Power Diameter Base curve SOFT TORIC CONTACT LENS PROF.DR.SAMIHA ABOULMAGD 1

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1 Fitting Soft Contact Lens Prof. Dr. Samiha Aboulmagd MD Head of fophthalmology l Department Al-Azhar University Fitting of contact lens Power Diameter Base curve 2 PROF.DR.SAMIHA ABOULMAGD 1

2 Fitting of soft contact lens Power same as spectacles If spherical above 4 D go to table as have to put into consideration the vertex distance If cylinder is less than 1D get its spherical equivalent and add it to sphere If cylindrical more than 1 D use toric contact lens 3 Fitting of soft contact lens Diameter Usually as large as or larger than the corneal diameter in order to maintain centration and stability 12mm 13mm 14mm 14.7mm 4 PROF.DR.SAMIHA ABOULMAGD 2

3 Fitting of soft contact lens Base curve Measured by the keratometer and transformed to base curve table Because of the large diameter, they should be fit Flatter than the flattest K Lens diameter & base curve are inversely related 5 Fitting of soft contact lens In order to arrive to the same fit, the base curve of the lens selected should be flattened as the lens diameter is increased Example: mm mm 6 PROF.DR.SAMIHA ABOULMAGD 3

4 Fitting of soft contact lens Small eyes require smaller diameters and steeper base curves Larger eyes require larger diameters and flatter base curves Soft lenses are fitted flatter than the flattest K Movement 0.5mm to 1.0mm 7 Fitting of soft contact lens Position : it should completely cover the cornea The uncovered cornea will show irritation and staining. Vision must be good, clear, constant before during and after blinking. 8 PROF.DR.SAMIHA ABOULMAGD 4

5 Soft Lens Evaluation (Diameter) Lens centering. Should cover the complete cornea [ use lens diameter mm larger than the horizontal visible diameter]. This is observed by using a biomicroscope and shining the beam at the edge of the lens which should be resting on the sclera. 9 Soft Lens Evaluation Cont. Movement while patient is looking up Mov.will vary between 0.5 and 1.0 mm. Keratometry = how the lens is fitting on the cornea mires clear at all times proper lens fit PROF.DR.SAMIHA ABOULMAGD 5

6 Soft Lens Evaluation Cont.(B.C) mires are clear before the blink blurred after and then clear once again.: Too flat go for steeper BC or diameter mires are blurry before the blink clear after and then blurry once again.: too steep go for flatter BC or diameter + x Evaluating the Fit for Soft CL.(Cont.). Why: The blurring mires are caused by the vaulting of the lens over the apex of the cornea. The mires clear since the pressure of the lid places the lens in the correct area for a moment. 12 PROF.DR.SAMIHA ABOULMAGD 6

7 TORIC CONTACT LENS Toric contact lens can be either Soft RGP WHICH?? One?? meticulous patients prefer RGP as it gives a sharper image, normal individuals don t notice the difference 13 How Does an Astigmatic See? Most people would see a stopwatch this way However, people with astigmatism see a distorted image. 14 PROF.DR.SAMIHA ABOULMAGD 7

8 Astigmatic patient: If you have an astigmatic patient and you told him that contact lenses are n`t for you, it may be worth taking another look. Many people with astigmatism can achieve good vision with today`s specially designed Toric contact lens. 15 Available Brands Of Toric CL 16 PROF.DR.SAMIHA ABOULMAGD 8

9 Specially Designed Toric Soft CL. They correct astigmatism by having more than one power shaped into them, and by having a stabilizing mechanism to keep the contact lens relatively stable on the eye when you blink, look up, down or from side to side. 17 Specially Designed Toric Soft CL. stabilizing mechanism Double slab- off design Le-Torque design 18 PROF.DR.SAMIHA ABOULMAGD 9

10 As a Contact Lens Practitioner It is your responsibility to decide which type of contact lens the patient should be wearing: Regarding the duration: Daily extended Fr.replacement - disposable Spherical or Toric, according to the amount of astigmatism present and how much the lens would correct. The patient can decide if he needs his lens coloured or not. 19 When to Use Toric? If spherical soft CL. Do not provide good VA. If cylinder power is over 1.0 D. If cylinder power is greater than spherical power. 20 PROF.DR.SAMIHA ABOULMAGD 10

11 Procedure: -6.0 X -2.0 X 180 Transport to minus cylinder Place Rx on the optical cross Compensate for vertex distance in each meridian if +/- 4 and over Take power off the optical cross ORDER x 1.75 x x 1.75 x Check the Axis Marking on the Lens Depending on the Lens Type Some will have one marking that should position at 6 o`clock. Others will have 3 marking at 6 o`clock area separated by 20 or 30 degrees. Some at the o`clock observe and use the LARS. Or CAAS 22 PROF.DR.SAMIHA ABOULMAGD 11

12 Toric Soft Lens Evaluation Cont. Axis Check the axis marking on the lens depending on the lens type CA CAAS Left add LARS Right subtract AS 23 Important Tip One hour = 30 degree L R ADD SUBTRACT PROF.DR.SAMIHA ABOULMAGD 12

13 Toric Soft Lens Evaluation Cont. Axis LARS CAAS Left eye Sp RX: x x Trial CL lens: x 1.5 x 180 Lens marking is 15 to right Lens RX to order: 2.0 x 1.5 x 155 NOTE LARS SYSTEM APPLIED TO SPECTACLE AXIS 25 Trial lens selection RT s LT A 1. Trial lens should be as close as possible to the spectacle lens allowing for vertex correction for powers more than -4D. 2. Cylinder power similar and if not available the lower power. 3. Axis should be the same, but if not available and falls between two available axes, the lens selected will depend on which eye is being fitted, as nasal rotation is more likely. Rx: -2.5/-1.5x 15 Right eye: -2.5/-1.5 x 10. subtract Left eye: -2.5/-1.5 x 20..add Rx: -3.25/-1.25 x 5 Right eye: -3.25/-1.25 x180 Left eye : -3.25/-1.25 x PROF.DR.SAMIHA ABOULMAGD 13

14 Evaluating the Fit for Toric Soft CL.(Cont.). Visual acuity. Each eye checked then both together. Observe if blurring occurs with blink as keratometer. If occurs lens fit is flat. When performing an over refraction if a spherical is found a sphere is added to the lens power 27 Evaluating the Fit for Toric Soft CL.(Cont.). Allow the lens to settle on the eye for minutes before you judge the lens fit. 28 PROF.DR.SAMIHA ABOULMAGD 14

15 Toric Soft Lens Evaluation (Summary). Visual acuity Power Lens centering (over sclera) Movement : No rotation or less than 15 after blinking in 1ry 2ry & 3ry eye movement mm Keratometry: If blurred after movement flat If clears after movement steep Axis LARS CAAS 29 Problems associated with fitting soft lenses Hazy or variable vision Check power, lens not inverted, deposits, re-evaluate the fit. Longer wearing time Burning & irritation Re-evaluate the fit, solutions, pollution. If dry eye,lens should be of low water Staining of cornea Decentred lens, protein built up, FB. 30 PROF.DR.SAMIHA ABOULMAGD 15

16 Problems associated with fitting soft lenses Epithelial oedema, vertical striae in cornea, fixed folds in Descemet`s membrane, compression, vascularization at limbus Due to steep lens that leads to hypoxia, anoxia to cornea Photophobia, excessive tearing Poorly fitting lens irritating the cornea by friction 31 A Final Word Astigmatic patients should be given the toric contact lens don t keep them on spherical lenses. If you follow the proper fitting guides you will be rewarded Toric contact lens calculators are available on the net 32 PROF.DR.SAMIHA ABOULMAGD 16

17 33 THANK YOU 34 PROF.DR.SAMIHA ABOULMAGD 17

18 THANK YOU 35 PROF.DR.SAMIHA ABOULMAGD 18