Continuing education CET Essential contact practice Part 7: Soft toric fitting Jane Veys, John Meyler and Ian Davies continue their series by discussing the latest fitting, evaluation techniques and lens designs required to ensure soft torics continue to be a routine part of contact lens practice for patients with 0.75D or greater of ocular . C 7424, two contact lens points suitable for optometrists, DOs and CLOs

oft toric contact lens fitting Key Points was previously regarded as a ‘speciality’ only to be ● Improvements in toric lens undertaken by experienced speed of orientation, lens stability, practitioners. corneal oxygen supply and repro- S In recent years, however, the number ducibility mean that practitioners of designs available has increased and the should be confident in fitting soft fitting approach simplified. The propor- toric when poor vision is due tion of new soft toric fits is now over to astigmatism 30 per cent in the UK, which correlates ● Assessing rotational stability in well with the incidence percentage all positions of gaze and between of the population with astigmatism blinks is the key to success between 0.75 and 2.50D.1 However, ● Practitioners should have at the proportion of soft toric lenses fitted least two lens designs to choose still remains low in many markets across from which include a prism the world.2 ballasted design and non-prism Soft torics are now available from stock ballast design and with an ever-increasing number Figure 1 Rotation of beam to align lens ● Practitioners should allow for offering the benefits of frequent replace- marking and measure lens position (Courtesy more than one lens per eye, both ment, daily disposability or silicone of Trusit Dave) in terms of time and financial hydrogel materials, toric lenses can be consideration, but only attempt a fitted empirically or from comprehen- maximum of two lenses per eye sive in-practice fitting banks. The latter now makes trialing astigmatic patients with single-use toric disposable diagnos- Table 1 tic lenses as convenient as spherical lens Incidence of astigmatism, from Bennett4 fitting. One of the reasons for this increase Power of correcting Percentage of Percentage of astigmatic in the simplicity of fitting toric lenses cylinder (D) total sample lenses has been advances in manufacturing 0 32.0 technology. The advent of new low-cost 0.25-0.50 34.6 50.9 moulding technology and wet moulding 0.75-1.00 17.7 26.0 techniques – allowing the lens to remain 1.25-2.00 9.8 14.4 hydrated throughout manufacture – has 2.25-3.00 3.8 5.6 led to improvements in contact lens reproducibility and optical quality. This 3.25-4.00 1.5 2.2 should give practitioners greater confi- Over 4.00 0.6 0.9 dence that the lens being dispensed is the same as the lens ordered. Nevertheless, a recent wearer survey showed the high levels of lens perform- oxygen availability has allowed greater Rigid gas-permeable lenses ance expected by toric lens wearers was thickness variations in lens design to RGP lenses will correct corneal astigma- not being achieved, especially when further improve orientation and stability tism. The advantage of a spherical RGP comparing comfort and vision ratings.3 characteristics of the lens on the eye. lens to correct astigmatism is the relative The need to improve performance Around 16 per cent of prescriptions ease of the fit, while the disadvantages further, along with a better understand- have more than 1.00DC of astigmatism are the reduced comfort associated with ing of the forces that influence toric (Table 1) which increases to approxi- rigid lenses, the difficulty in obtaining lenses, has resulted in the introduction mately over 30 per cent of the ametropic a well-centred lens in some cases and of more advanced designs in the last few population with 0.75D or more of refac- the frequent problem of three and nine years. Stock and custom made toric soft tive astigmatism.4 To correct this refrac- o’clock staining. However, a spherical lenses are now available in silicone hydro- tive error, the practitioner has a number RGP lens will not correct lenticular gel materials and the resultant increase in of alternatives: astigmatism. In cases of high corneal

28 | Optician | 07.09.07 opticianonline.net CET Continuing education

Figure 2 Prism-ballast designs (for illustration purposes only) Figure 3 The effect of Lenticular prism carrier a) b) Prismatic gravity on a zone prism ballasted toric soft lens (Courtesy of Chamfer Optic zone Peripheral Graeme comfort chamfer Young) a) Cross-section through a b) A prism-stabilised soft toric lens, prism-ballasted soft toric lens, showing the prism-free central optic zone showing the variation in thickness and the peripheral carrier with prism and comfort chamber, from Grant c) Prism zone

c) A prism-stabilised soft toric lens, Surface toricity showing the prism free central optic zone A rigid toric lens maintains its position and the peripheral carrier with prism and on the cornea through the alignment Optic zone comfort chamber to allow control of lens of the back surface of the lens with the Comfort chamfer thickness with different lens powers toric cornea, assuming that the cornea (adapted from Cox et al) has sufficient toricity to justify the toric fitting. If a soft lens is produced with a toricity the fit might become unstable acuity, resulting in full astigmatic correc- toric back surface, its reduced modulus and a toric periphery or full toric back tion with a soft toric contact lens.8 of elasticity means the lens will still drape surface will be required, as discussed in and so rotate on the eye. Most current Part 6 of this series. Having a full toric Soft toric lens moulded toric soft lenses incorporate a back surface on the lens provides the best The final option for the practitioner is to toric back surface and are equally suitable option in achieving an alignment fit. fit a soft toric lens. This has the comfort to fit on spherical corneas when correct- advantage of soft material and generally ing lenticular astigmatism. More recent Thick soft lenses improved visual performance over the designs have a spherical fitting curve An often-quoted strategy for correcting other soft lens options discussed. The which surrounds the back surface toric low degrees of astigmatism with soft rest of this article will discuss soft toric optic portion. However, to keep the astig- lenses is to increase the thickness of the contact lens fitting in practice. matic correction of the lens in alignment lens or use a higher modulus material. to that of the eye, the lens must be held The theory is that a thicker or stiffer lens Instrumentation in position. There are two basic ways to will drape less on the cornea and so mask The basic instrumentation required for achieve this: more astigmatism. soft toric lens fitting is the same as that ● Prism-ballasted design When controlled studies have been needed to fit regular soft lenses. A slit ● Non prism-ballasted design (eg double carried out, usually no significant effect lamp having a graticule with a protrac- slab-off, dual thin zone, accelerated stabi- has been reported for the majority of tor is of particular value in soft toric lisation design). patients.5,6 Likewise, a higher modulus lens fitting to assist in locating the axis. spherical silicone hydrogel material If this is not available, rotation of the slit Prism-ballast design has been shown to have no significant beam and a scale indicating the degree of This was the first and, although consid- impact on the amount of astigmatism rotation can be helpful (Figure 1). erably adapted over the years, is still masked when compared to a hydrogel the most common means of stabilis- soft contact lens.7 Overall it must be Lens trial ing a lens in the eye. In principle, the concluded that the degree of astigma- The ideal system would be to have a lens is produced with an increasingly tism correction by spherical soft lenses comprehensive bank of single-use trial thicker profile towards its base (Figure is clinically insignificant. lenses in practice to allow astigmatic 2a). The thinner portion of the lens patients to experience lens wear as locates under the upper eyelid, which Aspheric hydrogel lenses conveniently as their spherical counter- then squeezes the thicker portion of There is some evidence that the use of parts. The alternative is empirical fitting, the lens towards the lower lid (the so- aspheric front surfaces, which reduce whether fitting a disposable lens or called watermelon seed principle). It was the spherical aberration in the lens/eye conventional stock toric lens. If a dispos- considered for many years that gravity system, may improve visual perform- able lens fit, this means the practitioner did not play a part in the axis location. ance in low degrees of astigmatism orders a diagnostic lens for the specific However more recent research – which compared to spherical soft lenses even patient. Regardless of the approach, a lens observed what happens when prism- though the astigmatism remains uncor- must be assessed on the eye to allow the ballasted lens wearers lay on their side rected. However, aberrations of the eye practitioner to assess both the physical fit – shows gravity does have some effect vary considerably between subjects, of the lens and its rotational behaviour, as shown in Figure 3.9 In this position, which may explain in part why lenses of which will determine the optical result. the prism base swings towards the verti- this type meet the needs of some wearers Maintaining the rotational stability of cal. Lid position, blink and gravity are but not others. In addition, more recent the lens is the key to successful soft toric all important influences on lens orienta- research has shown that the perform- fitting, not just in the primary position of tion with this type of lens design. When ance of an surface when gaze, but maintaining stability also with prism-ballasted lenses rotate 45 degrees fitted to low astigmats decreased with more lateral eye movements as well as from their normal position, they rapidly larger pupils and did not match the visual during different head positions. re-orientate through the first 20 to 30 opticianonline.net 07.09.07 | Optician | 29 Continuing education CET

degrees under the influence of gravity. Non-prism ballast designs (for illustration purposes only) When gravitational force is no longer significant, most rotation occurs during a) Thin zone b) Thin zone the blink because of the rapid motion of the upper lid as it sweeps against the contours of the lens. The increase in the thickness of the lens means less oxygen is transmitted Thin zone Optic zone Thin zone Independent through the material and this can also optic zone lead to a decrease in comfort, especially against the lower lid. To overcome this, manufacturers remove as much of the a) Double slab-off c) stabilised lens design prism as possible from the lens through Zones of 360 degree comfort chamfers and eccen- thickness tric lenticulation, which are designed to b) Dual thin zone with reduce the thickness of the lens10 (Figure independent optic zone 2b). In addition, prism-ballast designs have seen further refinements, result- c) Accelerated stabilisation design with zones of thickness located Optic zone ing in prism-free optics (peri-ballast) outside the open eyelid and prism that is restricted to the lens periphery.11,12 Other designs aim to control the thickness profile vertically Figure 4 to limit unwanted rotational forces and minimise differences in stabilisation between lenses of different power and A B cylinder axis.13 (Figure 2c).

Non-prism ballasted designs These designs also rely on the interac- tion between lids and the lens to achieve stabilisation. Both eyelids play an active role unlike with prism-ballast designs that involve interaction primarily from the upper lid. These designs show little Figure 5A and 5B Axis marks on different soft toric lenses (Courtesy of Trusit Dave) or no rotation resulting from gravity. In early designs, stabilisation is achieved by designing a thin zone that is superior tight, which can encourage nasal rotation. Techniques and inferior to the optic zone, resulting As gravity has minimal rotational influ- in no additional thickness. The lids will ence on non-prism ballast designs, they Initial fitting squeeze against the thickness differential may be more optimal for certain more Lid position, the upward or downward across the lens, maintaining its stability. dynamic situations (watching or playing slope of the lids and palpebral aperture The advantage of this type of design is sport) or occupations such as dancers, size have been shown to be the main that the overall thickness profile can be mechanics, military personnel etc.9 patient factors associated with lens kept to a minimum, optimising physi- As no one soft toric design is suitable orientation and stability.16 Even with ological response and patient comfort. for all eyes, the practitioner should have increasing knowledge of soft toric lens Refinement to this stabilisation approach a minimum of two different designs fitting, it doesn’t yet allow practitioners includes designs that isolates the optical available, prism and non-prism ballasted to fit them without some trial and error, correction within an optic zone resulting with the optimal choice of material being however it does allow them to better in independent stabilisation areas.14 This silicone hydrogel. understand where problems may occur allows orientation consistency across As well as selecting soft toric lens and how best to solve them. The exact all powers and a thin overall thickness fitting sets with different designs, the fitting procedures for soft toric lenses profile to improve oxygen transmissibil- practitioner should also ensure the lenses may vary among the different brands. ity (Figure 4b). More recently, designs being fitted are reproducible and, for non- The basic principles, however, remain have maximised effectiveness by locat- disposable type lenses, that exchanges the same as long as a toric lens is used for ing thicker ‘active zones’ within the are available from the manufacturer, if on-eye assessment. Some manufacturers palpebral apertures while minimis- required. Soft toric lens reproducibility advocate empirical fitting – ordering the ing any thickness variation of the lens has improved over the years, although final lens without first observing a lens under the eyelids15 (Figure 4c). This lathe-cut lenses, in particular, might still on the eye and then making any neces- results in a lens that rotates quickly to show some variability. sary adjustments once the lens has been its desired position but reduces the likeli- All soft toric lenses require some form evaluated on the eye. Disposable toric hood of the lens to rotate away from its of marking on the lens if the practitioner lens fitting allows an individual trial lens intended position between blinks or due needs to identify the position of the cylin- to be ordered empirically or the appropri- to the sideways movement of the lower der power axes. A variety of symbols are ate powered lens to be selected from an lid during blinks. used by manufacturers to mark either the in-practice fitting bank. Non-prism ballasted designs can be six o’clock or prism base of the lens or the more beneficial on those patients with three and nine o’clock positions (Figures Physical fit a high lower lid, particularly if the lid is 5 and 6). The physical fit for a soft toric lens should

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be the same as for a spherical soft lens. the cylindrical axis should be made when lens power or degree of rotation, but to The lens should cover the cornea in all the choosing the initial trial lens. see how stable the end-point result is gaze positions, allow adequate tear flow As both the cylinder power and axis is and effectively assess lens stability. If the to enable metabolic debris to be removed varied on a lens, there is a risk that differ- patient reports that the vision blurs with and remain in alignment with the cornea ent stability and degrees of rotations may each blink, either the lens fit is unsuitable and conjunctiva. If a lens fit is borderline result, especially with designs where the or the rotational stability of the lens is between being adequate or having slight stabilising thickness profile is dependent poor. In either case, another lens needs excessive movement, the more mobile fit on lens power. Contrary to popular belief, to be inserted, either a different param- would generally be chosen to allow the axes of astigmatism are nearly equally eter (in the case of a poor fit) or design various forces to have the desired effect distributed around the clock face for (if the lens is rotationally unstable). on the lens rotation. lower amounts of astigmatism (Table 2). Assuming a clear end-point of Oblique cylinders are generally accepted can be obtained, the practitioner should Initial trial lens – choice and insertion as being more difficult to succeed with, go on to assess the lens fit and rotational The choice of back optic zone radius in terms of vision, although more recent position. (BOZR), total diameter (TD) and centre advanced designs attempt to minimise Before the physical fit is determined, thickness (tc) for a soft toric lens should be these rotational differences. the practitioner should look first for the made in the same way as one would select The goal of the trial fitting is two-fold: rotational stability of the lens. This is a spherical soft design. The power of the to assess the physical and physiological fit carried out by viewing the axis location lens should be chosen with the spheri- and response to the lens and to measure marks on the lens. These should not show cal and, more importantly, the cylindri- orientation position along with orien- rotation with each blink or in-between cal power and axis as close as possible tation stability. Following insertion, blinks and should be close to their to the predicted final lens parameters. the lens should be allowed to settle, as intended position (vertically or horizon- While earlier soft toric designs tended for a spherical soft lens, before the fit tally). If the lens position is more than to predictably rotate nasally by 5 to 10 is assessed. With more recent designs, 30 degrees from the intended position it degrees from the intended position, this speed of orientation is faster allowing suggests that there is inadequate stabilisa- is not the case with more modern designs. assessment within one to three minutes tion and an alternative lens design should A number of patient factors and lens fit following insertion. be considered. characteristics influencing soft toric lens If the location marks are stable in the orientation have been identified, but the Visual assessment primary position of gaze, the practitioner findings fall short of allowing practition- After the settling period, an over-refrac- should note their position in relation to ers to accurately predict toric lens orien- tion should be carried out. The purpose their intended position and the direction tation. Hence no initial compensation of of the over-refraction is not to determine and degree of rotation seen (if any). This

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opticianonline.net 07.09.07 | Optician | 31 Continuing education CET

Examples of axis marks on different soft toric lenses Table 2 Distribution of cylinder axis orientations, from Bennett4 Cylinder power Percentage distribution of axis orientation (D) in each cylinder power With the rule Against Axis oblique the rule 0.50 36 34 30 Figure 6 ExamplesExamples of axis marksshowing on different alignmen softt toric lenses 1.00 34 34 32 and mis-alignment of axis 1.50 35 31 34 2.00 38 24 38

Clockwise: 2.50 50 18 32 Add axis 3.00 54 17 29 3.50 49 17 34

Anti-clockwise: 4.00 50 15 35 Subtract axis Over 4.00 58 13 29

Figure 7 Examples showing alignment and mis-alignment of axis can either be measured using a graticule Alternatively, if the lens rotates to the for example when reading a broad sheet or the slit beam width rotation on the left the rotation should be added and if newspaper, a task which often involves slit lamp (Figure 1) or estimated using it is to the right it should be subtracted different positions of gaze, or when the axis marks as a guide (Figure 6, (LARS). watching TV when lying down. In these 7). Care should be taken when assess- cases, axis position and visual acuity in ing the location marks on a lens that Over-refraction the primary position of gaze may appear has decentred as it may appear the lens If the trial lens scribe marks lie within correct, however the symptoms suggest has rotated when actually there is no 10 degrees of the intended position, lens stability is inadequate and an alterna- rotation. An advantage of a toric lens vision can be assessed and a spherical tive lens design should be trialed. with two markings opposite each other is over-refraction carried out to determine If poor vision is found at dispensing, that by passing a slit-beam through both whether an alternate spherical power the practitioner should first review the marking, a more accurate measurement should be ordered. Lenses that position patient’s record to see what the power of of lens rotation is achieved, whether the off-axis will produce a residual refractive the trial lens was. If the power of the trial lens has decentred or not. Stability of error, which is a function of the cylinder lens (spherical and axis) was similar to that orientation should be assessed further power and degree of mis-orientation. For of the prescription lens, one or other of while the patient performs forced blink- example, a toric soft lens of power –3.00/- the lenses might differ from the marked ing and during version movements. 1.75x180 that matches the patient’s ocular parameters. In some cases, the reason for Ask the patient to look up, down, left prescription but orientates 20 degrees off- the poor vision is axis rotation, caused and right, while looking for any signifi- axis will result in an over-refraction of by the different effects of the eyelid on cant lens rotation. If the lens remains +0.50/-1.25x55. The stability of the end- the final prescription lens and on the relatively stable during this simulation, point gives a good indication that lens fit trial lens. This in turn can be brought on then it should provide relatively stable is adequate; however, it is impossible to by the different thickness profiles, and vision. Visual performance should also determine whether the spherical compo- therefore stabilisation effectiveness, of be assessed at near. nent of the final prescription to be ordered some lens designs. This problem can be The axis rotation gives the practitioner requires adjustment. Consequently, a avoided by using trial lenses that closely the information needed to order the lens. new trial lens should be inserted after match the patient’s ocular prescription or The rotation of the lens shows how far compensation of the cylinder axis for lens using lens designs that offer independent the axis of the cylinder will be mis- rotation to allow a meaningful spherical optical and stabilisation areas. located when the final lens is placed on over-refraction. The final order for the Figure 8 suggests a flowchart proce- the eye. This mislocation can be compen- lens should include BOZR, TD, tc (if dure to tackle poor visual acuity.17 sated for by ordering a lens with the axis variable) and the power in terms of the This approach is based on assessing the at a different position. sphere, cylinder and desired axis. rotational stability of the lens in the eye. If If, for example, an ocular refraction is the lens is rotationally stable but the axis is –3.00/-1.75x180 and a trial lens rotates Troubleshooting mislocated, the practitioner compensates clockwise by 10 degrees when placed for axis rotation and reorders the lens. If on the eye, the correction will be –3.00/ Poor vision the lens if rotationally unstable, either a -1.75x170 degrees and the vision will be The most common problem encountered different fit or design of the soft toric lens blurred. To compensate for this, if the with soft toric lens fitting is unaccept- is required. A sphere/cyl over-refraction lenses are ordered as –3.00/-1.75x10, the able or variable visual acuity. The most can be useful in determining whether 10 degree clockwise rotation will bring common reason for this is mislocation poor visual acuity is due to lens misloca- the axis round to 180 degrees and the of the axis. The visual acuity might be tion alone or resulting from differences required axis, and vision will be clear. found to be reduced, either at the time between labeled and actual specification. The basic rule is that if the lens rotates of dispensing, with the final lens or at a If the residual refractive error shows a clockwise the degree of rotation should subsequent aftercare examination. If at result where the cylinder power is numer- be added to the axis, but if it rotates aftercare examination, it is important to ically twice the sphere power, it is a good anti-clockwise the rotation should understand if there is a particular visual indication that the lens is simply sitting be subtracted from the axis (CAAS). task that results in poor visual satisfaction, off-axis.18

32 | Optician | 07.09.07 opticianonline.net CET Continuing education

Poor comfort Flowchart procedure to approach the problem of Lens comfort has been shown to be poor visual acuity with soft toric lenses related to overall lens volume. If a patient is complaining of comfort problems with Poor visual acuity soft toric lenses, the practitioner should Is the lens rotationally consider changing the design of the lens stable on the eye? to one that has a thinner profile. This can YES NO be achieved, for example, by moving to Is the lens orientating Is the lens fitting correctly a thinner prism-ballasted design or to a correctly? in all other aspects? thinner non-prism ballasted design. In YES NO YES NO addition, changing to a silicone hydro- Check Check Which Change Alter gel material can improve comfort and lens spectacle direction design or lens fit reduce dryness symptoms for many prescription prescription is the lens type contact lens wearers. rotating? of lens

Oedema Clockwise Anti-clockwise The increased thickness of soft hydrogel add subtract toric lenses over spherical soft hydrogel Degree of rotation from/to lenses means there is less oxygen supply cyl axis and reorder to the cornea, which can result in localised oedema and vascularisation. Early toric lens designs with low water content and Figure 8 increased thickness profiles did produce significant corneal oedema. To increase Staining soft toric lenses as for soft spherical lenses. oxygen flow with hydrogel materials, As soft torics are specifically designed to With silicone hydrogel torics, it is impor- practitioners should either use a design prevent rotation to achieve the desired tant to rule out the possibility that the with a thinner profile or higher water optical effect, this might result in reduced lens material/lens care combination being content or, ideally, a combination of both. tear exchange and entrapment of debris. used are the cause of the staining. In these With the increasing availability of soft In turn, this can result in corneal stain- cases a change to a more compatible lens silicone hydrogel toric lenses, oedema can ing. If corneal staining occurs, the same care solution for the particular material be avoided for the majority of patients. principles for its management apply for being used will reduce the staining. AP colorado 28/08/07 13:35 Page 1

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opticianonline.net 07.09.07 | Optician | 33 Continuing education CET

Conclusions Of the strategies to correct astigmatism Multiple-choice questions with soft contact lenses, the use of the soft toric lens provides the least compromised What percentage of prescriptions have an A lens of power -3.00/-1.75x180 that means. With the better understanding of 1astigmatism of greater than 1.00DC? 8matches the patient prescription but the forces that influence soft toric lenses on A 4 per cent rotates 20º off-axis will result in what the eye, designs continue to improve with B 10 per cent over-refraction? faster orientation when first inserted, as C 16 per cent A -3.00/-1.75x180 well as being more predictable and more D 25 per cent B +0.50/-1.75x55 stable during more dynamic vision situa- C +0.50/-1.25x55 tions. The availability of silicone hydro- What percentage of the population have D -0.50/-1.25x55 gel torics has improved both comfort 2no cylindrical refractive error? and oxygen availability to the cornea. In A 72 per cent For a 3.00D cylinder, which is the most many ways fitting a soft toric lens today B 65 per cent 9likely axis orientation? is as straight forward as fitting a spherical C 45 per cent A With the rule lens for the majority of patients and with D 32 per cent B Against the rule improving performance and patient satis- C Axis oblique faction, should continue to be an integral Which of the following lens designs most D Random distribution part of contact lens practice. ● 3rely on gravitational force for stability? A Double slab-off What is the likely cause of corneal References B Prism-ballasted 10stain with a soft toric lens? 1 Morgan P. Trends in UK contact lens C Dual thin zone A Tear debris stagnating under the stable lens prescribing. Optician, 2006; 231:6054 16-17. D Accelerated stabilisation B Toxic solution response 2 Morgan P et al. International contact lens C Poor fit prescribing in 2006. Spectrum, 2007; January. What is the advantage of non-prism- D Dessication 34-38. 4ballasted lens designs? 3 Hickson-Curran S and Dias L. Toric soft A They are cheaper to manufacture A lens of power -3.00/-1.75x180 contact lenses: where are we now? Optician, B They settle immediately upon insertion 11rotates clockwise by 10º. Which of the 2006; 231:6041 14-16. C They do not require any surface markings following should be ordered? 4 Bennett AG and Rabbetts RB. Distribution D They may maintain minimum overall thickness A -3.00/-1.75x20 and ocular dioptrics of ametropia. In: Clinical B -3.00/-1.75x10 Visual Optics (London: Butterworths), 1984; Which of the following designs is least C -3.00/-1.75x180 433-444. 5appropriate for an active sports player? D -3.00/-1.75x170 5 Cho PC and Woo GC. Vision of low astigmats A Double slab-off through thick and thin lathe-cut soft contact B Prism-ballasted Which of the following is true? lenses. Contact Lens Ant Eye, 2001;24: 153- C Dual thin zone 12 160. D Accelerated stabilisation A High modulus soft lenses will mould the 6 Bernstein PR et al. Masking corneal toricity cornea to mask any astigmatism with hydrogels:does it work? Int Contact Lens What is the least time that may be left B The degree of astigmatism masked by Clinic, 1991; 60:728-731. 6after fitting a soft toric lens before spherical soft lenses is clinically insignificant 7 Edmondson L et al. Masking astigmatism assessment? C High modulus soft lenses drape over the Ciba Focus Night & Day vs Focus Monthly, A 20 minutes cornea and produce a tear lens which Optom Vis Sci, 2003; 80:12 184. B 10 minutes neutralises astigmatism 8 Morgan PB et al. Inefficacy of aspheric soft C For some modern designs, 1-3 minutes D The first choice lens for astigmats is always contact lenses for the correction of low levels D For some modern designs no time is required an RGP of astigmatism. Optom Vis Sci, 2005; 82:9, 823-828. A lens of power -3.00/-1.75x180 rotates 9 Young, G. Toric lenses, gravity and other 7on the eye anti-clockwise by 10º. Which forces. Spectrum, 2007; January. 39-40. of the following should be ordered? 10 Grant R. Toric soft contact lenses: a review. A -3.00/-1.75 x 20 Optician, 1995; 209:5483, 16-24. B -3.00/-1.75 x 10 11 Tanner J. A new high water content soft C -3.00/-1.75 x 180 toric lens. Optician, 1996; 211:5549 20-21 D -3.00/-1.75 x 170 12 Ruston D. Success with soft torics and high astigmats: the Hydrasoft Toric. Optician, 1999; 217:5704 34-38. To take part in this module go to opticianonline.net and click on the Continuing Education 13 Cox I, Comstock T and Reindel W. A clinical section. Successful participation in each module of this series counts as two credits towards comparison of two soft toric contact lenses. the GOC CET scheme administered by Vantage and one towards the Association of Optician, 1999; 218:5730 32-36. Optometrists Ireland’s scheme. The deadline for responses is October 4 14 Hickson-Curran S, Veys J and Dalton L A new dual-thin zone disposable toric lens. Vis Sci, 2002; 79:1, 11-19. ● Jane Veys is education director, The Optician, 2000; 219:5736. 17 Davies IP. Soft toric contact lenses: Vision Care Institute, Johnson & Johnson 15 Hickson-Curran S and Rocher I. A new daily systematic approach to problem-solving. Vision Care. John Meyler is senior director, wear silicone hydrogel lens for astigmatism. Optician, 1989; 198:5211, 16-18. professional affairs, Europe, Middle East & Optician, 2005; 232:6067 27-31. 18 Edwards K. Problem solving with toric soft Africa, Johnson & Johnson Vision Care. Ian 16 Young G et al. Clinical evaluation of factors contact lenses. Optician, 1999; 217:5695 Davies is vice president, The Vision Care influencing toric soft contact lens fit. Optom 18-27. Institute, Johnson & Johnson Vision Care

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