LOW VISION

Introduction to low vision

WHAT IS LOW VISION?

Standard Definition (WHO 1992)

Impairment of visual functioning in better eye even

after treatment and/or standard refractive correction

and VA of <6/18 to light perception

or

a VF loss of <100 from point of fixation

but who uses, or is potentially able to use, vision for

the planning/execution of task

CLASSIFICATION

category Corrected VA- better eye

WHO definition

working Indian definition

0 6/6 – 6/18 Normal Normal Normal

1 <6/18 – 6/60

Visual impairment

Low vision Low vision

2 <6/60 – 3/60

Severe visual impairment

Low vision Blind

3 <3/60 – 1/60

Blind Low vision Blind

4 <1/60 - PL Blind Low vision Blind

5 No PL Blind Total blindness

Total blindness

WHO CLASSIFICATION

DISORDERIMPAIRMENTDISABILITYHANDICAPED

IMPACT OF OCULAR DISEASE ON THE PATIENT

Visual disorder

Anatomical changes in the visual organ caused by the disease of the eye

Visual impairment

Functional loss that results from the visual disorder

Visual disability

Refers to vision related changes in the skill and abilities of the patient

Visual handicap

Psychosocial and economic consequences of visual loss

PSYCHOLOGICAL FACTORS

PREVALENCE

Global burden of visual impairment

World wide (WHO 2001)

- Low vision : 124 million

- Blind : 37 million

World wide (children)

- Low vision : 7 million

- Blind : 1.5 million

Low vision : Blindness = 3.4:1

ETIOLOGY• Irreversible damage to ocular media or

visual pathway.

CHILDREN Albinism ROP Congenital malformation Optic neuropathy

YOUNG ADULT Keratoconus Ocular injuries Aniridia

OLD AGEARMDCataractMacular degenerationRetinal degeneration

COMMON CONDITIONS:

ARMDDIABETIC RETINOPATHYALBINISMRETINITIS PIGMENTOSAHISTOPLASMOSISSTARGARDT’S DISEASESANIRIDIA

GLAUCOMANYSTAGMUSOPTIC ATROPHYCOLOBOMACATARACTRETINAL DETACHMENTKERATOCONUS

Macular Degeneration

ARMD (AGE RELATED MACULAR DEGENERATION) Macula in the retina degenerates. Area effected – macula

VISUAL AFFECT LOW VISION AIDS•Fuzzy & Decreased vision •Good Lighting

•Metamorphopsia •Use of Strong color contrast

•Poor Central Vision •Magnifiers

•Photophobia •Non optical device

•Poor Color Perception •Vision Reabilitation

•Better vision at night

ARMD

DIABETIC RETINOPATHY

Breakage of retinal blood vessels and leaks.

People with long standing diabetics. Area affected – Retina.

VISUAL AFFECTS LOW VISION AIDS

•Decreased visual acuity •Various illuminators

•Fluctuating Vision •Work under direct light

•Loss of color vision, visual field

•Visual rehabilitation

•Inability to accommodate, floaters

Retinopathy

RETINITIS PIGMENTOSA

Retinal pigmentary degeneration. Rods of retina are slowly destroyed. Area affected – Retina.

VISUAL EFFECTS LOW VISION AIDS

•Decresed visual acuity •Optical aids – telescopes

•Difficulty in night vision •Nightscopes

•Loss of peripheral field vision •Fresnel prism, visual field expanders

•Photophobia •Use of filters

•Poor contrast sensitivity •High contrast letters

•Difficulty to adapt in changing illumination

•Rehabilitation

Retinitis Pigmentosa

GLAUCOMA Aqueous humor does not drain normally

& excessive pressure is built within the eye, resulting in damage of optic nerve.

Area affected – Optic Nerve.

VISUAL AFFECT LOW VISION AID•Gradual blurred vision •Magnifiers depending upon

extent of v.f

•Haloes around light •CCTV

•Reduced peripheral vision •CPF lens to reduce glare

•photophobia •Prism

Glaucoma

CATARACT Opacification of lens causing less amount

of light to the retina, vision becomes hazy & inconsistent.

Area affected – Crystalline Lens.

VISUAL AFFECTS LOW VISION AID•Blurred vision •Close work use direct light

•Glare, difficulty in bright light •Use sunglass to avoid glare

•Diplopia •Stand magnifiers for near work

•V.F normal. Sometimes Reduction in side vision

•Filters - amber, red brown filters

•Squinting and amblyopia

RETINAL DETACHMENT

Retina is separated from its supporting structures & receives no nourishment.

Blind area develops in area of detachment

Area Affected – Retina.VISUAL AFFECTS LOW VISION AIDS•Flashers & Floaters •High illumination

•Visual acuity is decreased •Filters, CPF lens

•Micropsia •Magnification for both near & distance

•Color vision is impaired •Non optical aids

•Loss of visual field

•Photophobia & glare

ALBINISM

Total or partial loss of pigments in the eye.

Characterized by light colored iris, eyebrows.

Area affected – Retina, macula.VISUAL AFFECT LOW VISION AIDS•Decreased visual acuity •Dim illumination

•DV more effected than NV •Dense sunglasses

•Painful photophobia •Absorptive lenses

•V.F is normal •Telescope for DV

•Color vision is normal •Colored or pinhole type CL

Albinism

Central field loss

Overall blur

Peripheral field

loss

Functional Effects of Low Vision:

BEHAVIORAL IMPLICATIONS

Loss of central vision (eg. macular degeneration, toxoplasma scar etc.) Difficulty reading Problems writing/ completing paperwork Inability to recognize distance objects and faces

Loss of peripheral vision (eg. Retinitis pigmentosa, glaucoma etc. ) Difficulty in mobility and navigation Difficulty reading if there is constricted central visual field Visual acuity may not be affected until very advanced disease

Cloudy media (eg. Corneal scar, vitreous hemorrhage etc.) Blurred vision Reduced contrast Problems with glare

CLINICAL ASSESSMENT

Evaluation

External observation

Detailed history taking

Functional vision assessment

Defining goals of the patient

Management

Trial & selection of LVD

Low vision device training

Counseling

EXTERNAL OBSERVATION

In the waiting area

On entering the examination room

Mannerisms of the patient

Physical appearance

Communication skill

DETAILED HISTORY

Patient details

a. Occupation

b. Living situation

c. General health

d. Other limitations

e. Family history

f. Previous low vision care

Difficulty in visual tasks

a. Distance visual tasks

b. Near visual tasks

c. Computer usage

d. Light sensitivity

e. Mobility issues

f. ADL

LOW VISION EVALUATION

Visual acuity

Refraction

Contrast sensitivity

Color vision testing

Visual field assessment

VISUAL ACUITY

Material required: Variable distance Log MAR chart [ Bailey Lovie/ETDRS chart] for distance.

Continuous text or word reading chart for near

Setup: Normal room illumination

Start with better eye first

Allow change in head posture, eccentric viewing, head movements etc.

Check monocular visual acuity followed by binocular

TYPES OF ACUITY CHARTS:

Distance:Snellen (projection)Feinbloom/ SOSHETDRSLea SymbolsBailey & lovie charts

Near:MN read acuity chartLight house near test chart.

DISTANCE CHARTS

NEAR CHARTS

REFRACTION

Perform retinoscopy instead of auto refractors

Calculate just noticeable difference

Aim to improve the quality of vision

CONTRAST SENSITIVITY

Purpose: To measure the ability to detect differences in luminance

Charts used:

a) Variable contrast fixed symbol size e.g. Pelli Robson

b) Fixed contrast with variable symbol size e.g. Bailey Lovie

Generally checked binocularly in patients with low vision

If contrast sensitivity is impaired, then advice and recommend the ways to enhance contrast in the living environment

CONTRAST TESTS:

COLOR VISION ASSESSMENT

Usually done with Farnsworth munsell d-15

Color discrimination

Performed in ambient illumination

With appropriate correction

Can emphasis on using vibrant Colors in the environment if required.

COLOR VISION TESTS:

VISUAL FIELD ASSESSMENT

Amsler grid:

• Assess central VF• Absolute scotoma• Relative scotoma• Metamorphopsia

Confrontation

• Assess peripheral VF• Checked in all 4 quadrants• Quick and basic.

MANAGEMENT OPTIONS IN LOW VISION

Low vision device:

It is a device that enables the patient to improve his/her residual visual performance & helps to attain functional vision for the particular task of concern.

Categories of LVD:a] Optical

b] Non optical

c] Electronic

d] Assistive devices

OPTICAL AIDSBASIC PRINCIPLE : MAGNIFICATION.

Enlarges image on retina to stimulate more retinal cells

Can be achieved in many waysRelative DistanceRelative SizeOptical / AngularElectronic.

TYPES OF MAGNIFICATION

Relative Size Magnification: Any activity of daily living in which the object being

viewed can be made larger (E.g. Large print Reader’s digest)

Relative Distance Magnification: Any activity of daily living in which the distance

between the object and the viewer can be reduced (E.g. moving closer to television)

Angular magnification: Use of an optical system between the eye and the

object to make the object appear larger (E.g. Use of a telescope to see a distant object)

DISTANT OPTICAL AIDS

1. Telescopes2.Projection Devices

3.Pin- Hole Spectacles4.See TV

SPECTACLES TYPES:

Near spectacl

es

BifocalsPAL upto

+3.

High Asperical

lenses +6.00 -

+20.00D

High Plus Prismatic

lens+4.00-

+14.00D

DISTANT OPTICAL DEVICES

TELESCOPE

Enable copying from the black board

Identifying street signs

Seeing traffic signals

Seeing bus numbers

Spot viewing

Watching movies in theatre

Enjoying sporting events

TELESCOPES

Work on the principle of angular magnification

Telescopes with magnification power from 2x to 10x are prescribed

They can be prescribed for near, intermediate and distant tasks

Field of view decreases with magnification

Types: Hand held monocular Clip on design Bioptic design: mounted on a pair of eyeglasses

aβ

ObjectiveEye piece

fo

fe

GALILEAN TELESCOPE

KEPLERIAN TELESCOPE

fo fe

α

Objective Eyepiece

β

Principal Telescopes consist of two lenses (in practice two optical systems) mounted such

that the focal point of the objective coincides with the focal point of the ocular.

Objective lens is a converging lens

Galilean telescope Keplerian telescope

The eye piece is a negative lens and the objective is a positive lens

Both eye piece and objective are positive lens

Resultant image is virtual and erect Resultant image is real and inverted. Prisms are incorporated to erect the image

Loss of light reduces brightness of the image

Loss of light is more in this system

Field quality is poor Field quality is relatively good

Magnification of a telescope is given by the formula M = fo/fe

Telescopes can be used to focus near objects by changing the distance between objective and ocular

lens Increasing the power of the objective lens

MONOCULARS MONOCULAR MONO

AUTOFOCUS

BINOCULARSSPECTACLE MOUNTED

NEAR OPTICAL AIDS

SpectaclesPrismatic ½ eyesBifocals

MagnifiersHand held vs. standIlluminated vs. non-illuminated

Electronic Devices

04/11/2023APPROACH & ASSESMENT OF LVC-CME 62

SPECTACLE MAGNIFIER

Spectacle magnifier is a spectacle mounted convex lens

This uses the principle of relative distance magnification

Full fields

Half eyes

Useful for prolonged reading

ADVANTAGES & DISADVANTAGES OF SPECTACLE MAGNIFIER

Psychologically acceptable

Short working distance

Useful for prolonged reading

Reduced illumination

Large field of view Inconvenient for spot reading

Binocularity is possible with lower magnification

Limited range of magnification

Useful for other near tasks such as writing

Not effective in constricted fields

04/11/2023APPROACH & ASSESMENT OF LVC-CME 64

STAND MAGNIFIER

A stand magnifier is a convex lens mounted at a fixed distance from reading material

Both angular magnification and relative distance magnification are used

Device of choice for tremors, arthritis, constricted fields

Self illuminated

Non-illuminated

STAND MAGNIFIERS

ADVANTAGES & DISADVANTAGES OF STAND MAGNIFIER

Predictable focus Poor posture unless reading stand is used

Device of choice for tremors, arthritis, constricted fields

Reduced illumination in case of non illuminated sand magnifiers

Portable Requires flat surface to keep reading material

Variable eye to lens distance

Reduced field of view

04/11/2023APPROACH & ASSESMENT OF LVC-CME 67

HAND HELD MAGNIFIERA hand-held magnifier is a convex lens that holds by means of handle at various distances from reading plane

Suitable in patients with eccentric viewing

May be self illuminated

Portable

HAND HELD MAGNIFIERS

CLOSED CIRCUIT TELEVISION SYSTEM Closed circuit television system (CCTV) consists of a

monitor, a camera and a platform to place the reading text

It has control for brightness, contrast and change of polarity

Magnification varies from 3X to 60X

ELECTRONIC MAGNIFIERS

NON-OPTICAL DEVICES Glare reduction devices Contrast enhancement devices Computer software Accessory devices

Talking watches, clocks, etcWriting guidesTactile markers

04/11/2023APPROACH & ASSESMENT OF LVC-CME 72

7 CATEGORIES OF NON - OPTICAL DEVICES

Relative size and larger assistive deviceGlare, Contrast and lighting control devicePosture and comfort maintenance deviceHand writing and written communication deviceOrientation and mobility techniques and devicesSensory substitution deviceMedical management and life skill device

NON OPTICAL DEVICES:

Reading lamp Reading stand Writing guide Reading guide Signature guide Bold line note books and papers Black ink bold tip pens Soft lead pencil – 2B,4B,6B Needle threader Notex etc…

WRITING GUIDE Black cards with rectangular cut outs horizontally along the card The patient can feel the empty cut out spaces and write

SIGNATURE GUIDE

NOTEX It is a rectangular piece of cardboard with steps on

top right corner which helps in identifying the currency of the note

1st cut indicates Rs. 500, 2nd cut indicates Rs.100, 3rd cut indicates Rs 50 and so on.

RELATIVE SIZE DEVICES

Larger object subtends a larger visual angle at the eye and is thus easier to resolve Large print material Large type playing cards, computer keyboards Enlarged clocks, telephones, calendars

CPF GLASEESo Attenuate 100% of UVB wavelengths.

o Block 99% of UVA wavelengths.

o The blue light portion of the visible spectrum is most likely to scatter in the eye, causing discomfort and hazy illusion.

o Attenuate 98% of high-energy blue light, with exception of CPF 450, which is 96% of high-energy blue light.

o The number of the CPF glasses correspond to wavelength in nanometers above which light is transmitted

04/11/2023APPROACH & ASSESMENT OF LVC-CME 79

NON OPTICAL DEVICES

04/11/2023APPROACH & ASSESMENT OF LVC-CME 80

EVEN MORE…

ASSISTIVE DEVICES'

ASSISTIVE DEVICES FOR NEAR Closed circuit television

[CCTV]

Monitor CCTV Portable CCTV Mouse model CCTV

04/11/2023APPROACH & ASSESMENT OF LVC-CME 83

ASSISTIVE DEVICES FOR DISTANCE

ONYX JORDY

04/11/2023APPROACH & ASSESMENT OF LVC-CME 84

PORTABLE CCTVS

BUDDY PLAYER QUICK LOOK ZOOM CLASSMATE READER

MN READ ACUITY CHART

Mostly used chart for assessing near acuity of a low vision patient.

It was developed at Minnesota laboratory for low vision research.

TYPES: 1. Black letters on white background. 2. White letters on black background.

USES: 1. Reading Acuity 2. Critical Print Size 3. Maximum Speed

TO THE DETAILS……………

Chart DesignMeasurement Of Reading Acuity

Measuring Reading Speed

CHART DESIGN: It’s a continuous-text reading acuity

chart. Each sentence contain 60 characters

printed in three lines. It contains 19 different print sizes. Its print style is similar to that found in

many newspapers and books. The text is printed with high contrast.

MEASURING READING SPEED

Formulae : Reading speed = 60*(10-

errors)/(time in seconds).

If more than 10 errors were made then reading speed can be assumed to be zero.

MEASURING READING ACUITY

Chart Illumination – Luminance at least 80cd/m.

Viewing Distance - 40cm Testing Procedure… Calculation formulae: Acuity = 1.4 –

(sentences*0.1)+(errors*0.01)

REMEMBER! “Visually disabled are not fallen souls”

“Positive attitude towards them will make them

socially amicable, psychologically adjustable and

educationally sound”

The unlimited opportunities and experiences

extended to them will make them physically fit

mentally alert and totally independent in the

community