Low Vision Devices For

Near

Presenter

Aarju Singh

3rd

year B.sc optometry

Def of Low Vision

According to WHO :- a person with low vision is one

who

Has a impairment of visual functioning even after treatment and /or standard refractive correction

Has a visual acuity less than 6/18 to light perception

Or visual field less than 10 degree from the point of fixation

But who uses , or is potentially able to use, vision for planning and/or execution of a task.

LOW VISION AIDS

The assistance given to the LV

patient to maximize the

functional level of vision by

optical or non- optical means is

called LV aids .

The optical device can be used

for distance and near .

Near Optical Devices :- are used for

close-up, detail viewing, such as reading,

writing, and sewing.

It includes :-

Spectacles Magnifier

Magnifiers :- Hand and Stand magnifier

Magnifying reading Glasses

Clip - on loupes

Telemicroscopic Glasses

Electrical devices :- CCTV, HMD

Spectacle magnifiers

High plus reading glasses to magnify the images

Given as an add to the best distance refraction

Used for Near work

Contd…Amount of add needed depends on the accommodation and

reading distance

Reading add can be predicted using the kestenbaum rule i.e

the amount of add needed to read 1M print is the inverse of

VA fraction

However usually greater add is required than predicted as

the patient also has reduced contrast sensitivity

Contd…

If the patient is monocular ,the poorer eye may be occulded

if it improves the functioning

When binocular correction are needed :-

base in prism are added to compensate for

convergence angle.

Optical center may be decentered.

Aspheric lenses may be used to reduce lenticular distortion

Advantages

Hands are free

Field of view larger when compared to

telescope

Greater reading speed

Can be given in both monocular and

binocular forms

More portable

Cosmetically accepatble

Disadvantages

Higher the power ,closer the reading

distance

Closer reading distances causes fatigue

and unacceptable posture

Patient with eccentric fixation are unable

to fix through these glasses

Magnifiers

Useful for near work

By keeping at near and distance ,we can

achieve different magnification

Two types :- Hand magnifier

Stand magnifier

Hand magnifiers

It consist of a convex lens surrounded by a plastic or metal carrier attached to a handle .

For maximum magnification with hand magnifier place the object at the focal point.

The distance from a hand magnifier to the printed page must be kept constant .

Contd…

To find this distance start the lens on

the page and slowly pull it away from

the print until optimal focus is reached.

It should be used with distance glasses

If the material is brought closer to your

eyes , bring the reading material closer

as well.

Available from +4.0 to 68.0 D (1x-17x)

Available designs

- Aspheric – reduces thickness and peripheral distortion

- Aplantic – flat and wide distortion free field and good clarity.

- Bispheric – eliminating aberrations from both surfaces.

Most patients accept upto 6x magnification

Contd…

Advantages

The eye to lens distance can be varied.

Patient can maintain normal reading distance

Work well with patient with eccentric viewing

Some have light source which further enhances

vision

Easily available ,over the counter

Disadvantage

One hand tied up

Difficult to held steady in proper position

at all times

Limited FOV ,depends on eye to lens

distance

Patient with tremors ,arthritis etc have

difficulty holding the magnifier

Stand Magnifier

Magnifiers are stand mounted

Patient needs to place the

stand magnifier on the reading

material and move across the

page to read

Has a fixed focus

Types

Variable focusable stand magnifier :- Have

lenses that can be adjusted closer to or

farther away from the material .

Fixed focus stand magnifier :- lens at fixed

distance from the base.

Advantages

Do not have to hold

Can slide across page

Constant lens to page distance

Inexpensive and easily available

Disadvantages

FOV is reduced or limited

To close reading posture is uncomfortable for the pt

Block good lighting unless self illuminated

Heavy , fatigue problem

Magnifiers Reading glasses

Allow an individual to read for longer periods of time

Also called as “microscope”

Advantages

Wide field of view

Portable

Hands are free

Disadvantages

Holding things very close

Clip-on loupes

Clip-on loupe attaches to glasses and allow

the person to be hands free while viewing

text , computer screen etc.

Advantage

Hands are free

Convenient and easy to use flip

Inexpensive

Disadvantage

For larger loupe , they may heavy

distracting

Telemicroscopic Glasses

Eyeglass mounted telescopes

can be made to focus at any

WD.

Advantages

More comfortable working

distances

Hands are free

Have excellent optics

Disadvantages

Smaller FOV

Reading difficulty especially if a book is

heavy ,reading longer period of time

Image may be some what dark

Feel heavy on your nose

Expensive

Electrical devices

CCTV

An electronic magnification

system for reading and writing

Consist of 3 major components

camera

monitor

movable reading platform

Contd..

It provide excellent contrast and magnification ,color .

Magnification upto 60x .

Advantages

Provides distortion free ,brighter ,magnified image

with enhanced contrast on a larger screen .

Disadvantages

Expensive , heavy and difficult move around .

Difficulty in operation for patient .

Head –mounted Display

It is display device ,worn

on the head or as a part of

a helmet ,that has a small

display optic in front of

one (monocular HMD) or

each eye(binocular HMD).