A Typical Rx Form Boot Camp Workshop: How to Take Accurate Spectacle Measurements ©2014 Alex Yoho, ABOM Alex Yoho has no financial interests to disclose. Check List • • • • • • • • • • Patient’s Name Date Patient’s PD Lens Type Lens Material Fitting height Coatings and tints Frame information Frame status Check account info Metric basics A Completed Form • • • • • • • • • • Patient’s Name Date Patient’s PD Lens Type Lens Material Fitting height Coatings and tints Frame information Frame status Check account info Prefix Name Prefix Symbol nano n 1/1,000,000,000 or .000000001 Prefix Value 10-9 micro µ 1/1,000,000 or 0.000 001 10-6 milli m 1/1000 or 0.001 10-3 centi c 1/100 or 0.01 10-2 one Meter 1 or 1.0 1 kilo k 1 thousand or 1000 103 mega M 1 million or 1 000 000 106 giga G 1 000 000 000 109 1 Metric basics Length vs Diopters 100 Centimeters D = Distance in Centimeters 2.50D = 1.75D = Patient’s PD 100 40 CM (typical reading distance) 100 55 CM (Computer reading distance) Patient PD • The Pupilometer A traditional method of taking the interpupillary distance 2 Corneal Reflection Pupilometer • Essilor • Pupilometers are more consistent and more accurate than the PD rule. • Pupilometers measure the corneal reflex and hence the distances between the visual axes and not just the pupil centers. This is why the pupilometer appears to read narrow. • Pupilometers have been shown to reduce reject rates for progressive lenses in practices which have changed from the PD rule to the pupilometer. • Pupilometers look more professional and give the patient a greater perception of accuracy when filling his/her Rx (appearances do count). • Pupilometers eliminate parallax errors, which are almost unavoidable when your PD differs appreciably from the client's. • Pupilometers take monocular PDs quickly, easily and accurately. • Pupilometers allow you to take near PD measurements for a range of working distances. • Pupilometers allow you to occlude one of the patient's eyes while taking measurements of someone with strabismus. • PD rules are great for measuring almost anything other than a PD. They are fine for frames; perhaps we should be calling them ‘frame rules’. Pupilometer • Breitfeld & Schliekert A Few Handy Rulers 3 A Few Handy Rulers How to take a PD using a Rule Patient’s PD Patient’s PD Estimating pupil center can be difficult especially on dark eyes It is usually better to use the limbus (edge of the iris) as a landmark Placing a finger below your left eye, ask the patient to keep their eyes fixed on your finger. While they are looking in the direction of your left eye, align the zero mark on the rule with the inner edge of their limbus. 4 Patient’s PD Now, without moving the ruler, move your finger directly below your right eye. As the patient’s eyes follow your finger to a resting place on your finger, observe the measurement of the rule at the outer limbus. This is the binocular interpupillary distance. What about an infant? • Simply measure from the inner canthus on one eye to the outer canthus on the other eye. Patient’s PD • Now have the patient look at the near point and quickly obtain a measurement for the near PD “A” Measurement • The “A” Measurement is actually the longest horizontal measurement of the lens shape. 5 “B” Measurement • Many people wrongly measure the longest measurement of the shape and consider it the “Effective Diameter” • The “B” Measurement is actually the longest vertical measurement of the lens shape. True “ED” • In fact the true “ED” is twice the longest radian of the lens shape from the geometric center. A False “ED” Measurement True “ED” In this example: 27.5 X 2 = 55 • The “ED” tells us what diameter lens blank is needed to cut the shape but does not take decentration into account. 6 A Quick “Guesstimate” Bridge size / DBL “A” + 3 ≈ ED • When you can’t find the true ED, add 3 mm to the “A” measurement for a reasonable approximation Bridge size / DBL • DBL Stands for Distance Between Lenses at their closest point Frame PD Note how the “T” rule with its extended zero point can give a very accurate frame PD •The “Frame PD” is actually the “A” measurement & the DBL added together • Measuring at the datum line will not give an accurate bridge size •This measurement is critical to knowing how much to decenter a lens 7 Measuring for frame selection • Selecting a frame intelligently demands that you know: • The patient’s PD • The frame PD • Why? Calculating Decentration Measuring for frame selection • It really makes a difference in lens thickness Choosing the right frame size to keep lenses thin • A+DBL= Frame PD • Frame PD – Patients PD = Decentration The weight and thickness are proportional to the size of the lens Lens thickness due to size The knowledge of the frame stylist must be conveyed to the patient 8 Choosing the right frame size to keep lenses thin A lens must be decentered if the eye is not exactly centered in the frame. The need for decentration is eliminated and the lens is the same thickness on each edge. Choosing the right frame size to keep lenses thin Try to select a frame whose frame PD closely matches the patients PD. A good rule for fitting is to keep the total decentration at 6mm or less. Lens thickness due to decentration Patient’s PD • Why do we take a PD? • To position the lens correctly before the eye • Note how the lenses thicken with decentration Patient’s PD Patient’s PD • Plus lenses thicken in the nasal area 9 Summary Checklist for Keeping Lenses Thin Calculating Minimum Blank Size • Measurements needed- ED & Total Decentration •Small frames make for thin lenses. •Decentering lens to match PD creates thickness. ED+Total Decentration= Minimum blank size needed to cut the lens shape. •Use High Index Materials •Use Aspheric Lenses Checking Progressives for Cut-Out • Place a dot on the sample lens exactly at the patient’s pupil. • Place the lens on the chart with the pupil dot on the cross. Circumference When using a tape-type C-sizer, be sure to close the lid to keep the tape from collapsing 10 Reading the C-Sizer Mutifocal heights Single vision MRP Pupil Iris Canthus Lid Margin 11 Bifocal Heights The “Invisible” Flat Top Trifocal heights Progressive Addition Heights 12 Seg height / Seg drop Multifocal Placement Progressive Trifocal Bifocal Temple Length Measuring Temple Length • Temples are measured from the butt to the tip as if the temple was straightened out • Skull • Cable 13 Custom Lengths are Possible Ball Tipped Calipers Holding the Calipers 14 The Caliper Scale Check the Zero Mark Reading the scale Lens Clocks • Used to measure lens curves 15 Lens Clocks Lens Clocks Measuring a Base Curve Base Curves • Hold the lens clock Perpendicular to the lens • Be sure all three legs are seated firmly against the lens • Be sure you are reading the correct scale (+/- & proper index scale) 16 Base Curves • Most lens clocks are calibrated by screwing either the center or the outer legs • Do not remove the cover or attempt to adjust the needle itself unless it has fallen off • Adjustment should be tried on several known standard curves and plane surface • Remember that what you read is an approximation due to index of refraction and human error Determining Slab-off Amount Rest the center pin on the slab line then all pins on one side of the slab line. The Difference is the amount of slab=off Screw Sizes 17 Using Screw Gauges Using Screw Gauges Using Screw Gauges Using Screw Gauges 18 19