low vision aid
TRANSCRIPT
PRESENTED BY MODERATOR
DR.R.HARIPRIYA PG IN OPHTHALMOLOGY SSSIHMS
DR.AMIT CHABRA DEPT OF OPHTHALMOLOGY
Visual Disorder-Anatomical changes Visual impairment-Functional changes Visual disability-Skills &abilities affected Visual handicap-Socio economic
consequences.
Legal Blindness◦ Best corrected distance visual acuity of CF-1MT
or worse in better eye◦ Visual field of 10 degrees or less in the better
eye Low Vision
◦ Best corrected visual acuity worse than 20/60 in the better eye(or) visual field of less then 10⁰ from the point of fixation.
1)Moderate visual impairment- best corrected VA less than 6/18 to 6/60.
2)Severe visual impairment- best corrected visual acuity of less than 6/60 to CF-3MTS (or) visual field diameter of 20⁰ or less.
3)Profound visual impairment- best corrected visual acuity of less than CF-3MTS to CF-1MT or visual field diameter of 10⁰ or less.
4)Near total vision loss- best corrected visual acuity of CF-1MT or less.
5)Total blindness- no perception of light.
Loss of central vision (visual acuity)
Loss of peripheral vision (visual field)
Glare and contrast
Difficulty readingProblems writing/ completing paperwork
Inability to recognize distance objects and faces
Need for additional lightingProblems with glare Increased adjustment to changes in illumination
Visual discomfort and fatigue
CLOUDY MEDIA: uncorrected refractive errors, dry
eyes,corneal dystrophies,keratoconus,corneal scarring from H.simplex,traumatic mydriasis,cataract,vitreous hemorrhage & posterior uveitis.
Location of scotoma important! Generalized loss of visual field difficult to compensate for
Mobility and independent travel
Reading may require adaptations
CENTRAL FIELD DEFICITS: Macular degenerations, macular hole,
diabetic macular edema and ischemia, myopic degeneration, toxoplasmosis , histoplasmosis, phototoxicity, drug toxicity, focal or grid laser for CSME, iatrogenic central and paracentral scotoma.
PERIPHERAL FIELD DEFICIT: Retinal dystrophies, RP , RD , PDR,
Glaucoma,Ischemic optic neuropathy,Stroke,Trauma,Tumour,Panretinal laser photocoagulation.
History/ intake Visual acuity Visual field testing Pupils Extraocular muscle testing Refraction Color vision and Contrast Testing Ocular Health
Confrontation Arc perimeter Automated perimetry Goldmann perimetry
Ishihara Color Vision Testing Made Easy D-15 Pelli-Robson Vistech Contrast System Mr. Happy
Enlarges image on retina to stimulate more retinal cells
Can be achieved in many ways◦ Relative Distance◦ Relative Size◦ Optical / Angular◦ Electronic
1)Magnifying spectacles2) Hand magnifiers 3)Stand magnifiers4)Telescopes5)Electronic magnifiers
Macular Degeneration
Glaucoma Diabetic
Retinopathy Stroke/ brain injury Retinitis
pigmentosa Optic Nerve disease
Albinism Nystagmus Cortical Visual
Impairment
Hand held telescopes Mounted telescopes Electronic systems
Spectacles◦ Prismatic ½ eyes◦ Full-field microscopes
Magnifiers◦ Hand held or Stand held◦ Illuminated or non-illuminated
Telemicroscopes Electronic Devices
Magnifying devices work by increasing the angle subtended by the object at the eye thus producing an enlarged retinal image(angular magnification).
MP= RETINAL IMAGE WITH USE OF INSTRUMENT/RETINAL IMAGE WITH OUT USE OF INSTRUMENT.
Convex lenses are used as hand held magnifiers or stand magnifiers.Here the object is located between the first principal focus and lens gives virtual,erect,magnified image for the eye.
As the object moves nearer to first principal focus,the virtual image becomes larger and is situated futher from the eye.
Field of vision depends upon size or aperture of the lens and on eye lens distance.
Greater the eye lens distance smaller the field of vision.
Conex cylindrical lenses which has no refractive power or only a low converging power in its long axis and high converging power in cross section provides vertical magnification of powers.
Galilean telescopes composed of convex objective and concave eye piece, seperated by difference of their focal length.
It produces a errect, magnified image. It mainly acts by increasing angle
subtended by the object at the eye.
Astronomical(keplers) telescopes consists of two convex lenses seperated by sum of their focal lengths.
This system produces a magnified,inverted image.
Prisms or mirrors are used to invert the image.
Types & designs- 1)Binocular spectales2) Monocular spectacles-standard aspheric
lenses from +4D to +20D in 2D increments -specially designed microscopic and double lenses
from +24D to 60D.3)Half eye glasses are preferable because they reduce
the weight,thickness & size for near vision.
4)High add bifocals or high add trifocals can be used to read large prints at great distance.
Cosmetically acceptable Comfortable and easy to use Both hands are free Field of vision is large Simultaneous vision for near & distance
vision is possible Less expensive
Spherical aberations are created with high plus lenes unless aspherical lenses are used.
Short focal length of high plus lenses makes the patient hold print close to the eye thereby illumination decreases.
Mainly used for near vision problem Does not require accomidation to see
the image Indications- -for spot or short time tasks in
patients with field of vision reduced to 10⁰ or more.
-as auxiliary lens for finer jobs.
Available from +4 to+40D Their magnification is variable,since the
power varies with distance between the object and focal point of magnifier.
These has wide field of vision,light weight, self contained illumination.
Working distance is more Accomidation is not required for reading Easy to view eccentrically
Hand is not free. Inconvenient and tiring Reduced field of vision when compared to
spectacles. Not useful in the absence of manual
dexterity. Need to be held at correct distance to
obtain maximum power.
Types & design- -available in two forms 1)Prefocused 2)Focusable -range in power from +4 to +60D. -self illuminated devices available which
prevent glare. -requires some accomidative effort.
Technically simple as they are prefocused and rest on a rigid mount.
Choice for patients with hand tremors.
Small field of vision Difficult to use if surface is not flat.
TYPES & DESIGNS: Monocular telescopes- easy to carry and
use
Binocular telescopes- offers a good grip, cumbersome to carry. If one eye is worse than other, these offers no improvement in viewing quality.
Telescopes can be either hand held or spectacle mounted.
The poorer the vision, stronger is the power of the telescope required.
The maximum power useful for hand held type is 8X and for spectacle type is 4X.
Telescopic spectacle systems are used for intermitent basis for sedentary distance viewing.
Telescopic systems are used when it is not possible to obtain magnification by moving closer.
Hand held and ring style telescopes are used for distance spotting.
For near and intermediate tasks, one can focus the telescope for near viewing by
a)adding plus lenses behind the optics of telescope
b)adding plus lenses infront of objective lenses
c)increasing the tube length of telescope.
Reduction in the field of vision Ring scotomas Parallax and a decrease in the depth of
focus Not useful for ordinary distance viewing as
illumination decreases. These are consider contravesial for driving
because of constricted fields.
Closed circuit television Large print computers Low vision enhancement system
In this camera picks up the reading material,magnifies it and displays it on the TV screen.
CCTV magnifiers provide excellent contrast and magnification(linear magnification electronically upto 60x).
It provides a distortion free, brighter, magnified image with enhanced contrast on a larger screen.
White letters on a black field helps in improvement of image clarity
Expensive Heavy Difficult to move around May be difficult for some patients to operate
it.
Computer can provide enlarged print on the screen through standardized or dedicated software.
Software is also available to provide speech for the computer.
Recent advances in low vision rehabilitation
It comprises surgical implantation of intraoccular telescopic aids.
Intraoccular low vision aids consists of special lense that provides a 3x magnification in the fundus of patients eye.
Resultant retinal image is perceived through peripheral retina.
Absorptive lenses- used to reduce the glare and dark adaptation time.
Especially used in patients with albinism.Types- Tinted lenses -Photochromatic lenses -Polarization -Filters
Field expanders used in patients with defects in
peripheral visual fieldsTypes- Fresnel prisms -Gottlieb field expanders -Reverse telescopes -Hemianopic mirrors
Approach magnification Lighting Contrast enhancement Increasing the size of the object to be
viewed Personal items Auditory aids
Electronic devices Writing and communication devices Medical assistive devices Mobility assistive devices Tactile substitute include
Braille,paperlessBraille outputs and non-Braille tactile outputs.
Orientation and mobility training Independent living skills training Support groups Braille instruction Computer training Genetic counseling