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Soft Toric Contact lens
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- 2. ASTIGMATISM • Astigmatism isa refractive condition in which a point object is not rendered as a point image by an optical system instead parallel rays comes to focus in 2 focal lines rather then a single focal point.
- 3. CLASSIFICATION & TYPES •Simple Hyperopic astigmatism • Compound Hyperopic astigmatism • Simple Myopic astigmatism • Compound Myopic astigmatism • Mixed astigmatism
- 4. CLASSIFICATION BY STRUCTURE •Corneal astigmatism • Lenticular astigmatism • Internal astigmatism • Total astigmatism
- 5. CLASSIFICATION BY THETYPE • Regular astigmatism • Irregular astigmatism Classification by Orientation • With-the-rule • Against-the-rule • Oblique
- 6. WHAT IS TORICLENS ? • Toric lens is a lens used to correct Astigmatism or Cylindrical number as it contains cylindrical component which standard soft contact lenses do not have. SPHERICALLENS TORIC LENS
- 7. DESIGNS & METHODSOF STABILIZATION OF TORIC SCL 1. The Watermelon seed principle • If a fresh seed of (watermelon) is squeezed between the thumb and forefinger it is rapidly expelled from the convergent (v- shaped) space between the fingers. Expulsion is a direct result of one of the two force of vectors of the pressure applied by each finger to the seed’s tapered surface. One vector attempts to compress the seed, the other attempts to expel the seed. • Expulsion is facilitated by the ‘slippery’ moist surface of the seed. The contact lens analogy to the watermelon seed is the tapered lens edge, especially the taper created by either prism ballast or double slab-off design.
- 8. PRISM BALLAST • Inits simplest form this lens design incorporates a base down prism and relies on lid forces (mainly upper lid forces) acting on the thickness differences induced by the base down prism (thickness taper) to orient the lens on the eye. • The thinner portion of the lens locates under the upper eyelid, which then squeezes the thicker portion of the lens towards the lower lid (the watermelon seed principle). • Gravity has been shown not to play a part in the axis location. • Base down prism of 1 to 1.5 prism diopters is used. This increases the thickness of the less inferiorly therefore less oxygen is transmitted through the inferior side of the lens and also lead to a decrease in comfort, especially against the lower lid.
- 9. DYNAMIC STABILIZATION ORDOUBLE SLAB-OFF • This technique also relies on the interaction between lids and the lens to achieve stabilization. Both eyelids play an active role unlike with prism-stabilized designs that involve interaction primarily from the upper lid. • Stabilization is achieved by designing thin zone superior and inferior to the optic zone. • The interaction of thin zones with the lids especially with the upper lid position and stabilizes the lens on the eye and gave rise to the term dynamic stabilization.
- 10. REVERSE PRISM • Thisdesign is an evolutionary and logical follow-on form true prism ballast designs. Because of the lens thickness inherent in the incorporation of prism, and the resultant need to chamfer (base up) interests of comfort, it was logical to incorporate both prism (base down) and the inferior chamfer (base up) into an integrated design, which should be both thinner and more comfortable.
- 11. PERI-BALLAST • This techniquestarts with a minus carrier design. • To create a prism base down effect, the superior carrier is slabbed-off or chamfered superiorly to reduce its thickness and influence. • This process allows the lens periphery to position comfortably under the lids.
- 12. TRUNCATION • Truncating thelens by removing part of the lower portion of the prism-ballasted lens is generally no longer carried out. It is not considered a current technique but can be employed as a last resort.
- 14. FITTING TORIC SOFTCONTACT LENSES • Three fitting techniques: • Diagnostic • Trial • Empirical
- 15. TORIC SCL MEASUREMENTOF LENS ROTATION Rotation is measured by laser marks which are at 3,6 and 9 o’clock positions Rotation can be measured by :- Narrow Slit – Lamp Beam Protractor Scale on the eye piece of K Spectacle Trial Frame Rotation is measured by laser marks which are at 3, 6 and 9 o’clock positions Rotation can be measured by :- Narrow Slit – Lamp Beam Protractor Scale on the eye piece of K Spectacle Trial Frame
- 16. TORIC FITTING PROCEDUREAT A GLANCE • Step 1- Perform Refraction & write prescription in –ve cyl form. e.g. – Spectacle prescription -3.00/-2.00 x 180. • Step 2- Perform Keratometry Add 0.80 mm to flattest meridian • Step 3- Perform Vertex distance Compensation for sphere & cyl separately. e.g. -3.00 /-1.75 x 180 • Step 4- Choose a toric trial lens (as close as to spectacle prescription.) • Step 5- Assess contact lens (Coverage, Centration, Movement, Comfort) (till this stage spherical & toric fitting is same) • Step 6- Asses Rotation (for axis finalization)-(LARS Left Add Right Subtract)
- 17. TORICAXISFINALIZATION TORICAXIS FINALIZATION • 3things can happen while assessing Toric lens rotation No rotation or minimal rotation of 5 degrees Rotation to L.H.S ( with reference to Practitioner) Rotation to R.H.S(Practitioner) • THUMB RULE LARS- Left Add Right Subtract
- 18. LENS ROTATION -10° • Rx required -3.00/-1.00 x 10 •Anticlockwise - subtract order -3.00/-1.00x180 •Clockwise - add order -3.00/-1.00x20
- 19. EXAMPLE 1 • SpectaclePres. -6.00/-3.00 x180 • Vertex Dist -5.50 / -2.50 x 180 • Trial lens - -3.00 /-1.25 X 180 @ 8.6mm • Rotation to R.H.S by 15degrees • Subtract- 180 - 15= 165degrees • Final lens prescription:- • -5.50/-2.50 x165 degrees @ 8.60mm
- 20. EXAMPLE 2 • SpectaclePres. -6.00/-3.00 x180 • Vertex Dist -5.50 / -2.50 x 180 • Trial lens - -3.00 /-1.25 X 180 @ 8.6mm • Rotation to R.H.S by 15degrees • Subtract- 180 - 15= 165degrees • Final lens prescription:- • -5.50/-2.50 x165 degrees @ 8.60mm
- 21. EXAMPLE 3 • Spectaclepres: -1.00/-3.00 x120 • Trial lens: -2.00/-0.75 x 908.30 • Rotation to R.H.S by 10 • Answer - -1.00/-2.75 x110 8.30 mm
- 22. TORIC SCL ASSESSMENTOF FIT • Good fit- Full corneal coverage, Good centration and movement, quick return to axis if mislocated • Tight fit Good centration, initially comfortable, Little or no movement. Slow return to axis if mislocated. • Loose fit Excessive movement, Poor centration, Uncomfortable. Lens orientation unstable and inconsistent.
- 23. THINGS TO REMEMBER •Do not make any changes in trial lens axis • Trial lens (Diagnostic lens ) fitting is a very reliable and scientific method of fitting Toric lenses • Choose trial lens axis as close as possible to spectacle axis • If trial lens axis & spectacle axis are different then do not attempt over refraction as it can lead to confusion • Final lens Base Curve should be same as Trial lens base Curve • Like the trial lens, final lens would also show similar rotation
- 24. BRANDS OF TORICLENS • Alcon • Bausch + Lomb • Cooper Vision • J&J • Custom made soft torics are also available from companies like Flexilens / Purecon etc .
- 25. SUMMARY • BAUSCH &LOMB MASTER MIND 3 MODULE • ICAL
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