Occupational dispensing

A reference guide to professional adviceand solutions for the workplace

Association of British Dispensing Opticians

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UPDATED JUNE 2

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Occupational dispensing

IntroductionThe eye, like all other parts of the body,is unique. From birth, through maturity toold age the eye constantly changes andwith these changes come challenges toensure visual capability, comfort andperformance are met. It is widelyrecognised that the ability to see is one ofthe most important human senses and assuch it is essential to ensure that thehealth of the eye is monitored on aregular basis. Regardless of age, it isessential that everyone has regular eyeexaminations, at specified intervals.

Interpretation of spectacle prescriptions isa highly skilled and complexcompetency. Understanding thecomplexities of the eye and the needs ofthe patient in order to achieve thedesired outcome is dependent on the skillof the individual undertaking the task. It istherefore advisable for the patient toseek professional advice at all timesduring the dispensing process.

This guide will consider the necessaryrequirements of eyesight and eyewearfor those in the workplace and in doingso will offer guidance for both correctiveand non-corrective situations. It is theintention to cover many areas ofworkplace situations where specificspectacle dispensing can obtaintangible results.

The eyeThe eye is an extremely complex structurewhich, in conjunction with the brain,provides the sense of sight. It is used in thevast majority of activities we performallowing us to see, interpret shapes,colours and dimensions of objects in theworld around us by processing the lightthey reflect or emit. It is able to detectbright or dim light, but is unable to sensean object when light is absent.

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Visual disordersWhen someone has what is best described as‘perfect vision’ the eye can be defined asbeing emmetropic. This would suggest a Snellenvisual acuity of 6/6, or better, in each eye withno discernible pathology present. When there isdeviation from emmetropia the eye is said to beametropic, and we come across the followingconditions affecting visual performance:

Myopia (short sight, the eye-ball is too long) iswhere rays of light entering the eye focusbefore they reach the retina. People withmyopia see objects more clearly when they areclose to the eye, whilst distant objects appearblurred or fuzzy, ie reading and close-up workmay be clear, but distance vision is blurry.

Hypermetropia (long sight, the eye ball is tooshort) is where rays of light entering the eyeconverge to focus beyond the retina. Vision isbetter for distant objects than those at near.

Presbyopia (occurs in middle age, due todeterioration of the flexibility of the crystallinelens and efficiency of the ciliary muscles withinthe eye) is the loss of the eye's ability to focuson close objects. It is a condition that occursas a part of the normal ageing process.Presbyopia progresses gradually over a numberof years and symptoms are usually noticeable inthose aged 40-45.

Factors affecting visual performance

In addition to conditions of the eye whichinfluence visual performance, there areadditional factors that are experiencedon a daily basis that have a considerableimpact on the eye. Many of which canbe related to the workplace.

GlareDifferent types of glare can affecteyesight in various ways ranging fromdistracting to disabling. By understandingthe effects of glare, appropriate solutionscan be employed when dispensingeyewear.

Distracting glareDistracting glare can be caused by carheadlights or streetlights at night. It canalso be as simple as light being reflectedoff the front surface of spectacle lenses,thereby making it difficult for others to seethe wearer’s eyes. Similarly, it may befrom light reflected off the back surface(ie the inner side) of the lenses, so that thespectacle wearer sees the distractingreflection of their own eyes and objectsbehind them in their forward field ofvision. As a result, this kind of glare maycause eye fatigue, annoyance anddistraction.

Discomforting glareGlare can be caused by every day,normal sunlight conditions. Dependingupon one’s light sensitivity, this glare can

be discomforting regardless of weather ortime of day. It can be present in any levelor intensity of light, or when moving fromone lighting condition to another.Discomforting glare often causes‘squinting’ and eye fatigue.

Disabling glareThis type of glare comes from excessive,intense light that can occur when facingthe sun. Disabling glare can block visionbecause the intense light can causesignificantly reduced contrast of theretinal image. It may come from lightreflected off smooth, shiny surfaces suchas water, sand or snow. In order todiminish the effects of blinding orreflected glare it is strongly advisable towear polarising filter lenses to counteractthe reflected light.

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Reduction of glarewith polarised lenses

Lens types and lens materials

Standard progressive lens Progressive lens specially adapted for drivers

Lens typesThe following information relates to thetypes of lenses and materials mostcommonly used in optical practice today.

Single vision lensesA single vision lens has the same focalpower across the entire lens surface(except if the lens is aspheric) and canbe used to correct myopia,hypermetropia, astigmatism andcombinations of the disorders mentioned.

Bifocal lensesA bifocal lens consists of two parts: theupper part is normally used for distancevision and the lower part (or segment)used for near vision tasks such as reading.

Trifocal lensesA tri-focal lens is similar to a bifocal withthe addition of a third segment generallyincorporating intermediate power.

Progressive lensesA progressive power lens (sometimescalled by its old name ‘varifocal’) hasno dividing lines as the focus changesprogressively from the upper to thelower portion of the lens to enablevisual comfort at all distances;distance, intermediate and reading.

Enhanced reading lensesAn enhanced reading lens provides agreater depth of focus than conventionalsingle vision lenses for reading and offersmore flexibility in working distance.

Occupational progressive lensesOccupational progressive power lens aredesigned for performing a particular jobor hobby however they are not meant forgeneral-purpose wear.

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Enhanced reading lens

Standard lens

Lens materials

Hard resinHard resin CR39 optical plastic is the mostcommonly used lens material in the UKtoday. This is because CR39 offers a goodbalance of clarity, durability, lightness ofweight, scratch-resistance (if hard-coated) and low price.

TrivexTrivex (also supplied under the brandnames of PNX and Trilogy) is thinner,lighter and more impact resistant (similarto polycarbonate) than CR39 withequally good optical properties, UVabsorption and chemical stability.

Polycarbonate Polycarbonate is an extremely highimpact material often used in safetyspectacles and for children’s spectacles.It does, however, have opticaldisadvantages.

Glass Glass is used infrequently nowadaysalthough still available for those whohave a preference. It should never beused for children or monocular patients orhazardous pursuits. Glass is notcompatible with the latest freeformmanufacturing techniques.

The workplaceWe will now look at specific areas in the workplace and occupationswhereby vision is fundamental to operating effectively.

DrivingIn many countries there are specificguidelines relating to vision and driving.Whilst regulations vary on means oftesting, it is common for the visionstandard to be at least 6/12 on theSnellen chart with both eyes open or inthe only eye if monocular. In recent timesthe UK Government has accepted thislevel of visual acuity as law when driving.*

For ‘Group 2’ drivers eg those individualswho drive large goods vehicles, lorries,busses etc. the vision in the good eyemust be at least 6/7.5 and at least 6/60 inthe other eye. Where glasses are worn tomeet the minimum standards, they shouldhave a corrective power ≤ +8 dioptres.The uncorrected acuity in each eye mustbe 3/60.

The minimum field of vision for safe drivingis defined as a field of at least 120° on thehorizontal and the extension should be atleast 50° left and right. In addition, thereshould be no significant defect in thebinocular field which encroaches within20° of fixation above or below thehorizontal meridian.

When wearing spectacles for driving, it ishighly recommended that users have ananti-reflection coating applied to reducethe effects of glare. Anti-reflectioncoatings are designed to achieve high

transmission in spectacle lenses andeliminate ghosting effects.

With uncoated CR39 lenses approximately4% transmission per lens surface is lost,resulting in a total reduction in lighttransmission of approximately 8%. But whenCR39 lenses are multi anti-reflectioncoated a light transmission factor (LTF) of99% is achieved, ie a loss of only 1%. In thecase of uncoated high index lenses, thereis an even greater transmission loss persurface, due to reflection; hence mostmanufacturers apply anti-reflectioncoating as standard procedure.

Historically, using lightly tinted lenses oryellow contrast enhancing tints for drivingwere popular, however, as technology hasdeveloped it is recommended that the useof anti-reflection coatings offer the bestsolution for driving at night or in non-sunnyenvironments, to the preclusion of tinting.

* Driver and Vehicle Licensing Agency. Assessing fitnessto drive - a guide for medical professionals (2016) isavailable at http://www.gov.uk/dvla/fitnesstodrive

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TrainsTrain drivers will almost certainly be drivingin differing climates and light conditions,therefore arrangements should be madeto cover all eventualities. In terms of visualacuity, the train driver will be required tohave visual acuity of 6/9 in the better eyeand 6/12 in the other eye, with near visionacuity of N8. Should any train driver havea colour deficiency they will not bepermitted to drive a train. It isrecommended that a train driver has aclear pair of spectacles, MAR coated,with an additional pair of tinted lens,whereby for obvious safety reasons colourdefinition is not compromised.

PilotsThe entry requirements for the aviationpilots require a visual acuity, withspectacles or contact lenses, to be 6/9 ineach eye with an ability to see 6/6

binocularly. Additionally there should beno anisometropia or astigmatism of morethan 2.00 dioptres. Pilots should carry aspare pair of spectacles at all times.

Sunglasses are an important piece ofprotective equipment in the cockpitenvironment. The tint should be neutral incolour, generally grey or brown areacceptable. The tint should be no darkerthan 80% absorption. It can also bebeneficial to consider a graduated tint,whereby the lens is tinted at the top andreducing in depth of tint at the bottom.

Polarised lenses reduce the amount oflight passing through the lens by selectivefiltering of certain electromagneticspectral planes. These lenses can causedistortion patterns from certaintoughened cockpit windshields.Historically these lenses were discouraged

Class Category Usage Tint Drivingtransmission restrictions

0 Clear or very Indoors or overcast 80 - 100% Nonelight tint

1 Light tint Light sunlight 43 - 80% Not suitable for night driving

2 Medium tint Medium sunlight 18 - 43% Not suitable for night driving

3 Dark tint Bright sunlight 8 - 18% Not suitable for night driving

4 Very dark tint Exceptionally Up to 8% Not suitable for drivingbright sunlight

Note: The above categories refer to Plano sunglasses, tinted prescription lenses with a transmission of less than 75% arenot suitable for use in twilight or night driving.

Driving and tinting categories

for use by pilots, however there havebeen advancements in technologywhereby the axis of the polarising filterhas been specifically controlled to ensurevisual recognition is not hindered allowingpilots to use if they so wish.

Light travels in all different directions,oscillating, which causes glare. Whena polarised filter is introduced the lightoscillates in one direction, p-state light.Polarising filters block or reduce lightreflected at certain angles from smooth,non-metallic surfaces such as glass orwater, thus reducing the effect of glareto the wearer.

Pilots who require spectacles will almostcertainly have specific needs. Whilst it isslightly easier to dispense spectacles tothose who require a distance-onlyprescription the objective is to achieveoptimum performance, in this caseconsidering strongly the merits ofbi-aspheric designed lenses to give asclear and natural fields of vision aspossible. However great care should betaken in dispensing these lenses, as veryaccurate vertical and horizontalcentration is essential.

When we start to deal with those who arepresbyopic it can become morecomplicated. Many will benefit from theuse of bifocals and progressive lenses

dispensed in a conventional manneralthough greater consideration must begiven to the working distancerequirements.

It is not uncommon to find pilots withdouble segment trifocals allowing them tohave pre-set working distances workedinto the lenses. This allows a pilot to see atdistance, intermediate and near.

Factory workersMany people such as engineers,processing personnel, cleaners, craftsmenetc. will work in a factory environment.Regardless of the risks associated with thespecific job it, is likely that in an industrialenvironment danger could arise from anumber of places and situations, whichhighlights the need to strongly considerthe risks to the eye. In many countriesaround the world, regulations are in placeto ensure that personal protectiveequipment (PPE), including protectiveeyewear, is used by all people operatingin such workplaces. Protective eyewearcan be prescription or non-prescriptionand come in a variety of options includingspectacles, goggles and shields. In termsof ‘safety’ spectacles, they will have sideshields attached to the sides of the frameto avoid any foreign objects entering theeye and surrounding area and it is likelythat the lenses supplied will be plastic(thickened CR39), toughened glass

(thermally or chemically), low energyimpact materials, or materials such aspolycarbonate or Trivex. Full details ofrequirements relating to safety can beobtained from ABDO publication'Protective eyewear'

Office workersThe modern day workforce in officeshave become extremely reliant upon theuse of computers, with many spendingthe majority of their working day viewinga screen. Often individuals will benefitfrom specific spectacles for use with acomputer screen, ie VDU spectacles.These can be used in addition to singlevision, bifocal or progressive lenses, whereworking distance is taken into account forthe individual’s workstation.

In an office environment, whilst workingwith computers, it is helpful to understand

more about ergonomics. Ergonomics is ascience concerned with the ‘fit’ betweenpeople and their work. It puts people first,taking account of their capabilities andlimitations. Ergonomics aims to make surethat tasks, equipment, information andthe environment suit each worker.

When we consider how they eye workswe must appreciate that everyone isdifferent, therefore visual capabilities andrequirements will alter dependant on theindividual worker.

These are some of the issues facingVDU users:

• The screen is poorly positioned - it is toohigh/low/close/far from the worker, or isoffset to one side

• The mouse is placed too far away andrequires stretching to use

• Chairs are not properly adjusted to fitthe person, forcing awkward anduncomfortable postures

• There is glare on the screen fromoverhead lights or windows, increasingthe risk of eyestrain

• Not enough breaks or changes ofactivity - prolonged use can lead tostaring and potentially dry eyes as aresult of insufficient blinking

• The office illumination is unsatisfactory,lighting intensity, incidental light orwindow position

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Maintaining correct and comfortable posture isessential to prevent neck and shoulder pains

These problems may result in mistakes andpoor productivity, eye strain, headaches,stress and other aches or pains.

When an office worker reachespresbyopia it will become more difficultto fulfil their needs with one pair ofspectacles. Generally speaking, it isn’tpossible to provide bifocals with theexpectation of satisfying all the wearer’sneeds, due to the positioning of thesegment, unless the lenses are specificallydesigned for intermediate and near use.Progressive lenses may achievefavourable results due to the progressionfrom distance through the intermediatecorridor to the reading zone. Freeformlenses should be considered, particularlydesigns that take into account theindividual fitting parameters, therebyoptimising visual performance. However itshould be remembered that mostprogressive lenses are designed for

‘general wear’ purposes and offer alimited intermediate area when it comesVDU use. Therefore the use of enhancedreading/occupational progressive lenses(OPALs) should be considered to caterspecifically for those using computers forprolonged periods. OPALs meet theergonomic criteria effectively as they canbe ordered to specific working distancesand offer increased fields of vision for therequired tasks. It is likely that wearers ofthese lenses will exhibit less headmovement than bifocal or progressivelens wearers.

Lens manufacturers have also introducedlenses aimed at those between the ages ofapproximately 30-45 who often find theeffects of extensive computer screen usetiring on the eyes. These lenses aredesigned in order to reduce the fatigueeffects of eye muscles by incorporating asmall amount of positive power in the lowerportion of the spectacle lens. These lensesare primarily used for everyday tasksinvolving the computer and concentratedactivities. Many who are pre-presbyopicfind such lenses particularly helpful formobile phone use.

Most office environments utilise fluorescentlighting, therefore added UV protectionmay also need to be considered.Anti-reflection coating is also stronglyrecommended for lenses used for VDU use.

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Progressive lenses canbe specially created foroffice workers

Teachers/Lecturers/PresentersFor people who have various visualrequirements it can be beneficial to havemultiple pairs of spectacles in order tooperate effectively. Regarding the roleof teachers, lecturers and those whodeliver presentations, it is clear thatneeds vary depending on the task. Forexample, if prolonged concentration isrequired to mark students’ work it wouldbe advisable to have reading glasses togive a full field of vision at a specifieddistance, however within the classroom

this will not be suitable. In the classroomteachers are standing most of the time,looking and walking around, leaningover their students to check their work,then writing on the board and also doingclose work, therefore distance and nearcorrection will be essential, as well asintermediate for the more maturepresbyope. For lesson preparation,intermediate and near correction isrequired. Progressive lenses should,perhaps, be the first consideration,

alternatively there might be a need forenhanced reading and intermediateuse with only a small requirement fordistance vision. In this situation, anoccupational progressive can beconsidered, with a limited distanceperformance but offering wideintermediate and/or near zones.

Occupational progressive lensescompliment the use of normalprogressives as they are designedspecifically for the work environment.

Considering this concept, it could bedescribed loosely as the reverse of that ofa conventional progressive lens, as thedistance vision has a considerablyreduced field whereas the intermediateand reading zones are designed to givewide optimum visual fields; ultimately anideal pair of spectacles for the workenvironment that can be interchangedwith normal progressive lenses dependingon the individual’s needs.

Shop workersShop workers will have various visualrequirements depending on their duties.Many will use tills, pricing equipment, dealwith written or printed orders and oftencomputers will be used. Essentially theadvice given to the office worker wouldreflect that given to teachers, though inthe office environment a wider distancefield would probably be required.

Outdoor activitiesOccupations where much of the workingday will be spent outdoors will requiresimilar visual considerations to many ofthe occupations mentioned already.However in this instance the additionalfactors of light and UV play a major parton final lens selection. For people such asgardeners, traffic wardens, police, roadworkers etc., additional lens options, suchas photochromic lenses, can beconsidered to ensure visual comfort isachieved. When photochromic lensesare exposed to ultraviolet rays theydarken and provide visual comfort indirect sunlight. The depth of tint will varydepending on the extent of the ultravioletlight and the outside temperature,though the latest photochromic materialsare much less affected by temperature.The depth of tint fades when moving outof the direct sunlight returning to a paletint indoors or to almost clear at night.The fact that the wearer can work

without changing spectacles is a distinctbenefit. Transitions photochromic lensesare available in Trivex andpolycarbonate material if the need foradditional impact protection is required,which is the case for many outdooractivities

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Please note the information in thisbrochure is only accurate at the timeof going to press.

AcknowledgementABDO would like to thank The Norville Groupfor providing many of the pictures thatappear in this brochure.

Association of British Dispensing Opticians199 Gloucester Terrace, London W2 6LDTelephone 020 7298 5100 Email general@abdolondon.org.ukWebsite www.abdo.org.uk

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