Penny Shaw MSc, FCOptom

Types Effects

Hypermetropia Axial length too short or refractive power too low Light would focus behind retina Accommodation 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 eyes Headaches Blur N and/or D – transient or permanent Increased problems in low light

Myopia Axial length too long or refractive power too high Focal plane infront of retina Accommodation is no use

Effects of myopia Blur beyond far point (e.g 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 planes Simple/myopic/hyperopic/ mixed Accommodation is of little use Irregular astigmatism results from corneal ectasia (eg. keratoconus), scarring, surgery Bar to military flying

Effects of astigmatism Blur D and N Doubling or ghosting of image Point sources spread along orientation of astigmatism Glare in bright light Headaches

Presbyopia

Effects of presbyopia Blurring at near Headaches Eyestrain/tired eyes after near work Difficulty refocusing to distance after near work First noticed in dim light / poor contrast (cockpits, maps!)

Questions?

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 read Note: people have good memories!

Recording vision Standard testing distance: UK=6m, US=20ft Vision 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 eye Letter size increases iaw similar triangles: e.g 6/12 letter is double the size of 6/6 letter Can also be recorded as decimal e.g. 6/6=1.0, 6/12=0.5, 6/3=2.0

Recording vision Snellen P ULHEEM S <6/608 6/607 6/366 6/245 6/184 6/123 6/92 6/61 6/41 V = vision without correction VA =Visual acuity with correction PULHEEMS 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

Questions?

Convex Concave Toric Recognition

Convex lenses - recognition Thicker in the middle Magnifying effect Face 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 effect Face 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

Questions?

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 refraction Best sphere Fit trial frame correctly Record monocular vision including Ph vision Unaided vision: correspondence to degree of refractive error esp. myopia e.g 6/60 approx -3.00, 6/12 approx Uncorrected hyperopia may not blur vision

Start with Does it blur? NO Add Does it blur? Yes Try instead Does it blur? No Try Does it blur Yes Try instead Does it blur? No Try Does it blur? Yes Reject last change END POINT – Record VA Subjective refraction Start with +ve lenses

Is it clearer ? Yes Add Is it clearer? Yes Add Is it clearer ? No Reject and add instead Is it clearer? No Reject and confirm with Does it blur by about 3 lines? Yes END POINT REACHED Record VA Subjective refraction Move to –ve lenses if myope Note unaided vision: start with appropriate strength e.g. V6/12 start with -1.00

Subjective refraction Best sphere – final check Final check with should blur vision by ~ 3 lines If VA remains below Ph level, consider astigmatism correction

Questions?

Types Aftercare Issues

Spectacles vs CL in aviation Depends on A/C type CFS mist up, restrict field of view, fall to bits, hurt CL: Some issues mainly to do with lens dehydration. CL generally preferred to CFS Daily 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 types Daily disposable: sph or toric designs, hydrogel/silicone hydrogel FRP: hydrogel/silicone hydrogel replaced weekly, 2-weekly or monthly. Durable: tailor-made hydrogels Complex fits eg keratoconus - kerasoft (hydrogel or silicone hydrogel)

Modalities Daily wear with daily disposable or FRP Flexible wear: occasional overnight use Continuous wear: up to 30 days Orthokeratology (OK): overnight rigid lenses give temporary correction

Aftercare intervals Daily wear Extended /flexible wear Initial fitting 7-10 days 1-3 months 6 months Initial fitting 1 week daily wear (practice lens handling) After 1 st overnight wear 1 week CW 3 months 6 months

Aftercare checks Vision: stability, over refraction Fit/comfort Wearing times Compliance Lens handling Ocular response

CL in aviation - advantages Full field of view Integration with head furniture No misting Aesthetics!

Contact lens complications (very few!) Subjective:  Drying  Excess movement  Poor/fluctuating vision  Lens supplies/storage  Solution use/storage

Objective: Corneal oedema/ hypoxia Drying CLPU Contact lens complications

Poor lens hygiene Lid reactions MK

Questions?