<ul>
 <li>Tests incomitant strabismus: squint angle changes depending on the direction of gaze</li>
 <li>Two types of incomitant strabismus</li>
 <ul>
 <li>Neurogenic/myogenic: nerve or muscle palsy</li>
 <li>Mechanical: eg. dysthyroid eye disease or orbital fracture</li>
 <ul>
 <li>In mechanical restrictions, the ductions are the same as the versions</li>
 </ul>
 </ul>
</ul>
<ul>
 <li>Assumptions of Hess charts</li>
 <ul>
 <li>Normal retinal correspondence (see above)</li>
 <li>No suppression</li>
 <li>Reasonable visual acuity</li>
 </ul>
 <li>Performed with both eyes open with each eye fixing in turn</li>
 <li>Patient sits 50cm from the screen</li>
 <li>Different coloured stimuli are used to to dissociate the eyes: no fusion</li>
 <ul>
 <li>
 The grid uses red lights and the patient wears red and green goggles so that only the one eye
 (the fixing eye) sees the lights
 </li>
 </ul>
</ul>
<HotTopic>
 Each Hess chart square represents 5 degrees (or 10 prism dioptres)
 <ul>
 <li>The central field is 15 degrees from the primary position</li>
 <li>The peripheral field is 30 degrees from the primary position</li>
 </ul>
</HotTopic>
<ul>
 <li>
 The fixing eye is directed to various positions and the position of the non-fixing eye is
 recorded
 </li>
 <ul>
 <li>The patient is asked to superimpose the green light onto the red light</li>
 <li>Their fixing eye can see the red targets through the red lens but the other eye cannot</li>
 </ul>
 <li>Therefore certain effects can be noted:</li>
 <ul>
 <li>
 Hering&rsquo;s law: during conjugate movements, equal and simultaneous innervation is directed
 to corresponding (yoke) muscles to contract
 </li>
 <li>
 Sherrington&rsquo;s law: during contraction of a muscle, a simultaneous signal is sent to
 relax its antagonist
 </li>
 <li>Primary deviation: the extent of deviation is noted when the normal eye is fixing</li>
 <li>
 Secondary deviation: the extent of deviation is noted in the normal eye when the affected eye
 is fixing
 </li>
 </ul>
</ul>
<HotTopic>
 Hess chart interpretation
 <ul>
 <li>The smaller chart indicates the eye with the underacting muscle (primary deviation)</li>
 <ul>
 <li>The greatest restriction will be seen in the main direction of the affected muscle</li>
 </ul>
 <li>The larger chart indicates the eye with the overacting muscle (secondary deviation)</li>
 <ul>
 <li>
 The greatest expansion is seen in the direction of the yoke muscle (according to
 Hering&rsquo;s law)
 </li>
 </ul>
 </ul>
</HotTopic>

## Muscle sequelae
<ul>
 <li>Defects become more concomitant with time, serving to reduce the squint angle</li>
 <li>
 Stage 1: concurrent overaction of the contralateral synergist according to Hering&rsquo;s law
 </li>
 <li>
 Stage 2: overaction of the ipsilateral antagonist due to its unopposed action leading to
 contracture (shortening) which manifests as overaction
 </li>
 <li>
 Stage 3: secondary underaction of the contralateral antagonist. Since less innervation is needed
 in the ipsilateral antagonist due to its contracture, by Hering&rsquo;s law the contralateral
 antagonist receives less innervation, so underacts
 </li>
</ul>
Strabismus is further explored in the Part 2 package

Clinical Techniques

Hess Chart

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

Vision

Visual Cycle And Phototransuction

Visual Pathway

Visual Acuity

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