SPLANCHO 2 EYE

Question 1

What are the two layers of the fibrous tunica of the eye?

Answer 1

They are the two outmost layers; the Sclera and the Cornea which is the bulging layer.

Question 2

What are the layers of the sclera?

Answer 2

Episclera: outermost, loose CT.

Sclera proper: intermediate, dense network of collagen fibers.

Lamina Fusca: Pigmentation, thinner collagen and elastic fibers. Melanocytes, fibroblasts and macrophages.

Question 3

What are the layers of the Cornea?

Answer 3

Corneal Epithelium : outermost, pain receptors, n-keratinized stratified squamous.
Bowmans Layer: Thick basal lamina.
Corneal Stroma: Thickest layer made of dense CT, collagen.
Descemet’s Layer: dense basal lamina.
Corneal Endothelium: In contact with the aqueous humour.

Question 4

What are the measurements of the Cornea?

Answer 4

Horizontal diameter of 11.5 mm, vertical diameter of 10.6 mm, thickness of 0.5-0.6 mm in the center and 0.6-0.8 mm at the periphery.

Question 5

What is the refractive power of the Cornea?

Answer 5

It provides 42 diopter of refractive power. The number comes from the total refractive power if the cornea minus the one of aqueous humour.

Question 6

Why is the Corneal Stroma layer a key to transparency?

Answer 6

It is much thicker in humans, very uniform collagen fibers, very regular Interfibrillar spaces, parallel orientation. Corneal transparency is due to these regular arrangements.

Question 7

Why is the Scleral Stroma not transparent?

Answer 7

Not uniform size of collagen fiber, not evenly spaced, different lengths, not arranged in parallel layer. Diameter of 25 to 300 nm.

Question 8

What is the Trabecular meshwork and the Schlemm canal?

Answer 8

Trabecular meshwork is composed by a number of cavities that help drain the anterior chamber of aqueous humour. It leads to the Canal of Schlemm which drains the humour into the venous system of the eye.

Question 9

What is the anatomy of the external eye?

Answer 9

The eye is covered by two membranous folds called superior and inferior eyelid, they are connected laterally by the Lateral Commissure. The space between the two eyelids is called Palpebral Fissure.

Question 10

What are the glands associated with the external eye?

Answer 10

Sebaceous glands: when associated to eyelashes they are called Glands of Zeis otherwise called Apocrine Glands of Moll. Largest one called Meibomian Gland.

Serous glands: Accessory lacrimal glands of Wolfring, those associated with the glands of Krause.

Question 11

What is the histology of the eyelids or palpebrae?

Answer 11

The anterior epithelium of both superior and inferior eyelids is stratified squamous keratinized epithelium. At the level of the eyelashes it changes into a non keratinized epithelium.

Question 12

What is the anatomy of the orbital cavity?

Answer 12

The external opening of the cavity is composed of the maxillary, frontal, zygomatic bone.
The left side is composed of the ethmoid and lacrimal bone entirely and parts of the curvature of frontal bone coming down and the maxillary coming up. The right side is made of the zygomatic and sphenoid bone. It has three posterior openings the superior medial canal aka Optic canal, superior orbital fissure between the sphenoid bone and the inferior orbital fissure.

Question 13

What does the superior orbital fissure contain?

Answer 13

Superior ophthalmic vein, lacrimali nerve, frontal nerve, trochlear nerve and muscles such as the lateral rectus, inferior rectus, superior rectus, oblique rectus.

Question 14

What are the layers of the Vascular tunic?

Answer 14

Iris, Ciliary body and Choroid.

Question 15

How is the ocular bulb suspended in the orbital cavity?

Answer 15

The ocular bulb is suspended by means of two different ligaments system. The first system is composed of two check ligaments, one on the medial side of the ocular bulb and the other one on the lateral side. The second system is vertical , it is made from the thickening of the inferior oblique muscle. The third system is the extra ocular muscles, there are four: superior, inferior, medial and lateral rectus.

Question 16

What is the clinical terminology for constriction and dilation of the pupil.

Answer 16

Miosis and mydriasis.

Question 17

What are the iris collarettes, crypts and radial furrows?

Answer 17

Serrated aspects that go from the root of the iris to the margin of the pupil.

External radiations which are much thicker and they can be Open which are the larges and closed if they are short.

Internal protrusion and are much thinner.

Question 18

What are the layers of the iris?

Answer 18

The iris has four layers, its anterior and posterior surfaces are covered by epithelia, posterior epithelium is pigmented. The anterior epithelium is made of fibroblasts called epithelioid cells, that cover the surface in a discontinuous manner. The anterior epithelium separates the iris from the anterior chamber, which contains the aqueous humor.
Underneath this epithelium, there is loose connective tissue that is pigmented at its surface. This loose connective tissue is called iris stroma. Posterior to the iris stroma, there are a few layers of smooth muscle cells, concentric smooth muscle cells which make up the sphincter pupillae muscle.

Question 19

What are the two regions of the Ciliary body?

Answer 19

Internal part called Pars plicata which is protruding with ciliary processes and an external part that is flatter called Pars plana.

Question 20

What composes the ciliary processes?

Answer 20

The surface of the body is characterized by a bi-stratified epithelium, composed of an external layer of non-pigmented cells called retinal epithelium, and an internal pigmented epithelium. This layer is composed of cells endowed with melanocytes. Internal to the pigmented epithelium is loose connective tissue with several fenestrated capillaries. Ciliary bodies receive arteriolar branches from the major arterial circle of the iris.

Question 21

What composes the choroid layer?

Answer 21

The choroid is a layer of highly vascularized loose connective tissue, found between the sclera (externally) and the retina (internally). Layers of fibroblasts separate the vascular layer form the sclera, and these are called Supra Choroid layers. The vascular layer is divided in Hallers layer which contains the larges vessels, Intermediate vessels in the Sattlers layer and capillaries in the Choriocapillaris layer. Finally Bruchs membrane that separates the Choriocapillaris layer from the retinal epithelium.

Question 22

What is the lens?

Answer 22

The lens is a biconvex, avascular, colorless and transparent optical structure. The lens contributes 18 diopters to the power of the eye, the cornea contributes 42 diopters. The refractive index of the lens (n=1.409) is higher than that of the cornea (n= 1.306). The lens is kept in place by ligaments forming the apparatus called zonular fibers. The function of the lens is to accommodate to facilitate near vision.

Question 23

What is the lens composed of?

Answer 23

It has an external capsule which is a thick basal lamina, underneath we find bistratified epithelium. Anterior layer contains cuboidal cells and the posterior stretched cylindrical cells. We have a germinal zone that contains stem cells which give rise to lens fibers.

Question 24

What is the retina?

Answer 24

The retina is a thin, semitransparent, multistratified neuroepithelium which is lining the inner aspect of the posterior two thirds of the eyeball. The retina starts anteriorly at the ora serrata, and then interrupts abruptly at the level of exit of the optic nerve.

Question 25

What is the name of the exam by means of which the physician evaluates the retina?

Answer 25

Ophthalmoscopy or fundoscopy.

Question 26

What vessels does the optic nerve contain? What do they branch out it?

Answer 26

Central artery of retina and the central vein of retina.

They branch out each into 4 vessels so 8 total vessels. 4 inferior, 4 superior, and 4 nasal and 4 temporal.

Question 27

What vessels bring blood to the ganglion cell layer and the inner nuclear layer of retina?

Answer 27

Instead the superficial arteries- superior and inferior nasal and temporal arteries are giving rise to a number of collaterals which are penetrating the inner layers of the retina more specifically the ganglionic cell layer and inner nuclear layer of retina.

Question 28

What are some anatomical regions of the fundus of the retina?

Answer 28

The normal fundus of the retina is dominated by the 2 areas. One on the nasal and another on the temporal side. On the nasal side we see a bright area called an optic disc, which has a brighter region in the center called physiologic cup, which is surrounded by a less bright area called neuroretinal rim. From this area vessels are entering and exiting. Arteries are brighter red and narrower than veins. About 2.5 optic discs far of the optic disc itself there is on the temporal side a depressed area which is called macular region. Macular region is containing an internal area, which is smaller, darker and more depressed and is called Fovea.

Question 29

What is the optic disc?

Answer 29

The optic disc is the place where 1 million axons coming from the ganglionic cell layer of the retina are exiting the eye to form the cranial nerve 2 (optic nerve).

Question 30

What are some characteristics of the macular region of the fundus?

Answer 30

Macular region is very depressed area of the retina which is centered on the optic path. In respect of the optic disc it is on the temporal side of the retina. This area contains much more depressed area called fovea. Fovea is mainly composed of cones as the major components of the photoreceptor layer

Question 31

What are the layers of the retina?

Answer 31

(1) First layer is Bruch’s Membrane, a membrane which is separating the choroid layer of vascular tunic from retina. (2) Internal to Bruch’s membrane there is monolayer of cuboidal cells called Retinal Pigmented Epithelium. (3) Layer of rods and cones is proceeding layer, with the outer segment of photoreceptors. (4) Then the Outer Nuclear layer which is containing the nuclei of photoreceptors. (5) Then going into the inner part of the retina, it begins with Outer Plexiform layer, that is the synaptic layer between the inner nuclear layer and outer nuclear layer - between bipolar cells which are populating the inner nuclear layer and the photoreceptors which are populating the outer nuclear layer. (6) Inner Nuclear layer is the next layer, which is containing the nuclei of the bipolar cells together with horizontal and amacrine cells. (7) Then we have Inner Plexiform layer that is the synaptic layer between the inner nuclear layer, between the bipolar cells and ganglion cells. (8) Ganglion Cells are internal to the inner plexiform layer and are forming an independent layer. Ganglion cells are the projecting neurons of retina and they are sending axons into the Nerve Fiber layer (9), which is sealed from the vitreous humor by the Inner Limiting membrane (10)

Question 32

How is Bruch’s membrane connected to the Retinal pigmented epithelium? How are the cells of the RPE connected to each other?

Answer 32

Hemidesmosomes and Tight junctions.

Question 33

What are the main functions of the RPE cells?

Answer 33

The most important function is light absorption. regulation of transport of glucose, vitamin A, chloride, potassium and sodium ions as well as water through specialized aquaporins. Visual cycle. Secretory activity, they release a cytokines called Vascular Endothelial Growth Factor and Pigment Epithelial Derived Factor.

Question 34

What is the limbus?

Answer 34

Anatomical location where the cornea meets the sclera.

Question 35

What are the layers of the Cornea?

Answer 35

1. Anterior corneal epithelium: non keratinized squamous epithelium.
2. Bowmans membrane: fine collagen fibrils, type I,III and V. 22nm, It is composed of type 1 collagen, laminin, and several other heparan sulfate proteoglycans.
3. Corneal stroma: 25 nm collagen fibers, fibroblast are present. Keratocytes maintain the integrity of this layer.
4. Descemets membrane: basement membrane
5. Endothelium

Question 36

What are the measurements of the layers of the cornea?

Answer 36

11.5 mm horizontal diameter, 10.6 mm vertical diameter, 0.5/0.6 mm thickness in the center and 0.6/0.8 mm at the periphery.

Question 37

What are the components of the layers of the retina?

Answer 37

Starting innerly:
ILM: basement membrane, termination of muller cells.
NFL: Ganglion cell axons, run parallel to retinal surface.
GCL: Bodies of ganglion cells.
IPL: dendrites of ganglion cells.
INL: cell body of horizontal, bipolar, amacrine, muller cells.
OPL: Rods and cones fibers.
ONL: Only rod and cone cell bodies.
ELM: junctions between photoreceptors and muller cells.
PL: outer and inner segments of rods and cones.

Question 38

What are muller cells?

Answer 38

They are specialized radial glial cells which wrap up all retinal neurons and their processes. They have a high potassium conductance, help maintain the retinal structure and regulate retinal blood flow.

Question 39

What are some characteristics of descemets basement membrane?

Answer 39

This basal lamina in the cornea is unusually thick and retains the ability to regenerate. It thickens with age.