August 2012 1 24/07/2012 14:13 Page 1
Total Page:16
File Type:pdf, Size:1020Kb
DO August 2012_1 24/07/2012 14:13 Page 1 dispensingoptics Dispensing Optics PO Box 233, Crowborough TN6 9BD Telephone: 01892 667626 Fax: 01892 667626 Email: [email protected] August 2012 Website: www.abdo.org.uk DO August 2012_1 24/07/2012 14:13 Page 2 DO August 2012_1 25/07/2012 14:50 Page 3 3 dispensingoptics CONTENTS August 2012 3 Cover point 4 Continuing Education and Training Common technical enquiries Cover point by David Jones 14 Patient and practice management Calling in the creatives by Antonia Chitty 16 Membership matters Supporting members locally and nationally 18 Frequently asked questions by Kim Devlin 20 ABDO Conference and New Articles of Association being held in Stratford-upon-Avon on Exhibition By now, all full members who are Saturday 29 September 2012. Conference agenda entitled to vote should have received, by post, all the documentation for the Future conference plans 22 Member musings ballots that will take place regarding As from 2013 the Association’s annual Here come the men in white coats the new Articles of Association and meeting will move to the spring, as will by Dave Wright the proposed name change. Anyone the conference, which will take place entitled to vote and not in receipt of on alternate years to Optrafair. 24 Newsbrief the appropriate mailing is urged to 25 The President’s diary contact Katie Docker in the Next year we will hold our annual by Jennifer Brower membership department (01227 meeting at Optrafair 2013 along with 733912) as soon as possible. an ABDO CET event, which will 37 Optician Index highlight innovations in optics. May 2012 summary I hope as many members as possible will take the opportunity of casting In the spring of 2014, we will hold our 40 Disjointed jottings from their vote. next conference and details, a DO’s desk . regarding time and venues, will be Social media or unsocial person The result of the ballots will be announced in the near future. by Louise Ballantyne announced at the end of the AGM We have made these changes in 42 CET answers response to feedback from members, Colour vision and traffic recognition sponsors and exhibitors and hope you all will feel able to support the 43 Diary of Events Association as we continue our work of promoting the profession and the skills of our members. Tony Garrett n ABDO works in partnership with: Front cover: Shamir Run lenses designed with the Runner in mind ABDO also activity works in conjunction with: The Worshipful Company of Spectacle Makers DO August 2012_1 24/07/2012 14:13 Page 4 4 dispensingoptics August 2012 Common technical enquiries by David Jones Competencies covered: Optical appliances Target groups: Dispensing opticians, optometrists The creation of this article was balancing of anisometropic The sags of the surfaces can be found stimulated by the variety of questions prescriptions will be discussed, from the following formulae, where s = presented to the author by members explaining the advantages or sag*; r = radius of curvature; y = half the of the optical professional disadvantages of the various diameter of the lens; n = refractive index manufacturing industry. proposed methods. of material; F = surface power in dioptres Topics covered range from the s = r - √(r2 – y2) Changes in lens curvature consequences of base curve requests (why and why not) r = ((n – 1)1000) ÷ F (to give r in mm) changing, the difference between the There are a number of reasons why a minimum fitting cross height of a dispensing optician would wish to If F1 = +8.50 and n = 1.500 then r1 = 58.824mm Progressive Power Lens (PPL) and its specify a non-standard curvature for a Similarly, r2 = 200mm optimum fitting height. Also included is particular prescription. Sometimes the an explanation of the term prism reason is simply to match the s1 = 5.58mm for 8.50 curve thinning, its effect upon the thickness curvature of frame. Frequently it is in s2 = 1.57mm for 2.50 curve of a progressive lens and why it alone the belief that flatter lenses will be t = 5.58 -1.57 = 4.01mm may not necessarily provide the thinner lenses. patient with the thinnest possible With positive prescriptions there is a In flatter form . lenses. minor reduction in thickness if the F1 = +6.50 and F2 = - 0.50 lenses are made on flatter curves Sag of 6.50 would be 4.18mm An explanation of the reasons for and when compared to the standard Sag of -0.50 would be 0.31mm results of ordering lenses which are higher curve. Example 1 shows the advertised as being supplied with a thickness difference for a theoretical t = 4.18 – 0.31 = 3.87mm prescription which has been optimised thin lens made using a front surface A thickness saving of 0.14mm (less than or compensated for the "as-worn curve of +8.50D with a rear surface of - 2/10th of a millimetre). The thickness position". 2.50D, compared with a flatter form of saving is insignificant. the same power, made 50mm in * Traditionally, ‘s’ has been used as the symbol Reference is also made to the diameter, knife-edged. for the sag of a curve, and is used throughout regulations governing tinted lenses this article. However, readers may find in some with particular reference to the usage Deducting the sag of the rear surface modern texts that ‘z’ is used to represent the sag.’ of tints for driving purposes. from the sag of the front surface will give the centre thickness once the Example 1: thickness and form Finally, the options available for the value has been added to the edge This article has been approved for 2 CET points by the GOC. It is open to all FBDO members, including associate member optometrists. Insert your answers to the twelve multiple choice questions (MCQs) online at www.abdo.org.uk, or on the answer sheet inserted in this issue and return by 19 September 2012 to ABDO CET, 5 Kingsford Business Centre, Layer Road, Kingsford, Colchester CO2 0HT OR fax to 01206 734156. If you complete online, please ensure that your email address and GOC number are up-to-date. The pass mark is 60 per cent. The answers will appear in our October 2012 issue. C-18352 DO August 2012_1 24/07/2012 14:13 Page 5 Continuing Education and Training thickness of the uncut lens. If the would be present if a flattened non- power of each surface is reduced and aspheric base curve were used. the back vertex power remains the same there will be only a very small It is possible to simplistically decrease in centre thickness. demonstrate the effect on an image when viewed away from the centre of Inappropriate prescription/frame a flattened form spherical lens using a combinations torch and a flat wall. The torch beam Another reason for the request for a should be circular and the flatter curvature might be an attempt demonstrator should stand by the dispensing optician to match approximately one to one and half the curvature of the lens to that of the metres from the wall. Switch on the rim curvature of frame. torch and point the beam directly at the wall. The image on the wall will be Although not always stated by the circular demonstrating the lack of manufacturer of the frame, there is image corruption when looking often a limit to the prescription range through the optical centre of a which can satisfactorily be mounted spherical lens. Now direct the beam into a frame, particularly if it is a type away from the original position as if with less flexible rims. Metal frames on scanning with the eye. It will be noted which the lens mounting rim is brazed that the image of the torch beam is to the back of the front tend to have no longer circular, but has now less flexibility in accommodating become elliptical in shape higher curved lenses, particularly if the representing the oblique astigmatic frame has been manufactured with a error. If one were to stand in the relatively low rim curvature. For centre of a circular room such as example, if the curvature of the rim those found in some old lighthouses, was to be +4.00 this might suit a range the demonstration would not work so of mid minus to low power positive lens well if the torch beam was directed prescriptions with front curvatures from perpendicular to the surface of the +3.00 to +5.50. curved wall! Lens prescriptions requiring a front Requests for increased curve significantly greater or less than curvature those suggested could result in an Spectacle frames with rim curves of insecure lens fit, or a lens which fits the +8.00D or even +10.00D demand frame but protrudes excessively relatively highly curved lenses. forward or backward from the frame Prescriptions with powers of +5.00D or rim. greater often have the front surface curve which closely matches the The dispensing optician may consider frame curve. The problem arises when ordering lenses on flatter bases to the dispensing optician attempts to fit match the rim curve. The reduction in a low plus prescription or even worse a curvature possible for the given negative prescription to such a frame. prescription is governed to some It is not uncommon to receive an extent by the resulting lens form. A enquiry requesting that the lens be simple example is if a +6.00 was to be manufactured on a +7.00D convex requested to be made on a front curve and then to be told that the curvature of +5.00 nominally the rear prescription is for a -8.00D sphere.