CORNEAL EDEMA

Dr. Kishore Khade

corneaThickness of the cornea in the centre is 0.52mmWhile at periphery is 0.67mm.Epithelium is 50-90μmthickBM 8-14μmStroma 0.5mm thick &constitute most of cornea.Dm is 10-12μmEndothelium 18-20μmwith 2400-3000cells/mm2

CORNEA

• To perform its primary function of refraction of light the cornea must be relatively thin & dehydrated with smooth anterior surface.

• In normal cornea, optical transparency is directly related to the state of hydration of the tissue.

• If cornea swells, it increases its thickness , its surface becomes irregular both changes downgrades its optic properties.

CORNEAL HYDRATION

• Cornea is relatively in dehydrated state for its transperancy.

• Water content of cornea is 80% which is highest of any connective tissue in body.

• If hydration becomes above 80% its central thickness increases & transperancy reduces.

• Cornea swells only in the direction of its thickness therefore, corneal thickness & hydration are linearly related.

CORNEAL HYDRATION

• Hydration is maintained by:-A}Factors draw water in to the cornea:-1)Swelling pressure of stromal matrix ( GAGs).2)Intraocular pressure.B} factors which prevent flow of water into the

cornea:-1)Mechanical barriers.2) Na+-K+ active pump of endothelium.

Hydration

stromal pressure

barrier

Na-k pump

IOP

Evaporation

{A} Stromal swelling pressure

• Pressure exerted by corneal stroma mainly GAGs is stromal pressure (SP).

• Sp is 60 mmhg, is a keystone of corneal biophysics.

• Anionic charges on GAGs molecule expands the tissue, draws fluid with equal but negative pressure called imbibation pressure.

Contd.....

• In vivo imbibation pressure is reduced by IOP, so IP= IOP – SP

• IP= 17- 60, IP = -43mmhg.• In vitro IP = SP• Sp generates interfibrillar tension may be

biophysical mechanism to maintain fibrils normal arrangement.

• Cornea has an swelling pressure, which is maintained by endothelial metabolic pump

{B} Barrier mechanism

• Both epithelium & endothelium acts as a barrier for excessive flow of water & diffusion of electrolytes into stroma.

• As compare to endothelium, epithelium offers twice resistance.

• Endothelium allows diffusion of small solutes like NaCl & urea, while epithelium produces hypertonicity of the solution bathing the cornea.

Barrier mechanism

• Endothelial cells are attached to each other by discontinuous tight junctions i.e maculae occludentes.

• Endothelial barrier function is mainly calcium dependent.

• A calcium free solution will reduce the barrier function & cause stromal edema.

{C} Na+- K+ pump

• Present in endothelium, several fold more active than its epithelium counterparts.

• Activated ATPase mediates active extrusion of Na from stroma to the aqueous.

• It causes diffusion gradient for water.• Na conc in aqueous is more compare to

stroma, which draws water from the stroma.

Sodium activity across endothelium

Na 134meq/l

stroma

Aqueous humour

Na-K pump

• Bicarbonate dependent ATPase has also been reported in the endothelial cells.

• Depletion of bicarbonates induces swelling.• Carbonic anhydrase enzyme has also been

implicated in fluid transport, CAE inhibitors decreases flow of fluid from stroma to aqueous ( found only in endothelium).

H2O

Wounded cornea

Aqueous humourNA

149.8Meq/l

142.3meq/l

{D} EVAPORATION

• Evaporation of water from precorneal tearfilm increases its osmolarity relative to cornea.

• Hypertonicity of tear film could draw water from cornea.

• However this water loss is readily replaced by aqueous, it results in only a little corneal dehydration.

{E} Intra ocular pressure

• Most of early writers assume corneal edema is due to mechanical forcing of aqueous into the cornea.

• But experimental event found out that to achieve this,effect pressure required is 200mmHg.

• More likely explanation is that the determining factor is endothelial damage.

EDEMA

• Word edema is derived from greek word oídēma 1400bc , means "swelling“.

• Formerly known as dropsy or hydropsy which means accumulation of excessive fluid.

• Etiology of corneal edema: SECONDARY CAUSES PRIMARY CAUSES

CORNEAL EDEMA

[I] Mechanical trauma

1) Blunt non penetrating injury causes edema by injury to endothelium, mostly it is reversible.

2) Perforating injuries cause direct damage to the cornea, intra ocular FB in AC can cause edema mainly in inferior periphery where FB mainly settles.

3) Forceps delivery cause pressure on globe, may cause edema due to DM tear.

DESCEMET’s TEAR

Mechanical trauma

4) Noxious chemicals mainly alkalies which penetrates cornea cause endothelium damage.

5)Intraocular sx can cause acute endothelial loss most notably in superior & central cornea.

6) BROWN McLEAN syndrome: peripheral edema with brown black discolouration of underlying endothelium seen in ICCE, ECCE,CCPE, pars plana vitrectomy.

Brown Mclean Syndrome

Mechanical trauma

7)Cold induced reversible corneal edema has been reported in trigeminal nerve dysfunction.

8) Certain systemic medications like amantadine & cefaclor can cause edema.

9) Lasers used for iridotomy can cause focal corneal edema.

10) High altitude corneal decompensation has been reported causing hypoxia induced corneal edema.

[ II ] GLAUCOMA

• Acute rise in IOP which exceeds swelling pressure of stroma causes epithelial edema.

• Hypoxic Endothelial decompensation occurs due to diminished aqueous flow.

• When corneal endothelium is compromised, edema occurs even @ lower level of IOP.

• Chronic elevation of IOP permanently damages the endothelium.

• Irreversible corneal edema may occur.

GLAUCOMA

GLAUCOMA

• Penetrating keratoplasty is the only treatment of choice in irreversible corneal edema, but IOP must be first controlled.

• In hypotony, AC is shallow or flat. Mechanical trauma by cornea iris or iris corneal touch leads to edema.

• Normal human volunteers experiment study can be explained by hypotony induced edema,(corneal edema occurs in tightly patched eye).

[ III ] Contact lenses

• Most common cause of corneal edema is prolonged use of contact lens.

• It is mainly due to insufficient supply of oxygen to epithelium.

• Edema presents as microcystic epithelial edema near the center of resting position of the lens.

• It is best seen with scattered illumination of slit lamp referred as Sattler’s veil.

Contd....

• If allowed to continue, it‘ll cause stromal edema, descemet’s membrane folds.

• Edema easily clears if contact lens is removed.• Even altering the fit of contact lens is also

successful in reducing edema if it provides sufficient oxygen to the epithelium.

• The response & recovery from edema is independent of age.

[IV] ICE syndrome

• Iridocorneal endothelial syndrome is basically spectrum of disorders that includes

A) Progressive iris atrophy. B) Chandler’s syndrome. C) Iris nevus syndrome ( Cogan Reese)

Chandler syndrome

• Corneal endothelial abnormalities (hammered silver).

• Presents with blurred vision & haloes due to corneal edema

• Corectopia may be mild to moderate• Glaucoma may be less severe & but at

presentation IOP may be normal.• Chandler syndrome have more severe edema.

Cogan Resse syndrome

Characterised by diffuse naevus Which coversiris or iris nodule.Iris atrophy may be absent in 50% of patients, but corectopia & GlaucomaMay be severe.

Iris atrophyEssential iris atrophy characterised by distortionOf pupil, peripheral anterior synechie & iris atrophyWith full thickness holes.Glaucoma commonly present in the involved eye.Unilateral occurs in 4th & 5th

Decades of life in caucasians

[V] Essential corneal edema

• Idiopathic , episodic & often cyclic may be unilateral.

• Presents with typical features of corneal edema like fb sensation,diminished vision & haloes which persists for months then disappears.

• Recurrent erosions on cornea may be noted.• It may progress to the formation of bullae with

ciliary injection & urgent symptoms of pain & photophobia.

Essential corneal edema

• Pupils may be semidilated & sluggishly reacting to light.

• If secondary infection does not set up attack passes of & the condition eventually cleans up.

• Some of these cases may be early presentation of dystrophic changes like Fuch’s dystrophy.

[VI] Metabolic disorders

• Some vague concepts suggested by corneal edema occuring in some metabolic conditions like myxedema.

• It has also seen in hypercholesterolemia.• In malaria mainly in patients taking mepacrine

for its treatment, in this condition edema is limited to basal layer of epithelium & superficial layer of stroma.

PRIMARY CAUSES

A) Primary endothelial dystrophies: dystrophies involving endothelium & descemet’s membrane causes symmetrical marked stromal edema which is gradually progressive over a period of years.

B) Primary endothelial dystrophy which develop later in life are fuch’s dystrophy.

Primary Endothelial Dystrophy

• Congenital hereditary endothelial dystrophy: characterised by diffuse edema at birth or soon thereafter, without significant anterior segment abnormalities.

• Posterior polymorphous dystrophy: B/L vesicular or linear lesions at the level of descemet’s membrane & endothelium is present, it presents with congenital corneal edema.

FUCH’s dytrophyAD pattern of inheritance,Earliest changes are limitedTo posterior cornea &presents with central B/Lasymmetrical corneal Guttata.In fuch’s dystrophyendothelial cells transforminto fibroblastLike cells capable ofsecreting collagen fibrils.Contribute to BM thickening.

FUCH’s dytrophy

• Progressive endothelial decompensation leads to stromal & epithelial edema.

• Fluid in the stroma permeates the epitelial layer causes microcystic epithelial edema.

• Individual epithelial cells burst, intercellular edema occurs & typical blisters or bullae formed.

• These changes are confined to centre of cornea initially.

Bullous keratopathy

It represents the terminal stage of severe or Prolonged epithelial edema.In the affected area the epithelium is steamyIrregular & on its surface one or more large bullaeAppears, raised in the form of blebs.

Bullous keratopathy

• After 2-3 days the bullae rupture only to reappear, the cycle associated with considerable irritation & pain.

• Treatment is extremely difficult; retrobulbar injection of alcohol, removal of endothelium by scraping, cauterisation of cornea by tincture iodine, trichloro-acetic acid.

• Bandage contact lens to relieve pain.• Lamellar grafting, if measures of therapy fails & if

recurrence persists treatment is enucleation.

Manifestations of edema

Depends upon cause & degree of the condition.

Mild discomfort in conditions like fuch’s dystrophy.

Severe neuralgic pain is seen in bullous keratopathy.

Colour haloes. Severe visual loss.

Visual acuity

• Small amount of epithelial edema can result in substantial reduction in visual acuity.

• Although 70% stromal edema is compatible with normal visual acuity.

• Decreased acuity is more severe in early morning.

• IOP, iritis glaucoma & optic nerve changes may contribute to reduced acuity.

Pain & discomfort

• As edema increases epithelium is detached from basement membrane to form bullae.

• This rupture of bullae causes severe pain, photophobia, epiphora & narrowing of palpebral fissure.

• Photophobia is due to light scattering in the edematous cornea.

• Coloured haloes.

Coloured haloes

Evaluation of corneal morphology

Slit lamp examination.Specular biomicroscopy.Pachymetry.Optical coherence tomography.Scheimpflug camera.Orbscan.

Slit lamp examinationSlit lamp examination revealscornea guttata, stromal density,Descemet’s membrane folds.Bullae are easily observed by slitlamp. In case of chronic Corneal edema neovascularization,pannus formation or dystrophiesare visible. In case of stromal edema thickness exceeds 0.6mm.

Specular biomicroscopy

Measures cell density.Normally endothelialcell count is 3000 --2000 cells/mm2.Cell count less <1000poorly tolerate ocularSurgery.Used in assesing cellsin Corneal grafting,LASIK, dystrophies corneal edema.

Pachymetry

Pachymetry• Corneal pachymetry;- is the process of measuring

the thickness of the cornea. It can be done using contact methods, such as ultrasound and confocal microscopy (CONFOSCAN), or noncontact methods such as optical biometry with a single Scheimpflug camera (such as SIRIUS or PENTACAM), or Optical Coherence Tomography (OCT) and online Optical Coherence Pachymetry (OCP, such as ORBSCAN).

Optical coherence tomographyOptical coherence tomographyis an establishedmedical imaging technique. It is widely used to obtain high-resolution imagesof the retina and theanterior segment of the eye.Corneal thickness can also be measured.

Scheimpflug camera.Pentacam trade name,Is a diagnostic unit ableTo perform five functions;

Image of AS.3D anterior chamber analyzer.pachymetry.Corneal topography.Cataract analyzer.

ORBSCAN IIThe Orbscan II topographeranalyses the physicalshape / contours of cornea and allows the surgeon to decide if it has suitableshape, is healthy and thickenough for treatment.It is the onlytopographer currently availablethat measures the shape of both the front and back surface of theentire cornea (other systemsonly measure the front surface) and can therefore provide acomplete picture of the thickness of cornea

management

• In all cases of corneal edema if documented IOP is high, its control with topical anti glaucoma drugs or systemic CAE inhibitors are given.

• Even in moderately elevated IOP patients control may significantly reduces epithelial edema.

• If IOP remains elevated despite maximum tolerated medical therapy surgical intervention must be considered.

• Cyclocryotherapy/ trabeculectomy are considered.

Local therapy

• Early morning reduced vision can be improved by exposing eyes to warm air eg:hair dryer.

• Topical application of hyperosmotic agents like 5%NaCl solution or ointment can reduce edema to an little extend.

• If inflammation is a contributory cause of corneal edema topical application steroids may be very helpful.

Local therapy

• If the etiology of edema is not apperent 10 days course of topical steroids can serve as diagnostic as well as therapeutic purpose.

• In patients with early corneal decompensation & mild edema a careful refraction may improve vision.

• Therapeutic hydrophilic contact lens can be used .

Local therapy

• Thin hydrophilic lens fitted flat on cornea allow maximum contact between lens & irregular cornea.

• Application of radiodiathermy or other forms of electrocautery on bowman’s membrane.

• This produces adhesion between stroma & basal layer of epithelium preventing formation of bullae.

management

• Gundersen conjunctival flap with or without lamellar keratectomy can be performed to relieve pain.

• Retrobulbar alcohol injection or tarsorrhaphy also may relieve pain.

• In painful blind eye or in absolute glaucoma enucleation may represent the optimal procedure.

Penetrating keratoplasty

• If visual recovery exists penetrating keratoplasty is performed before cauterisation of BM or conjuntival flap procedure.

• In case of multiple graft failure & corneal thickness exceeds 1.5mm, the use of keratoprosthesis has been advocated.

• Keraoprosthesis is considered as an last ditch effort for visual rehabilitation.

keratoplasty

Keratoprosthesis

Keratoprosthesis causes high rate of failure & Complications.In case of bilateral corneal edema Keratoprosthesis in worst eye & keratoplasty infellow is Performed.

Keratoprosthesis

THANKYOU