Pseudoexfoliation syndrome


Pseudoexfoliation syndrome

Description, Causes and Risk Factors:

Pseudoexfoliation: A condition simulating exfoliation(a thin flake of dead epidermis shed from the surface of the skin) in some respects, but in which the surface layer is not actually detached.

Pseudoexfoliation syndrome is an age-related systemic disorder of the extracellular matrix that is characterized by abnormal microfibrillar production and deposition in intra- and extraocular tissues. Structures in the anterior segment of the eye are most often involved, including the lens, the iris(muscular diaphragm that controls the size of the pupil which in turn controls the amount of light that enters the eye; it forms the coloured portion of the eye), the ciliary body (the part of the tunic of the eye between the choroid coat and the iris) , and the zonular apparatus. Progressive pathological accumulation of pseudoexfoliation deposits both from local production and secondary deposition from the aqueous humor appears to lead to obstruction of the trabecular meshwork and subsequent elevation in intraocular pressure . This can lead to optic nerve damage and the development of pseudoexfoliation glaucoma which is the most common identifiable cause of secondary open -angle glaucoma in the world . Compared to primary open-angle glaucoma (POAG), patients with pseudoexfoliation glaucoma demonstrate more rapid pressure increase, resistance to medical therapy, and more need for glaucoma surgery .

The molecular events underlying the deposition of proteins seen in pseudoexfoliation syndrome are only partly understood. Some research has been done on the role of homocysteine in pseudoexfoliation syndrome. There are also contrasting studies on the correlation between pseudoexfoliation syndrome and lower plasma levels of certain vitamins essential to homocysteine metabolism (i.e., vitamin B6, vitamin B12, and folate). Further research, however, is required.

Pseudoexfoliation syndrome can cause vision-threatening sequelae. In particular, owing to tissue alteration, patients are predisposed to secondary open-angle glaucoma and cataracts. Glaucoma arises from the accumulation of pseudoexfoliative material and pigmentary granules within the trabecular meshwork — the fluid drainage system of the eye. Because aqueous humour continues to be produced, the increased resistance to outflow induced by the pseudoexfoliative material causes the intraocular pressure (IOP) to rise. This in turn causes progressive loss of retinal ganglion cells, which form the optic nerve. This process is termed glaucomatous optic neuropathy, and is a common cause of blindness.

Recent studies have identified a single-nucleotide polymorphism in the lysyl oxidase-like protein 1 gene that demonstrates a strong association with cases of pseudoexfoliation syndrome glaucoma in a number of populations. The test is not diagnostic, as the alleles are found in many non-pseudoexfoliation syndrome glaucoma patients as well, suggesting other genetic or environmental factors affecting the expression of the lysyl oxidase-like protein 1 gene.

In a recent genome-wide association study, researchers identified three single nucleotide polymorphisms (SNPs) of the lysyl oxidase-like (LOXL1) gene as important genetic susceptibility factors for pseudoexfoliation in Icelandic and Swedish populations. Subsequent replication studies performed in the United States, Australia , and Europe have confirmed that two nonsynonymous coding SNPs and one intronic (an intron is any nucleotide sequence within a gene that is removed by RNA splicing to generate the final mature RNA product of a gene) SNP from LOXL1 are genetic susceptibility factors for pseudoexfoliation.

In Indian , Japanese , and Chinese cohorts, the association was also replicated and confirmed that this is the strongest risk allele across different ethnicities. However, the causative nature of these SNPs is unclear since other studies have shown inverse relationships for the reported risk alleles. Therefore, the functional significance of the LOXL1 gene in the pathogenesis of pseudoexfoliation is unclear at present.

LOXL1 is located on chromosome 15q24.1 and is part of a family of five lysyl oxidase (LO) enzymes (LOX, LOXL1, LOXL2, LOXL3, and LOXL4) that collectively play a key role in cross-linking between collagen and elastin in connective tissues . Individually, LOXL1 catalyzes tropoelastin cross-linking and regulates elastin fiber formation and remodeling . Moreover, a growing body of molecular and biochemical evidence indicates that XFS arises from a stress-induced elastic microfibrillopathy. Although the exact pathogenesis of PXS remains unknown, it is believed to involve inadequate breakdown and/or excessive production of elastic fiber components. Although familial occurrence of exfoliation syndrome has been described by a number of authors, no clear hereditary pattern has been discerned (detect with the senses). Researchers suggested that exfoliation syndrome may occur as a dominant trait. Researchers found two homozygous twin pairs discordant for exfoliation syndrome, while found two pairs concordant and 3 discordant(lacking in harmony). Exfoliation syndrome is so common that it is difficult to draw conclusions and, because it develops in older patients, multiple affected family members are difficult to find. The possibility of both exfoliation and primary open-angle glaucoma occurring in the same pedigree further confuses the issue.

Symptoms:

Patients with pseudoexfoliation syndrome remain asymptomatic until an advanced glaucoma develops. The condition is most common in the sixth to eighth decade, with actual glaucoma developing later in this age range. There is no racial, sexual, or geographic predilection. Typically, pseudoexfoliation syndrome begins unilaterally, but becomes bilateral within about six-to-seven years.

The patient presents with a fine, flaky material on the anterior lens capsule at the pupillary margin. Over time, this coalesces into a characteristic "bulls-eye" pattern seen in pseudoexfoliation. There is often increased transillumination of the iris at the pupillary(relating to the pupil of the eye) margin and there may be pigment granules on the endothelium and iris surface. Within the angle, there may be observable pigment or clear flaky material. Initially, intraocular pressure is unaffected; however, elevated IOP (intraocular pressure) develops in up to 80% of patients. In these cases, glaucomatous cupping and visual field loss may ensue.

Diagnosis:

Pseudoexfoliation syndrome without a pressure rise requires only periodic monitoring of IOPs (intraocular pressures), discs, and visual fields. Ultrasound biomicroscopy is rapidly proving valuable in analyzing the mechanisms of various types of glaucoma. There are numerous potential applications to the analysis of eyes with exfoliation syndrome. Our finding of deeper anterior chambers in eyes with exfoliation syndrome is consistent with clinical and subclinical phacodonesis(tremulousness of the lens of the eyes in affected eyes. The presence of a wider angle in the temporal quadrant suggests the possibility that zonular involvement is more pronounced temporally than nasally. This may be correlated with the finding that exfoliation material is found earliest in temporal quadrants. Temporal versus nasal angle disparity may prove to be a useful test for early exfoliation syndrome and might serve as a predictor for possible complications at the time of cataract extraction. However, further studies are necessary to compare angle widths in normals and to determine confidence intervals for accuracy of these measurements.

Another biometric method, Scheimpflug photography, is useful in analyzing iris contour in eyes with angle-closure glaucoma. It has been reported to be potentially valuable in detection of early stages of exfoliation syndrome prior to clinical involvement on slit-lamp examination. This technique may also be useful in measuring angle width.

Treatment:

Pseudoexfoliation can be treated by traditional intraoccular pressure medications. These are less effective than on traditional glaucoma but are still first-line drugs. Another very effective method is treating glaucoma naturally using eye targeted exercises and learning how to completely relax the eyes.

In case the patient develops pseudoexfoliation glaucoma, the treatment will be with anti-glaucoma eye drops and also glaucoma laser surgery in which patient will have excellent respond to laser trabeculoplasty (photocoagulation of the trabecular meshwork of the eye using the laser in the treatment of glaucoma). In case the patients have poor response to anti-glaucoma medications and to laser treatment, surgical treatment is the only option available.

Treat pseudoexfoliative glaucoma in the same manner as primary open angle glaucoma. Use topical beta-blockers, topical carbonic anhydrase inhibitors, prostaglandin analogs and alpha adrenergic agonists if not systemically contraindicated. However, the IOP level in pseudoexfoliative glaucoma is typically higher than in POAG(primary open-angle glaucoma) and is more difficult to temporize laser trabeculoplasty and filtration surgery are often employed earlier than in POAG.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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