Corneal specimens that influence clinical decisions Refractive surgery Corneal dystrophies Microbial infections J. Douglas Cameron, MD Chief, Ophthalmic Pathology Division Neuropathology Department Armed Forces Institute of Pathology Washington, DC, 20306
45 year-old man with progressive corneal opacification and extreme pain
Critical Anatomy Tear film Oxygen delivery system Passive resistance to infection Mucous Lysozymes Glycocalyx Active resistance to infection Non-nodal lymphocytes Langerhans cells
Stratified squamous epithelium Conserved radius of curvature Homogeneous cell population Lipid barrier to drug delivery Sensory nerve plexus Able to secrete proteolytic enzymes
The Limbus; junction of cornea and sclera Arteriovenous arcades Lymphatic channels Stem cells; source of corneal epithelial cells
Bowman s membrane Acellular No mechanism for repair
Corneal stroma (matrix) Type I collagen and proteoglycans (nonrenewable_ Resting keratocyte (fibroblast) population Collagenase Gelatinase High tensile strength Limited repair capacity
Descemet s membrane Resistant to proteolysis Not attached to collagen matrix Not attached to endothelium
Corneal endothelium Not vascular endothelium A type of mesothelium Not renewable Can undergo fibrous metaplasia
Refractive Surgery Surgical methods for changing the optic characteristics of the eye Usually performed on the cornea Does not completely eliminate the need for glasses.
Radial Keratotomy Obsolete procedure Free-hand incisions of the cornea 4 to 40 incisions Compromised architectural integrity Unstable radius of curvature-changing vision through the day Wound rupture with minimal trauma
LASIK (Laser assisted in situ keratomileusis) [?LAISK] Thinning a cornea with an excimer [excited dimer] laser Short wave length superficial penetration Surface pain and scarring Superficial flap Apply laser energy directly to corneal matrix
LASIK Short circuits host defenses; alters repair mechanisms Microbial infection Epithelial ingrowth Altered biochemical environment Sands of Sahara syndrome Epithelial ingrowth
Corneal Dystrophy Visible, heritable, biochemical abnormality of the cornea Classification changing with new genetic mapping Bilateral Progressive, variable clinical expression
Keratoconus Progressive weakening of the architectural strength of the cornea (? Proteolysis, matrix metalloproteinases) Progressive change of corneal curvature Risk of rupture of Descemet's membrane [corneal hydrops] Risk of rupture of the fullthickness cornea [corneal perforation]
Keratoconus Risk of perforating Descemet s membrane; corneal hydrops Sudden onset Partially reversible Risk of perforating fullthickness cornea A surgical emergency Risk of bacterial endophthalmitis
Recurrence of Corneal Dystrophies Granular dystrophy Abnormal protein produced by epithelium Graft epithelium is replaced by host epithelium Lattice corneal dystrophy Amyloid (? keratocytes) Primary localized amyloidosis Graft keratocytes replaced by host keratocytes.
Fuchs endothelial dystrophy Progressive dysfunction of the corneal endothelium since birth Clinical expression at age 60 to 80 years Progressive corneal edema (endothelial pump failure ) Treatment Penetrating keratoplasty Deep lamellar endothelial keratoplasty (DLEK)
Endothelial Failure (PKP) Epithelium Subepithelial bullae Intraepithelial basement membrane formation Descemet s membrane Generalized thickening Localized thickening (guttata) Loss of endothelial cell density
Endothelial Failure (DLEK) Anterior cornea remains intact Deep lamellar keratoplasty Posterior corneal stroma replaced Descemet s membrane replaced Descemet s membrane Excrescences of Descemet s membrane En face sections of guttata Few if any endothelial cells identified.
Microbial Infection of the Cornea Host defenses Passive Tear film Mucous Glycocalyx Lipid epithelial barrier Vulnerable posterior to corneal epithelium Limited density and activity of keratocytes Langerhans cells Non-nodal lymphocytes
Pseudomonas Keratitis Contact lens overwear Oxygen deprivation Loss of passive proteins Adhesion of pseudomonas organisms Production of collagenase By the organism By PMN Progressive corneal proteolysis ( melting )
Crystalline Keratopathy Prolonged treatment with topical steroids Corneal surgery allergic keratitis Creation of localized immune deficiency Proliferation of bacteria in colonies Separated by stromal lamellae, appearance of crystals S. epidermidis
Herpes Simplex Keratitis (HSV-1) Primary cutaneous infection Residual organism in ganglia (dormant) Reactivation and migration to cornea epithelium via sensory axons
Epithelial Herpes Simplex Keratitis (Dendritic keratitis) Intraepithelial proliferation Loss of desmosomes (vesicles) Cell death; linear ulceration dendritic figures Spontaneous resolution Mechanical removal Antivirals
Stromal Herpes Simplex Keratitis (Discoid keratitis, Herpes metaherpetica) Recurrence at unpredictable rate and interval Change in antigen status of stromal matrix Giant cell reaction to membranes Proteolysis of matrix Corneal perforation Tissue adhesives Penetrating keratoplasty
Acanthamoeba Keratitis Acanthamoeba Protozoan commonly found in water Forms Trophozoite Encysted Organism neurotrophic Presents with extreme pain Progressive ring opacity followed by ulceration
Acanthamoeba Corneal Risk Factors Contact lens overwear Oxygen deprivation Microrupture of corneal epithelium Large areas of epithelial cell loss (corneal abrasion) Exposure to high organism concentration in hot tubs Exposure to stagnant water (Mississippi River Flood 1993)
Acanthamoeba Infection Crosses lipid barrier Stimulation of corneal nerves Production of proteases and migration through the corneal matrix Able to penetrate to and through Descemet s membrane Not associated with endophthalmitis Both cornea and conjunctiva are infected
Acanthamoeba Organism Clinical confocal microscopy Trophozoites not visible Double wall of encysted organism Light microscopy Trophozoites not visible Any stain Thick walled cysts Usually no inflammatory infiltrate Treatment: unsatisfactory
Cornea: Review of Important Points (1): The corneal epithelium is the principle dynamic element in corneal pathology Protects the structurally essential nature of the collagen matrix from infection Able to contribute to structural damage by producing proteases Biochemical abnormalities of the epithelium may lead to progressive corneal opacity (granular dystrophy)
Cornea: Review of Important Points (2): Refractive surgery potentially compromises the function of the cornea Loss of architectural strength (radial keratotomy [RK]) Corneal scarring (photorefractive keratectomy [PRK]} Circumvent corneal defenses (laser-assisted in situ keratomileusis [LASIK])
Cornea: Review of Important Points (3): Corneal dystrophies recur following penetrating keratoplasty The biochemical defect is in the cells of the host The donor cells of corneal transplantation are replaced by host cells
Cornea: Review of Important Points (4): Corneal infections are often associated with proteolysis leading to corneal ulceration and possible corneal perforation Pseudomonas keratitis Herpes simplex keratitis Acanthamoeba keratitis
Corneal specimens that influence clinical decisions Refractive surgery Corneal dystrophies Microbial infections J. Douglas Cameron, MD Chief, Ophthalmic Pathology Division Neuropathology Department Armed Forces Institute of Pathology Washington, DC, 20306
USCAP 2010: AAOP Society Companion Meeting 20MAR10 1) Corneal specimens that influence clinical decisions: refractive surgery, corneal dystrophy, microbial infections. 2) Case presentation: 45 year-old man with progressive corneal opacity and extreme pain a) Commonly used clinical terms i) Corneal infiltrate = corneal opacity (1) Most likely due to edema of the cornea and loss of transparency (2) Not associated with a cellular inflammatory infiltrate ii) Corneal melting = loss of corneal tissue (1) Most likely due to proteolysis (2) Not due to a change in temperature (3) Change in temperature would cause shrinking and opacification due to denaturation of collagen 3) Critical anatomy a) Tear film: Components produced by the conjunctiva and eyelid i) Oxygen delivery system ii) Passive resistance to microbial infection (1) Mucous (2) Lysozymes (3) Glycocalyx iii) Active resistance to microbial infection (1) Non-nodal lymphocytes (2) Langerhans cells b) Stratified squamous epithelium i) Conserved radius of curvature ii) Homogeneous cell population (no goblet cells) iii) Lipid barrier to drug delivery iv) Sensory nerve plexus v) Able to secrete proteolytic enzymes c) Limbus i) Arteriovenous arcades ii) Lymphatic channels iii) Stem cells, source of epithelial cells d) Bowman s membrane i) Acellular collagen ii) No mechanism of repair e) Stroma i) Type I collagen and proteoglycans (non-renewable) ii) Resting keratocyte (fibroblast) population iii) Keratocytes able to produce collagenase and gelatinase iv) High tensile strength v) Limited repair capacity 1 P a g e
USCAP 2010: AAOP Society Companion Meeting 20MAR10 f) Descemet s membrane i) Resistant to proteolysis ii) Not attached to collagen matrix iii) Not attached to endothelium g) Endothelium i) Not vascular endothelium ii) A type of mesothelium iii) Not renewable iv) Can undergo fibrous metaplasia 4) Refractive surgery a) Surgical methods for changing the optical characteristics of the eye i) Usually performed on the cornea ii) Does not completely eliminate need for glasses b) Refractive keratotomy- compromise of architectural strength i) Obsolete surgical procedure (1) Free-hand incisions of the cornea (2) 4 to 40 wounds (3) Compromised architectural integrity of the cornea ii) Unstable radius of curvature- variable refractive error through the day iii) Wound rupture- with minimal trauma c) LASIK (Laser-assisted in situ keratomileusis)[mileusis: Greek carving] i) Currently used surgical procedure (1) Thinning of the cornea with a excimer (excited dimer) laser (a) Short wavelength (193 nm) (b) Superficial penetration (2) Surface application; post-operative pain and corneal scarring (3) Superficial stromal application; access via a surgically created flap ii) Short circuits host defenses, alters repair mechanisms (1) Microbial infection- destroys host tissue, no repair mechanism (2) Epithelial ingrowth - creates correctable opacity iii) Altered biochemical environment- favors inflammation, protein deposits (1) Sands of Sahara syndrome (2) Acceleration of opacification in granular dystrophy 5) Corneal dystrophy a) A visible, heritable, biochemical abnormality of the cornea i) Classification changing with new genetic mapping (5q31) ii) Bilateral, may be symmetrical iii) Progressive, but with variable clinical expression b) Keratoconus- most common, generally non-heritable i) Weakening of corneal architecture-?proteolysis [matrix metalloproteinase] ii) Progressive change of corneal curvature-non-homogeneous 2 P a g e
USCAP 2010: AAOP Society Companion Meeting 20MAR10 iii) Risk of perforation of Descemet s membrane-corneal hydrops (1) Sudden onset (2) Partially reversible iv) Risk of perforation of full-thickness cornea (1) A surgical emergency (2) Risk of bacterial endophthalmitis c) Recurrence of stromal dystrophies i) Granular corneal dystrophy- (1) deposition of abnormal protein produced by host epithelium (2) donor epithelium replaced by host epithelium ii) Lattice corneal dystrophy- deposition of amyloid (primary localized amyloidosis) d) Fuchs endothelial dystrophy i) Progressive dysfunction of corneal endothelium since birth (1) Clinical expression at age 60 to 80 years (2) Progressive corneal edema (endothelial pump failure ) ii) Treatment of Fuchs dystrophy (1) Penetrating keratoplasty (PKP) (a) Epithelium (i) Subepithelial bullae (ii) Intraepithelial basement membrane (b) Descemet s membrane (i) Generalized and localized thickening (guttata) (ii) Loss of endothelial cell density (2) Deep lamellar endothelial keratoplasty (DLEK) (a) Excrescences of Descemet s membrane (b) Few if any endothelial cells 6) Microbial infection a) Host defenses i) Passive (1) Tear film (2) Mucous (3) Glycocalyx ii) Lipid epithelial barrier (1) Vulnerable posterior to the epithelium (2) Limited density and reactivity of keratocytes b) Pseudomonas keratitis i) Contact lens overwear; oxygen deprivation ii) Adhesion of pseudomonas organisms iii) Production of collagenase (1) Organism itself (2) Polymorphonuclear leukocytes (PMN) 3 P a g e
USCAP 2010: AAOP Society Companion Meeting 20MAR10 iv) Progressive corneal matrix proteolysis c) Crystalline keratopathy i) Prolonged treatment with topical steroid (1) Usually following corneal surgery (2) Resistant corneal allergy ii) Creation of local immune deficiency iii) Proliferation of bacterial organism between collagen lamellae ( crystalline serrated edges) iv) Intrastromal colonies of bacteria (Staphlococcus epidermidis) d) Herpes simplex keratitis (Herpes simplex type I) i) Primary cutaneous infection ii) Residual organisms in ganglia, dormant iii) Reactivation and migration to corneal epithelium, sensory axons iv) Intraepithelial proliferation (1) Loss of desmosomes: vesicles (2) Cell death: linear ulceration, dendritic figures v) Spontaneous resolution vi) Recurrence at unpredictable rate and interval vii) Change in antigen status of stromal matrix; stimulates inflammation viii) Proteolytic destruction of stroma ix) Corneal perforation x) Treatment (1) Tissue adhesives (2) Penetrating keratoplasty e) Acanthamoeba keratitis i) Protozoan commonly present in water supplies ii) Forms (1) Trophozoite; mobile (not seen by light microscopy) (2) Encysted; unfavorable environment iii) Presents with extreme pain (1) Organism neurotrophic (2) Progressive ring opacity/ulceration of cornea iv) Infection (1) Cornea compromised by (a) Contact lens overwear (i) Oxygen deprivation (ii) Microrupture of epithelium (iii) Large areas of epithelial cell loss (abrasion) (b) Exposure to high organism content in hot tubs (c) Exposure to stagnant water; e.g. Mississippi River flood 1993 (2) Neural trophism; associated with extreme pain (3) Lipid barrier lost 4 P a g e
USCAP 2010: AAOP Society Companion Meeting 20MAR10 (a) Trophozoite produces protease (b) Migrates through full thickness of cornea (c) Does not cause endophthalmitis v) Identification of organism (1) Confocal microscopy; method of clinical identification (2) Light microscopy (a) Stains with all routine stains (b) May not be accompanied by an inflammatory reaction. 7) Summary of Important Points a) The corneal epithelium is the principle dynamic element in corneal pathology i) Protects the structurally essential nature of the collagen matrix from infection ii) Able to contribute to structural damage by producing proteases iii) Biochemical abnormalities of the epithelium may lead to progressive corneal opacity (granular dystrophy) b) Refractive surgery potentially compromises the function of the cornea i) Loss of architectural strength (radial keratotomy [RK]) ii) Corneal scarring (photorefractive keratectomy [PRK]} iii) Circumvent corneal defenses (laser-assisted in situ keratomileusis [LASIK]) c) Corneal dystrophies recur following penetrating keratoplasty i) The biochemical defect is in the cells of the host ii) The donor cells of corneal transplantation are replaced by host cells d) Corneal infections are often associated with proteolysis leading to corneal ulceration and possible corneal perforation i) Pseudomonas keratitis ii) Herpes simplex keratitis iii) Acanthamoeba keratitis 5 P a g e