Penny ShawMSc, FCOptom

Types Effects

HypermetropiaAxial length too short or

refractive power too lowLight would focus behind

retinaAccommodation needed

to bring image into focus

Accommodation is the increase in power of the intraocular lens effected by contraction of the ciliary muscle

Effects of Hypermetropia

Nothing!Tired, irritable eyesHeadachesBlur N and/or D – transient or permanentIncreased problems in low light

Myopia

Axial length too long or refractive power too high

Focal plane infront of retinaAccommodation is no use

Effects of myopia

Blur beyond far point (e.g. -1.00 myopia = blurred after 1m)

Glare from light sources affects night driving / flying

Occasionally headaches

Astigmatism

Irregular curvature of the refractive surface(s), usually the cornea

2 or more focal planesSimple/myopic/

hyperopic/mixedAccommodation is of

little use

Irregular astigmatism results from corneal ectasia (eg. keratoconus), scarring, surgery

Bar to military flying

Effects of astigmatismBlur D and NDoubling or ghosting of

imagePoint sources spread along

orientation of astigmatism Glare in bright lightHeadaches

Presbyopia

Effects of presbyopiaBlurring at nearHeadachesEyestrain/tired eyes

after near workDifficulty refocusing to

distance after near work

First noticed in dim light / poor contrast (cockpits, maps!)

Snellen chart at exactly 6 metres (or other known distance)

Well illuminated (preferably internally)

Use occluder, avoid pressing on eye, squeezing eye shut or looking through fingers

Record smallest line correctly readNote: people have good memories!

Recording visionStandard testing distance: UK=6m, US=20ftVision recorded as the fraction: test distance/letter

size“Standard vision”: UK 6/6, US 20/20“Standard vision”: Each limb of the letter subtends

1’ arc at the eyeLetter size increases iaw similar triangles: e.g 6/12

letter is double the size of 6/6 letterCan also be recorded as decimal e.g. 6/6=1.0,

6/12=0.5, 6/3=2.0

Recording visionSnellen PULHEEM S

<6/60 86/60 76/36 66/24 56/18 46/12 36/9 26/6 16/4 1

V = vision without correctionVA =Visual acuity with correctionPULHEEMS Recording under EE R V/VA L V/VA

e.g. 7/2 4/1

R Unaided 6/60 corrects to 6/9, L Unaided 6/18 corrects to 6/6

ConvexConcaveToricRecognition

Convex lenses - recognition

Thicker in the middleMagnifying effectFace looks larger

within spx frame“Against” movement

of image

Convex lenses - use

Correction of hyperopia and presbyopia

Concave lenses - recognition

Thinner in the middle

Minifying effectFace looks smaller

within spx frame“With” movement of

image

Concave lenses - use

Correction of myopia:

Toric lenses - recognition

Can be concave, convex, simple or mixed

Swivel test produces “scissor” effect

Toric lenses - use

Correction of astigmatism

Refraction determines the position and orientation of each focal plane

Spectacle lenses

Spx lenses are thin, curved to improve visual comfort and appearance

Convex

Concave

Subjective refraction

Aim

To determine the lens strength needed to focus parallel light from distant object on to the retina of the relaxed eye

Subjective refraction

Use maximum plus to ensure relaxed accommodation

Use minimum minus to ensure accommodation is not stimulated

Clearest image with relaxed eye

Subjective refraction

Subjective refractionBest sphere

Fit trial frame correctlyRecord monocular vision including Ph visionUnaided vision: correspondence to degree of

refractive error esp. myopia e.g 6/60 approx -3.00, 6/12 approx -1.00

Uncorrected hyperopia may not blur vision

Subjective refractionBest sphere – final check

Final check with +1.00 should blur vision by ~ 3 lines

If VA remains below Ph level, consider astigmatism correction

Types Aftercare

Issues

Spectacles vs CL in aviation Depends on A/C typeCFS mist up, restrict field of view, fall to

bits, hurtCL: Some issues mainly to do with lens

dehydration. CL generally preferred to CFSDaily disposables preferred

Survey of Refractive correction in RAF Aircrew :2004: Shaw P, Scott RAH, Mushtaq B, Coker W

Refractive Correction in RAF Aircrew: 2006: Partner A, Scott RAH, Shaw P, Coker W

Lens typesDaily disposable: sph or toric designs,

hydrogel/silicone hydrogel FRP: hydrogel/silicone hydrogel

replaced weekly, 2-weekly or monthly. Durable: tailor-made hydrogelsComplex fits eg keratoconus -

kerasoft (hydrogel or silicone hydrogel)

ModalitiesDaily wear with daily disposable or FRPFlexible wear: occasional overnight useContinuous wear: up to 30 daysOrthokeratology (OK): overnight rigid lenses

give temporary correction

Aftercare intervalsDaily wear Extended /flexible wear

Initial fitting7-10 days1-3 months 6 months

Initial fitting1 week daily wear

(practice lens handling)After 1st overnight wear1 week CW3 months 6 months

Aftercare checks

Vision: stability, over refraction

Fit/comfortWearing times ComplianceLens handlingOcular response

CL in aviation - advantages

Full field of viewIntegration with head furnitureNo mistingAesthetics!

Contact lens complications (very few!)

Subjective:

Drying Excess movement Poor/fluctuating vision Lens supplies/storage Solution use/storage

Objective:

Corneal oedema/ hypoxia

DryingCLPU

Contact lens complications

Contact lens complications

Poor lens hygieneLid reactionsMK