ numbers

Documentation

• Record visual acuity (VA) for each eye • Include pinhole (PH) if used • If wearing glasses or contact lenses please document • Artificial eyes need to be noted too Examples:

RVA 6/9 LVA 6/6 (with glasses) PH 6/6

RVA 6/60 LVA prosthesis PH no improvement

Documentation (cont)

• If the patient cannot see the top line of the chart, walk patient towards the chart so they are at 3 metres.

• Still can’t read the chart? Ask patient to count how many fingers you are holding up at 1 metre. Keep fingers still. Recorded as Count Fingers (CF @1m)

• If they cannot count fingers see if they can see a moving hand. Recorded as Hand Movements (HM @1m)

• Still no result: can they see a pen torch light : Light perception (LP)

• Unable to perceive light: No Light Perception (NLP)

Documentation Examples

RVA HM @1m LVA 6/60 (forgot glasses)

PH6/60 PH 6/9

RVA 6/9 LVA HM @1m

PH no improvement PH CF @1m

RVA 6/60 @3m LVA 6/6

PH no improvement

VISUAL ACUITY MALINGERING (FUNCTIONAL VISUAL LOSS)

Visual Acuity Malingering

Mirror test A mobile full size mirror is placed in front of the subject , and he/she is told to look at it both eyes open. When moving the mirror slightly to and fro examiner looks at the subject's eyes secretly. If the subject looks at himself in the mirror, it means he/she can see

Visual Acuity Malingering

• Snellen test in mirror Six-meter of regular visual acuity assessment distance could be easily doubled via mirror and subject is made think his/her visual acuity irregularly reduced.

Visual Acuity Malingering

Optokinetic nystagmus (OKN) • OKN is thought to occur

because the eyes are trying to keep a moving image stationary on the fovea.

• The reflex is fully developed by 5-6 months, but is present in a crude form in newborn infants.

Visual Acuity Malingering

• The visual evoked potential (VEP), or visual evoked response (VER):

• measurement of the electrical signal recorded at the scalp over the occipital cortex in response to light stimulus

Confrontation visual field testing

Perimetry Test

Color Vision

ISHIHARA’S TEST

Stereoscopic Vision

and

Depth Perception Testing

Depth Perception Testing

• In order to see 3D and with stereo depth perception your brain has to use the visual information from both eyes.

• If the two eye views are too different and cannot be matched up, the brain will be forced to make a choice. It will reject all or part of the information from one eye.

• The brain can ignore, suppress or turn off visual information it cannot use.

Eye Accidents

• Between 5% and 19% of all industrial injury.

• Superficial foreign body

• Penetrating foreign body

• Chemical injury

• Electromagnetic injury

Eye Strain and Visual Ergonomics

• Impaired vision, double vision and blurred vision

• Itchy dry eyes and discomfort while looking at the VDT

• Headaches

• Eye fatigue that can have serious impact later in life

Computer Vision Syndrome (CVS)

• Bad monitor resolution, flickering, or glare at the monitor

• Poor lighting and conditions in the computer room

• Electromagnetic radiation emitted by the VDT (UVA)

• Staring at anything for a long period of time will cause blurred vision