CBT Revision 2 PDF

Closed Book Test 1 Optical Definitions 2 Optical Crosses & Types of Astig 3 Simple Transposition 4 Thin Lens 5 Prism & DPE & Final Checking 6 Dispensing Recommendations Closed Book Test Closed Book Test – Tuesday Morning Two Hour Exam Part A –...

Closed Book Test 1 Optical Definitions 2 Optical Crosses & Types of Astig 3 Simple Transposition 4 Thin Lens 5 Prism & DPE & Final Checking 6 Dispensing Recommendations Closed Book Test Closed Book Test – Tuesday Morning Two Hour Exam Part A – Dispense Optical Appliances Part B – Dispense Atypical Prescriptions Pass both sections individually Anatomy Definitions All definitions – in particular the “a” words.. Anisometropia Is a refractive error of the same type in which there is a substantial difference (2.00D or more) in the prescription of each eye. Antimetropia Is a refractive error in which there is a substantial difference in the prescription of each eye. One eye myopic, one eye hyperopic Aniseikonia Ocular condition where the image in one eye is a different size or shape from the image in the other eye. Aphakia Absence of crystalline lens Aspheric Thinner, Flatter, Lighter, Increased FOV, Reduce Aberrations, Cosmetics Definitions All definitions Spectacle Magnification Is the ratio of the retinal image size after correction to the image size before correction. Back Vertex Distance is the distance between the pole of the cornea and the back vertex along the optical axis. High Ametropia is a prescription that has powers above +/-6.00D Polarising Filter Polarized filters are laminates applied to lenses designed to reduce glare Glaucoma Irreversible peripheral vision loss due to damage to the optic nerve Macular Degeneration Irreversible vision loss due to damage to the optic nerve Definitions All definitions Concentric Rings High minus lenses caused by total internal reflection and excess edge thickness Ring Scotoma / Jack in the Box It is a wedge shaped blind area in the periphery of the lens caused by a prismatic effect. (Only an issue for plus powered lenses) Antireflection Coating An optical coating applied to the surface of lenses to reduce reflection. It improves the efficiency of the lens since less light is lost due to reflection producing a slight increase in contrast and visual acuity, therefore giving better optics. Chromatic Aberrations Is noticed when colour separation occurs due to prism splitting white light into its various colour components. The Optical Cross Right Eye: Left Eye: -3.00 / -0.50 x 180 -4.50 / -0.50 x 180 90 90 180 -3.00 180 -4.50 -3.50 -5.00 The Optical Cross Answer 1) Draw the Optical Cross and name the 90 Astigmatism for these prescriptions: 1) +1.50 / -0.50 x 180 180 +1.50 2) +4.50 / -1.50 x 90 3) -3.25 / -0.75 x 125 4) +1.50 / -2.25 x 60 +1.00 5) +1.75 / -1.75 x 70 Compound Hyperopic Astigmatism The Optical Cross Answer 2) Answer 3) +4.50 / -1.50 x 90 -3.25 / -0.75 x 125 90 125 35 180 +3.00 - 4.0 0 - 3.2 5 +4.50 Compound Hyperopic Astigmatism Compound Myopic Astigmatism The Optical Cross Answer 4) Answer 5) +1.50 / -2.25 x 60 +1.75 / -1.75 x 70 70 60 150 160 0.00 +1.50 - 0.7 5 +1.75 Mixed Astigmatism Simple Hyperopic Astigmatism Simple Transposition Transpose the Answer 1) following prescriptions into Step 1: their alternate forms: we get -1.00 (-2.00 + +1.00) Step 2: the +1.00 changes to -1.00 1) -2.00 / +1.00 x 45 Step 3: 2) +3.25 / -1.25 x 60 45 changes to 135 (45 + 90) 3) -0.25 / +0.50 x 95 Answer: 4) +2.50 / +1.25 x 80 -2.00 / +1.00 x 45 transposes to -1.00 / -1.00 x 135 5) -1.75 / +1.75 x 10 Simple Transposition Question 2) Question 3) +3.25 / -1.25 x 60 -0.25 / +0.50 x 95 \ +0.25 / -0.50 x 5 Step 1: we get +2.00 (+3.25 + -1.25) Question 4) Step 2: +2.50 / +1.25 x 80 the -1.25 changes to +1.25 \ +3.75 / -1.25 x 170 Step 3: 60 changes to 150 (60 + 90) Question 5) Answer: -1.75 / +1.75 x 10 +2.00 / +1.25 x 150 \ Plano / -1.75 x 100 Lens Power F Represents the total power in dioptres (D) F₁ Represents the front surface power in dipotres (D) F₂ Represents the back surface power in dioptres (D) This is the thin lens formula Lens Power Basic lens form using the thin lens formula v Bi-convex (e.g: F1 = +4.00D F2 = +3.00D) v Bi-concave (e.g: F1 = -4.00D F2 = -3.00D) v Plano-convex (e.g: F1 = 0.00D F2 = +4.00D) v Plano-concave (e.g: F1 = 0.00D F2 = -3.00D) v Meniscus convex (e.g: F1 = +5.00D F2 = -3.00D) v Meniscus concave (e.g: F1 = +3.00D F2 = -5.00D) Types of Strabismus vPhoria (tendency) vTropia (constant) v Hypotropia (downward) v Hypertropia (upward) v Exotropia (outward) v Esotropia (inward) Splitting Prism For horizontal prism: Divide the number and keep the word the same. For vertical prism: Divide the number, have the words different, but keep the original word with the original eye. Splitting Prism Dividing prism power between a pair of eyes: Horizontal Example RE +2.00D LE +2.00D 4D IN Can be split to give: RE +2.00D 2D IN LE +2.00D 2D IN Splitting Prism Dividing prism power between a pair of eyes: Vertical Example RE +1.00D LE +1.00D 6 D DOWN Can be split to give: RE +1.00D 3 D UP LE +1.00D 3 D DOWN Splitting Prism Questions v RE +2.00D 2DIN LE +2.00D RE +2.00D 1DIN LE +2.00D 1DIN v RE -5.00D LE -1.00D 6DOUT RE -5.00D 1DOUT LE -1.00D 5DOUT v RE +2.50D 4DUP LE +2.50D RE +2.50D 2DUP LE +2.50D 2DDOWN v RE -1.50D 10DOUT LE -1.50D 7DUP RE -1.50D 5DOUT LE -1.50D 5DOUT & 3.5DDOWN & 3.5DUP Prentice Rule P = cF Where: P is the prismatic power in prism dioptres c is the distance from the centre in cm F is the lens power To convert from mm to cm, divide by 10 To convert from cm to mm, multiply by 10 Differential Prismatic Effect Rules v Base OUT & Base OUT ADD v Base IN & Base IN ADD v Base IN & Base OUT SUBTRACT v Base UP & Base UP SUBTRACT v Base DOWN & Base DOWN SUBTRACT v Base DOWN & Base UP ADD Meaning of the symbols Power tolerances SV / MF example Using the excerpt from the table above will you accept or reject this order? Example One As ordered: -3.25 / -1.00 x 90 As checked: -3.37 / -0.75 x 90 Fail Power tolerances Progressive Powers example Using the excerpt from the table above will you accept or reject this order? Example Two Distance portion ordered as: +1.50 / -0.25 x 45 As checked in the distance checking circle: +1.62 / -0.37 x 45 Pass Axis tolerances Axis tolerances Do the following axis Pass or Fail? +1.75 / -0.75 x 80, measured at 85 Pass -1.00 / -2.75 x 40, measured at 44 Fail +6.00 / -2.00 x 178, measured at 3 Fail -3.75 / -0.25 x 25, measured at 15 Pass Addition tolerances Positioning tolerance Progressive centration example You are final checking the following completed progressive spectacles: RE -2.75 / -0.75 x 60 | LE -0.50 / -0.50 x 65 | Add +2.00 They were ordered with: CD’s of 31 / 29 Heights of 24.5 / 25 When final checking you note the: CD’s are 31.5 / 29.5 Heights are 24 / 26 Do these fitting errors pass or fail the Aust/New Zealand Standard? If they fail, include why, and what corrective action needs to be taken next. Progressive centration answer RE CD 31.5 – 31= 0.5mm difference LE CD 29 – 29.5 = 0.5mm difference No more than one millimeter difference individually = PASS RE Heights 24.5 – 24 = 0.5mm difference (below) LE Heights 25 – 26 mm = 1mm difference (above) More than one mm COMBINED difference = FAIL Prism Final checking question Calculate the amount of unwanted prism in the below; Rx: RE –2.50D LE -3.00 D made at Ordered PD: 32 / 32 mm Measured CD: 35 / 34 mm Horizontal DPE: RE LE P = cF P = cF P = 0.3 x 2.50 P = 0.2 x 3.00 P = 0.75D?? P = 0.60D?? Final checking question Ordered PD: 32 / 32 mm Measured CD: 35 / 34 mm RE LE EAR NOSE EAR 3mm 2mm Final checking question Calculate the amount of unwanted prism in the below; Rx: RE –2.50D LE -3.00 D made at Ordered PD: 32 / 32 mm Measured CD: 35 / 34 mm Horizontal DPE: RE LE P = cF P = cF P = 0.3 x 2.50 P = 0.2 x 3.00 P = 0.75D?? P = 0.60D?? P = 0.75DIN P = 0.60DIN Total Horizontal DPE = 1.35DIN Final checking question Calculate the amount of unwanted prism in the below example: Rx: RE –2.50 / -1.00 x 90 LE -3.00 /-1.50 x 180 Ordered CD to match PD of: 32 / 32 mm Measured CD: 34 / 35 mm Step one – Optical cross! RE LE -2.50 -4.50 180 -3.50 180 -3.00 90 90 Final checking answer RE P = c F = 0.2 x 3.50 = 0.70 ∆ Base ___ LE P = c F = 0.3 x 3.00 = 0.90 ∆ Base ___ Final checking answer 2mm 3mm RE LE Final checking answer 2mm 3mm RE P = c F = 0.2 x 3.50 = 0.70 ∆ IN LE P = c F = 0.3 x 3.00 = 0.90 ∆ IN Total DPE = 1.6 ∆ in. RE LE Final checking answer cont… o To check if it passes or fails, we first need to determine the tolerance of this pair of specs. o First identify the highest absolute principal power of the pair of lenses. This would be -4.50D. o As no prism was ordered, and the highest principal power is over +/-3.37D, we must calculate the tolerance. It will be 0.2 x 4.50 = 0.90 ∆ o Therefore, fails by 1.6 – 0.9 = 0.70∆ o The specs need to be remade. But in this instance, we could just remake the LE. If it was remade perfectly, then the DPE would be 0.7∆ and would therefore pass. DPE A patient wears; RE +3.00 / -1.00 x 90 LE +1.00 / -0.50 x 90 They look 7mm down and 3mm in to read. Calculate the DPE they would experience Vertical DPE: RE LE P = cF P = cF P = 0.7 x 3.00 P = 0.7 x 1.00 P = 2.10DUP P = 0.70DUP Total Vertical DPE = 1.40DUP in the RE DPE A patient wears; RE +3.00 / -1.00 x 90 LE +1.00 / -0.50 x 90 They look 7mm down and 3mm in to read. Calculate the DPE they would experience Horizontal DPE: RE LE P = cF P = cF P = 0.3 x 2.00 P = 0.3 x 0.50 P = 0.6DOUT P = 0.15DOUT Total Horizontal DPE = 0.75DOUT Dispensing Recommendations What would you recommend to improve the appearance and give best optical performance for the following RX: RE: -4.50/-2.75 X 180 3 Δ Base up LE: -3.50/-3.00 x 180 Plastic full frame Shallow in depth Symmetrical in shape Small MSU to reduce edge thickness Split prism 1.5 Δ Base Up RE, 1.5 Δ base down LE Anti-reflective coating Hi index 1.74 lens Aspheric lens design Dispensing Recommendations What would you recommend and what actions would you take for the following RX: RE: +8.50/-1.50 X 80 Plastic full frame LE: +9.00/-0.75 X 90 Symmetrical shape Reduce BVD as much as possible – keyhole effect Increase facial wrap as much as practical Aspheric design HI Index 1.74 CORR Mono heights Mono PD Pupilometer Anitireflective coating Small MSU MSU Calculations Client PD: 31/32 Frame: 54/16 ED = 60 Dec = ((eye size + DBL) / 2) – PD MSU = ED + (2 x dec) RE: LE: De = ((54 + 16) / 2) - 31 Dec = ((54 + 16) / 2) – 32 = 4 inwards = 3mm inwards MSU = 60 + (2x4) MSU = 60 + (2x3) = 68mm = 66mm