DISPENSING THE HIGHER OR UNUSUAL RX FITTING, EDGING & DISPENSING. Sponsored by the CAO/CCOA Program

Transcription

1 DISPENSING THE HIGHER OR UNUSUAL RX FITTING, EDGING & DISPENSING OAO APRIL 2017 MARILYN SMITH RO Sponsored by the CAO/CCOA Program

2 DO NOT BE AFRAID Often the higher the Rx dioptre value, the less lens choices Offer the best lens choice and best coatings possible Be meticulous with measurements

3 LARGE FRAMES CREATE THICKER LENSES As fashion change & may dictate larger frames be aware: -create thicker lenses despite high index lens materials warn patients! - increase overall weight of glasses -may sit on cheeks! Edge thickness increases in minus lenses Nasal thickness increases in plus lenses Guide patient through frame selection for fashion AND Rx thickness VS BOX MEASUREMENTS!!! ED = 49mm ED = 64mm

4 FRAME DEPTH & OC SV lens in lower Rx is usually set with 3mm above Geometrical Centre (GC) with no vertical prismatic issue Larger frame = Deeper B measurement High Rx s -measure pupil height for SV lenses to have pupil centred at OC vertically (keep pantoscopic angle in consideration!) & remove vertical prismatic issues Warn patient lens will be thicker at lower edge (minus) -thicker at upper edge (plus) Smaller A measurement = less decentration therefore less edge thickness Smaller B measurement = less vertical thickness

5 POWER CROSSES HOW THE LENSES WILL LOOK IN THE FRAME x x PL 2.25 x x PL In a power cross, the SPHERE is attached to the AXIS direction This is very beneficial when considering lens thickness in a frame design

6 SPECTACLE MEASUREMENTS Always take monocular PDs Use pupilometer properly Adjust frame thoroughly before taking measurements For single vision lenses record pupil height Multifocal measurements should be precise & be compared to previous pairs Computerized devices can be helpful Take all measurements at least twice!

7 MINUS VS PLUS Minus Lenses Frame PD = Patient PD Rounded frame edges Vertex distance Hi Index Lenses Aspheric Design Temple hinges Nosepads Plus Lenses Frame PD = Patient PD Rounded frame edges Vertex distance Aspheric Design Hi Index Lenses Nosepads

8 FRAME SELECTION HIGH RX regular shape, metal or plastic smaller eyesize best (PD = Frame PD) head clearance look for wider hinges thicker full eyewire can help cover edge thickness, zyl frame? nosepad/guard arm clearance? discourage rimless GOOD, ADJUSTABLE GUARD ARMS A MUST!

9 HIGH MINUS LENSES Edge thickness of lens changes with smaller frame choice Keep frame PD as close to patients PD as possible for minimum decentration & thinnest lens Larger frame choice Smaller frame choice Frame PD/2 Patients Monocular PD = Decentration per Eye Effective Diameter (ED) + (2 x dec n per eye) = Minimum Blank Size Consider TOTAL power & where lens will be thickest!

10 THICKER TEMPLES Terrific for hiding edge thickness for high minus! Warn about limited peripheral vision in Rx frame or sunglasses!! Adjustment Tip for Thick Temples: Height of temple and pantoscopic angle cannot be adjusted at the front hinge only by adjusting temple end up or down!

11 PRESCRIBING FOR HIGH MINUS RX High index 1.56,1.6, 1.66 for Rx s up to -6.00* 1.67, 1.74 (both aspheric) for higher minus 1.8 & 1.9 glass - no safety hardening - thinner but heavier - safety issues, can break *Polycarbonate (1.589) is less expensive, safe & a good choice for children/cost, but low abbe 30 Tribrid Trivex material in a 1.6 index, abbe 41, 100% UV protection, very safe, more $$$ than polycarb

12 HIGH MINUS EDGE THICKNESS Use charts or computer apps for thickness demo! Dot pupil centre on chosen frame and hold over chart to show thickness in each index or put info into app to show & compare. Using the same frame/pd dimensions approximately: 1.6 = 20% less thickness 1.67 = 25% less thickness 1.74 = 30% less thickness 1.8/1.9 = less thickness but weight/safety issues

13 COMPUTERIZED DISPENSING Patient wears adjusted frame, picture uploaded Calculation shows lens thicknesses in all meridians Can compare indexes, show thickness variations, various frames Most companies have software, some for ipads GREAT for helping choose frames too!!

14 HIGH MINUS BEVEL Split bevel so thickness is shifted towards front of frame Hides thickness of minus lens Reduces thickness & keeps F2 away from lashes/face Huvitz 20/20 Magazine Can also be helpful to split thickness in high prism lenses!

15 HIGH MINUS BEVEL Back bevel sharp Roll or feather back bevel to protect from injury to px Polish edges choice of px Show sample, sometimes too shiny 20/20 Magazine Automated edgers are terrific BUT!!

16 LENS STRESS Seen thru polarized lens or polaroscope Stress usually in corners or around outside of lens Can cause lens warpage or ill fitting lenses Low power/thin centres Mark stress & re-edge to eliminate Polarized sunglasses show stress in windshields etc HOYA

17 HIGH MINUS - LENTICULAR Lenticulated design for over approx D Myodisc -scooped out minus aperture with carrier Blended Myodisc (Optilenti) - aperture edges blended Rx aperture from mm available in 2mm increments Aperture size changes lens thickness (smaller = thinner BUT less peripheral vision) Noticeable edge Better cosmetics

18 HIGH MINUS - LENTICULAR To choose either minus style lenticular (myodisc or blended) design depends on Rx, frame choice & patients expectations F1 (base curve) is plano or minus depending on Rx Up to -20D can be ok in a full field lens design if frame is small enough Have samples to show patient From Darryl Meisters OptiCampus website

19 HIGH MINUS - LENTICULAR Measure pupil height to centre the aperture OC for best vision Measure height to pupil using Box Measurements with adjusted frame Carrier is thinned to outer edges towards frame for better fit into frame and thinner outer edges Vision is limited by aperture size, no vision thru carrier Not all patients adapt if moving from Myodisc to Blended Myodisc (blurred edges of aperture are noticeable)

20 HIGH MINUS - APERTURE Aperture size depends on frame size, Rx & patient preference Using B measurement helpful for determination of aperture size Smaller aperture = less thickness but less peripheral vision

21 HIGHER PLUS LENSES Aspheric CR-39 for to Aspheric design flattens front surface, reduces thickness & magnification Hi index + aspheric for above an option Higher indexes 1.67/1/74 are automatically aspheric design Aspheric polycarbonate an excellent low cost hi index option very safe for kids Flat F2 can be a problem for long eyelashes

22 HIGH PLUS LENSES - ASPHERIC Aspheric designs flatten F1 Reduce thickness & weight Reduce look of magnification Reduce peripheral aberrations Centre approx 10mm is original spherical base curve Depending on Rx, CR-39 or hiindex lens material Hi index less benefit with high plus Rx edges can only be made to knife-edge

23 ASPHERIC LENSES - MAGNIFICATION Aspheric lenses keep image consistent across lens surface Reduces magnification of image (and eye) in plus Rx s Reduces minification of eye in minus Rx s Better vision and better cosmetics Can be beneficial in high - Rx Consider pantoscopic angle & OC height, must be precise for aspheric lens design

24 ASPHERIC LENS DESIGN How can you tell if a lens is aspheric? Centre 10mm are the base curve Gently place lens gauge across F1 (don t pull across F1 could scratch lens surface!) If curvature changes from centre lens may be aspheric design

25 FITTING HIGH PLUS RX - FRAME Smaller eyesize (not as big a concern as minus sometimes helpful for thinnest edge!) Regular (more rounded) shape Little or no decentration Short vertex distance Adjustable nosepads with good guard arms (plus lenses centre edge!!) Cable temples or snug fitting skull temples Rimless discouraged

26 LENTICULAR HIGH PLUS LENSES Lenticular design an option to reduce weight & thickness 40 mm lens Rx zone with plano carrier reduces weight & thickness fits into frame edge better than thick + lens edges looks like a fried egg high plus lenses over +12D no choices in aperture size 40mm 65mm

27 HIGH RX & F2 CONCERNS Watch for: -Long eyelashes -Thicker Rx s (especially plus prescriptions) -Flatter bridged people -Round cheeks & high cheekbones -Frames with no nosepads

28 HIGH PLUS WITH BIFOCAL LENSOMETRY REMINDER High plus prescriptions create thick lens issues Refraction & true power of distance Rx on F2 Lined multifocals are created on F1 Turn lens over, check distance & near Rx Difference is true add power

29 BASE CURVE (F1 OF LENS) Base Curve on Spectacles lowest curve on F1 Base Curve of lenses should stay consistent from one pair of spectacles to the next Always record base curve in patient record Base curve cannot be duplicated if changing from one lens index to another Counsel patient some adaptation may need to occur when changing base curves Lens gauge readings can be incorrect if index is unknown

30 ADD POWERS WITH LENS GAUGE If lined multi-focal is one-piece design Check add power by comparing F1 curves in distance and near Difference in curvatures = approximate add power Varies by index!

31 LENS GAUGE VS LENSOMETER Lensometer bends light = true power Lens gauge measures surface power BUT based on index of lens If lensometer lens gauge (total power), lens is a different index from lens gauge Calculate to find true index!

32 HOW TO DETERMINE LENS INDEX Lens gauge curves (Total Power = F1 + F2) will not be equal to power from lensometer Lens gauge is calibrated to specific lens index Lensometer only bends light = true power of lens Some lens gauges have 1.49 AND 1.6 dials

33 HOW TO DETERMINE LENS INDEX Take lens curve from lens gauge with known index value & determine power of lens in one meridian Neutralize lens in lensometer for true power in same meridian n = index of the Lens L n = index of the Lens Measure (lens gauge) LM F V = power of the lens from Vertometer (lensometer) F = power of the lens from Lens Measure (lens gauge) LM Will determine exact index of lens material Based on thin lens design good reference for optics/formulas etc

34 EXAMPLE Using 1.49 index dial, lens curve from lens gauge is = Lensometry power value in same meridian = n = (1.49 1) x ( 5.75 ) n = (0.49) x (1.27) + 1 n = n = 1.62 The index of the lens material is 1.6

35 HIGH ADD POWERS Straight Top Bifocals - Adds up to +8.00D Round Top Bifocals - Adds up to D steps up to D steps to D Progressive Addition Lenses - Adds up to +300D in all designs - Adds up to +4.00D in limited PALs - Digital designs have unlimited possibilities!

36 AR COATING A MUST! Use best AR coating available Not an option (except for young children when expense for many Rx changes is possible) Increases light into eye for any Rx Better visually & cosmetically

37 VERTEX DISTANCE Distance from cornea to F2 of spectacle lens Effective power can change noticeably depending on Rx Refraction with phoropter approx 13mm Even 2mm shift in spectacle fitting can have impact on rx s over +/-10D Rule of thumb: take vertex distance for rx s over -8.00D or over +6.00D

38 MEASURING VERTEX DISTANCE Adjust frame on patient Use distometer to measure distance from patients eye to F2 (with eye closed) Distometer automatically considers lid thickness Arrow points to vertex in mm (some hold the arrow in place, some don t!) Include both measurements on lab order form (vertex & refracted at) Lab will calculate new rx Remember to keep records of new spectacle rx!

39 EFFECTIVE/COMPENSATED POWER CHANGES Minus Lenses Effective power decreasesas the lens moves away from the eye power away from the eye power closer to the eye To compensate the Rx required for shift in vertex distance power if further from phoropter setting power if closer than phoropter setting Plus Lenses Effective power increasesas the lens moves away from the eye power away from the eye power closer to the eye To compensate the Rx required for a shift in vertex distance power if further from phoropter setting power if closer than phoropter setting

40 EFFECTIVE POWER CALCULATION CAP Closer Add Plus You can calculate the effectivepower (what power the lens will be when moved from the phoropter vertex) OR You can calculate the compensatedpower (what power is needed to create the same Rx at the new vertex distance) Dl De = ddl Dl Dc = ddl d = distance in metres d is +if moved towards face d is-if moved away from face

41 NEW EFFECTIVE POWER CREATED Rx is D Vertex Distance on phoropter refracted at 13mm Spectacles Vertex Distance fitted at 16mm What happens to the power?? Dl = d =.003m (3mm) away from the face = m De = ( x ) = = D Therefore the effective power created by the shift from the phoropter to the frame fitting is -0.50D less.

42 NEW COMPENSATED POWER NEEDED Rx is D Vertex Distance refracted on phoropter at 13mm Spectacles Vertex Distance fitted at 16mm What new power is needed to match Rx at phoropter?? Dl = d =.003m (3mm) away from the face = m Dc = ( x ) = = D Therefore the power must increase from the phoropter Rx to the fitted Rx by -0.50D more.

43 CYLINDRICAL RX? Calculate each individual meridian Ie x 180: Calculate and meridians separately Cylinder value is still the difference between the powers, at the same axis Compensated power is usually calculated to compensate for frame fit vs phoroptor refraction distance but could be due to frame movement or Rx comfort Darryl Meisters OptiCampus website: Samples questions/answers will be posted to LEARN

44 HIGH RX S - CONSIDERATIONS Things to always consider with high Rx s - Frame selection frame pd = patients pd, rounded shapes, nosepads with good guardarms, add nosepads?, wider hinges for minimum eyesize and best fit - Lens selection hi index and/or aspheric, AR a must! - Photochromic, a good option check availability - Measurements monocular PDs, pupil height, refracted distance, vertex distance, base curves - Counselling even small changes are an issue: change of frame size, lens index and vertex should be discussed when ordering not on delivery - Listen to client concerns, be realistic and honest

45 LENS MATERIALS MATERIAL INDEX ABBE VALUE CR-39 PLASTIC TRIVEX PLASTIC POLYCARBONATE PLASTIC TRIBRID PLASTIC 1.66/ /67 32 PLASTIC CROWN GLASS GLASS GLASS GLASS

46 IN-HOUSE EDGING Edging equipment in the practice Best to have an employee who has experience Money made on SV lenses (less on surfaced & digital multifocal lenses) Excellent client care Redo s are your responsibility! waterloo-optometrist.ca

47 IN-HOUSE EDGING In-house lens selection choice of the practice 1.6 with AR if only one lens as stock, other choices only if viable for patient base! Polycarb is dry edging /1.59 Envelope shows Rx, BC, index, lens blank size Photochromics? Larger blank size to fit frame sizes, larger decentration etc

48 EDGER MAINTENANCE Follow manufacturers guides & have technician service once a year Follow daily automated calibration Have calibrated frame Trace, PD, size, wrap, Bevel, Rx accuracy Replace water every 100 lenses Use debris sock or cheesecloth Dispose of lens debris, recycle if possible Water can be re-used if no glass edging Clean out machine if not running efficiently, unclog hoses

49 WHEN IN DOUBT Quarterly book or onlind with all up North American frames & Lenses Quarterly Lenses book or On-line All info Rx range, photochromics, blank sizes, add range in EVERY lens sold in North America!

50 DIGITAL LENS DESIGN Can be advantageous, depending on Rx Customized F1, F2 or both can minimize peripheral distortion & create best visual points across lens surface Single vision & PALs Now ST bifocals The future of surfacing moving away from conventional semi-finished blanks & will allow inventive customization! Keep copies of lab orders will not match refracted Rx in file!!!

51 FRESNEL PRISM Fresnel Prisms Adhere to lens with water Usually on F2 Temporary use to check prism value High prisms to reduce lens thickness May solve field loss Also spheres & add fresnel prisms available OD Upper Add OS Prism Field loss

52 PTOSIS CRUTCH - Added to frame, mono or bilateral - Soldered to metal frame (must be sure frame can be soldered) - Embedded into plastic frame - Metal moulded to fit under orbital bone to hold up eyelid(s) - Causes dry eye easily - Surgery possible - Rare now

53 HIGH RX S Questions? Thank You! marilyn.smith@uwaterloo.ca All slides are the property of M Smith & may not be duplicated without specific permission