Direct ophthalmoscope a valued tool for examining optic disc

January 15, 2006

Chicago—Examining the optic disc using the direct ophthalmoscope is a preferred method among some glaucoma specialists, including George Spaeth, MD, who spoke at the American Academy of Ophthalmology annual meeting.

"Our job as physicians and our privilege is to try to prevent those who are already disabled from becoming worse and those who are not yet disabled from becoming so," said Dr. Spaeth, director, William and Anna Goldberg Glaucoma Service and Research Laboratories and the Louis J. Esposito Research Professor, Wills Eye Hospital/Jefferson Medical College, Philadelphia. "Diagnosis of glaucoma is based primarily on whether the optic disc is damaged and follow-up is based on whether the disc is deteriorating."

He emphasized the lack of time in clinical practice and the need to concentrate on the essentials. Regarding the diagnosis, determining the width of rim/disc ratio and the size of the disc are essential elements.

During follow-up of patients, clinicians should look for a narrower width of the rim than previously or a circumferential extension of absence of the rim.

"Clinicians should concentrate on the size of the disc and on the width of the narrowest rim," Dr. Spaeth emphasized.

Importance of optic disc

Concentrating on the disc is important in diagnosing glaucoma, he noted, because a disc with an abnormally narrow rim or an area of rim absence is a highly reliable sign (more than 90% likelihood of being correct) of glaucoma. The disc is also a valuable prognostic sign, because if a person has developed glaucoma as determined by development or progression of a damaged disc, the damage will almost certainly continue unless effective treatment is started.

Finally, the disc is useful in following the patient: when the disc has gotten worse, the glaucoma has gotten worse. The disc is the most reliable sign that glaucoma will worsen. A deteriorating disc will be worse in almost all cases.

The value of disc examination is greater than for most "risk factors," he said. For example, in patients with a thin central cornea and an IOP greater than 27 mm Hg, he explained, clinicians will err in almost two-thirds of such cases if they suspect that the patients' condition will deteriorate.

Dr. Spaeth pointed out that he relies primarily on the direct ophthalmoscope.

"It is a beautiful instrument, few physicians use it, and most who do use it do so improperly," he said. "I use the Disc Damage Likelihood Scale to diagnose and manage glaucoma, and I also examine masked to earlier patient information."

He likes the direct ophthalmoscope because it allows illumination of the optic disc and peripapillary retina from different angles, which creates shadows and provides texture. This appreciation of the disc and peripapillary retina is possible because the direct ophthalmoscope allows the light to be shined from side to side, which, Dr. Spaeth pointed out, cannot be done to the same degree with any other instrument.

The direct ophthalmoscope is also advantageous in that it provides higher magnification, which allows visualization of the small blood vessels. In addition, the direct ophthalmoscope also allows illumination of the optic disc without illuminating the retina; this is valuable because when the beam includes the retina the disc color cannot be noted accurately.

When using the direct ophthalmoscope, Dr. Spaeth explained, the beam has to be smaller than the disc. The beam is scanned over the surface of the disc.