Disc Damage Likelihood Scale
Chat Highlights
February 15, 2006

On Wednesday, February 15, 2006, Dr. Jeff Henderer, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Disc Damage Likelihood Scale."

Moderator:  Everyone's first question is going to be, “What is the Disc Damage Likelihood Scale (DDLS)?”

Dr. Jeff Henderer:  The DDLS is a new way to describe the optic nerve.  Instead of a cup/disc (c/d) ratio, you generate a rim/disc (r/d) ratio and measure the nerve size.  That's a better way for two reasons.  First, you can eliminate the effects of disc size (which is so variable in people) and second, you can concentrate on the rim, which is the actual part that is damaged.

P: Who developed the DDLS?

Dr. Jeff Henderer:   Dr. George Spaeth designed the DDLS and I helped to test it.  A lot of research fellows have also assisted.

P: Is the DDLS a diagnostic tool?  A risk assessment tool?  What is it used for?

Dr. Jeff Henderer:   Any disc staging scale should provide (1) diagnostic ability, that is, to recognize disease, (2) the ability to determine the extent of disease, (3) the ability to monitor for change.  The DDLS has ten stages, like the c/d ratio, to accomplish those three goals.

P: What does the DDLS tell you that you can't see from looking at the optic disk or from a visual field test?

Dr. Jeff Henderer:   Not much.  I guess we only know what glaucoma is because someone who came before us described a nerve rot that had some characteristic features.  In other words, it's glaucoma because we call it glaucoma.  There's no blood test.  The optic nerve changes are something that you can see without the DDLS, but this staging system allows you to better record and communicate your observation.  The visual field is the same.  You can see it, but a scale makes it easier to record your impressions.

P: Will the DDLS replace the c/d ratio system?  Is the DDLS widely used?

Dr. Jeff Henderer:   We hope that the DDLS, or a scale like it, will replace the c/d ratio.  Right now, it is not widely used, but we hope to change that.  We have been modifying the scale over the years, and so we've created confusion ourselves.  Now the scale seems to be set, so we'll see.

P: I was diagnosed by an optometrist as a glaucoma suspect because of large (.5) cupping.  Then I was examined by a glaucoma specialist, and I took a visual field test.  The specialist said I have no damage to my optic nerve, my visual field test is normal, and so are my intraocular pressures.  In my situation, would the DDLS be useful?

Dr. Jeff Henderer:   The DDLS would be very useful because it measures disc size.  It turns out that since we all have about the same number of nerve cells and we all have very different sized nerves, some nerves will be more "filled" than others.  That means big nerves will have big cups and small nerves will have small ones.  The c/d ratio misses this fact; the DDLS does not.  Without knowing the nerve size, you can't know the expected amount of cupping.

P: At what stage on the DDLS do visual field defects usually occur?

Dr. Jeff Henderer:   With the most recent version of the scale for an average size nerve, I believe that 4 or 5 would be the stage that would show a field defect.  Maybe early stages, too, but you'd expect a defect by 4 or 5.

P: What would be the rim/disc ratio of an optic nerve with no cupping?

Dr. Jeff Henderer:   Actually, a nerve with no cup will have a maximum rim/disc ratio of 0.5.  The minimum would be an area of no rim, and then we add areas of rim loss to record more and more damage.  The rim/disc ratio would be the narrowest rim width over the disc diameter in that same location.

P: Is the DDLS easy for other doctors to learn and adopt?

Dr. Jeff Henderer:   The DDLS is really nothing more than a system that codifies what we all do anyway.  No doctor looks at the cup only.  We all look at the rim.  But we record the cup.  A bit odd, but that's the way we've done it since the Sixties.  So anyone can do this.  Now, remembering the nerve sizes and the specific details of the actual stages can be tough, but it's not too bad.

P: Is it important to follow up with the same doctor for consistency?

Dr. Jeff Henderer:   Yes, but if there is an accurate description of the nerve in the chart (photo, drawing, or such), then anyone should be able to understand what is going on.  What is not very helpful is an isolated c/d ratio. That's not very useful.

P: My cup/disc ratio is .7 right and .5 left.  Would DDLS give some additional information?

Dr. Jeff Henderer:   Yes, because you would highlight areas of abnormally narrow rim and you would know if the asymmetry was due to rim loss in one eye, or if is due to a physiologic (normal) asymmetry between the size of the nerves.

P: Where can doctors find information about using the DDLS?

Dr. Jeff Henderer:   Information about DDLS has been published in the American Journal of Ophthalmology and the most recent version of the DDLS (or one very close to it) was recently published in Highlights of Ophthalmology (2003).

[Editor's Note: See also "The Optic Disc:  That Which Must Be Understood in Glaucoma and the DDLS" by Dr. Jeffrey. D. Henderer, M.D. http://www.willsglaucoma.org/2003symp/henderer.htm ]

P: What is the future of the DDLS?

Dr. Jeff Henderer:   We want to be sure that we test its validity (that is, how it compares to the visual field) and see how it performs against the c/d ratio at detecting change.  We also need to investigate how the DDLS can be combined with the visual field to create an overall glaucoma risk scale.

The scale's concept of understanding the effects of disc size and recording the rim, not the cup, is widely accepted.  The details of the scale are not so widely accepted, because it is a new thing to learn and there are three scales (for small, medium, and large nerves) to learn.

P: Could my doctor begin to use this scale just by locating and reading the literature?

Dr. Jeff Henderer:   Yes.  That's an easy way for your doc to learn about the scale.

Moderator:  There is a good article about DDLS and some good photos on the Wills site.  [See: "The Disc Damage Likelihood Scale and Patient Care" by Ken Parker, Ph.D. in Searchlight On Glaucoma, Vol 12, No. 2, August 2003.] http://www.willsglaucoma.org/searchlight/vol12no2.html

P: There's something I'm not understanding about DDLS.  It seems to me that an optic nerve with a c/d ratio of 2/3 would have a rim/disc ratio of 1/3; a nerve with a c/d of 3/4 would have a rim/disc ratio of 1/4.  In all cases, the ratios add up to 1, and in all cases you're still looking at the same data, really.  I don't see what the real difference is in the systems.  Can you explain a little more?

Dr. Jeff Henderer:   I suppose that if you had a perfect circle inside a perfect circle then you'd really not gain much.  But the cup and disc are not circles.  That means some areas of the rim are wider than others. It's the loss of this expected pattern of rim width that is highlighted by the rim/disc ratio.  The disc size is the other issue.

On February 22, Dr. Wilson discussed "The Normal Tension Glaucoma Workup" in the Chat room. Click here for highlights of that meeting.

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