Progressive Powered Lenses 2023 PDF

OPT505 Clinical Skills and Refractive Management: Progressive Lenses Claire Wright Core Competencies 4.1.1 ABILITY TO ADVISE ON, ORDER AND TO DISPENSE THE MOST SUITABLE FORM OF OPTICAL CORRECTION TAKING INTO ACCOUNT DURABILITY, COMFORT, COSMETIC APPEARANCE, AGE AND LIFESTYLE (MULTIFOCAL DIS...

OPT505 Clinical Skills and Refractive Management: Progressive Lenses Claire Wright Core Competencies 4.1.1 ABILITY TO ADVISE ON, ORDER AND TO DISPENSE THE MOST SUITABLE FORM OF OPTICAL CORRECTION TAKING INTO ACCOUNT DURABILITY, COMFORT, COSMETIC APPEARANCE, AGE AND LIFESTYLE (MULTIFOCAL DISPENSE) 4.1.2 ABILITY TO ADJUST A SPECTACLE FRAME OR MOUNT TO OPTIMISE PHYSICAL AND OPTICAL PERFORMANCE Learning Outcomes Define a Progressive Lens (progressive lens surface) List advantages and disadvantages of progressive lenses Understand different design criteria (hard and soft) Understand prism thinning Define ‘free-form’ surfacing and its impact on lens design Discuss Aspects of Fitting Consider reasons for non-tolerance to PPL’s Follow a plan for Verification and Duplication Progressive Power Lenses Continuous vision at all distances Considered to have 3 areas of vision like a Trifocal Power of lens increases over the progression of the lens Distance at top, near at bottom (most of the time) PPLs Advantages No jump Lots of lens design choice Cosmesis PPLs Disadvantages Alters relationship between eye turn and head turn Areas of indistinct vision - Areas of surface astigmatism Greater accuracy required in fitting Frame size/shape may affect lens availability/choice Lens design choice Power profile of a plano lens with +2.00 Add Plano +1.00 +2.00 +3.00 Power profile of a progressive power lens The progressive surface of a PPL is a surface which displays a continuous shortening of the surface radii This causes unwanted astigmatism as a result E.g. Lens Performance 1. Iso-cylinder lines 2. Vector plots 3. Mean power plots 4. Power profile Lens Performance: Iso-cylinder lines Isocylinder lines are lines joining points where the surface astigmatism changes by 0.25 or 0.50D Lens performance:Vector plots Indicate the amount and direction of astigmatism Lens Performance: Mean Power Plots Illustrates how the mean power varies across the progressive surface Lens performance: Power profile Start of the power progression Lens performance Each of these can indicate how a lens works, and tells us the design of the lens Combined together, we can get a good overview of lens performance Which have you seen in practice? Hard and Soft Designs PPLs can be described as hard and soft based on the distribution and amount of surface astigmatism Hard Design Soft Design Hard Designs Surface astigmatism limited to nasal and temporal areas Usually have a narrow progression corridor, relatively wide reading area and a full width distance portion Closely spaced isocylinder lines indicate a rapid change in surface astigmatism Hard Design Hard Designs Wide distance and near Narrow intermediate May be better for ‘eye movers’ Less foveal vision More peripheral softness Better for hypermetropes? Soft Designs The surface astigmatism extends into distance portion This allows a reduction in its amount and produces a wider progression corridor Some astigmatic blur is introduced into distance portion Soft designs have a narrower reading area Easier to adapt to Soft Design Soft Design Wider intermediate area Surface astigmatism more spread out May be better for ‘head turners’ Myopes? Hard Vs Soft Hard Soft Drivers Everybody else! Bifocal wearers Intermediate users High Adds Low Adds Avid readers (SV?) Surface astigmatism Area of surface astigmatism depends on: Reading addition Progression length Lens design Short progression lengths and high reading additions are not a good combination! Long Corridor PPLs Preferred by hypermetropes Good for long vertex distances Provide wider intermediate areas Less head tilting when reading Greater frame depth required Short corridor PPLs Preferred by myopes Smaller intermediate areas Good for short vertex distances May require more head tilting Fits into shallower depth frame Better for anisometropia Traditional PPLs Spherical distance portion Spherical near portion Linked by aspheric progressive surface This surface is on the front of the lens Traditional PPLs Progressive surface is obtained by moulding or casting: This provides the add Results in a semi-finished blank Progressive surface will always be on the front Back surface then worked to give the required distance prescription Prism Thinning As the progressive surface has a gradually reducing radii, the bottom edge would normally be noticeably thinner than the top edge Prism Thinning Prism Thinning Amount of prism removed is approximately 2/3rds of Add This will leave base Down prism measurable at prism reference point Prism thinning must be the same for both eyes Lens Markings Free-form Technology Term applies to a surface not a lens A surface that cannot be defined mathematically Surface is described by its sag at thousands of points using x, y and z coordinates Free-form Surfacing Addition on the back surface so can incorporate cyl correction Addition can be split between front and back surfaces Better/more complex designs to control aberrations Improves off-axis performance Manufacturers can compensate for lots of variables such as frame fit, Rx Front Surface Vs. Back Surface Most PPLs have the progressive surface worked on the front, and the distance Rx on the back By working it on the back we can increase the field of view for near and intermediate Progression on front surface Progression on back surface In the vertical, narrower field from front progression gives desirable short corridor HoyaluxID has horizontal progression on back, vertical progression on front HoyaluxID By splitting the progressive surfaces aberrations between the front and back surfaces. Hoya claim to: Reduce wavy swim and skew deformation Have wider fields of clear view, with shorter corridors (14mm or 11mm options) Requires extra measurements including working distance Individualised PPLs Requires additional measurements Individualised PPLs BBGR Anateo Essilor Series XR (Physio f-360 & Comfort Max f-360) Hoya iDMystyle Nikon Seemax Norville SentorHD Rodenstock Impression 2 Zeiss Individual 2 Dispensing PPLs When dispensing PPLs, two thoughts should be uppermost in the practitioners mind: Choosing the Lens Choosing the Frame PPL Terminology Fitting cross Progression Corridor Corridor length Long Short Prism reference point Fitting PPLs Monocular centration points Vertical fitting cross position – from centre of Px’s pupil Minimum vertex distance Pantascopic angle approx. 10o Check depth of frame Fitting Cross For most PPLs the progression starts 2-3mm below the fitting cross This will give about +0.12D more than the distance Rx Lens Markings Failure to Adapt Incorrect prescription Anisometropia Incorrect measurements Poor frame fit and/or selection Poor lens design Glazing issues Frame Selection Pantascopic Tilt If visual axis (line of sight) does not pass through optical axis at right angles then aberrational astigmatism will result SV Px complains of oval plates, sloping floors, door frames are shaped like trapezium (narrower at top or bottom) or parallelogram (skewed to one side) Incorrect fitting heights Most common is too high Px will complain of blurred distance Less common – too low Shallow frame has similar effect Adaptational Difficulties Uncorrected vertical phoria Moderate to high astigmatism with oblique axes Can cause vertical differential prismatic effect Anisometropia More problematic with hyperopes Short corridor design recommended Fitting tips Always follow guidelines for minimum fitting height At least 10mm is usually required above the fitting cross Use as short a vertex distance as possible Place fitting cross on pupil centre not corneal reflex Always fit the frame before taking measurements *Manage expectations* Recommended reading Jalie, M. (2008) Ophthalmic Lenses & Dispensing, 3rd Ed, Chapter 12. Jalie, M. (2001) The Principles of Ophthalmic Lenses, Chapter 13, Section 109 Gilbert, P. (2015)Ophthalmic Lens Availability ABDO Tunnacliffe, A. (2007) Essentials Of Dispensing, Dispensing PPL’s page 35-56 ABDO Griffiths, A. (2003) Practical Dispensing, Chapter 15. ABDO Jalie, M (2016) Progressive power lenses -part 2 and 3 –Optician September/October 2016