Low Vision and Visual Impairment

Low Vision

• WHO definition: Visual acuity of 20/70 or worse and/or a visual field of 20 degrees or less.

ODP 414

Diabetic Retinopathy (DR)

• Preventing DR progression with controlled blood glucose level
• Lifestyle modifications:
  • Comprehensive eye examination (yearly, 6-12 months, or 2-4 months depending on severity)
  • Refractive error management with spectacles or contact lenses
• Treatment options:
  • Laser photocoagulation (stops abnormal vessel growth and treats hemorrhages and macular edema)
  • Injection (Anti-VEGF and Corticosteroids)

Achromatopsia

• Definition: Inherited or acquired disorder characterized by significantly reduced or total loss of color discrimination
• Also known as 'total color blindness' or 'monochromacy'
• Types:
  1. Complete Achromatopsia (Rod Monochromatism)
     • All types of cones are either non-functional or missing
     • Occurs in around 0.003% of people
     • Autosomal recessive inheritance
  2. Incomplete Achromatopsia (Cone Monochromatism)
     • Less severe than rod monochromacy
     • Visual acuity preserved (around 20/60-20/200)
     • Can be categorized as Blue Cone Monochromacy, Green Cone Monochromacy, or Red Cone Monochromacy
  3. Cerebral Achromatopsia
     • Problem lies in the brain, not in the eyes
     • Total color blindness due to brain damage

Retinopathy Secondary to Diabetes

• Causes disability and handicap
• Symptoms:
  • Completely unable to distinguish colors
  • Reduced visual acuity
  • Hemeralopia (severe light sensitivity)
  • Nystagmus
  • Central scotoma

Diagnosis

• Color Vision Testing
• Electroretinogram (ERG)
• Molecular Genetic Testing

Treatment & Management

• Gene Therapy (Early Phase)
• Filters
• Magnifiers

Retinitis Pigmentosa (RP)

• Definition: Collection of genetic retinal disorders involving degeneration of photoreceptors
• Causes progressive vision loss
• Symptoms:
  • Nyctalopia
  • Reduced visual field
  • Photopsia
  • Glare
  • Difficulty in dark and light adaptation
  • Bony Spicule Deposits
  • Arterial Narrowing
  • Optic Disc Pallor
• Inheritance patterns:
  1. Autosomal Recessive
  2. Autosomal Dominant
  3. X-linked
  4. Mitochondrial Inheritance
• Prevalence: 1 in 3000-5000 people
• Carriers estimated to be 1 in 100 people### Retinitis Pigmentosa (RP)
• Photopsia is a common symptom of RP and other degenerative retinal diseases
• Vitamin A supplements have minimal effect on slowing the progression of RP, and large doses are discouraged
• ABCA4 form of RP can worsen with high doses of Vitamin A

Gene Therapy

• Uses a viral vector to administer CRISPR mechanism to correct defective genes in photoreceptors
• Luxturna Gene Therapy is the first FDA-approved gene therapy for RP, specifically for RPE65 type of RP
• Approved by the FDA in January 2018 for biallelic RPE65 mutation in people over 1 year old

Stem Cell Therapy

• Involves converting skin cells to fibroblasts and then to photoreceptors, which can be reimplanted into the retina
• Aims to replace damaged photoreceptors in RP patients

Bionic Chips

• Argus II is a three-part device that allows some perception of light and motion in patients with RP
• Can help improve daily functioning, but has limitations and is not a cure for RP

Impact of RP

• Can lead to blindness, affecting daily life, independence, and psychological well-being
• Counselling and support are essential for patients with RP

Glaucoma

Definition

• A group of ocular diseases associated with progressive optic nerve neuropathy
• Characterized by increased intraocular pressure (IOP) and optic nerve damage

Types of Glaucoma

• Open Angle Glaucoma (OAG)
• Angle Closure Glaucoma (ACG)
• Normal Tension Glaucoma

Prevalence

• 57.5 million people worldwide have glaucoma
• 8.4 million people are bilaterally blind due to glaucoma
• OAG is the most common type, but ACG is more likely to lead to blindness

Risk Factors

• Age: prevalence is higher in the geriatric population
• Race: African-Americans and Hispanics/Latinos are at higher risk
• Family History: 13-25% of people with glaucoma have a positive family history

Open Angle Glaucoma (OAG)

• Chronic progressive disease with decreased aqueous outflow
• Can lead to optic nerve damage and visual field loss
• Elevated IOP causes compression of ganglion cell axons, reducing blood flow to the posterior pole of the optic nerve, and activating cellular damage proteins