Corneal Surgeries

1) Tear film of the cornea

Provides requisite smooth optical surface for eye; subdivided into 3 layers: inner mucous (goblet cells), middle aqueous (main lacrimal gland) & accessory lacrimal gland of Krause & Wolfring; outermost oil (meibomian glands & gland of Zeis)

2) corneal epithelium

• most anterior layer

• 5 - 7 cell layers thick

• Basal layer

• Contains sensory nerve endings

Bowman’s Layer of cornea

• lies between basement membrane of corneal epithelium & stroma

• Acellular condensation of collagen type 1 & type 2

• Purpose regarding maintenance of normal corneal function remains uncertain

Corneal Stroma (middle layer)

• 90% of total corneal thickness

• Comprised of regularly order layers of collagen, proteoglycans, keratocytes

• Non considered a uniform matrix (anterior 3 more keratocytes than posterior)

Descemet membrane

• basement membrane of endothelium

• Peripheral edge visible clinically w/ gonioscopy (Schwalbe’s line)

• Most resilient of all corneal layers in conjugation w/ endothelium

Endothelium

• most posterior layer

• Simple cuboidal epithelium

• Limited mitotic division

• Discontinuous tight junctions (flux of aqueous humor from AC)

• Heavily associated w/ Na-K, ATPase pumps (involved in fluid removal from corneal stroma)

Keratoplasty (corneal transplant/ corneal graft)

Operation to remove all or part of a damaged cornea & replace it w/ healthy donor tissue

Optical grafting

Keratoconus, scarring, corneal dystrophies, pseudophakic bulbous keratopathy, corneal degenerations

Tectonic grafting

Restore or preserve corneal integrity in eyes w/ severe structural changes such as thinning

Therapeutic grafting

Removal of infected corneal tissue in eyes unresponsive to antimicrobial therapy

Penetrating Keratoplasty (PK)

Surgical procedure involving complete replacement of the host cornea w/ a full thickness donor corneal graft

Superficial Anterior Lamellar Keratoplasty (SALK)

Partial thickness excision of corneal epithelium through anterior portion of stroma (untouched layers: deep stroma, descemet, endothelium)

Deep Anterior Lamellar Keratoplasty (DALK)

Partial thickness excision of corneal epithelium through the stroma (untouched layers; Descemet & endothelium)

Endothelial Keratoplasty

Partial thickness removal of Descemet & endothelium following corneoscleral or corneal incision; Descemet Stripping Endothelial Keratoplasty (DSEK) & Descemet Membrane Endothelial Keratoplasty (DMEK)

Most common indication for endothelial Keratoplasty

Fuchs endothelial corneal dystrophy

DSEK

• layers transplanted include: small amount of posterior stromal thickness, Descemet, Endothelium

• Indications include: Fuchs Endothelial Dystrophy, Bullous keratopathy, Failed previous graft

DMEK

• layers transplanted include: Descemet’s Membrane, Endothelium

• Indications include: Fuchs Endothelial Dystrophy, Bullous keratopathy, Failed previous graft, posterior polymorphous membrane dystrophy, congenital hereditary endothelial dystrophy, iridocorneal endothelial syndrome

Superficial Keratectomy (SK)

Manual dissection of superficial corneal layers w/ out tissue replacement; layers impacted are dependent on condition (untouched layers are Descemet & Endothelium)

Phototherapeutic Keratectomy (PTK)

Procedure involving an excimer laser that is applied to superficial corneal layers (untouched layers include Descemet & endothelium)

Superficial Keratectomy is completed w/

• surgical blade> for removal

• Diamond burr> smoothing/ polishing, helps increase strength of hemidesmosomes

Excimer laser for Phototherapeutic Keratectomy (PTK) is utilized to

Remove tissue (damaged/ irregular) & smooth corneal surface