Understanding Low Vision and AMD

Low Vision

• Low vision definition: Best corrected visual acuity (VA) with glasses is reduced bilaterally, old px (patient)/VA of 6/60-6/30 depends on visual field (VF), Px can have 6/6 with low vision due to extensive VF loss or small central vision.
• Visual impairment classification by distance/near: Mild is less than 6/12, moderate is less than 6/18, severe is less than 6/60, blindness is less than 3/60, near is less than N6.
• Blindness definition: Degree of constriction of central visual field in the better eye is less than 10 degrees.
• AMD (Age-related Macular Degeneration): Degenerative disease affecting patients aged 50+, can be wet or dry.
• Dry AMD: Early AMD with gradual loss of central vision in both eyes, reduced night vision, fundus shows multiple drusen (yellow spots) at the macula, no treatment, lifestyle changes are recommended.
• Wet AMD: Central vision loss, develops choroidal neovascularisation, build-up of sub-retinal fluid (new BV form trying to improve blood supply), treated with regular anti-VEGF injections.
• Glaucoma: Peripheral vision loss or optic neuropathy (optic nerve damage) linked with significant visual field loss, no treatment is available, early glaucoma is asymptomatic, regular VF to identify.
• Cataract: All-over vision (not central/peripheral), treatable blindness causing gradual decrease in VA + CS (contrast sensitivity), referral at 6/12, increased glare driving at night.
• Retinitis Pigmentosa: Peripheral vision loss, inherited, affects teens, is bilateral, reduced night vision, advances and develops pale/waxy optic nerve, lose tiny island of remaining central vision.
• Diabetic Retinopathy: Type 1 diabetes, screening, eyes photographed regularly, macula swelling treated with laser, fired at the retina causing scarring, reduced peripheral vision, retinal detachment (scarring pulls retina off).
• Classifications of visual impairment registration: Sight impaired; VA of 3/60-6/60 with full visual fields/VA of up to 6/24 with moderate visual field constriction/VA of 6/18 or better with gross visual field defect (hemianopia)/severely sight impaired VA of <3/60/VA from 3/60-<6/60/VA of 6/60 or better with gross visual field constriction.
• Charles Bonnet Syndrome: Visual hallucinations caused by the brain to adjust to significant vision loss, seeing dead people they used to live with, need for social and/or emotional support.

Telescopes

• Types of magnification:
  • Relative size magnification: Increase in retinal image size, working distance stays constant, enlarges the size of objects (e.g., bus timetables, clocks).
  • Relative distance magnification: Reduces working distance, halves image size, hand-held magnifiers.
  • Transverse magnification: Provides real enlargement, electronic image enhances image quality (e.g., EVES/CCTV).
  • Angular Magnification.
• Purpose of telescopes: Optical instruments used to magnify the apparent size of distant objects, produces images of distant objects, creates larger visual angles.