The prescription +2.00DS/-1.50DC x 90 is to be manufactured in UCC Optical company. a. Generate the different surface curves using the following toric bases: i. +6D ii. -6D b. Ske... The prescription +2.00DS/-1.50DC x 90 is to be manufactured in UCC Optical company. a. Generate the different surface curves using the following toric bases: i. +6D ii. -6D b. Sketch with specific surface powers, lens designs with base +6D and -6D c. Indicate with reasons, which of these two prescriptions will be most ideal for use by the patient. Read more

Steps to Solve

1. Understanding the Prescription

The prescription is given as $+2.00DS/-1.50DC \times 90$. This means:

• Sphere power (DS): +2.00 D
• Cylinder power (DC): -1.50 D
• Axis: 90 degrees

This can also be written in its principal meridians:

• $+2.00 D$ at $90^\circ$
• $+2.00 + (-1.50) = +0.50 D$ at $180^\circ$

2. Calculating Surface Curves with +6D Base Curve

For a +6D base curve, we'll place this on the front surface of the lens:

• Front surface powers: +6.00 D in both meridians initially.

To achieve the prescription, the back surface powers must correct the front surface power to arrive at the required prescription powers. Let $F_1$ be front surface power and $F_2$ the back surface power. The lens power $F$ is $F = F_1 + F_2$.

For the meridian at $90^\circ$: $+2.00 = +6.00 + F_{2(90)}$ $F_{2(90)} = 2.00 - 6.00 = -4.00 D$

For the meridian at $180^\circ$: $+0.50 = +6.00 + F_{2(180)}$ $F_{2(180)} = 0.50 - 6.00 = -5.50 D$

Therefore, the back surface is a toric surface with powers -4.00 D and -5.50 D. This can be written as a -4.00D sphere with a -1.50D cylinder i.e. $-4.00DS/-1.50DC \times 180$.

3. Calculating Surface Curves with -6D Base Curve

For a -6D base curve, we'll place this on the front surface of the lens:

• Front surface powers: -6.00 D in both meridians initially.

For the meridian at $90^\circ$: $+2.00 = -6.00 + F_{2(90)}$ $F_{2(90)} = 2.00 + 6.00 = +8.00 D$

For the meridian at $180^\circ$: $+0.50 = -6.00 + F_{2(180)}$ $F_{2(180)} = 0.50 + 6.00 = +6.50 D$

Therefore, the back surface is a toric surface with powers +8.00 D and +6.50 D. This can be written as a +6.50D sphere with a +1.50D cylinder i.e. $+6.50DS/+1.50DC \times 90$.

4. Sketching Lens Designs

For the +6D base curve:

• Front surface: +6.00 D (spherical)
• Back surface: Toric, with powers -4.00 D and -5.50 D (or $-4.00DS/-1.50DC \times 180$)

For the -6D base curve:

• Front surface: -6.00 D (spherical)
• Back surface: Toric, with powers +8.00 D and +6.50 D (or $+6.50DS/+1.50DC \times 90$)

5. Determining the Ideal Prescription

A +6D base curve generally creates a flatter lens, better for plus powers. A -6D base curve will create a steeper more curved lens. For a low plus prescription like this, a +6D will reduce the magnification and be cosmetically more appealing since it keeps the lens flatter to the face.