Optics 3 Lecture 1 Low Vision magnification

Spectacle Mag

unintentional magnification

Plus lenses ________ and minus lenses ________.

magnify, minify

Intentional Mag

magnification for vision enhancement

In macular degeneration we ______ magnification

want!

If we magnify the image beyond the edges of the central blindspot, the patient will be able to see more of it and interpret what they are seeing more easily

In what condition do we want to minify the image

Glaucoma

decreased peripheral vision - minify to fit in the view

Prescribe magificaiton basde on the patients specific

goals!

If a patient can see 20/100 at neat and they want to see 20/40 in order to see the newspaper, they need _____X mag

2.5x magnification

100/40 = 2.5

three ways we can increase the angle subtended at the plane of the eye

1. Relative size magnification (make the object larger)

2. Relative distance magnification (move the object closer)

3. Lens magnification (use a magnifying lens)

Retinal size magification =

y2'/y1'

new image size / old image size

Relative distance magnification

compares the retinal image size before and after the object is moved

RDM = reference distance/ new object distance

reference distance

initial or normal viewing distance

inverse of the Add power

if no reference distance assume 25 cm

When we change the working distance we must

change the add power

IFfthe patient is young and has enough accommodation they are fine when we change the working distances

lateral magnification

the size of the image as compared to the original object

image size to object size

The image then becomes the object for the eye

If you place the object beyond the focal point the image will be

Magnified

inverted

blurred

If you place the object at F1 the image will be

infinitely magnified and cannot be resolved

If you place the object within F1 the image will be

upright

magnified

and potentially clear!

When the object is within F1 we have _____ light reaching the eye

diverging

As long as we have enough accommodation we can handle this diverginf light!

Two ways to minimize the amount of accomoadtion requires

hold the object just inside F1

Change vertex distance ---> stand further

Stand magnifier

- object sits at a set distance from the lens (just inside the focal point)

- the patient doesnt have to worry about object distance, they can slide it over the pafe

- tell them not to put teir head too close

Total magnification

RSM x RDN x LM

Product formula

Mt = (where the patient normally holds their reading material/the current distance from the eye to the object) x (1-h * the vergence entering the lens/ 1 - h * the vergence exiting the lens)

As vertex distance increases

the wavelength flattens and we dont need to accomdate as much

There is an ____ relationship between vertex distance and mag

inverse

as vertex distance increases, magnification

decreases

as vertex distance decreases, magnification

increases

If you back up from the magnifier it takes less effort to the see the image clearly but there's a tradeoff -

you get less mag