THYROID IN EYE DISEASES

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THYROID IN EYE DISEASES
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WHAT IS THYROID GLAND?

• ITS ANATOMY PHYSIOLOGY
• AND
• FUNTIONS

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HORMONES

• The follicular cells synthesise thyroxine which
  is also called T4 because it contains four atoms
  of iodine, and triiodothyronine or T3 which
  contains three atoms of iodine.
• T3 is more active and several times more potent
  than T4 but it is secreted in smaller amounts.
• T4 is converted into T3 by removal of one iodine.
• T3 and T4 are synthesised by attaching I to the
  amino acid tyrosine by enzymatic action, stored
  some time and then secreted into the blood.

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FUNCTIONS

• To regulate metabolic rate.
• To regulate metobolism by stimulating protein
  synthesis.
• To maintain normal body temperature.
• To regulate the development of mental faculties.
• To enhance some actions of neurotransmitters
  adrenaline and non adrenaline.

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Disorders Resulting from Malfunctioning of
Thyroid Gland

• Hypothyroidism
• It can result from
• Primary failure of thyroid gland itself.
• Secondary to hyposecretion of TRH, TSH or both.
• An inadequate dietary supply of iodine.
• The symptoms include reduction in overall
  metabolic activity and poor tolerance to cold

• Hyperthyroidism
• Graves disease (exopthalmic goitre)
• It is an autoimmune disorder in which the person
  produces antibodies that mimic the action of TSH
  but are not regulated by normal negative feed
  back control. These patients have peculiar edema
  behind the eyes called exopthalmos which causes
  the eyes to protrude.

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GRAVES DISEASE

• Also known as thyrotoxic exopthalmos.
• Caused due excessive secretion of thyroxine
  hormone or thyrotoxicosis.
• Commonly occurs between the ages of 15 and 45
  years and is more common in females.
• In half of the cases the condition shows heredo
  familial tendency.
• It may occur with or without occular
  manifestations.

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ETIOPATHOGENESIS

• Thyrotrophic exopthalmos could be associated with
  hyperthyroidism, hypothyroidism or even the
  euthyroid state.
• There is evidence to support the contention that
  a substance called exopthal producing substance
  (EPS) released from the anterior pituary is
  responsible.
• EPS is currently TSH fragments. Another substance
  called human specific thyroid stimulator (HTS)
  has also been isolated.

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ETIOPATHOGENESIS

• It has been postulated that EPS aide by HTS binds
  to the orbital tissue and stimulates synthesis of
  orbital fat and hydrophilic mucopolysaccharides.
• These mucopolysaccharides drain water, and cause
  increased volume of the orbital tissues due to
  intercellular oedema.
• Lymphocytes and mast cells also infiltrate the
  orbital tissues.

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PATHOLOGY

• The extraocular muscles are greatly swollen, pale
  and oedematous.
• There is degeneration of the muscle fibres with
  round cell infiltration.
• Some degree of oedema and round cell infiltration
  also occur in the orbital tissues with diminution
  of fat content.

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PATHOLOGY

• Although the extra ocular muscles show
  disorganisation of muscle fibres and loss of
  striation, these are thought to be secondary
  changes the primary one being interstitial
  inflammatory oedema.

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OCCULAR MANIFESTATIONS OF GRAVES DISEASE

• LID RETRACTION -
• The upper lid covers the upper part of the cornea
  for about 2-3mm at 12 oclock and lid retraction
  is present when the upper lid margin is at the
  level of or above the upper limbus.
• Lid retraction is more obvious when the eyes are
  turned down and a rim of sclera is visible above
  the cornea.
• The lower lid does retract in this condition.

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OCCULAR MANIFESTATIONS OF GRAVES DISEASE

• In exopthalmos scleral rim is seen both above and
  below the cornea while in lid retraction, it is
  seen only above the cornea.
• Lid retraction is more commonly found in diffuse
  toxic goitre and very rarely in nodular goitre.
• EXOPTHALMOS-
• Moderate degree of exopthalmos is common in
  graves disease and is probably due to excessive
  deposition of fatty tissues in the orbit.

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Difference Between Thyrotoxic and Thyrotrophic
Exopthalmos

• Thyrotoxic Exopthalmos
• Due to excessive thyroxin secretion.
• Retraction of the upper lid.
• Weakness of convergence.
• Sometimes pgmentation of the skin of the upper
  lid.

• Thyrotrophic Exopthalm
• Due to excessive secretion of the thyrotrophic
  hormone of the anterior pituitary.
• Marked proptosis of both the eyes which is
  irreducible on pressure.

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Difference Between Thyrotoxic and Thyrotrophic
Exopthalmos

• No chemosis of conjuctiva.
• fundus normal
• Lid lagging ie an attempt to look down the upper
  lid does not follow the eyeball but lags behind
  it.
• Seen in hyperthyroid pts.

• Chemosis of conjuctiva.
• Shows optic atrophy.
• Ext opthalmoplegia- at 1st the movts of elevatn
  and abductn are affected but later on all movts
  are hampered.
• Seen in euthyroid pts.

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TREATMENT

• Thyrotoxic exopthalmos-
• The routine treatment consisting of rest,
  sedation, iodide or thiouracil with or without
  partial thyroidectomy, is largely effective in
  controlling the toxic symptoms.
• Exopthalmos rarely requires special attention.
• Tarsorrhaphy required for cosmetic reason and for
  exposure keratopathy when present.

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