Presentation on theme: "Penny Shaw MSc, FCOptom. Types Effects Hypermetropia Axial length too short or refractive power too low Light would focus behind retina Accommodation."— Presentation transcript:
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. -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 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
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
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 -1.00 Uncorrected hyperopia may not blur vision
Start with +1.00 Does it blur? NO Add +1.00 Does it blur? Yes Try +0.50 instead Does it blur? No Try +0.50 Does it blur Yes Try +0.25 instead Does it blur? No Try +0.25 Does it blur? Yes Reject last change END POINT – Record VA Subjective refraction Start with +ve lenses
Is it clearer ? Yes Add -0.50 Is it clearer? Yes Add -0.50 Is it clearer ? No Reject and add -0.25 instead Is it clearer? No Reject and confirm with +1.00 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 +1.00 should blur vision by ~ 3 lines If VA remains below Ph level, consider astigmatism correction
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
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