Single Gene Controls Brain, Lens, Retina Development

Researchers at St. Jude’s Children’s Research Hospital are expanding their understanding of how a key gene, designated Six3, regulates the development of the eye as well as the cerebrum. Several years ago, a related team of researchers at St. Jude’s showed that if the Six3 gene is defective, it leads to a failure of the cerebrum to divide properly into two lobes, a condition known as holopresencephaly. Because the eye normally grows out of the brain in normal fetal development, its connection with eye growth is normal, but just how much it controls the eye continues to be revealed.

The first portion of eye development shown to be linked to the Six3 gene is the development of the lens. The Six3 gene activates another gene, known as the Pax6, which controls several other genes that work together to create the lens. Now researchers have linked the Six3 gene to retinal development. When the Six3 gene is expressed in the retina, it blocks another protein, which has the power to stop the development of the retina, although the exact mechanism by which that blocking occurs is unknown.

The hope is that understanding the process of retinal development will allow for future gene therapy that can replace retinal and optic nerve cells lost to conditions like age-related macular degeneration and glaucoma. The current line of research represents the most recent in a number of promising avenues for gene therapy to counteract common vision problems.

Currently, glaucoma and age-related macular degeneration are two of the more significant threats to vision faced by older Americans. Glaucoma has no symptoms and few signs before vision loss occurs. Once diagnosed, glaucoma treatment can be effective, but currently there is no way to reverse damage to the retina and optic nerve. Therefore, people are encouraged to get regular glaucoma screenings to avoid this “silent thief of sight.” Currently, no treatments are available that can stop or reverse the progression of age-related macular degeneration.

To schedule your glaucoma screening and learn about the best treatment options available today, please contact a local ophthalmologist today.

Intraocular Pressure Measurement a Challenge in Glaucoma Treatment Monitoring

GOLDEN, CO: Most cases of glaucoma are associated with elevated intraocular pressure (IOP). The most common form of glaucoma, primary open-angle glaucoma, is associated with elevated intraocular pressure due to a clogging of the open angle where intraocular fluid drains from within the eye to the eye surface. This leads to an elevation of intraocular pressure. The intraocular pressure, in turn, presses on the retina and the optic nerve, leading to damage and loss of vision.

The goal of most glaucoma treatment, including eye drops, laser surgery, and stents, is to reduce intraocular pressure. However, measuring intraocular pressure is a challenge. Although good instrumentation exists to measure IOP, it varies throughout the day. Furthermore, some evidence indicates that it is the peak IOP that is most indicative of glaucoma treatment, so knowing when to take IOP measurements to check on the progress of glaucoma treatment is difficult. Evidence suggests that any single IOP measurement is 75% likely to miss the pressure maximum.

In the past, it was proposed that people had a regular diurnal pattern of IOP, and that learning a person’s pattern would allow ophthalmologists to schedule appointments allowing for measurements that would be more likely to catch the maximum IOP.  However, a recently-published study found that people’s daily IOP changes are anything but regular. The study looked at the daily variation in IOP among forty people without glaucoma. The subjects underwent two sessions of daily IOP monitoring two weeks apart, and it was found that the daily IOP variation curves had uniformly poor agreement. The agreement was so poor as to suggest a completely random association, meaning that charting a person’s daily IOP would be unlikely to give a good indication about when to measure IOP to get a good idea of the maximum IOP.

As we continue to learn more about glaucoma, it is hoped that new monitoring techniques will help us track the success of different treatment options. To learn more about advanced glaucoma treatments, you can get in contact with an ophthalmologist in your area using our Eye Doctor Directory.

FDA Approves Bimatoprost 0.01% Eye Drops for Glaucoma Patients

Washington, D.C. – The Food and Drug Administration (FDA) has recently approved bimatoprost 0.01% ophthalmic solution for the treatment of elevated intraocular pressure in individuals suffering from open-angle glaucoma or ocular hypertension. Bimatoprost 0.01% solution is sold under the brand name Lumigan and is manufactured by Allergan.

This new product presents patients with an alternative glaucoma treatment to Allergan’s 0.03% bimatoprost solution, which has been on the market for years. Both medications are administered once a day in the evening by applying one drop in each affected eye.

The FDA approved Lumigan 0.01% after a three-month study demonstrated that the drug lowered intraocular pressure by as much as 7.5 mm Hg from an average baseline of 23.5 mm Hg. This reduction is similar to the results achieved by the 0.03% solution, which has been shown to lower intraocular pressure by as much as 8 mm Hg.

The main upside of taking the new formulation is that patients can achieve almost identical results with only one third of the drug exposure. This reduction in drug exposure has resulted in greater tolerability of the treatment by patients as well as a decrease in adverse side effects such as:

  • Hyperemia
  • Eyelash growth
  • Ocular pruritus

An additional benefit of this new formulation is a significant drop in the discontinuation rate after one year of usage. Patients taking Lumigan 0.01% experienced an 8.1% discontinuation rate compared to 13.4% for patients taking Lumigan 0.03%.

Other adverse effects of bimatoprost solution include increased pigmentation in the iris, eyelid, and eyelashes. While the pigmentation changes experienced in the eyelid and eyelashes are generally reversible once treatment is discontinued, the pigmentation changes in the iris are often permanent. Hopefully, the new reduced-dosage formulation will reduce the risks of pigmentation changes as well.

Lumigan 0.01% should be available by prescription by the end of 2010.

FDA Advisory Panel Recommends Approval for IOP-Lowering Stent

Washington, DC: An advisory panel has voted to recommend approval for a new glaucoma treatment: the iStent Trabecular Micro-Bypass Stent, to be used in combination with cataract surgery. The stent is used to treat primary open angle glaucoma, the most common form of glaucoma.

In primary open angle glaucoma, a rise in intraocular pressure is caused by clogging of the drainage angle. This prevents fluid from leaving the eye and pressure to increase as new fluid is produced. Currently, there are several approved treatment options for glaucoma, including pressure-reducing eye drops, canaloplasty, and filtering microsurgery.

The iStent is essentially a tiny tube, similar to the vascular stents that are used to support arteries during angioplasty. This tiny tube, which is inserted during cataract surgery, allows increased drainage of intraocular fluid, reducing the intraocular pressure.

The FDA advisory panel reviewed research data from studies submitted by the manufacturer and considered whether there was reasonable assurance that the device was safe, effective, and that the benefits of the device likely outweighed its risks. The panel voted 7-1 that there was “reasonable assurance” that the iStent was reasonably safe for use. The panel also voted 6-2 that there was “reasonable assurance” that the stent was effective at reducing IOP. Finally, the panel voted 7-1 that there was “reasonable assurance” that the benefits of the device outweighed its risks. In every case, the recommendations were for placement of the stent during cataract surgery for the treatment of elevated IOP for patients with mild to moderate open angle glaucoma currently being treated with ocular hypotensive medication.

The primary reservation expressed by the committee was that, although the device was safe, its effectiveness seemed to be relatively low. Furthermore, “the panel noted a lack of effectiveness at 24 months and recommended that the indication for use reflect the temporary nature of the device’s effectiveness.” For more information, you can read the advisory panel minutes here.

Since there are currently many treatment options for glaucoma, it is uncertain whether this new treatment would benefit very many people. Currently, many surgeons recommend combined glaucoma / cataract surgery, especially for people with relatively mild glaucoma. For patients with advanced glaucoma, separate surgery is more often recommended.

To learn whether combined glaucoma and cataract surgery might be a good treatment for you, talk to an ophthalmologist in your area.

Higher Body Weight May Reduce Risk of Normal Tension Glaucoma

San Francisco, CA:Glaucoma, serious damage to the optic nerve that may eventually result in blindness, is typically associated with elevated intraocular pressure. Mysteriously, though, one form of glaucoma occurs without elevated intraocular pressure. What is often described as normal-tension glaucoma (NTG) is still a mysterious disease, and, according to a new study, it may be even more mysterious. A study published in the August 2010 issue of Ophthalmology, the journal of the American Academy of Opthalmology, showed that body weight was not correlated with a higher risk of primary open angle glaucoma, and the risk of normal-tension glaucoma for women seemed to actually decrease with weight.

The study considered the medical records of 78,777 women enrolled in the Nurses Health Study (from 1980 through 2004) and 41,352 men enrolled in the Health Professionals Follow-up Study (1986 through 2004). They compared body mass index (BMI) of subjects and compared them to the incidence of primary open angle glaucoma and found that there was no correlation between BMI and glaucoma risk across all subjects. This was surprising because glaucoma is often associated with high blood pressure and type 2 diabetes, both of which can result from lifestyle and diet that also commonly result in high BMI. Even more surprising, they found that for women increasing BMI actually seemed to decrease risk of normal-tension glaucoma, by about six percent per point of BMI.

Since BMI is calculated using height and weight, researchers used further statistical analysis to show that the correlation was stronger between the weight parameter than the height parameter. As a result, the lead researcher, Dr. Louis R. Pasquale of the Massachusetts Eye and Ear Infirmary, said, “It’s reasonable to speculate that hormonally-controlled factors released from adipose or lean tissues may alter the risk of NTG in women. Higher BMI in postmenopausal women is linked with higher estrogen levels, which might positively affect estrogen receptors in the optic nerve.”

The hope is that this study will provide a stepping stone for future research to explore the possible connections between hormonal factors and normal tension glaucoma, potentially leading to a reliable treatment for this challenging, vision-threatening illness.

To learn more about your personal risk of glaucoma, find an ophthalmologist near you and schedule a consultation.