🥇 Anatomía del OJO 1/3 - Generalidades y Túnica Externa

Anatomy of the Eye: Overview and Structure

Introduction to the Series

• The video series by Juan José Sánchez focuses on the anatomy of the eye, divided into three main videos covering different aspects.

• Additional videos will discuss external structures like extraocular muscles and the lacrimal apparatus.

Layers of the Eyeball

• The eyeball consists of three primary layers:

• Outer Tunic (Fibrous Tunic): Composed of sclera (posterior) and cornea (anterior).

• Tunica Media (Vascular Tunic): Includes choroid (posterior), ciliary body (middle), and iris (anterior).

• Internal Tunic (Nervous Tunic): Primarily made up of the retina.

General Characteristics of the Eye

• The eye is described as a relatively circular organ weighing between 7 to 7.5 grams.

• Its dimensions include an anteroposterior diameter longer than its transverse diameter, measuring approximately:

• Anteroposterior: 25 mm

• Transverse: 23 to 24 mm

• Vertical: Approximately 23 mm

Ocular Topography and Anatomy

Key Anatomical Features

• The eye has two poles:

• Anterior Pole: Located at the central part of the cornea.

• Posterior Pole: Found at the central part of the sclera.

Equator and Hemispheres

• The equator divides the eye into anterior and posterior halves, maintaining equal distance from both poles.

• Hemispheres are defined relative to this equator:

• Anterior Hemisphere: Front half above equator.

• Posterior Hemisphere: Back half below equator.

Understanding Meridians

• A meridian is a cut through both poles, which can be vertical, oblique, or horizontal. It does not have to pass through the center but must touch both poles.

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Anatomy of the Eye: Cornea and Sclera

Overview of the Cornea

• The outer tunic, known as the fibrous tunic, consists of two structures: the cornea and sclera. The cornea is described first as it forms the anterior lens of the eye.

• The cornea is a vascular tissue that makes up approximately one-sixth of the eye's anterior structure, with its diameter being longer transversely than vertically (12 mm vs. 11 mm).

Structure and Measurements

• The thickness of the cornea varies; at its center, it measures between 0.5 to 0.8 mm thick, while it is thicker at the periphery (approximately 1 mm). This asymmetry contributes to its overall shape.

• The junction between the cornea and sclera is termed the sclerocorneal limbus, where conjunctiva also attaches, providing protection to both structures.

Important Features

• A notable feature at this junction is trabecular reticulum—a network of fibers visible under microscopic examination—important for understanding fluid dynamics in the eye.

• The iridocorneal angle is crucial for aqueous humor reabsorption; understanding this angle helps explain intraocular pressure regulation within the eye.

Layers of the Cornea

• The cornea comprises several layers:

• Anterior epithelium

• Anterior limiting membrane (also called Bowman's layer)

• Stroma (the main substance)

• Posterior limiting membrane (Descemet's membrane)

• Posterior epithelium (often referred to as mesothelium). Each layer plays a role in maintaining transparency and structural integrity.

Transition to Sclera

• Following discussion on corneal anatomy, attention shifts to scleral anatomy—the white part of the eye—which forms five-sixths of its posterior structure and varies in thickness from about 1 mm anteriorly to approximately 0.4 mm in mid-region before thickening again posteriorly.

Anatomy of the Eye: Understanding the Sclera and Associated Structures

Structure of the Sclera and Bulbar Aponeurosis

• The sclera, episcleral tissue, and bulbar aponeurosis are crucial components of the eye's anatomy. The bulbar aponeurosis is penetrated by extraocular muscles that insert at the sclera.

• In the posterior part of the sclera, where it converges to form the optic nerve, there are no complete holes; instead, cribriform fibers create a sieve-like structure for nerve passage.

Optic Nerve and Its Membrane

• The optic nerve (second cranial nerve) is surrounded by a membrane that integrates with scleral fibers, forming a cohesive unit essential for function.

Scleral Venous Sinus (Schlemm's Duct)

• A microscopic view reveals key structures such as the cornea, sclera, sclerocorneal limbus, and Schlemm's duct located in the iridocorneal angle between iris and cornea.

• Schlemm's duct plays a vital role in reabsorbing aqueous humor produced in the eye. This process will be elaborated upon in future discussions regarding aqueous humor circulation.

Importance of Schlemm’s Duct in Glaucoma

• Understanding anatomical points like Schlemm’s duct is critical due to its association with glaucoma—a condition characterized by increased intraocular pressure caused by obstruction preventing aqueous humor reabsorption.

Overview of External Tunic Components

• The video concludes with an overview of external tunic components including conjunctiva continuity with eyelids and sclera. It emphasizes understanding how these structures interact within ocular anatomy.