
<ul>
  <li>Objects in the visual field subtend the &ldquo;visual angle&rdquo; at the retina</li>
  <li>Arcminute: 1/60th of a degree</li>
  <li>Arcsecond: 1/60th of an arcminute</li>
  <li>
    Minimum resolvable task (ie. identification of small objects): possible at 30-60 seconds of arc
  </li>
  <li>Neonatal VA approximated to about&nbsp; &lt;6/60</li>
  <li>Neural pathways to the visual cortex continue to develop to age 8 years</li>
  <li>Angle alpha: angle between the optical and visual axes</li>
  <ul>
    <li>Describes the degree of "offset" of the eye compared to the optical axis</li>
    <li>Usually around 5.2 degrees horizontally</li>
  </ul>
  <li>
    Angle kappa: angle between the pupil axis and visual axis (ie. the angle between
    the centre of the pupil and the visual axis)
  </li>
  <ul>
    <li>Usually around 2.6 degrees horizontally</li>
    <li>Less reliable due to decentering of the pupil</li>
  </ul>
</ul>
<ul>
  <li>Visual axis: line from image to the fovea</li>
  <li>Pupillary axis: line through centre of pupil</li>
</ul>

## Optotype acuity (subjective measurements)
<ul>
  <li>
    Optotype tests are based on the Landholt C test: the &lsquo;gap&rsquo; in a C or E subtend 1
    arcminute while the whole letter subtends 5 arcminutes
  </li>
  <li>
    Based on the idea that the &lsquo;average&rsquo; person can resolve two points separated by 1
    arcminute
  </li>
  <li>Snellen VA = 1/minimum angle of resolution</li>
  <li>Therefore:</li>
  <ul>
    <li>6/60 = 1/MAR</li>
    <li>MAR = 10 arcminutes</li>
    <li>
      The reciprocal of the VA fraction is the angle of resolution of a single element of the
      optotype (eg. for 6/6, each element of the optotypes subtends 1 arcminute; and for 6/60, each
      element subtends 10 arcminutes)
    </li>
  </ul>
  <li>Snellen fraction:</li>
  <ul>
    <li>
      Visual acuity = Distance at which test is readDistance at which optotype substend 5 arcminutes
      at eye
    </li>
  </ul>
</ul>
<ul>
  <li>LogMAR: five letters per line, spacing proportional to letter size</li>
  <ul>
    <li>Reduces &lsquo;crowding&rsquo; phenomenon</li>
    <li>Read from 4m</li>
  </ul>
  <li>Potential acuity meter: projects a Snellen type chart on the fovea</li>
  <li>Laser interferometry: forms diffraction grating on retina</li>
  <li>
    Sheridan-Gardiner and STYCAR charts use optotypes but are limited to letters that children
    recognise
  </li>
  <li>Kay&rsquo;s and Cardiff tests use pictures for preschool children</li>
  <li>Catford drum uses oscillating dots and is used for babies</li>
  <li>
    Sonksen-Silver use crowded optotypes so are useful for detecting reduced visual acuity in
    amblyopia
  </li>
</ul>
<div className="bg-blue-200 px-4 rounded-md shadow-lg dark:text-gray-700">
  <table>
    <tbody>
      <tr>
        <td>
          <strong>Paediatric visual acuity testing</strong>
        </td>
      </tr>
      <tr>
        <td>
          <strong>0 to 2 years</strong>
        </td>
        <td>Preferential looking cards with gratings</td>
        <td>Teller</td>
      </tr>
      <tr>
        <td></td>
        <td></td>
        <td>Keeler</td>
      </tr>
      <tr>
        <td></td>
        <td>Preferential looking cards with imagery</td>
        <td>Cardiff</td>
      </tr>
      <tr>
        <td>
          <strong>2+ years</strong>
        </td>
        <td>Picture optotypes</td>
        <td>Kay</td>
      </tr>
      <tr>
        <td>
          <strong>3+ years</strong>
        </td>
        <td>Picture +/- letter optotypes</td>
        <td>Sheridan-Gardiner</td>
      </tr>
      <tr>
        <td></td>
        <td></td>
        <td>Sonksen-Silver (with crowding)</td>
      </tr>
      <tr>
        <td></td>
        <td></td>
        <td>Keeler-logMAR</td>
      </tr>
    </tbody>
  </table>
</div>

## Objective measures of VA
<ul>
  <li>Visual evoked potentials as above can approximate to VA</li>
  <ul>
    <li>Size of the checkerboard patterns and luminance can be adjusted</li>
    <li>Flash VEP is best for infants/uncooperative patients</li>
  </ul>
  <li>Oculomotor responses: useful for infants</li>
  <ul>
    <li>Requires functioning oculomotor system</li>
    <li>Sinusoidal grating target commonly used</li>
  </ul>
</ul>


Vision

Visual Acuity

Intro

FRCOphth Part 1 Study Notes

Orbit and ocular adnexae

Orbit

Extraocular Muscles

Orbital Blood Vessels

Paranasal Sinuses

Lacrimal Glands

Tear Film

Eyelids

Blinking

Anterior segment - ocular surface

Conjunctiva

Conjunctivitis

Sclera

Cornea

Corneal Structure And Development

Corneal Physiology

AC to Lens

Angle

Ciliary Body

Aqueous Humour Dynamics

Iris

Pupil

Lens

Posterior segment

Choroid

Vitreous

Retinal Macrostructure

Neurosensory Retina

Retinal Pigment Epithelium

Neuroanatomy

Venous Sinuses

Cerebral Ventricles

Cerebral Blood Supply

Supranuclear Gaze Pathways

Head And Neck Autonomic Nervous Supply

Head And Neck Glands

Osteology

Nerves

Muscles And Pharyngeal Arches

Extraocular Nerves

Sensory Nerves

Physiology

Physics Of Blood Flow

Neuronal Control Of Blood Vessels

Oxygen-Haemoglobin Dissociation Curve

Cytochrome p450

Pituitary Gland

Thyroid Hormone Production

Insulin

Glucagon

Parathyroid Hormone

Corticosteroids

Catecholamines

Cardiac Cycle

Renal Physiology

Fluid Balance

Acid-Base Balance

Muscle Physiology

Sensory Fibres

Cutaneous Receptors

Endocytosis

Glycosaminoglycans

Condensed Ocular Biochemistry

Eye Movements

Accomodation

Visual Cycle And Phototransuction

Visual Pathway

Colour Vision

Binocular Vision

Pathology

Collagen

Tissue Damage

Inflammation

Disease Entities

Wound Healing

Thrombosis / Atherosclerosis

Cell Growth

Neoplasia

Histopathology

Nystagmus

Free Radicals And Antioxidants

Immunology

Ocular Immunology

Microbiology

Viral Infections

Bacterial Infections

Fungal Infections

Protozoa

Nematodes

Antimicrobials

Genetics

Chromosomes

Mitosis

Meiosis

Genes

Polypeptide Synthesis

Histones

MicroRNA

Hardy-Weinberg Equilibrium

Mutations

Chromosome Defects

Autosomal Inheritance

X-Linked Inheritance

Mitochondrial Inheritance

Multifactorial Inheritance