Eye: Anatomy and Vision Loss

• Vision is a major quality-of-life issue, that directly impacts an individuals independence and well-being.
• Diseases causing vision loss may not receive as much attention as life-threatening conditions.
• Age-related macular degeneration (AMD) is the most common cause of irreversible vision loss in the U.S.
• Eye study requires knowledge of dermatopathology, brain and central nervous system pathology.
• The eye is the only site where microcirculatory disturbances, like arteriosclerosis and angiogenesis, can be directly visualized.
• Pathologic angiogenesis is responsible for corneal neovascularization, diabetic retinopathy, and some forms of age-related neovascularization.
• Vascular endothelial growth factor (VEGF) antagonists treat the aforementioned conditions to save vision.
• The study of the eye is based on ocular anatomy.

Orbit

• The orbit is a closed compartment, so any increase in orbital contents displaces the eye forward, leading to proptosis.
• The proptotic eye may not be fully covered by the eyelids, causing corneal exposure, pain, ulceration, and infection.
• Proptosis can be axial (directly forward) or positional.
• Enlargement of the lacrimal gland displaces the eye inferiorly and medially.
• Masses within the horizontal rectus muscles cause axial proptosis (eye bulges straight forward).
• Glioma and meningioma are primary optic nerve tumors that cause axial proptosis.

Thyroid Ophthalmopathy (Graves Disease)

• Axial proptosis is an important clinical sign of Graves disease.
• Proptosis results from accumulation of extracellular matrix proteins and fibrosis in the rectus muscles.
• Development of thyroid ophthalmopathy can be independent of thyroid function.

Other Orbital Inflammatory Conditions

• Sinus infections can spread to the orbit.
• Granulomatosis with polyangiitis may start in the orbit or extend from the sinuses.
• Idiopathic orbital inflammation (orbital inflammatory pseudotumor) is a condition that can be unilateral or bilateral.
• It can affect all orbital tissue or be confined to the lacrimal gland, extraocular muscles, or Tenon capsule.
• IgG4-related disease should be excluded before diagnosing idiopathic orbital inflammation.

Morphology of Idiopathic Orbital Inflammation

• Characterized by chronic inflammation and fibrosis.
• Inflammatory infiltrate includes lymphocytes, plasma cells, and sometimes eosinophils.
• Germinal centers may indicate reactive lymphoid hyperplasia.
• Vasculitis may suggest an underlying systemic condition.
• Necrosis and degenerating collagen with vasculitis suggest granulomatosis with polyangiitis.
• Can occur with sclerosing inflammation in other areas, especially as a manifestation of IgG4-related disease.

Neoplasms

• Common primary orbital neoplasms are vascular in origin: capillary hemangioma (infancy/childhood), lymphangioma, and cavernous hemangioma (adults).
• Few orbital masses are encapsulated (e.g., pleomorphic adenoma, dermoid cyst, neurilemmoma).
• Non-Hodgkin lymphoma can affect the entire orbit or just parts like the lacrimal gland.
• Orbital lymphomas are classified using the WHO classification system.
• Primary orbital malignancies are classified like tumors of the parent tissue.
• Metastatic prostatic carcinoma may mimic idiopathic orbital inflammation.
• Metastatic neuroblastoma and Wilms tumor can cause periocular ecchymoses.
• Neoplasms can invade the orbit from the sinuses.

Key Concepts

• Proptosis is caused by lesions or changes in the orbit that take up space.
• Orbital inflammation can result from local disease (e.g., sinusitis) or systemic disease (e.g., granulomatosis with polyangiitis).
• The most common primary orbital tumors are vascular (e.g., capillary and cavernous hemangiomas).