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Understanding Glaucoma

Understanding Glaucoma

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Glaucoma is caused by optic nerve damage, secondary to an increased intraocular pressure (IOP) resulting from dysfunction of the normal drainage system of the eye. Glaucoma is the leading cause of irreversible blindness worldwide, afflicting up to 102 million people – the World Glaucoma Congress expects this number to double in the next 16 years with an aging population – and represents a $5.8 billion market in the U.S. alone. Currently available treatments – medications, surgeries, lasers and implantable devices – are expensive and have been shown to, at best, simply slow this relentlessly progressive condition. The most common surgical interventions today are based on suboptimal strategies developed in 1969 – tube shunt technologies and trabeculectomy procedures. Despite the consequences and economic burden associated with untreated glaucoma, the World Health Organization has eliminated most routine screening due to the lack of practical and effective therapies.

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MIGS - A New Class of Treatment

MIGS - A New Class of Treatment

Over the past decade, minimally invasive glaucoma surgical devices (MIGS) have emerged as a promising mode of glaucoma treatment, and several MIGS devices are in varying stages of the US and European regulatory cycle.  Though each utilizes unique materials, they all share one fundamental trait – they are shunting excess aqueous humor from the anterior chamber to one of three enclosed spaces in the eye:

 

Sub-conjunctival space: of the three locations to shunt inside the eye, the sub-conjunctival space appears to produce the most consistent reductions in IOP.  However, implants in this location require formation of a bleb – essentially a blister that serves as a reservoir for aqueous humor.  The fluid in the bleb is then primarily absorbed by the venous and lymphatic systems.  As seen with traditional trabeculectomy procedures (also requiring a bleb), there is a significant risk of bleb leak or infection, and the conjunctiva can eventually scar over, rendering the bleb and associated implant useless.

Schlemm’s canal:  implants in Schlemm’s canal attempt to bypass the diseased trabecular meshwork and utilize the eye’s native drainage pathway.  Implants in this location require technical expertise beyond that of the usual eye surgeon.  And, IOP reductions are highly variable and generally less than can be achieved with a sub-conjunctival approach.   

 

Suprachoroidal space: the suprachoroidal space is between the choroid and the sclera.  This is often a more difficult implant to place than one in Schlemm’s canal.  Various ways to shunt aqueous humor into the suprachoroidal space have been attempted for many years, with inconsistent and usually temporary effectiveness. Scarring over at the inner end of these devices has been a particular problem. 

 

Because all of these implants drain to enclosed spaces inside the eye, they are prone to failure from encapsulation due to foreign body inflammatory responses.  Most are also affected by the recumbent nighttime episcleral venous pressure increase that contributes to nighttime increases in IOP.

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