Week 1 - causes and effects of low vision

• What are some needs a low vision patient might have?

  Optical and non-optical aids, environmental solutions such as large print, audio description, or braille, and personal solutions like goal changes or different techniques.
• Would a patient with BCVA of 3/60 be considered to have ‘low vision’?

  Yes
• What does a patient with BCVA of 6/6 and very restricted visual fields tell us about the definition of a low vision patient?

  Visual field restrictions can be another key factor in defining a low vision patient.
• What are the UK registration criteria for visual impairment?

  • Severely Sight Impaired (SSI; blind)
  • Sight Impaired (SI; partially sighted)
• What are the legal and registration criteria for Severely Sight Impaired (SSI) in the UK?

  Legal Definition: ‘So blind as to be unable to do any work for which eyesight is essential.’ (National Assistance Act, 1948)

  
  

  Registration Criteria:

  1. VA worse than 3/60 with a full visual field
  2. VA 3/60 to 6/60 with contraction of the visual field
  3. VA 6/60 or better with a clinically significant contracted field of vision that is functionally impairing the person
• What are the legal and registration criteria for Sight Impaired (SI) in the UK?

  Definition: ‘Substantially and permanently handicapped by defective vision caused by congenital defect, illness or injury.’ (Department of Health Guidelines)

  
  

  Registration Criteria:

  1. VA 3/60 to 6/60 with a full visual field
  2. VA 6/60 to 6/24 with moderate contraction of the field
  3. VA 6/18 or better with a marked field defect
• What are the main steps in the certification and registration process for visual impairment in England?

  1. Gain patient consent
  2. Refer to HES giving relevant data
  3. Consultant ophthalmologist completes Certificate of Visual Impairment (CVI) = Certification
  4. CVI registered with local authority with patient’s permission = Registration
  5. Receive benefits of registration (details covered later)
• Who is considered a ‘low vision patient’?

  A patient with visual acuity that cannot be improved to better than 6/18 with appropriate correction, affecting daily living activities.
• Would a patient with BCVA of 6/5 be considered to have ‘low vision’?

  No
• What information is included in a Certificate of Visual Impairment (CVI)?

  Personal details, signed consent, visual function (VA / VF), diagnosis, living conditions, other disabilities, further info / assistance, and driving status. Copies are sent to the patient, GP, hospital, and local authority.
• Define epidemiology and its key components.

  Epidemiology: the study of the incidence and distribution of diseases and other factors relating to health

  
  

  Incidence: the proportion of people getting a disease in a given time frame

  
  

  Prevalence: the proportion of people having a disease at a given time, depending on incidence and duration of disease
• What are the key differences between the registration criteria for SI and SSI in terms of visual acuity and visual field?

  | Category | Visual Acuity | Visual Field |

  |---|---|---|

  | Sight Impaired | 3/60 – 6/60 | Full |

  | 6/60 - 6/24 | Moderate contraction |

  | 6/18 or better | Marked field defect |

  | Severely Sight Impaired | Less than 3/60 | Full |

  | 3/60 – 6/60 | Contraction |

  | Better than 6/60 | Clinically significant contraction |

  
  

  Note: VA measures should be best corrected, and visual function is considered binocularly or in the better eye.
• What is the prevalence of visual impairment in the UK according to HSCIC, 2014?

  2 million with ‘low vision’ (<6/18)
• Which resource provides age-related data for those registered SI / SSI?

  RNIB Sight Loss Data Tool
• What framework is used to assess the functional impact of visual impairment?

  WHO ICF framework
• Explain the components of the WHO ICF framework.

  1. Health condition
  2. Impairment (changes to body functions & structure)
  3. Activity limitation
  4. Participation restriction
• What types of solutions can be offered to address activity limitations (AL) and participation restrictions (PR) in visually impaired patients?

  Address AL / PR:

  
  

  Environmental solutions:

  • Provision of large print
  • Audio description
  • Braille

  
  

  Personal solutions:

  • Change goal
  • Use different device or technique
  • Use sighted guide
• How does the impact of sight loss depend on the eye condition and its effects?

  The impact will vary depending on:

  
  

  1. Type of field loss:

  • Central field loss (CFL)
  • Peripheral field loss (PFL)
  • General visual reduction

  
  

  1. Underlying pathology and its severity
• What are the key conditions affecting the macula that can lead to Central Field Loss (CFL)?

  • Age-related macular degeneration (AMD) – wet or dry
  • Inherited macular dystrophies; e.g. Stargardt’s, Best’s
  • Diabetic maculopathy
• How does Central Field Loss (CFL) impair visual function?

  It reduces DVA, NVA, and CS, and causes visual field changes like central scotoma and metamorphopsia.
• What are the main causes of Peripheral Field Loss (PFL)?

  General peripheral loss:

  • Glaucoma
  • Inherited retinal disorders, e.g. Retinitis Pigmentosa (RP), Usher’s syndrome
  • Diabetic eye disease

  
  

  Sectoral peripheral loss:

  • Hemianopia
  • Quadrantopia following cerebrovascular accident (CVA)
• What are the initial and progressive signs of visual impairment in Retinitis Pigmentosa (RP)?

  Initial nyctalopia (night blindness) followed by progressive peripheral VF loss, starting as a ‘doughnut’ pattern and progressing to a ‘tunnel’ VF, with central VA / CS affected later.
• What are some activity limitations and participation restrictions associated with Peripheral Field Loss (PFL)?

  Activity Limitations:

  • Difficulty with orientation and mobility tasks
  • Limited awareness of surroundings

  
  

  Participation Restrictions:

  • Inability to travel independently, affecting independence
  • Reduced ability to participate in social activities
• Describe the impact of general visual reduction caused by different eye conditions.

  1. Cataract:

  • Light scatter: decreased contrast sensitivity, increased glare, reduced visual acuity (both distance and near)

  
  

  1. Albinism:

  • Lack of ocular pigment: photophobia (light sensitivity), reduced visual acuity

  
  

  1. Nystagmus:

  • Visual acuity decreased due to involuntary eye movements

  
  

  1. Multiple sclerosis:

  • Demyelination of optic nerve fibres: reduced visual acuity / contrast sensitivity, oscillopsia (image movement)
• What are the key areas covered in the lecture structure for assessing low vision patients?

  Adaptations to refraction, visual function assessment, distance VA, and VF assessment
• What is the primary objective of the second phase in assessing low vision patients?

  Clarifying the problem
• What is the primary learning outcome related to refracting low vision patients?

  Be able to have a good go at refracting a low vision patient in the clinic
• Why is assessing visual function important for low vision patients?

  It aids in early detection of disease, establishes baselines for comparison, and quantifies the patient’s subjective problems
• How should logMAR visual acuity be scored?

  On a letter-by-letter basis at any working distance
• How should visual acuity be related to registration criteria when assessing low vision patients?

  Compare the patient’s VA score to the standard registration criteria to determine the level of visual impairment
• Name two key GOC competencies related to visual impairment assessment.

  • Ability to accurately quantify visual impairment
  • Understanding of the assessment of visual function, including specialist charts for distance and near vision
• At what stage of GOC competencies does the ability to assess visual fields of patients with reduced visual acuity fall?

  Stage 2
• What are some key adaptations to refraction for low vision patients?

  • Maximize field of view in trial lenses
  • Use a trial frame, not a phoropter
  • Utilize full (not reduced) aperture lenses
  • Allow eccentric eye and head positions
  • Consider over-refraction with Halberg clips
• When should a low vision patient be refracted?

  • If booked in for an NHS eye examination
  • Specifically for low vision assessment
  • Last Rx dated >1 year ago
  • Suspected Rx change
  • Patient feels vision has changed since last refraction
  • Addition or subtraction of a lens improves VA
  • Pinhole improves VA
  • Needs have changed
  • New glasses needed regardless of Rx change
  • Glasses needed for a new working distance not covered by current Rx
  • 10% of patients referred for low vision assessment just need an updated Rx
• Name two objective refraction techniques.

  Retinoscopy and radical retinoscopy
• Why is it important to use a target that can be seen during sphere refinement in subjective refraction?

  It ensures the patient can accurately perceive the sphere power adjustment
• How should the bracket size be adjusted during sphere refinement?

  The bracket size should be reduced as the refraction is refined
• What are the bracketing steps recommended for different levels of visual acuity in sphere refinement?

  • 6/7.5+ ±0.25
  • 6/9-6/12 ±0.50
  • 6/18-6/36 ±0.75
  • 6/60- ±1.00
  • No ret result Try a big bracket!
• What is a common method for cylinder refinement in subjective refraction?

  • Use a round target such as a Snellen Verhoeff ring (6/6 + 6/12)
  • Start with high power x-cylinders (±0.75 or 1.00D)
  • Use manual x-cylinders, fan and block method
• When should you adjust the distance visual acuity Rx for close working distance?

  If the test chart is used at <6m