Low Vision Aids

Low vision,LVA

1. LOW VISION AIDS By Capt Ayinun Nahar Dept of Ophthalmology Armed Forces Medical Institute

2. Definition “A person with low vision is one who has impairment of visual functioning even after treatment, and/ or standard refractive correction, and has a visual acuity of less than 6/18 to light perception or a visual field of less than 10 degrees from the point of fixation, but who uses, or is potentially able to use, vision for the planning and/or execution of a task .” (WHO/PBL/93.27)

3. Definition “A person with low vision is one who suffers visual acuity between 6/18 to 3/60 in the better eye after the best possible correction or a field of vision between 20 to 30 degrees.” ( WHO : ICD-10 definition)

4. Visual dysfunctions Disorder Impairment Disability Handicaped

5. Visual dysfunctions Visual disorder Deviation from normal visual structure by disease, injury or anomaly affecting vision Visual impairment Reduction of visual function results from the visual disorder

6. Visual dysfunctions Visual disability Reduced ability to perform a certain task Visual handicap Non-performance of the tasks related to individual and social expectation because of visual disability

7. Categories Category Corrected VA- better eye WHO definition Working 6/6 – 6/18 Normal Normal 1 <6/18 – 6/60 Visual impairment Low vision 2 <6/60 – 3/60 Severe visual impairment Low vision 3 <3/60 – 1/60 Blind Low vision 4 <1/60 - PL Blind Low vision 5 No PL Blind Total blindness

8. Low vision Aids An optical/non-optical device that improves or enhances residual vision by magnifying the image of the object at the retinal level.

9. Basic principle of LVA Optical LVAs are based on the fact that with sufficient magnification, the normal retina surrounding the damaged central retina can be used for central vision.

10. Types of magnification Low vision aids make use of angular magnifications by : Relative size Relative distance

11. Angular : It is the apparent size of the object compared with true size of the object seen without the device. Angular magnification M = ω ’/ ω

12. Relative size : By making the object appear bigger (no accommodation required) eg . CCTV

13. Relative distance : By bringing the object closer (requires good accommodation)

14. Indication Children : Albinism ROP Congenital malformation Optic neuropathy Yound Adult : Keratoconus Ocular injuries Late menifestation of congenital malformation

15. Indication Old age : Glaucoma ARMD Diabetic maculopathy Macular degeneration Retinal degeneration Chorioretinitis Optic atrophy Myopic degeneration

16. Types of LVA Optical devices Non-optical devices

17. Optical LVA : Magnifying spectacles Hand magnifiers Stand magnifiers Telescopes Intraocular low vision aids Other optical devices

18. Non-optical devices : Approach magnification Lighting Contrast enhancement Increased size object Electronic magnifiers ( CCTV, LVIS, V-max) Writing and communication devices Orientation and mobility LVAs

19. Magnifying Spectacles

20. Magnifying Spectacles Optical Principle Magnification by a convex lens is obtained by bringing the object within it’s focal length An erect,virtual and magnified image is produced

21. Magnifying Spectacles High plus lens is used to magnify the images Magnification is 1/4 th the power of the lens. Suited for near and intermediate distance Monoocular or binocular

22. Magnifying Spectacles Advantages : Hands are free Field of view larger when compared to telescope Simultaneous near and intermediate vision Can be given in both monocular and binocular forms More portable Cosmetically acceptable

23. Magnifying Spectacles Disadvantages: Spherical aberration Higher the power, closer the reading distance Close reading distance causes fatigue and unacceptable posture Patients with eccentric fixation are unable to fix through these glasses Illumination problem

24. Hand magnifiers Indicated for spot or short-time tasks in patient with field of vision reduced to 10’ or more. Available from + 4.0 to + 40 D. Available in three designs: Aspheric Aplantic Biaspheric

25. Advantages : Working distance is more Accommodation is not required Easy to manipulate for viewing eccentrically Some have light source which further enhances vision Disadvantages: It occupies both hands Not useful in absence of manual dexterity Field of vision is limited Need to be held at the correct distance

26. Stand Magnifier Forms a virtual image a short distance behind the lens The patient needs to place the stand magnifier on the reading material and move across the page to read Has a fixed focus

27. Advantages : Technically simple They are a choice for patients with tremors, arthritis and constricted visual fields. Disadvantage : Small field of vision Too close reading posture is uncomfortable for the patient Difficult to use if the surface is not flat

28. Telescopes Used to magnify distant objects Work on the principle of angular magnification Telescopes with magnification power from 2x to 10x are prescribed

29. Optical 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

30. Types : 1. Galilean telescope 2. The astronomical ( Keplar’s ) telescope

31. Advantages : Best possible LVA to enhance distant vision Disadvantage: Restriction of the field of view Depth perception is distorted Loss of light transmission Expensive and costly

32. Other Optical Devices Absorptive lenses - Tinted lenses - Photochromatic lenses - Filters - Polarization - Corning CPF filters Visual field enhancement devices - Fresnel prism - Hemianopic mirrors

33. Approach Magnification Partially sighted patients should be encouraged to move as close as possible to the object

34. Illumination Positioning To the side of better eye Moving light closer Higher levels of illumination is required : macular degeneration Glaucoma Diabetic retinopathy Retinitis pigmentosa Chorioretinitis Reduced illumination required : Albinism Aniridia

35. Contrast Enhancement Using a typoscope Contrast modification of visual environment

36. Relative size devices Large print material Enlarged clocks, telephones, Calendars, computer keyboards Large type playing cards

37. Electronic magnifiers Close-circuit television Low vision imaging system V-max

38. Writing and communication devices Writing guides Signature guides Check guides Notex Tactile or raised line papers

39. Sensory Substitute Assistive Device Auditory substitutions -Talking books Tactile substitutions - Braille - Paperless braille output - Tactile Braille output

40. Mobility assisting devices Patients with low vision suffer a major problem of mobility Long canes Strong portable lights

41. Newer technology Intraocular LVAs Keratoodontoprosthesis Bionic eye

42. Evaluation Of Low Vision History Visual acuity Colour vision Visual field analysis Glare and Contrast sensitivity Look for dominant eye

43. Prescribing LVAs Aim Simple, lightweight, portable and flexible Patient’s visual and mental status, needs, and motivation Working distance and field of vision decrese with an increased magnification All the devices should be tried Both eyes should be corrected Careful consideration of children, old age and single eyed person

44. Conclusion

45. THANK YOU