EYE FACTS

The beauty of a soul is reflected is one’s eyes. However, there is a lot more to eyes than what fills our first glace. Here are some stunning facts about the eye that can enthrall you.

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Glaucoma: A brief description

Known as a silent killer of eye sight, Glaucoma is Hereditary. It is called a silent killer because it has no symptoms like pain for the patient to recognize the disease in time.

It is caused when there is a disturbance to the constant ratio of inflow and out flow of a fluid called "Aqueous" inside the eye which ends up building pressure on the eyeball. The normal pressure is 21mm of Hg and when raised starts pressing the optic nerve. This leads to gradual loss of peripheral vision to start with and may even lead to total blindness.

Regular examinations are the solution to this problem. This helps the doctors to identify such a condition at the right time so you can avoid any further damage to your eyes.

Diagnosis Process

When you arrive at any of our clinics, checking the pressures within your eyes is a part of the simple tests explicitly carried out. Our doctors shall further examine your vision fields to determine any damage to the periphery. Following the test results, the doctor can offer you simple medical treatment in the form of drops, tablets or laser treatment. Only if the extent of the damage is found to be is too high, an operation would be necessary. For further details, you can contact us and book an appointment with any of our specialists.

Non-Contact Tonometry & Applanation Tonometry

Non-contact tonometry and applanation tonometry are the two most popular methods used by optometrists to measure the Intraocular Pressure (IOP) within your eyes. The IOP is what helps the doctors to determine and find the extent of Glaucoma.

Non-Contact Tonometry

This procedure uses a device called Non-contact Tonometer (NCT) and hence the name. The NCT uses a puff of air to create an applanation event on the cornea. This produces changes in characteristics of the corneal light reflex is measured electronically. The instrument senses the correct alignments made by the operator to fire a test pulse where the digital readout eventually shows the measure of the IOP.

No anesthetics or dyes are required in NCT and this has led to an increase in its popularity among optometrists for glaucoma screening.

Applanation Tonometry

Applanation tonometers (AT) are also extensively used to determine the IOP. This device indents a known area of the cornea. When the correct indentation is observed, the pressure resisting indentation equates to the force applied, resulting in an estimate of the intraocular pressure. Some standard ATs that are commonly used require a slit-lamp to obtain the readings.

GDX - the latest diagnosis for Glaucoma

Maxivision houses the latest equipment and the most sophisticated methods like GDX, apart from Visual Fields and NCT machines, to treat Glaucoma.

GDx is the most advanced glaucoma detection technology currently available. It has been considered a significant breakthrough over other existing tests.

The test is used to measure the nerve fiber layer - a thin layer of tissue surrounding the optic nerve. The GDx laser passes polarized light through the layer and can measure it up to 65,000 points. The measurements are then processed by a powerful computer that map the nerve fibers and instantly compare them to a database of healthy glaucoma-free patients. The thinning of the fibers indicates glaucoma.

The GDx has been found to be highly precise and accurate to detect glaucoma. It is quick and takes a little to complete. The test is also quite comfortable for the patients and is a part of our commitment to provide the most advanced & comprehensive eye care service to our patients.

HVF - Humphry's Visual Field Analyser

Humphrey Automated Visual Field Analyzers, the gold standard in perimetric testing, have a proven track record of 25 years in the domain of "visual field" development and research. Our field analyzer is the latest model from Humphrey which has all the latest software and databases. It is one of the fastest and most accurate field testing tools currently available in the market.

The device has been vital in detecting glaucoma along with many other ocular conditions. Patients who either have glaucoma or are suspected of having glaucoma undergo repeated testing with this instrument.

During the test, light beams of varying intensities appear in different parts of the visual field while the patient's eye is focused on a central spot. The results are then compared against the normal healthy eye in order to determine if any damage has occurred. The procedure which is quite easy can performed quickly and takes approximately 10 minutes.

Yag Laser Iridotomy

Laser Iridotomy is a surgical procedure that is performed to treat angle closure glaucoma*. Angle closure of the eye occurs when the trabecular meshwork, the drainage site for ocular fluid, is blocked by the iris. The procedure was first used to treat angle closures in the year 1956. Laser iridotomy procedure involves making a hole in the iris of the eye to change its configuration. When this occurs, the iris moves away from the trabecular meshwork and enables proper draining of the intraocular fluid.

The purpose of a laser iridotomy is to allow an equalization of pressure between the anterior (front) and posterior (back) chambers of the eye by making a hole in the superior peripheral iris. Once the laser iridotomy is completed, the intraocular fluid flows freely from the posterior to the anterior part of the eye, where it is drained via the trabecular meshwork as mentioned above. The result of this surgery is a substantial decrease in IOP.

* Angle closure glaucoma: A condition of increased pressure in the front chamber (anterior chamber) that is caused by sudden (acute) or slowly progressive (chronic) blockage of the normal circulation of fluid within the eye. The block occurs at the angle of the anterior chamber that is formed by the junction of the cornea with the iris. All one needs to do to see this angle is to look at a person's eye from the side.

Trabeculectomy

Trabeculectomy is a surgical procedure used in the treatment of glaucoma to relieve intraocular pressure within the eye by removing part of the eye's trabecular meshwork and adjacent structures. It is the most common glaucoma surgery performed and allows drainage of aqueous humor from within the eye to underneath the conjunctiva where it gets absorbed.

This procedure was most commonly performed under monitored anesthesia care using a retrobulbar block or peribulbar block or a combination of topical and subtenon (Tenon's capsule) anesthesia. Due to the higher risks associated with bulbar blocks, topical analgesia with mild sedation is becoming more common. However, general anaesthesia is rarely used but with patients who have an inability to co-operate during the surgery.

Procedure

An initial pocket is created under the conjunctiva and Tenon's capsule. The wound bed is treated for several seconds (and may go up to a few minutes) with mitomycin C (MMC, 0.5-0.2 mg/ml) or 5-fluorouracil (5-FU, 50 mg/ml) soaked sponges. These chemotherapeutics help to prevent failure of the filter bleb from scarring by inhibiting fibroblast proliferation.

Alternatively, non-chemotherapeutic adjuvants can be implemented to prevent super scarring by wound modulation, such as collagen matrix implant or biodegradable spacer. Some surgeons prefer "fornix-based" conjunctival incisions while others use "limbus-based" construction at the corneoscleral junction which may allow easier access in eyes with deep sulci. A partial thickness flap with its base at the corneoscleral junction is then made in the sclera after careful cauterization of the flap area. A window opening is created under the flap with a Kelly-punch to remove a portion of the sclera, Schlemm's canal and the trabecular meshwork to enter the anterior chamber. Because of the fluid egress, the iris will partially prolapse through the sclerotomy and is therefore grasped to perform an excision called iridectomy. This iridectomy will prevent future blockage of the sclerotomy. The scleral flap is then sutured loosely back in place with several sutures. The conjunctiva is closed in a watertight fashion at the end of the procedure.

Glaucoma surgeries combined with Cataract procedures

Combined cataract extraction and glaucoma surgery (like Trabeculectomy, Glaucoma drainage implant surgery, or any of the newer surgical approaches for glaucoma) should be carefully selected and individualized depending on clinical findings in each case. The following points are also to be remembered -

  • Cataract surgery alone is sufficient for patients with well controlled IOP in early stages of moderate optic nerve damage.
  • Patients with uncontrolled IOP in the presence of severe optic nerve damage should receive glaucoma surgery first followed by cataract extraction. (a few months later)
  • Combined surgery may be best suited for a patient with a visually significant cataract with uncontrolled glaucoma despite maximal medical therapy and/or laser Trabeculoplasty. Cost is often an issue for many patients and eliminating medications can help reduce the financial burden.
  • Improper compliance with glaucoma medications can also be an issue to consider both procedures together.

Potential Advantages

  • Patient Convenience: A single visit to the operating room may be beneficial in terms of cost, risks of anesthesia, presence of other medical conditions precluding additional stress of multiple surgeries and other social issues.
  • Avoid potential postoperative IOP spike which can be seen after cataract surgery, especially for cases with advanced optic neuropathy
  • Long-term control of IOP with glaucoma surgery and quick visual recovery from removal of a significant cataract

Potential Disadvantages

  • There may be higher risk involved in intraoperative and postoperative complications when both the surgeries for cataract and glaucoma are performed together rather than being performed separately.
  • Cataract surgery in patients with glaucoma may prove to be more challenging due to chronic miosis/poor pupil dilation from medications or presence of synechiae.
  • Patients with glaucoma secondary to trauma or exfoliation syndrome may have weak/fragile zonules, which may lead to zonular dehiscence and vitreous loss. The vitreous loss may lead to failure of glaucoma surgery. More inflammation is induced with combined cases, especially with one site surgery.
  • Combined procedures may be less effective than glaucoma surgery alone in controlling IOP, especially for eyes with advanced glaucomatous damage
  • Longer vision recovery time

Potential Complications

The potential complications are similar to the ones encountered when cataract surgery and Trabeculectomy are performed separately. For additional information, please refer to the section on Trabeculectomy.

  • Shallow or flat anterior chamber
  • Persistent inflammation
  • Choroidal effusion
  • Bleb leaks
  • Filtration failure
  • Corneal Allen
  • Suprachoroidal hemorrhage
  • Endophthalmitis
  • Chronic hypotony
  • Maculopathy

The risk of persistent hypotony and associated complications such as maculopathy, late-onset bleb leaks, infection of the bleb, and endophthalmitis may be increased with the adjunctive use of antifibrotic agents.

Ahmed Valve

The Ahmed Glaucoma Valve (AGV) is a medical shunt used in the treatment of glaucoma to reduce & control intraocular pressure (IOP). The AGV is effective in all types of glaucoma due to its unique valve system, exhibiting a level of control only a true valve can offer. The device works by bypassing the trabecular meshwork and redirecting the outflow of aqueous humor through a small tube into an outlet chamber or bleb. The IOP generally decreases from around 33 to 10 mmHg by removing aqueous on average 2.75 microliters per minute.

Different Types

There are also several different glaucoma drainage implants. These include the original Molteno implant (the year 1966), the Baerveldt tube shunt and the later generation pressure ridge Molteno implants.

The flow tube is inserted into the anterior chamber of the eye and the plate is implanted underneath the conjunctiva to allow the flow of aqueous fluid out of the eye into a chamber called bulb. Ahmed Valve itself is available in many types in order to fit patients of all ages.

Indications

The glaucoma valve implant is indicated for glaucoma patients not responding to maximal medical therapy, with previous failed guarded filtering surgery (trabeculectomy) or in cases where conventional drainage surgery is unlikely to succeed. Common situations where the use of a glaucoma implant as a primary procedure is indicated include:-  

     
  • Neovascular glaucoma -- glaucoma associated with vascular disease of the eye (often diabetes).
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  • Cases of Uveitis -- acute or chronic inflammation of the eye.
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  • Traumatic glaucoma -- glaucoma associated with injury to the eye.
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  • Silicone glaucoma -- glaucoma due to Silicone used to repair a detached retina.
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  • Infantile/Juvenile glaucoma -- often associated with developmental defects of the eye.
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Surgical technique

The flow tube is inserted into the anterior chamber of the eye and the plate is implanted underneath the conjunctiva to allow the flow of aqueous fluid out of the eye.  

     
  • The first-generation Molteno and other non-valved implants sometimes require the ligation of the tube until the bulb formed is mildly fibrosis and water-tight. This is done to reduce postoperative hypotony (sudden drops in postoperative intraocular pressure).
  • Valved implants such as the Ahmed glaucoma valve attempt to control postoperative hypotony by using a mechanical valve. Studies show that in severe cases of glaucoma, double-plate Molteno implants are associated with lower mean IOP for much longer when compared to Ahmed valve.
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Complications

The on-going scarring over the conjunctival dissipation segment of the shunt may become too thick for the aqueous humor to filter through. This may require preventive measures using anti-fibrotic medication like 5-fluorouracil (5-FU) or mitomycin-C (during the procedure) or may even create a necessity for additional surgery.

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