Brown McLean Syndrome
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Brown-McLean Syndrome (BMS) describes a condition in which the peripheral (2-3mm) inferior cornea become edematous and progresses circumferentially, sparing the central cornea in most cases.  First described in 1969 as “peripheral corneal edema after cataract extraction,” it was later renamed to Brown-McLean syndrome.
Although it was initially believed to be associated with an underlying endothelial dystrophy, further supported by a possible genetic predisposition as some cases of relatives presenting with this condition have been identified,  no causative dystrophy or gene has been identified. 
While its pathophysiology is still unknown, it was initially described in aphakic patients classically after intracapsular lens extraction.  Most patients were elderly although patients as young as 12 years old have been reported.  It typically occurs several years after surgery, averaging 6-16 years post-operative. Some speculations that a genetic predisposition for endothelial disease coupled with endothelial trauma have been proposed. Other surgeries have been associated with BMS including include PK, anterior chamber intraocular lens (ACIOL), phacoemulsification, and pars plane vitrectomy with lensectomy.
Interestingly, endothelial trauma is not necessary to induce BMS. Ultrasound biomicroscopy does not always reveal the presence of iridocorneal apposition and the presence of an iridectomy is not always reported as protective.  Non-surgical cases of BMS include patient who ha ve had lens subluxation, spontaneous lens resorption, endothelitis, keratoconus, angle closure glaucoma or myotonic dystrophy.
As mentioned above, a prior history of intracapsular or extra capsular lens extraction is often present but other intraocular surgeries as well as non-surgical ocular conditions can also be seen with BMS.
Slit lamp examination often reveals peripheral inferior corneal edema initially, involving the limbus. It generally spares the superior cornea although rare case reports describe the involvement of superior peripheral corneal edema at the onset.
Iridodenesis is often present, believed to cause intermittent endothelial trauma and the characteristic deposition of brown/orange endopigment in BMS.  Iris atrophy underlying the areas of corneal edema have also been described.  The central cornea tends to have few if any guttae.  While transient central corneal swelling associated with elevated rises in intraocular pressure has been noted in these patients,   persistent central edema occurs rarely and in severe cases. Gonioscopy appears wide and deep with variable pigmentation of the trabecular meshwork.  In the setting of a transplanted cornea with BMS, pigment and edema was found to start more centrally in the donor graft with a peripheral zone of no pigment prior to the graft host junction. High myopia is sometimes associated with BMS, with prevalence ranging from 40-61% in some cases.
Specular microscopy studies reveal that central corneal endothelial count and morphology remain normal; the peripheral corneal endothelium often have decreased cell count and morphology although can be normal as well. endothelial count often decreases and morphology alters although can also be normal.   
Similarly, in vivo confocal microscopy of the peripheral cornea generally shows enlarged corneal nerves, and fibrosis of the Bowman’s layer as well as irregularly shaped and sized basal epithelium but can also be normal in some cases. In vivo confocal microscopy of the central cornea generally normal endothelium but did reveal grouped large keratocytes with prominent nuclei in the posterior stroma as well as thick corneal nerves.
On electron microcopy, the peripheral corneas of BMS showed abnormal posterior collagen in Descemet’s with destroyed endothelial cells. Scanning electron microcopy can show a distinct line between normal and diseased endothelium. Anterior segment optical coherence tomography (AS-OCT) shows thickened peripheral cornea. Scheimpflug imaging shows thickened peripheral cornea with normal thickness central cornea.
Most cases of BMS are responsive to hypertonic saline and topical steroids.   Patients can also trial contact lenses, which has been shown to be well tolerated despite the peripheral corneal edema.
For refractory or symptomatic cases, surgical management may be warranted. In recurring cases of epithelial bullae secondary to BMS, an annular amniotic membrane transplant using two trephines of different diameters placed basement membrane side up has been shown to be successful while maintaining central visual acuity. Anterior stromal puncture with 23-G or 25-G needle can be used as well to induce collagen expression thereby improving epithelial cell adhesion and subepithelial fibrosis, both of which improve blockade of fluid penetration into the corneal epithelium. 
In the cases of ACIOL-associated BMS, treatment often includes removal of the ACIOL for resolution of the corneal edema. In untreated cases where central corneal decompensation occurs, a corneal transplant may be necessary.
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