cornea

Anatomy , physiology, corneal breaks and emergencies

By MAIS IBRAHIM M.D

SYPERVISED BY RASHA GAZALI M.D

Anatomy

• Vertical diameter : 12 mm

• Horizontal diameter : 11 mm

• Radius of curvature : ant, 7.8mm – post, 6.5mm

• Thickness : 1mm peripherally – 0.5 mm centrally

Anatomy

• Five layers :

• 1- Epithelium

• 2-Bowman

• 3- Stroma

• 4-Descemet Membrane

• 5-Endothelium

anatomy

Epithelium

• 50 micro m (5-10% )

• 1- basement membrane

• 2- columnar basal cells (single layer)

• 3-wing cells (2 to 3 layers )

• 4- surface cells

• Stem cells at the limb

Epithelium

• Superficial cells : microvilli and microplicae

coated with “glycocalyx”

• Glycoprotein : stability of tear film and wetting of cornea

• Sugar residues of plasma membrane glycoprotein and glycolipids : wound healing ,attachment of microbes

Epithelium

• Penetrating the epithelium : uncharged molecules

• Penetrating stroma : charged

• It should be able to dissociate at physiologic PH and temperature (biphasic)

Bowman layer

• Collagen fibers type I and type V

• 8-10 micro m

• Acellular and packed distribution ; prevent keratocytes from growth factor

• PRK and LASEK ; corneal haze

• Can not regenerate

• Scar tissue after injury

PRK

LASIK flap

Stroma

• 90% of the cornea

• 1- keratocytes (2.4 millions)

• 2- ground substances ( proteoglycans)

• 3- collagen lamellae

Stroma

• Collagen fibers ; center to center

• Collagen type I ; 70% of stroma

• Type III ; wound healing

• Type V , VI , VII , XII , XIV

PROTEOGLYCANS

• 10%

• Hydrophilic properties

• 1-keratan sulfate 60%

• 2-chondroitin sulfate

• 3-dermatan sulfate 40%

• Regulation of spacing between collagen fibrils

MMPs

• Degradation of the components of the extracellular matrix

• MMT-2 ; normal cornea

• MMT-1 , MMT-3 , MMT-9 after injuiry

Descemet membrane

• True membrane

• 10-12 micro M

• Increases with age

• Secreted by endothelium

• Type IV is the most one

• Ending peripherally at shwalbe line

Descemet membrane

• Anterior banded zone – posterior nonbanded zone

• Resistance to the flow of solvent

Descemet defects

• 1- descemet folds

• 2-haab’s striae

• 3-vogt striae

• 4- hydrops

Descemet folds

• Inflammation: infection

• Inflammation after surgery : normal or complicated surgery, retained lens fragments, RD, endo

• Inflammatory conditions: belpharitis, phlyctenulosis, episcleritis, scleritis

• Trauma , injury

Descemet folds

Haab’s striae

• In primary congenital glaucoma

• Breaks in descemet membrane

• Stretching of the cornea

• Horizontal in CG

• Vertical or oblique : descemet’s tears in birth trauma

Haab’s striae

Vogt striae

• Vertical

• Keratoconus

• Disappear with compression

Vogt striae

Vogt striae

Corneal hydrops

• Acute onset of corneal edema

• Break in descemet membrane

• Advanced keratoconus

• Air or gas into AC may help recovery

• Scars, corneal flattening may occur

Hydrops

Endothelium

• Mono layer of polygonal/hexagonal cells

• 3000/mm

• Decreases with age 0.6% per year

• 500/mm === EDEMA

Endothelium function

• 1- permeability barrier

• 2- pump to maintain dehydration state

• 3-negative hydrostatic pressure

After injuries

• Endothelium cells become fibroblastic

• Synthesize retrocorneal fibrous membrane (RCFM )

• Decrease in VA

• Express type I

RCFM

Dua’s layer

• 15 micro m

• Strong and impervious to air

• Type II air bubbles

• Optical and electron microscopy

• May improve outcomes for patients will have grafts and transplants

CORNEAL INNERVATION

• Long posterior cilliary nerves (branches of V1 the ophthalmic division of cranial nerve V)

• Cold and pain

CORNEAL NERVES

Corneal nerves

CORNEAL NUTRITION

• Oxygen : tear film, eyelid vasculature, AH

• Glucose :

Stroma; AH , carrier mediated transport through the endothelium

Epithelium; tear film and limbal blood vessels

Endothelium ; AH

Corneal nutrition

• Glucose metabolized :

• 1-tricarboxylic acid (TCA) cycle

• 2-anaerobic glycolysis

• 3-hexose monophosphate (HMP) shunt

• Epithelium and endothelium : HMP (35-65)%

• Keratocytes : little glucose via this way cuz they lack 6-phosphogluconate dehydrogenase

• Endothelium : TCA more than epithelium

• Pyruvic acid : TCA ; aerobic

• Lactic acid : anaerobic .. Accumulation ; edema; affect VA (contact lenses)

Emergences

• Chemical burns

• Trauma

• Foreign body

• Corneal erosions

Chemical burns

• Alkali, acid, alcohol .

• Alkali worse ; increased penetrating

• First aid: irrigation

Chemical burns - signs

• Epithelial defect

• Cloudy cornea

• Conj. Hyperaemia

• Caution : if cornea limbus is blanched

Chemical burns

Chemical burns

Chemical burns-after recuvery

Chemical burns-management

• Irrigation

• Topical antibiotics, steroids, citrate and ascorbate ( buffer alkali and inhibit proteinase enzymes, support new collagen from keratocytes)

• vitamins A

Trauma

• Laceration, perforation

• Full thickness , urgent surgery

• SEIDEL TEST

• No drops

• History, ct

Corneal foreign body

Foreign body removing

FB after recovery

Corneal abrasion/erosions/welding flash burn

• Large or small

• Chloramphenicol

• Contact lenses ?

Flashing weld burns

Erosions

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