Tag Archives: Optic Nerve

New Technology at Total Eye Care Predicts Glaucomatous Vision Loss

Pattern Electroretinography (PERG) Gives up to 8 Years of Advanced Warning

NOVA-ERGDeviceIncorporating the most advanced technology available in caring for our patients is important to the way we practice at Total Eye Care. The Diopsys® Pattern Electroretinograph is the newest addition to our suite of technology. The Pattern ERG (PERG) measures the signal strength of the retinal information being sent to the optic nerve. Studies show that a 10% decrease in this signal can be detected up to 8 years earlier than a 10% loss of nerve fibers detected by the scanning laser ophthalmoscope or optical coherence tomographer, thus allowing for a much earlier diagnosis and treatment.

Early detection and treatment of glaucoma is important due to the fact that nerve tissue cannot be regenerated. Twenty years ago, in the absence of a very high intra-ocular pressure, it was a common practice to wait until a visual field defect was present before initiating treatment. There is a significant amount of redundancy in the retinal nerve fibers, thus studies have shown that a patient must lose approximately 50% of the nerve fibers serving a given section before the loss of nerve fibers result in a detectable visual field defect. The scanning laser ophthalmoscopes changed all of that allowing us to detect earlier, more subtle changes in the retinal nerve fiber layer. Now patients are treated before visual field defects become apparent.

The Diopsys® Pattern Electroretinograph is the next step in early detection. The PERG will not replace the scanning laser ophthalmoscopes such as the Zeiss Cirrus Optical Coherence Tomographer (OCT) in the diagnosis of glaucoma; however, it gives us another valuable tool in the diagnosis and treatment of glaucoma.

How Does Glaucoma Damage the Eye?

We are frequently asked to explain how glaucoma causes blindness. Glaucomatous damage to the eye is caused when the pressure within the eye is greater than the optic nerve can tolerate. How does the pressure cause blindess? The simple answer is we don’t know exactly, however there are two main theories as to why the damage occurs. Neither theory fully explains how the optic nerve damage occurs in the different types of glaucoma.

The Vascular Theory of Glaucoma

The premise of the vascular theory is that high pressure inside the eye restricts blood flow to the optic nerve causing the optic nerve to slowly die from lack of oxygen and nutrients.

The Mechanical Theory of Glaucoma

Physical damage is the underlying hypothesis of the mechanical theory of glaucoma. It is thought that the high pressure damages the optic nerve fibers.

So Which One Is It?

That’s a good question the leading researchers can make a convincing case for both theories and neither theory, by itself can completely explain how glaucoma damages the eye. In reality both probably play a role in how an eye is damaged by glaucoma.

Stumble It!

Q: If My Blood Pressure is High Does That Mean the Pressure in My Eye is High Too?

A: This is a great question that gets asked a lot. The pressure inside your eye is completely unrelated to your blood pressure. The intra-ocular pressure system and the blood pressure are completely separate systems and fluid is not exchanged between them. Therefore, if you have high blood pressure you won’t necessarily have glaucoma.