E C BTZ FCLBO toebhfc Z EBHCLFOB cbfzetfbocze EZCOBFCH E L B Z VISUS , =°.5 Jana Sokolová Šidlová Visual Acuity • Definition: ability of the visual system to detect spatial changes • Performed at viewing distance of 5 or 6 m and 40 cm for near Minimum separabile • Emetropic eye: we can only distinguish two points from one another if there is between two cones irritated to the retina one cone not irritated • These two cones are observed at an angle of one minute Minimum separabile • The average length of a cone is approximately 0,005 mm and the retinal distance from image modal point of the eye is approximately 17 mm. The angular distance still distinguishable poinds are: • tga=0,005/17 -> a~l angular minute 17 mm tga = 0,005 / 17i=>a= 0,0167°= 1 ühlovä minuta The principle of VA measurement ■ Types of measurements: Unaided VA-visual acuity without correction (natural, native) abbreviations: UCVA =, Vsc =, VAsc =, VN= Habitual VA-own glasses or contact lenses (existing spectacle correction) abbreviation: VAcc = Optimal VA - best corrected VA after subjective clinical refraction abbreviations: BCVA =, Vcc =, VAcc = Stenopic aperture (pinhole disk) • The target with a small hole in the center • The part of trial lens kit • May be used diagnostically to determine a patient's potential VA • It transmits only narrow parallel rays of light • In stenopic vision the refractive error is ruled out. If poor vision persists - it is not the case of a refractive error. • Experiment - now we can try Evaluation of visual acuity ■ used to measure the visual acuity during clinical refraction-optotypes ■ Snellen optotypes: letters, numbers, pictures, symbols ■ Each symbol is inscribed in a square visible from a specified distance below the viewing angle of 5' ■ The symbol thickness (not size) is equal to one fifth of the square and corresponds to angle of 1' ■ Examination distance: 5 m or 6 m (the eye is in the rest, the acommodation is less then 0,25 D - the eye is looking to infinity, it does not acommodate) ■ We measure first the right eye and then the left eye Optotypes ■ According to the design: printed panels, light panels, projection charts and LCD optotypes, 3 D charts ■ Snellen, Pfluger, Landolt, pictures, LEA, ETDRS optotypes ■ The most of optotypes chats have the range of visual acuity - 1,6 - 0,1 Projection optotype with mirror image Optotyp zrcadlo Optotype symbols are turned over, optotype - placed over the patient's head, opposite the patient is the mirror at eye level Snellen optotypes • Herman Snellen (1834-1908) - a Dutch ophthalmologist • 1862 - Snellen optotypes • 6/60, 6/36, 6/24, 6/18, 6/12, 6/8, 6/6, 6/5, 6/4 • The signs: C, D, E, F, L, N, O, P, T, Z • The patient have to identify minimum 60% of the optotype sign at the line Landolt C optotype is recommended by the ICO is the standard optotype ( C - a standardized symbol) for acuity measurement in most European countries. It was standardized. The Landolt C consists of a ring that has a gap, thus looking similar to the letter C ( The width of the gap and the thicknes of the line of the symbol is V5 of the diameter, and the gap width is the same) 8 different positions of the gap (comparison to the positions of a clock face) j Pfluger E (hooks) = (Tumbling E test) • Can be performed on children or patients who do not speak the same language as the practitioner • The directions of E in 4 ways (up, down, right or left side) • higher probability of guessing • The aid: the child's hand or E in (rotation of the direction the letter E) —. •••• ®ss 3 • e lu m m 3 W E 3 in 3 e n 3 EPIBE« ji 3 m e hi m - LEA SYMBOLS DO • to measure the clarity of vision of children or analphabet • test for near and for far • symbols: circle, square, house, apple Optotypes for children 5 LU S 4 d o 3 LU 2 3 S H * □ E III 3 9 2 7 O a 2 e e s O □ ö h a t a ? r Iii m e 3 kl 3 E PI 11 ■ a ■ a ? ■ ? a * ■■ a- -i ■ th □ n * * a ■ ¥ n * Cr tr ri y a e m ] e ETDRS optotype (LogMAR chart) LOGARITHMIC 1 5DAI ■VJJI'f I!MAI;r .IJHS CHART "1" N C K Z O R H S D K D O V H R C Z R H S o n h r c D K S N V Z S O K N c k d n r 5 R Z K □ H Z O V C - N V □ O K - ETDRS optotype (LogMAR chart) ■ Named after study of Ricka Ferrise „Early Treatment of Diabetic Retinopathy Study" ( Developed for testing VA before and after retinal koagulation by diabetic retinopathy) Logaritmic optotype chart log MAR ■ Are standard for clinical studies or clinical tests in ophthalmic devices or drugs ■ 14 lines with log.progression, the line always has the same number of symbol (5 symbols) ■ The hight of the flatter correspond with logaritmic progression and increases in the same step in 0,1 log MAR ■ same space between lines and symbols ■ examination distance was 4 m (modificate for 5 and 6 m) ■ each letter has a score value of 0.02 log units (Minimal Angle Resolution - MAR) n c k z o R H S D K D O V H R c z r h s O N H R C D K S N V ----z s o k n - C K D N n ETDRS optotypes ooocoawmujECOHZV c o o o o o c o o o c o c o o O O o c o oooee 6 e e o o o vd c o eoooe ••••• •••«• m e lu m 3 E LU E 3 fTl 3 m 111 E 3 ui e m a m E 3 III in 3 ■ ■ ■ ■ ■ s z n d c V K C N R k C r h n Z K D V C H V O rK m h s o n Z D V ft • A M C O N O O O □ D □ O D O O a □ o o o O □ Q O Q o o □ o o DOOOfl o o o o o oeooo eoooo a at ft CP