Basic Principals

Glaucoma is a disease of the optic nerve where there is a progressive loss of neurons usually related to high pressure within the eye (elevated intraocular pressure or IOP over 21 mm of mercury). In a subtype of glaucoma called normal tension glaucoma, vision loss can occur with IOP’s less than 21. This type of glaucoma can be more difficult to diagnosis since low pressures can mask the diagnosis.

Glaucoma is one of the most common causes of blindness in the United States, along with cataracts, diabetic retinopathy and macular degeneration

If the nerve is damaged beyond a certain point, the quality of vision suffers. The loss unfortunately is irreversible.

Visual loss in glaucoma has been described as silent and insidious.

If you are worried or concerned about glaucoma, our center is to will analyze your eyes and advise you appropriately. Along with Dr. Stone, his technical and professional staff are specialized in glaucoma care. The office is equipped with the most up to date equipment and computer imaging for glaucoma detection and monitoring.

basic_prin1         Normal right eye                                                                             Early glaucoma left eye

Optic Nerve Anatomy

The optic nerve travels from the eye to the brain and carries over 1,000,000 neurons of vision information. It is only 2.0 mm in diameter. It has two components: an outer portion called the optic disk and inner portion called the cup. The cup is always smaller than the disk and the relative size of one to the other is called the cup disk ratio. The cup disk ratio (C/D) ranges from 0.0 to 0.99. An average cup/disk ratio is 0.1 to 0.5. The lower the cup disk ratio the less likelihood of glaucoma.

Cup disk ratios over 0.5 are suspicious as are any patients where the cup disk ratio differs by .2 or more between the two eyes.

There are other portions of the nerve referred to as the ganglion cell layer and the retinal nerve fiber layer.

These are portions of the nerve where the thickness can be measured and
compared to age matched controls with advanced imaging called Zeiss Ocular Coherence Tomography (OCT). This remarkable device takes sections of the optic nerve and retina with optical imaging analogous to a CAT scan. Stone Eye Center was the first glaucoma practice in Chicago to adapt spectral domain Cirrus OCT as its standard for glaucoma detection.

Dr. Stone devised a novel approach to early glaucoma detection at the American Academy of Ophthalmology in 2009, after which time his methodology has become standard. One of the precepts was that the RNFL test was one of the most important test for early detection. Other important aids for detection are: intraocular pressure, corneal thickness, visual field testing, and cup disk ratio assessment. Equally important to identifying glaucoma, is being able to discern those that do not have glaucoma, thus avoiding unnecessary treatment.

In its early stages the optic nerve may show some damage, yet the peripheral vision testing is still normal. At Stone Eye Center, we are leaders in diagnosing glaucoma in this pre-vision loss stage. . Untreated glaucoma takes 15 years on average to ravage the nerve. At the time of diagnosis one eye may be more advanced than the other.