Lecture 2B CL Optics

What is spectacle magnification?

How much a corrective lens magnifies or minifies the retinal image

What is the equation for spectacle magnification?

What is the spectacle magnification for:

BVP: -8.00 D

BC: F1: +2.00

t= 5 mm

n= 1.50

Vertex distance 14 mm

0.88619—> (-11.38%)

What do contacts do to Spectacle Magnificaiton?

Reduces:

Minification in minus lenses

Magnification in plus lenses

****Shape factor is clinically insignificant

For HIGH myopes, how can CL help?

1-2 lines better VA

For HIGH hyperopes, how can CL help?

1-2 lines worse VA

What is the clinical ESTIMATE change in magnification for CL?

<1: Less magnification with CL

>1: More magnification with CL

What do CL help the best with?

Refractive Cases

What is Prentice’s Rule?

P = d(BVP)

d—> distance from optical center in cm

What are the prismatic effects for Minus and Plus Lenses?

MINUS: Thinner center

PLUS: Thicker center

What is the vergence demand with spectacles?

Plus Lenses: More demand at near

Minus Lenses: Less demand at near

What is the vergence demand with CONTACTS?

Minus Lenses: More vergence demand at near

Plus Lenses: Less vergence demand at near

Why do CL’s help reduce prismatic effects?

Optical center moves with the eye

What is Accommodative Demand?

Difference in vergence of light on the cornea between light originating at distance and at near.

What is the Accommodative Demand for Emmetropes?

Equal to the vergence of light emitted by the object at that specific distance.

What is the Accommodative Demand for Hyperopes?

MORE with spectacles

Less with CL

What is the Accommodative Demand for Myopes?

Less with spectacles

MORE with CLs

What are the steps to calculate for Accommodative demand?

1. calculate vergence at DISTANCE

2. Calculate vergence at NEAR

   1. Subtract the vergence at near from distance

      ****Light exiting object is negative

Solve This Example

+3.19 D

What is the clinical Relevance for Accommodative Demand?

1. Pre-presbyopia: be cautious with new MYOPIC CL wearer: May be beneficial for Hyperopic CL wear

2. Anisometropic Accommodative Imbalance: can be resolved w/ CL

Is Accommodation for an Emmetrope the SAME as a Myope and Hyperope in CL?

True

Yes

Yep