Aspheric Lenses - Optometry Today

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CET CONTINUING & EDUCATION TRAINING 1 FREE CET POINT OT CET content supports Optometry Giving Sight Approved for: for: Optometrists Optometrists 4 Dispensing 4 Dispensing Opticians Opticians 4 4 Having trouble signing in to take an exam? View CET FAQ Go to www.optometry.co.uk 48 46 21/09/12 20/04/12 CET to which quiet means activities that, at each (eg, point puzzles on the surface and colouring) (apart from the rather centre than of the allowing lens) there children is surface to astigmatism, become which excited is utilised by playing to counteract with any oblique aberrational astigmatism. This active items. Remember that children in turn results in an improvement in optical may resent being dragged away from a quality of the retinal image formed. The other toy corner to have an eye examination. corresponding feature of aspheric lenses is Think about the equipment on display in that the sag of the lens is smaller than that of your a spherical examination lens of the room. same Is diameter. it unfamiliar As such, and this allows scary? thinner Is it computerised lenses to be manufactured, and highly attractive which also makes to inquisitive lenses correspondingly fingers? Can lighter. you place unnecessary equipment behind a Evolution of aspheric lenses screen? Can you replace your information posters Aspheric lenses with were children’s first described pictures? in the Arrange early 1900s your and Zeiss appointment subsequently book produced to avoid a famous unnecessary range called waiting the Katral and lenses, to which give utilised concave ellipsoid surfaces to eliminate flexibility. Some practitioners like to oblique astigmatism and reduce pincushion reserve one whole session per week for distortion. 2 These lenses were usually dispensed children. For older children, reserving to patients post-cataract extraction, with after-school resulting high appointments hyperopic refractive can be errors useful. that When exceeded the the appointment +7.00DS limit is made, of Tscherning’s it may be helpful ellipse; lenses to discuss of such parental power cannot concerns be made and determine free of oblique whether astigmatism an extended if made or second in the appointment spherical form might (Figure be needed. 2). 1 It was Remember not until to the allow 1960s, time however, during when the changes examination occurred to explain following what the introduction is going to happen of CR39 and as a after lens the material. examination Then, the to most discuss widely the used outcome aspheric lenses employed convex ellipsoid surfaces to with both the child and the parent(s). eradicate oblique astigmatism and diminish Some children, particularly those distortion and transverse chromatic aberration. with special needs, may be nervous. Consider allowing children to visit the practice before their first appointment, to meet the staff and see the room WOLLASTON where the examination will take place. In order to successfully test + 20 children, There are children’s books about eye it may be necessary to purchase tests tests available so consider loaning a specifically designed for the age group. BEST FORM + 15 book at the time the parent makes the +2.00D Of LENSES equal importance is the attitude appointment. Some practitioners create of all staff, the practice environment their own leaflets especially for children. and the approaches taken + 10 to make Staff training may be OSTWALT needed as not the entire experience child-friendly. everyone has a natural rapport with In this case leave the door open or have another member of staff join you. Conclusion About the author + 25 children. Ensure that all members of staff are familiar with child protection issues Maggie Woodhouse is senior lecturer PL and local protocols (see the College of at the School of Optometry and Vision Optometrists’ -25 -20guidelines -15 on -10 examining -5 Sciences, PL Cardiff +5 University, +10 where she the younger child and consider LENS studying POWERspecialises in paediatric optometry. the e-learning module on safeguarding She runs the Special Assessment Figure 2 children provided by DOCET). It is Clinic, which caters for patients of all Tscherning’s ellipse. The focal power of the ellipse is about +7.00DS and lenses above this power good practice to ensure that a child is ages with disabilities. Her particular will experience aberrations such as oblique astigmatism that need aspheric lens designs to never eliminate. alone with a member of staff. interests are visual development in This extends to the examination; ensure children with Down’s syndrome and the that Mo Jalie a parent patented or a design guardian with comes the aspheric into the surface examination the front room surface with of positive the child. lenses previously impact of described, visual defects and on their education. surfaces are denoted by a complex mathematical This (convex may hyperboloid) not always and be on the possible back surface eg, a polynomial References equation. They combine the parent of negative may lenses need to (concave take a hyperboloid). distracting 4 advantages See www.optometry.co.uk/ of lenticular and full aperture lens The reduction in thickness is possible through designs and so result in thinner and lighter sibling outside, or an older child may clinical. Click on the article title and the use of hyperboloid surfaces, which means lenses with no distinct dividing line, no annular not want the parent to accompany them. then on ‘references’ to download. that the lens is flatter, which reduces the lens scotoma and improved optical performance. 4 This trend continued in the 1970s, whereby sag, which in turn reduces lens thickness flatter Module ellipsoid curves questions were used to eliminate Course (see the first code: article of this C-18705 series, OT August O/D Current aspheric lens designs aberrations, but resultant uncut diameters of 17, 2012). Flattening of the lens also reduces Modern aspheric spectacle lens forms are now PLEASE NOTE There is only one correct answer. All CET is now FREE. Enter online. Please complete online by midnight on May 18, 2012 – You will be unable to submit the exams lenses after were this very date. large Answers and, to in the fact, module using will this be published spectacle on www.optometry.co.uk/cet/exam-archive. magnification whilst the aspheric CET points made for according these exams to will far be more uploaded complex to Vantage criteria. flatter on May form 28, resulted 2012. Find in out overcorrection when CET points of will oblique be uploaded surface to Vantage serves at to www.optometry.co.uk/cet/vantage-dates eliminate the high levels of They are produced by taking into account astigmatism at the lens periphery, inducing oblique astigmatism. Such lenses are used parameters such as refractive power, final 1. Diagnosing a congenital colour vision defect in early childhood c) Uses a flashing colourful target large has amounts the following of mean benefits oblique EXCEPT: error and giving in today’s low power d) Uses aspherics a large for target hyperopic lens thickness, face-form (dihedral) angle, poor a) The peripheral defect can visual be treated acuity. Lenses using such prescriptions, but not for myopic corrections pantoscopic angle and back vertex distance. b) Teachers can understand a child’s colour choice in artwork 3. Success in eye health examination of a young child may be improved if flatter c) Inappropriate curves were career subsequently plans can be avoided introduced due to the lack of the toroidal practitioner: surfacing tools. Consequently aspheric surfaces comprising to d) the Alternatives market to as colour blended coding lenticular can be used lenses. 2 In the latter 1970s a) and Asks early the child 1980s, to sit the as still use as possible polynomial for as long surfaces as it takes have been produced and In 1976, Davis and Fernald were granted US of computer-aided b) design Asks the child enabled to keep more looking at this an interesting has been picture made on possible the wall, with no matter computer 2. Measuring eye movements in children is likely to be more what patents successful for a if series the practitioner: of aspheric lenses based on complex polynomial c) aspheric Uses a slit-lamp lens surfaces and a Volk to lens numerical control (CNC) technology. The ways improved a) Moves the cosmetic target very appearance slowly and minimum be manufactured. These d) Examines surfaces sections are generally of the eyes in in separate which intervals polynomials differ from blended b) Avoids distracting the child by speaking tangential error best form principles. 3 4. Practice preparation may include all of the following EXCEPT: In 1981, of a higher order than the conic surfaces lenticulars are that they have excellent + 5 BASE CURVE a Novartis company Find Find out out when when CET CET points points will will be be uploaded to to Vantage at at www.optometry.co.uk/cet/vantage-dates
Sponsored by Sponsored by a Novartis company optical properties in their aspheric zones and (Abbott Medical Optics Inc., Santa were compared before instillation of not been statistically validated at the the blending which occurs is concave. Like Ana, California, USA) for the duration Blink’n’Clean eye drops, five minutes time of this publication, the results blended lenticulars, polynomials are thinner of the study. They were instructed to after the first eye drop instillation, are preliminary but not conclusive. and lighter than full-aperture lenses of the maintain their regular correct cleaning and 14 days after twice daily use. same prescription and there is no dividing line regime between zones. (rub The and patient rinse) has as a wide well field as of Pre-lens non-invasive tear break-up Analysis and results their view and normal ring replacement scotoma. Aspheric schedule. designs Types for myopes of utilise contact convex lenses oblate used ellipsoid in this or convex investigation polynomial surfaces were in Biofinity order to (CooperVision, produce thinner and Fairport, flatter point New focal York, lenses. time (NIBUT) was evaluated without application of fluorescein dye with different types of mires, such as placido disc of the videokeratograph or mires Subject’s gender is not a parameter to be included in the analysis since the distribution of values is not balanced sufficiently (nine men and 42 women). The USA), Atoric Acuvue lenses differ Oasys, from Acuvue standard Oasys aspheric for of the keratometer. This allowed age distribution in the sample was normal Presbyopia, surfaces in Acuvue that the Advance oblique (all astigmatic Johnson calculation of the NIBUT without (Kolmogorov-Smirnov test, p=0.66). aberrations are controlled along both meridians & Johnson Visioncare Inc., Jacksonville, interfering with tear film stability. The distribution of NIBUT values and so the p-value (eccentricity of the curve) of the Florida, USA) Air Optix, Air Optix Corneal staining, which was analysed was normal (Kolmogorov-Smirnov aspheric surface differs from a minimum along Night & Day (both CIBA Vision, Duluth, with the application of fluorescein dye, one meridian to a maximum along the other. test, p>0.05 on all occasions), and Georgia, USA) and PureVision (Bausch and hyperaemia were assessed according therefore parametric tests were applied & Low Lomb, powered Rochester, aspheric New lensesYork, USA). to Figure the Cornea 3 and Contact Lens Research (ANOVA with post hoc analysis and Subjects It is in more were recent wearing years that lenses aspheric for at designs least Unit Benefits (CCLRU) of aspheric grading lenses. The scale spectacles (School shown have lenses of +6.00DS power. The lens on the Pearson’s correlation coefficient). The left of the image is of spherical form whilst that on the right of the image is of aspherical form. five have hours been used per to day correct and prescriptions were examined of low of The Optometry aspheric lens and is clearly Vision flatter Science, and thinner. The Other remaining differences parameters in properties follow are also categorical shown. at positive the power. following The use intervals: of such lenses before again University of New South Wales, Sydney, scaling and therefore non-parametric administration confers the benefits of Blink’n’Clean of making eye the drops, lenses Australia). tilt, the vertical LIPCOF centres were should also be counted, decentred tests Case scenario were applied 1: myope(Chi-square, thinner and lighter. The reduction in thickness 1mm down (by applying the dispenser’s rule) five minutes after the first instillation of vertically below the temporal limbus. Friedman Prescription -7.00/-1.00x90 ANOVA, and R+L Wilcoxon is as a result of initially making the lens flatter • The dihedral (face-form) angle of the frame Blink’n’Clean eye drops, and 14 days A subjective questionnaire (Table 1) When dispensing aspheric lenses for such a matched-pairs signed-ranks tests). in form by utilising a shallower base curve, front should be 5° for right and left sides. myopic patient, the index of the material needs after first use of Blink’n’Clean eye drops. was also given to wearers five minutes whilst also having a sag which is smaller than This ensures that there is no horizontal to be discussed with the patient. The patient is The authors used the modified Rudko after first instillation of Blink’n’Clean Non-invasive break-up time a spherical surface of the same vertex radius prismatic effect at the near centration points likely to be concerned by the edge thickness validated (and for any scale lens 10,11 diameter) (Figure (Figure 1) 3). This for and • Keep again the back after vertex distance 14 days to a minimum of twice as Results showed significantly higher and weight of the finished lens and these assessment flatter aspheric of deposits lens form on contact also neutralises lenses. daily the back use. surface It of is the necessary lens will be flatter to point than NIBUT values after 14 days (13.4±6.7 can naturally be reduced with a higher index Heaviness, oblique aberrational extent and astigmatism. type of The deposits same out in a spherical that, since lens, which the questionnaire enables the lenses has to seconds) material. Combining of twice-daily this with an anti-reflection use of principles apply to negative lenses with regard be fitted closer to the eye. However, owing to coating will provide the best lens of choice. Such to flattening them to make them thinner. Here the flatter back surface, consider the patient’s 1. During a normal day within the last week, how often was the wearing comfort of your contact lenses lenses give a unpleasant? reasonable degree of control over one surface is made aspheric to restore the eyelashes as they should not touch the lens the edge substance while providing good offaxis off-axis Never performance of the Rarely flatter lens form. • Unlike Sometimes spherical lens forms, prism Often should performance Always in oblique gaze, whilst serving It is generally accepted that convex oblate not be provided by decentration in aspheric to control the effects of distortion. In addition, ellipsoid 2.When exactly surfaces did are you used note to this reduce unpleasant edge wearing lenses. If comfort? an aspheric lens were to be there is less minification of the eyes too. For thickness Never of negatively powered Early morning lenses. This decentred, Noon the vertex of the aspheric Evening surface this prescription, All 1.74 dayaspheric hard and MARcoated lenses would be a good option. It is also lens form enables positive surface astigmatism no longer occupies the position assumed to 3. neutralise If you felt the this negative unpleasant oblique wearing astigmatism comfort, when how unpleasant originally designing was this the feeling lens at and, the as end of the contact lens wearing time? important to be sensible with frame selection which results from the flat-form lens. 2 such, the aspheric surface will no longer – consider shape and size carefully and fit the No problem Slightly unpleasant Unpleasant Annoying Extremely annoying occupy a position in which symmetry occurs spectacle frame with as small a vertex distance as Dispensing 4. During a normal of aspheric day within the lenses last week - how for ocular often rotations did you have away the from feeling the optical that your contact possible. lenses If considering are dirty? glass lenses, it is important When dispensing aspheric lenses, there are some axis. Therefore prismatic correction must be to remember the refractive index of the lens rules Never by which to abide. These Rarely listed below: incorporated Sometimes during working of the Often lens 5 increases with density Always (mass divided by volume). • Ensure correct horizontal centration of the • The flatter curves of aspheric lenses result 5. How was the wearing comfort after using Blink’n’Clean? If weight is the patient’s priority, then a plastic lens lenses by taking monocular pupillary distances in unwanted reflections, which are inevitably has to be the material of choice. It is, of course, • Much Ensure worse correct vertical centration Worse of the lenses by noticed by Same the patient. For this reason, aspheric Better important to ensure Much that better the material best suited taking heights of the optical centres. The vertical lenses should always be dispensed with a to the patient’s requirements is always dispensed. 6. How was your vision after using Blink’n’Clean? centration should then be compensated for the multi anti-reflection (MAR) coating. This also pantoscopic Much worsetilt of the spectacle Worse frame to ensure improves Same the cosmetic appearance of the Better lenses Case scenario Much 2: better hyperope that the optical axis of the lens passes through • Distortion may be greater in aspheric lenses Prescription +7.00/-1.00x90 R+L Table the eye’s 1 centre of rotation. The pantoscopic tilt compared to spherical lenses and so the When dispensing aspheric lenses for a hyperopic angle should be measured and for every 2° of patient may require some time to adapt 6 patient, nasal edge thickness, centre thickness, Subjective questionnaire used to evaluate the effect of Blink’n’Clean eye drop use on contact lens comfort and vision For For the the latest latest CET CET visit visit www.optometry.co.uk/cet 47 49 23/03/12 21/09/12 CET CET
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