As a paid speaker I have not been sponsored by any companies mentioned in this lecture • I am not a consultant to nor an employee of any ophthalmic company. • Robert Lee, OD Western University College of Optometry OptoWest 2012 This course reviews common pt. scenarios that may present in a typical optometric practice. In a busy practice it is often practical to delegate to your optical staff. This course will review optics based problem solving that you may want to delegate or find you may need to handle on your own. Where’s my lens clock? Where’s the base curve? F1 (front) or F2 (back) surface? Red or black scale? Your pt. complains of “distorted” vision through her new SV glasses she bought outside the practice. “Lines are bent and doors look crooked”. • Your optician wants you to troubleshoot this complaint. What are you thinking you should check first? • The Rx and PD checks out within ANSI stds. • The frame is straight on the face. • +4.00 +3.00 +3.00 +3.00 A +3.00 Lens Can Be Made From a Variety of Front Curves 6D 5D 4D 3D -3D -2D -1D 0D Steepest • • • • • OD +5.00 ‐ 1.00 X 180 Add +2.50 OS +4.00 ‐1.50 X 180 CR‐39 lenses in a 54 eyesize metal frame Lens edge thickness 2mm • How thick will her OD lens be in Polycarbonate? SA = (Fh2) ÷ 2000(n ‐ 1) S1 = 4.5(272) ÷ 2000(1.586‐1) = 2.79mm • Are we done? • Rx: – ttotal = sag + tedge sag Flattest A 65 year old female presents with complaints of her bifocals "never fitting right". Her lenses have always been heavy and thick. She seldom drives at night due to glare from oncoming car headlights. She is retired and enjoys gardening and has just started taking piano lessons. Rx: OD +5.00 ‐ 1.00 X 180 Add +2.50 OS +4.00 ‐1.50 X 180 Recommendations? Determine the center thickness of this Rx in CR‐39 How much thinner will my lenses be if…? Don’t use millimeters, use % Numerator = current lens n excess over 1 Denominator new lens n excess over 1 • CR‐39 to Polycarbonate? • 1.498 = 498 = .85% as thick or 1.586 586 15% thinner • Keep or delegate? • • • • • • You have purchased a patternless lens edger and want to process most of your SV Rxs in‐ house. How can you save $ on lens blanks (uncuts)? Use the smallest uncut possible to make the glasses (minimum blank size or MBS) Calculate the MBS given the following data: A = 52 mm B = 48 mm DBL = 18 mm ED = 57 mm Patient’s PD = 62 Frame PD – Pt. PD = decentration total Add to frame “A” or “ED” which ever is larger (A +DBL) – PD = 8, ED + 8 = order 65mm uncut Rather than inconveniencing the pt., use the FRAMES book Find the frame and compare the “B” measurements If you don’t have book access compare the eyesizes or “A”. Your pt. likes the frame from the frame board however it is too large (60 eyesize). You don’t have the correct 48 eyesize on your frame board and have to order it. How do you measure the correct bifocal height if the frame is too big or small? Should you have the pt. come back when the correct frames arrives and then again when the glasses are ready? Take the “A” difference and divide by 2 Add this number to the final seg hgt. if the original frame was too small and subtract if the original frame was too large Frame in office is a 60 eyesize. Your measured BF hgt. is 24mm. Frame needed is a 48 eyesize. What BF hgt. will you order? 36 mm 2. 30 mm 3. 18 mm 4. 12 mm Keep or delegate? You forgot to measure the BF height and the pt. has left the office. What do you do now? 1. • • • • • • • • Use the “3 below” trick Take ½ the “B” and subtract 3mm. B = 40.0 (39.5) ½ B = 20.0 20.0 – 3 = 17mm Actual measured hgt = 18mm NOT BAD! Keep or delegate? You forgot to measure the BF height and the pt. has left the office. What do you do now? Use the “3 below” trick Take ½ the “B” and subtract 3mm. The new pt. states he wears vertical prism in his PAL Rx. Your optician asks you to check the Rx for vertical prism. How do you do it? . Now what?? . . Horizontal? Vertical? OD OD Horizontal? OD Vertical? . . OD OS 0 vertical, 0 horizontal 2. 0 vertical, 3 ½ base out 3. 2 base up, 0 horizontal 4. 2 base down, 0 horizontal 5. 2 vertical, 3 ½ base out Keep or delegate? 1. OS Horizontal? OS Vertical? OS A patient’s wears an Rx of OD +3.00 ‐3.00 x 030 and OS +2.75 ‐1.00 x 060. He complains of having to shut one eye when he reads. He states that the words look “double.” The EOMs, pupils, CT, Rx power and axis check out OK. Pt. PD = 64mm DBOC = 68mm Any ideas what’s wrong? OD +3.00 – 3.00 x 030 OS +2.75 – 1.00 x 060 What is the difference in power in the horizontal meridian? OD +3.00 + (‐3.00)( sin2 theta) = +2.25 OS +2.75 + (‐1.00)(sin2 theta) = +2.00 Is there an easier way vs. using trig. functions? OD +3.00 – 3.00 x 030 = +2.25 PD = 64 OS +2.75 – 1.00 x 060 = +2.00 DBOC = 68 How much prism is induced and what is the base direction? Do you instruct your optician to dispense the Rx or send it back as a lab redo? 090 (100%) 090 (100%) 060 (75%) 64 045 (50%) 030 (25%) 0 -180 (0%) 59 y.o. Hispanic female presents with cc of blurred vision OU both far/near • Hx of DM x 25yrs, PDR w/ PRP and vitrectomy • 30Δ AXT distance and near • New PAL Rx • – OD +2.50 – 1.50 x 085 20/30 – OS ‐3.50 – 2.50 x 080 20/40 – Add +2.00 OU 20/40 • Prescribing considerations? 68 Δ R = (0.2)(+2.25) = 0.45 Δ base out Δ L = (0.2)(+2.00) = 0.40 Δ base out option for >1.5Δ imbalance (.5Δ steps) large Δ imbalance can be corrected for (up to 15Δ SV, 12Δ RD) creates BU thus placed on the most minus (least plus) lens Reverse slab off is preferred due to lower cost and quicker processing OD OS Slab off Reverse slab off Calculate the Slab off / reverse Slab off Which lens should it be ordered on? What would the pt. complain about if you ordered • • • it on the wrong lens? When the glasses are received how do you know the prism is correct? Cheaper and faster processing from lab… OD OS • • • • OD power in the vertical meridian? OS power in the vertical meridian? Unless stated otherwise assume pt. looks 10mm below distance OC to read (reading level) Net vertical lens power difference is 6D. Δ = F x d 6 x 1 = 6Δ Slab comes in ½Δ increments Reverse slab off of 6.00 goes on least minus lens thus OD PROCEDURE A Hope so… I trust the lab… Let the pt. try it… PROCEDURE B Slab off Reverse slab off Check it… Use the correct instrument… …and procedure Lens surface: F1 or F2? Clock scale: black or red? I forgot the next step… Something to do with these . .. • Visualize the appearance of the lenses… • Clinical pearl: Slab off on PALs not recommended – Anticipate the pts. reaction – Ruins the “no line” appearance – Patients rarely understand (confidence) – Have to refund $ or remake the glasses ($) B A . .. . .. . .. . .. 59 y.o. Hispanic female presents with cc of blurred vision OU both far/near Hx of DM x 25yrs, PDR w/ PRP and vitrectomy 30Δ AXT distance and near Why do we prescribe prism (slab off) in the first place? Is slab off indicated in this case? Keep or delegate?
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