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# Dispensing BSc (4).pptx

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### Dispensing BSc (4).pptx

1. 1. Dispensing BSc (4) Dr. Atif Babiker Mohamed Ali Faculty of Optometry 2014 -2023
2. 2. The crossed or compound cylinder form • To transpose a sphero-cylinder to crossed cylinders: • A- the sphere power (S) become the power of one cylinder (C1) with axis at right angle to that of original cylinder ( C ). • B- the sum of the sphere (S) and cylinder ( C) becomes the power of the second cylinder (C2) with axis parallel of original cylinder ( C).
3. 3. • Example: transpose - 1.0sph/- 2.0 CX90 to crossed cylinder form. • A- -1.0 CX 180 • B- - 3.0 CX 90 • The form is − 1.0 𝐶𝑋 180 − 3.0𝐶𝑋90 • Transpose - 2.0sph/+3.0 CX30 to crossed cylinder form. • A- -2.0 CX 120 • B- +1.0 CX 30 • The form is -2.0 CX 120/ +1.0 CX 30.
4. 4. • To transpose crossed cylinder to sphero- cylinder. • A- select any of cylinders (e.g. C1) to become sphere (S). • B- The difference between the two cylinders (C2 - C1) become the new cylinder (C) with axis of second cylinder (C2 ). • E.g. Transpose + 1.0 CX 180/+1.5 CX90 to sphero- cylinder form. • A - + 1.0 sph • B - + 1.5 – (+1.0) = +0.5 CX 90 • +1.0 sph/+ 0.5 CX 90
5. 5. • For example: transpose - 1.50CX90/ - 2.50CX 180 to sphero-cylinder form. • A- - 1.50 Sph • B- - 1.0CX 180 • Result: - 1.50 Sph/ - 1.0CX 180. • Or select C2 instead of C1 to become the sph. • A- - 2.50 sph • B- - 1.5 – (-2.5) = + 1.0 CX90 • Result – 2.5sph/ + 1.0 CX 90
6. 6. Toric lenses • Like meniscus lenses, torics have one convex and one concave surface, but only one of these is spherical. The other surface which required to correct astigmatism is known as toroidal surface. • The base curve is the surface power in the meridian of least curvature. • The cross curve is the surface power in the meridian of maximum curvature.
7. 7. • E.g. if the base curve were +6.0D and the cross curve +7.50D, this toric surface could be specified as +1.50D cylinder. • There is a simple rule can be used to express the power of a toric lens in the usual sphero- cylinder or cylinder notation. • Sphere power = Base curve + power of spherical surface. • Cylinder power = Cross curve – base curve • Sph = BC + SC • Cyl = CC - BC
8. 8. Toric transposition • In case of toric transposition if the spherical surface is given. Transpose the cylinder of sphero-cylinder form to opposite sign of spherical. • In case of toric transposition if the Base curve is given. Transpose the cylinder of sphero- cylinder form to same sign of Base curve .
9. 9. • Transpose – 1.0/ - 0.5 CX 180 to toric form given base curve – 6.0D. • Sph = BC + SC • Cyl = CC - BC • - 1.0 = - 6.0 + SC or (SC = + 5.0) • - 0.5 = CC - ( -6.0) or (CC = - 6.5) • 𝑆𝐶 𝐵𝐶/𝐶𝐶 • +5.0𝑆𝑝ℎ −6.0𝐶𝑋90/−6.5𝐶𝑋180
10. 10. • Transpose +2.0/+1.5 CX 30 to toric form given spherical surface +9.0Dsph. • Transpose to opposite cyl sign +3.5/ - 1.5 CX 120 • Sph = BC + SC • Cyl = CC – BC • +3.5 = BC + (+9.0) or (Bc = - 5.5) • - 1.5 = CC – (-5.5) or (CC = - 7.0) • 𝑆𝐶 𝐵𝐶/𝐶𝐶 • +9.0𝑆𝑝ℎ −5.5 𝐶𝑋30/−7.0𝐶𝑋120