Describe proptosis and the common orbital disorders.

Anatomy and Assessment

• The orbit is a pear-shaped bony cavity of about 30 mL, of which the globe occupies only about a fifth; the remainder is fat, muscle, vessels and nerves.
• Because it is rigid on all sides but open in front, any increase in its contents displaces the globe forward.
• Seven bones form the orbit — frontal, sphenoid, zygomatic, maxilla, lacrimal, ethmoid and palatine

The Common Orbital Disorders

• Thyroid eye disease is the commonest cause of both unilateral and bilateral proptosis in adults. An autoimmune orbitopathy in which the muscles and fat are infiltrated and expand within a rigid orbit
• Its features — lid retraction (Dalrymple sign) and lid lag on downgeze (von Graefe sign), which are highly characteristic; proptosis; restrictive myopathy in the order inferior, medial, superior, lateral rectus; exposure keratopathy; and compressive optic neuropathy at the crowded apex, which is the sight-threatening complication and may occur without much proptosis — indeed a tight orbit that cannot proptose is at greater risk
• It may occur with hyper-, hypo- or euthyroid status, and smoking is the strongest modifiable risk factor and worsens the outcome of every treatment. Managed with lubricants, control of thyroid function, selenium in mild disease, steroids, teprotumumab or radiotherapy in active disease, and surgical decompression for optic neuropathy
• Orbital cellulitis is the commonest cause of proptosis in children, spreading from ethmoid sinusitis through the lamina papyracea. It is an emergency
• Preseptal versus orbital cellulitis is the critical distinction: preseptal has lid swelling with normal vision, normal pupils, NO proptosis and full painless eye movements; orbital has proptosis, painful and restricted movements, reduced vision, chemosis and an afferent pupillary defect, with fever and systemic upset
• Orbital cellulitis requires admission, intravenous antibiotics, CT of the orbit and sinuses, and drainage of any subperiosteal abscess; it can lead to cavernous sinus thrombosis, meningitis, brain abscess and blindness
• Mucormycosis must be considered in a diabetic in ketoacidosis or an immunosuppressed patient with orbital signs: a black eschar on the palate or nasal mucosa, rapid progression and cranial nerve palsies. It requires urgent amphotericin B and radical surgical debridement, and carries a high mortality. Its incidence rose sharply in India during the COVID-19 pandemic with steroid use in diabetics