Day 9 (1): Anatomy and Physiology of the Uveal Tract Flashcards
What is the Uvea?
- comes from the Latin word “uva” meaning grape
- middle, VASCULAR, spongy, PIGMENTED layer of the eye
- extends from the optic nerve to the pupil
Where are the uvea and the sclera firmly attached?
- Scleral Spur
- Exit points of vortex veins
- Optic nerve/disc
What are the parts of the uvea?
- Anterior: iris, pars plicata (ciliary body)
- Intermediate: vitreous base, pars plana
- Posterior: choroid (with or without retina)
What is the iris?
- most ANTERIOR extension of the uvea
- subdivides the anterior segment into the anterior and posterior chambers
- functions:
1. Color of eye
2. Regulation of pupil size: via dilator and sphincter muscles
Note:
Eye is divided into 2 segments:
1. Anterior segment: anterior to lens and zonules
- contains AQUEOUS
+ Anterior chamber: anterior to iris
+ Posterior chamber: posterior to iris but anterior to lens
2. Posterior segment: posterior to lens and zonules
- contains VITREOUS
What are the parts of the iris?
- Pupil: aperture or orifice of the iris
- Pupillary Zone
- central zone adjacent to the pupil
- thinner: atrophy of the mesodermal layer
- shallow surface crypts - Iris Collarette
- circumferential ring of tissue 1.5 mm from pupil margin
- boundary between the pupillary and ciliary zone
- THICKEST portion
+ location of the MINOR Vascular Circle of Iris: anastomoses between the arterial and venous arcades
+ attachment of the embryologic PUPILLARY MEMBRANE - Ciliary Zone
- peripheral zone closer to the ciliary body
- wider and thicker zone
- deeper surface crypts
Remember:
MINOR Vascular Circle of Iris - in the iris collarette
MAJOR Vascular Circle of Iris - in the CB apex NOT in the iris
What are the layers of the iris?
- ENDOthelium
- transparent, most anterior layer
- ABSENT in the crypts - Border layer
- anterior condensation of the stroma
- avascular
- some melanocytes + collagen + HA - Vascular layer ~ Stroma
- bulk of the stroma
- vessels are THICK-walled to prevent collapse when pupil size changes
- NON-fenestrated
- RADIAL course: from the MAJOR circle to the pupil margin
- BULK of melanocytes
+ located more posteriorly
+ iris COLOR = density or concentration of pigment granules
- SPHINCTER muscles:
+ arranged in a CIRCULAR pattern in the PUPILLARY ZONE
+ cut edges do NOT retract due to circular arrangement of muscle
+ derived from neuroectoderm (NOT mesoderm)
+ function: CONSTRICTS the pupil - Posterior membrane
- poorly developed in newborns
- DILATOR muscles:
+ arranged RADIALLY in the CILIARY ZONE
+ derived from neuroectoderm (NOT mesoderm)
+ contain melanosomes
+ PARALLEL to posterior pigmented epithelium
+ function: DILATES the pupil - Posterior PIGMENTED EPIthelium
- bilayered:
+ anterior layer: spindle-shaped cells
+ posterior layer: cuboidal cells
- HEAVILY-pigmented
- continuous with NON-pigmented Epithelium of the CB <– NSR
What is the ciliary sulcus?
Small space between the posterior surface of the iris base and the anterior surface of the ciliary body
What is the ciliary body?
- 6 - 7 mm right-triangular body bridging the anterior and posterior segments
- “cilia” due to presence of ciliary processes
- actual SITE of aqueous humor production
- apex: pointed POSTERIORLY towards the ora serrata
- base:
+ continuous with the IRIS and the CHOROID
+ attached to the sclera near the SCLERAL SPUR via longitudinal muscle fibers - functions:
1. Lens accommodation: relaxing zonule tension
2. Aqueous production
3. Aqueous drainage: uveoscleral flow
What are the parts of the ciliary body?
- Pars Plana
- 4 mm wide, posterior, AVASCULAR, smooth and FLAT zone
- extends from ora serrata to the pars plicata
- safest approach to retinal surgery - Pars Plicata
- anterior, VASCULAR, irregular and CILIATED zone
- with 60 - 70 ciliary processes which attach to the lens zonules
- continuous with the iris
What are the layers of the ciliary body?
7 Layers
- Layers 1, 2, 3: Main bulk
- Layers 4, 5A, 5B, 6: Continuous with retina
- Lamina fusca
- most external layer and closest to the sclera
- continuous with the SUPRACHOROIDAL SPACE - Muscle layer: functions as a unit but with 3 distinct layers
- LONGITUDINAL: outermost; attached to the scleral spur and extends to equator
- RADIAL: oblique midportion
- CIRCULAR: girdle-like innermost part; contraction causes relaxation of zonules and lens accommodation - Vascular layer: synonymous to stroma
- connected to the Ciliary arteries
- where most antibody-producing PLASMA CELLS are located - Lamina Vitrea
- anchors epithelium to underlying stroma to withstand traction by lens zonules
- continuous with BRUCH’S MEMBRANE - Epithelium: bilayer with fusion of apices by tight junctions
5.A. Outer Pigmented Layer
- continuous with RPE: (+) melanin granules
- BM on the stromal side and apex fused with inner epithelium
- uniformly cuboidal all throughout
5.B. Inner NON-Pigmented Layer
- between aqueous and outer pigmented epithelium
- continuous with NSR
- pigmented anteriorly and becomes the PIGMENTED Posterior Epithelium of the Iris
- columnar in the pars plana and gradually shortens to cuboidal towards the iris
- site of aqueous humor production
- BLOOD-AQUEOUS BARRIER: tight junctions/zonula occludens between epithelial cells
- Internal Limiting Membrane
- continuous with ILM of retina
- basement membrane of the INNER NON-pigmented epithelium that separates the epithelium from the aqueous humor
What is the choroid?
- comprises the posterior uvea
- spongy mass of vessels extending from the optic nerve to the ora serrata
- thins out (0.25 mm –> 0.10 mm) and less pigmented anteriorly
- function: provides nutrients to outer retina (RPE, PRL, ONL, OPL)
- highly vascular:
+ tissue with the highest blood flow
+ high risk for metastases and infectious emboli
+ venous oxygen content only 2 - 3% lower than arterial
What are the layers of the choroid?
- Suprachoroid Space
- outermost layer adjacent to the sclera
- continuous with the LAMINA FUSCA
- pathway of blood vessels and nerves that supply the uvea
- cellular layer: fibroblasts, melanocytes, myocytes
- firmly attached posteriorly: detachments common anteriorly - Vascular Layer
- largest layer
- NON-fenestrated blood vessels
- 2 portions with INDISTINCT delineation:
+ Haller’s: outer portion with LARGE vessels
+ Sattler’s: inner portion with MEDIUM vessels - Choriocapillaris
- large capillaries in a single plane beneath the RPE
- thin, fragile, FENESTRATED walls
- DENSER in the fovea and WIDE APART in periphery
- ends in the ORA SERRATA: does not continue in the CB - Bruch’s Membrane
- innermost layer
- continuous with the LAMINA VITREA
- fusion of the basal lamina of the RPE and choriocapillaris
- forms the OUTLINE or border of the OPTIC DISC
- extends from the margin of the optic disc to the ora serrata
- 5 zones:
+ Basal lamina of choriocapillaris
+ Outer collagenous zone
+ Elastic fiber zone
+ Inner collagenous zone
+ Basal lamina of RPE
Which structures in the retina and choroid are contiguous with structures in the ciliary body and iris?
Choroid/Retina –> Ciliary Body –> Iris
- ILM –> ILM –> NONE
- Neurosensory Retina –> Inner NON-pigmented epithelium –> Posterior Pigmented Epithelium
- Retinal Pigment Epithelium –> Outer Pigmented epithelium –> NONE
- Bruch’s Membrane –> Lamina Vitrea –> NONE
- Choriocapillaris –> NONE
- Suprachoroidal Space –> Lamina Fusca –> NONE
Major blood supply to the intraCRANIAL contents?
Internal Carotid Artery
Major blood supply to the intraORBITAL contents?
Ophthalmic Artery
- major branch of the ICA just after it becomes intradural
Orbital group: vessels to the orbit and surrounding parts
SSLIDE
1. Lacrimal artery
2. Supraorbital artery
3. Supratrochlear artery/Frontal artery
4. Ethmoidal artery (Anterior and Posterior)
5. Internal palpebral artery (Medial and Lateral)
6. Dorsal nasal artery
Ocular group: vessels to the eye and its muscles
CAMP
1. Central retinal artery
2. Posterior ciliary arteries (Long and Short)
3. Anterior ciliary arteries: may arise from muscular arteries
4. Muscular arteries (Superior and Inferior)
