Keratopathy

BASICS


DESCRIPTION


A condition in which corneal endothelial failure leads to chronic edema resulting in the formation of epithelial bullae or vesicles. These bullae often rupture causing episodes of severe pain.


EPIDEMIOLOGY


Incidence


The postcataract surgery reported incidence of bullous keratopathy (BK) ranges from 0.06% to 2%. It was 0.06% with posterior chamber implants, 1.2% with anterior chamber implants, and 1.5% with iris fixated lens after 1 year. The incidence increases in the setting of vitreous loss, iris fixated or closed loop anterior chamber lens, and in patients with underlying endothelial dysfunction. However, since the advent of viscoelastic substances to protect the endothelium and the improvement in lens design the incidence has been decreasing.


RISK FACTORS


• Complicated cataract surgery with vitreous loss


• Fuchs endothelial dystrophy (FED)


GENERAL PREVENTION


• Use of retentive-dispersive viscoelastic during anterior segment procedures to protect the endothelium especially when operating in eyes with endothelial dystrophies


• Minimizing phaco power and time during cataract surgery


• Adequate control of postoperative inflammation and intraocular pressure


PATHOPHYSIOLOGY


• When some of the endothelial cells are damaged or lost the remaining cells rearrange to cover the area occupied by the damaged cells. This causes the cells to enlarge (polymegathism) and assume irregular shapes (pleomorphism). With increasing loss, the endothelial pump eventually fails to deturgesce the cornea and the stroma starts to swell. In FED new basement membrane (Descemet’s) is laid down by dystrophic endothelial cells. This is thickened, wavy, and differs in density and surface characteristics from the original Descemet’s resulting in a silver beaten appearance. Eventually fluid accumulates between the basal epithelial cells clinically manifesting as epithelial edema. Fluid vesicles may coalesce to form epithelial and subepithelial bullae stretching the nerve endings causing pain, which can be severe when the bullae rupture exposing the subepithelial nerve plexus.


• Edema also causes separation of stromal lamellae. Visual loss is more due to epithelial rather than stromal edema. At night the cornea becomes more edematous due to lack of evaporative loss of fluid and poor endothelial cell metabolism. This results in the classic symptom of misty vision on waking, which clears with the passage of time. The time taken for improvement is related to the functional capacity of the residual endothelium.


ETIOLOGY


• Corneal endothelial dystrophies such as FED and posterior polymorphous dystrophy


• Glaucoma: End stage of acute primary and secondary glaucoma (absolute glaucoma)


• Chronic keratouveitis


• Corneal graft failure:


– Primary endothelial failure


– Endothelial rejection


– Endothelial cell loss over time


– Detached endothelial graft


• Endothelial trauma:


– Latrogenic: Complicated cataract surgery, glaucoma filtering surgery, anterior chamber phakic and pseudophakic implants, irrigating solution toxicity, instrument-related injury, Descemet’s membrane detachment or tear


Pediatric Considerations


• Birth injury to the cornea during forceps delivery can cause loss of endothelial cells with corneal edema at birth or at any time later on.


• Congenital hereditary endothelial dystrophy (CHED)


• Congenital glaucoma


DIAGNOSIS


HISTORY


• Reduced vision and mistiness typically in the morning which clears after a few hours. The duration to clearing increases as the endothelial failure proceeds eventually leading to permanent visual loss.


• Ocular surface irritation or gritty sensation associated with corneal epithelial irregularity


• Repeated episodes of severe pain photophobia and lacrimation


PHYSICAL EXAM


• Externally, the lids may be edematous with a narrow palpebral aperture. The cornea appears dull and lusterless.


• Slit lamp examination:


– Corneal epithelium – superficial punctate keratitis and surface irregularity due to intact and ruptured epithelial bullae. On fluorescein staining the intact vesicles present as negatively staining dark dots and the ruptured bullae as green dots when visualized with cobalt blue light.


– Stromal edema – manifests as a sectorial or generalized increase in corneal thickness and intrastromal clear fluid clefts.


– Superficial or deep corneal vessels may be seen in longstanding cases.


– Irregularity of Descemet’s membrane is seen as folds or corrugations.


• Features of the underlying disease may be seen such as silver beaten appearance and guttata in FED; pigment dusting and old keratic precipitates in chronic uveitis and iris atrophy or a dilated fixed pupil of absolute glaucoma.


• The intraocular pressure (IOP) may be elevated, normal or low. In the presence of excessive corneal edema, IOP measured by Goldman’s applanation tonometer or the Tonopen can be misleading and “finger palpation” of the eye ball may be required to assess IOP.


DIAGNOSTIC TESTS & INTERPRETATION


Imaging


• Specular microscopy will demonstrate the reduction of endothelial count with pleomorphism and polymegathism.


• In vivo confocal microscopy: Shows bullae within the basal layers of the epithelium, diffuse bright reflections at Bowman’s zone with the absence of nerves, diffuse increased light reflections due to stromal edema alternating with dark bands representing that lacunae can be seen primarily in the anterior stroma. These findings are from BK in FED.


Diagnostic Procedures/Other


Pachymetry: Corneal thickness >590 μm in a pseudophakic eye may be associated with irreversible corneal edema


Pathological Findings


• Epithelium: Intracellular epithelial edema with formation of vesicles.


– Elongated fibrocyte like cells above Bowman’s zone


– Attrition of sub-basal nerve plexus


• Stroma: Thickening, collagen degradation, and keratocyte depletion.


– Aberrant stromal nerves


– Superficial and deep vascularization at times


• Endothelium: Cell loss and features of associated of FED if present – guttata and Descemet’s membrane thickening.


DIFFERENTIAL DIAGNOSIS


• Certain acute conditions may present with features resembling BK:


– Acute hydrops in keratoconus


– Endothelial detachment or tear secondary to trauma or surgery.


– Acute primary or secondary glaucoma


– Disciform keratitis


TREATMENT


MEDICATION


First Line


• Hypertonic sodium chloride (5%) drops or ointment 2–4 times especially in the first half of the day


• Warm air (from a hair dryer) blown across the open eye(s)


• Reduction of intraocular pressure with medication


Second Line


Extended wear hydrophilic contact lens can reduce the pain and may improve the vision slightly by reducing surface irregularities. However, proper lens fitting is an issue as a loose lens can cause further damage to the epithelium and a tight lens can cause hypoxia leading to further edema and anterior uveitis (toxic lens syndrome).


SURGERY/OTHER PROCEDURES


• The definitive treatment for BK is an endothelial or penetrating keratoplasty (1)[B]. This should be considered in all eyes with visual potential


• In eyes with no visual potential or when graft material is not readily available and relief from symptoms is warranted, one or a combination of the following can be tried:


– Anterior stromal puncture (ASP): Over areas of bullae induces subepithelial scarring which allows the epithelium to adhere securely. It leaves behind small scars which can interfere with vision.


– Phototherapeutic keratectomy (PTK) with the excimer laser (2,3)[B]


– Amniotic membrane transplant (AMT): The loose bullous epithelium is removed and a circular disk of amnion, 9–11 mm in diameter, is glued or sutured to the corneal surface. New epithelium from the limbus migrates on the amnion (graft), which becomes incorporated into the anterior corneal stroma (2)[B].


– Historically, conjunctival flaps have been proved to be useful in treating several ocular surface epithelial conditions including BK.


• Retrobulbar alcohol, enucleation, or evisceration: In patients with no visual potential as in end-stage rubeotic glaucoma, these measures may be considered to relieve pain and other symptoms.


ONGOING CARE


COMPLICATIONS


• Corneal ulceration


• Secondary bacterial infection


• Corneal hypoesthesia


• Scarring and vascularization



REFERENCES


1. Dapena I, Ham L, Melles GR. Endothelial keratoplasty: DSEK/DSAEK or DMEK – the thinner the better? Curr Opin Ophthalmol 2009;20:299–307.


2. Said DG, Nubile M, Alomar T, et al. Histologic features of transplanted amniotic membrane: implications for corneal wound healing. Ophthalmology 2009;116:1287–1295.


3. Vyas S, Rathi V. Combined phototherapeutic keratectomy and amniotic membrane grafts for symptomatic bullous keratopathy. Cornea 2009;28:1028–1031.

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Nov 9, 2016 | Posted by in OPHTHALMOLOGY | Comments Off on Keratopathy

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