LASER SURGERY IN THE TREATMENT OF GLAUCOMA

Ophthalmologist Carolina Valdivia, MD answers a question about laser surgery in the treatment of glaucoma.

Hello Dr. Valdivia. I am writing on behalf of my Dad, who is 72 years old. He was diagnosed with type 2 diabetes over 10 years ago. Last year he was diagnosed with glaucoma in his left eye and was given laser surgery for treatment. His right eye had no glaucoma or any other health issues but laser treatment was given as a precautionary measure. He recently has lost full sight in his right eye and has been diagnosed with neovascular glaucoma, a detached retina, sub-retinal hemorrhage and an eye pressure of 46 in his right eye. Could the laser surgery to the right eye have caused damage to the vessels, leading to the above diagnosis? Or is there another reason why my Dad could have all these health issues? Before the laser surgery, my Dad didn't have anything wrong with his right eye. Is it standard practice to treat an eye without glaucoma with laser treatment?

Thank you so much for your time.

Regards



Thank you for your question and for your interest in glaucoma-eye-info.com. There are some things that I would like to explain before going into the specifics of your father's case.

Laser therapy for the treatment of glaucoma typically is conducted on the retina, iris, and trabecular meshwork, a structure located in the iridocorneal angle (the angle formed by the iris and cornea).

Laser surgery sometimes is performed on patients with primary open-angle glaucoma. In these cases, changes in the structural integrity of the trabecular meshwork impede the flow of a fluid called aqueous humor out of the eye, consequently elevating intraocular pressure. A surgical procedure called trabeculoplasty uses a laser to create tiny holes in the iridocorneal angle.

In the case of laser surgery involving the iris, a procedure is used called peripheral iridectomy (also known as iridotomy). This consists of making a small hole near the outer rim of the iris in order to prevent a pupillary block from occurring and closure of the iridocorneal angle.

Peripheral iridectomy is used in patients diagnosed with primary angle-closure glaucoma or in patients with elevated intraocular pressure in the presence of a narrow iridocorneal angle, but that do not yet show evidence of glaucoma. In these instances, it could be said that the laser surgery is performed as a prophylactic measure (a treatment designed to prevent a disease from occurring). However, in actuality the ophthalmologist operates under the scientifically based assumption that damage to the optic nerve already has occurred, but is not yet detectable. Laser surgery is performed to prevent any further damage and to preserve as much of the patient's normal eyesight as possible.

Prophylactic treatment to prevent the occurrence glaucoma in an ostensibly normal eye is unique to people with narrow iridocorneal angles. This was likely the case for your father and would account for why laser surgery was performed on both eyes.

It is important to remember that a diagnosis of glaucoma is determined by the presence of one or both of the following two factors: evidence of damage to the optic nerve and/or deterioration of the visual field. In most cases, it also is associated with increased intraocular pressure (IOP), but having elevated IOP alone does not mean that a patient has glaucoma.

The main causes of neovascular glaucoma are diabetic retinopathy and central retinal vein occlusion (CRVO).

Blood carries oxygen and nutrients to cells and removes waste products and carbon dioxide. Permeability of blood vessel walls means that the efficiency of this process is significantly diminished. This results in hypoxia (lack of oxygen) in the cells of the retina, leading eventually to cell death. The body attempts to rectify this situation through a process called neovascularization (proliferation of new blood vessels), but these vessels are fragile and also leak fluids. The new vessels also can proliferate to the front of the eye and fill the iridocorneal angle, resulting in neovascular glaucoma.

This problem typically occurs in diabetic patients who have had diabetes for more than 8-10 years, and whose blood glucose levels have been high on a sustained basis, often due to poor patient adherence to treatment. In some cases, diabetic retinopathy is treated with a procedure called laser photocoagulation, which seals off leaking blood vessels and destroys new vessel growth. Laser photocoagulation does not cause pain, because no nerve endings are present in the retina.

One thing that caught my attention in your description is that you mention that your father was diagnosed with glaucoma in his left eye one year ago and, at that time, his right eye apparently was healthy. Diabetic retinopathy usually is a progressive disease that moves through several stages. Passage of the disease through all of these stages is a slow process that can range from several months to several years. It is unlikely that a diabetic person diagnosed with a healthy eye, meaning without evidence of diabetic retinopathy, will move into the later stages of the disease and even exhibit the appearance of neovascular glaucoma in the span of just one year. But exceptions do occur; there are no absolutes in medicine.

CRVO is an acute event, meaning that it is sudden. It has an extremely negative effect on the retina and can lead in many cases to subsequent neovascular glaucoma.

Prophylactic peripheral iridectomy is applied to the iris (front part of the eye). It does not involve the retina or its blood vessels, which are located in the back of the eye. Therefore, this laser surgery procedure would not cause neovascular glaucoma.

I recommend that you speak to your ophthalmologist regarding her/his assessment of what caused the neovascular glaucoma in the right eye of your father. If the cause was central retinal vein occlusion (CRVO), strict monitoring of blood glucose, triglycerides, cholesterol, and blood pressure will be required, as the left eye also may be at risk for a similar event. There are several tests available that your ophthalmologist can perform to assess the status of retinal blood circulation, in both of your father's eyes. A number of systemic factors can cause or contribute to CRVO. Each must be ruled by your physician, so that the primary causative factor can be identified and monitored.

Carolina Valdivia, MD

REFERENCE:

Shaarawy TM, Sherwood MB, Hitchings RA, and Crowston JG. Glaucoma Volume 2: Surgical Management. New York: Elsevier, 2009.

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