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Excerpt from Keratopathy, Pseudophakic BullousSynonyms, Key Words, and Related Terms: corneal edema, pseudophakic bullous keratopathy, PBK, aphakic bullous keratopathy, ABK, cataracts, cataract extraction, cataract surgery, intraocular surgery Please click here to view the full topic text: Keratopathy, Pseudophakic BullousBackground: Corneal edema occurs for many reasons, but it often is seen as a sequela of intraocular surgery. Corneal edema resulting from cataract extraction is called either pseudophakic bullous keratopathy (PBK) or aphakic bullous keratopathy (ABK). The structure of the cornea and the proper functioning of its layers are instrumental in understanding corneal edema.Pathophysiology: Pathologically, bullous keratopathy is caused by changes in the corneal endothelium, allowing the cornea to be in an abnormal state of hydration. As endothelial cells are damaged, the remaining cells rearrange themselves to cover the posterior corneal surface. These cells are shaped irregularly and enlarged. The Descemet membrane is produced in increased amounts by any pathologic process that affects the endothelial cells, resulting in cornea guttata. As the endothelium becomes increasingly unable to act as a pump to deturgesce the cornea, the stroma begins to swell, especially in the central cornea. As the stroma swells, the cornea thickens and folds are seen in the Descemet membrane. The edema may fluctuate in response to changing intraocular pressure. At this point, maintenance of intraocular pressure at a low level is important. The combination of variable endothelial function and variable intraocular pressure determines the extent of corneal edema. Epithelial edema manifests as fluid accumulation between the basal epithelial cells. As more fluid accumulates, blisters and then bullae develop. The mechanism of epithelial edema may result from anterior movement of aqueous and fluid in the stroma driven by intraocular pressure. With a small amount of epithelial edema, environmental factors (eg, temperature, humidity) may affect evaporation of tears with blinking. At night with the eye closed, epithelial edema is typically worse because of lack of tear evaporation and hypertonic environment, resulting in symptoms that are then generally worse in the morning hours. Patients with bullous keratopathy demonstrate decreased visual acuity and pain or discomfort. Decreased visual acuity is related to inability of the stroma to maintain deturgescence, which often is followed by epithelial edema. Epithelial edema can be responsible for great changes in visual acuity due to irregularity in the corneal refractive surface. Examination with contact lens over refraction may be the best way to confirm the status of the posterior segment. Pain or discomfort associated with corneal edema results from exposure of corneal nerves to an often noxious environment. As the edema progresses and bullae are formed, rupture of bullae results in pain, photophobia, and epiphora. These epithelial defects predispose the cornea to infection and can contribute to anterior uveitis. Frequency: Several studies in the 1980s demonstrated rates of corneal decompensation after uncomplicated extracapsular cataract extraction with posterior chamber intraocular lens placement to be 0.1-0.5%. In the setting of vitreous loss, the rate of corneal edema 4 years postoperatively has been reported to increase to ..... |
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