Examining the optic nerve head is crucial both for diagnosing glaucomatous damage and managing patients with glaucoma or suspected to have glaucoma. Previous studies examining subjective assesments of the cup to disc ratio have demonstrated a low level of interoberserver, and even intraobserver agreement.
Since Armaly described cup to disc ratio as a method of optic nerve head(ONH) classification in 1969, it became the most commonly used method of ONH assesment. However, the disadvantage of this method leads to a lot of confusion on documenting glaucomatous optic disc considering the effect of optic nerve size and the focal rim loss, etc.
The Disc Damage Likelihood Scale (DDLS) is a method of assesment of the optic nerve developed by Professor George Spaeth, Wills Eye Hospital. The DDLS was designed in an attempt to provide a more accurate and valid method for defining glaucomatous optic nerve damage.
Henderer JD et al did a study on DDLS and concluded that DDLS had higher sensitivity and specificity for detecting glaucomatous changes versus cup to disc ratio. In another study he showd that inter and inra observer agreement for DDLS is greater than the Armaly cup to disc ratio.
The DDLS Step by Step as described by Prof. Spaeth:
Step 1
Dilate the eyes if necessary. The pupils must be sufficiently large to allow a clear view of the fundus.
Step 2
Get an idea of both of the patients optic nerves by a brief examination with a strong plus lens (eg. +66.00 D) using the slit lamp. Determine the vertical size of the discs. For example, if you use a +66.00D lens, the graticule on the slit lamp from Haag-Streit AG (Koniz, Switzerland) with indicate the size in millimeters. Multiply this figure by 0.9 for a +60.00D lens or by 1.3 for a +90.00 D lens.
Step3
Choose one of the patients eye to concentrate on first. With a direct ophthalmoscope, examine the optic disc for an area where its outer edge is clearly distinguished from other ocular tissue such a sclera. Then, determine the full circuference of the outer edge.
Step4.
Define the inside edge of the neuroretinal rim(outer edge of the cup) by direct ophthalmoscopy. Estimate the rim to disc ratio by comparing the with of the neuroretinal rim with that of the disc diameter on the same axis. Perform this comparison at several clock positions. If the rim to disc ratio is different at various parts of the rim, note the area at which the rim is narrowest and calculate the rim to dic ratio there.
Step 5
Draw the shape of the optic disc. When sketching the neuroretinal rims inner edge, indicate clear demarcation with a thick line and less clear demarcation with a thin or hatched line. Note the course of blood vessels that help determine the rims width and any pertinent features of the disc(eg. notches, pallor, hemorrhage etc.)
Step 6
Determine the DDLS by using your drawing of the disc, the narrowest rim to disc ratio, the size of the disc, and the DDLS nomogram (figure 1). If the nerve is smaller or larger than average, you must adjust the DDLS score appropiately. An easy method is to stage the nerve as if it were of averaage size and then increase the stagae by one if the nereve is small or decrease the stage by one if it is large. Note the DDLS score in the patients chart.
Step 7
Repeat steps 3 to 6 for the patients other eye.
Staging is done as follows:
The Glaucoma graph is a simple way of explaining patients about the progress of disease.
The single best indicator that the glaucomatous process is or was present is the existence of glaucomatous damage. Every other prognostic factor is indirect. The only indication that glaucomatous process is continuing is continuing damage. DDLS is the best way to asses whether the damage is present and whether the damage is continuing.
The general oder of examination is to look at the right optic nerve first, and then the left optic nerve, getting the rough assesment as to the DDLS. The important factors that need to be considered are
1. The diameter of the optic disc
2. The width of the neuroretinal rim
3.Valid definition of the outer edge of the disc and the outer edge of the cup using direct ophthalmoscope
4. Definition of internal edge of the neuroretinal rim, that is the outer edge of the cup
5. Drawing of the disc
6. Caliculating the Disc Damage Likelihood Score
7. The size of the dics needs to be taken into consideration during scoring [ small <1.5mm,>2.omm in vertical diameter]
8. The two important factors considered during staging are, the narrowest width of the rim and extent of absence of neuroretinal rim
Uses of DDLS:
1. It is used in the diagnosis of glaucoma
Discs with a DDLS of 5 or more are not healthy. Such discs are not necessarily glaucomatous, but they are virtually always pathologic.
A DDLS so stege 1 would be extremely rare in a patient who had glaucoma.
THe DDLS has a lower positive predictive value when the score is 2. Stage 2 disc could be a deterioration from stage 1 or stage 2 could be entirely normal for that person
2. DDLS can be used as a way to categorize the severity of the condition
Visual field loss does not develop until patients deteriorate to stage 4 of the DDLS. Patients who do not have visual field loss usually do not have visual symptomatology from glaucoma. DDLS stages 1,2 or 3 does not damage the person functionally. We can wait and watch in these patients. At the other end of the spectrum, DDLS stages 5,6, 7, or 8, the conditon has declared itself by showing certain damage in the visual field.
3. DDLS can be used as a method of monitoring the course of glaucoma
There are some associated signs which are of highest predictive value in indicating that the changes are actually glaucomatous.
Aquired pit of the optic nerve - Pathognomonic
Absence of neuroretina rim ina focal area - Highly suggestive
especially inferotempora or superotemporal
Notch in the rim - Highly suggestive
Documented progressive narrowing of - Highly suggestive
a rim/width ratio for more that 1 stage
Hemorrhage across the rim - Moderate value
Asymmetry of DDLD between 2 eyes - Moderate value
Summary:
The Disc Damage Likelihood Scale provides a quantitative method of assessing the glaucomatous optic nerve damage. Combining DDLS with other information like patients symptoms and patients risk factors helps in establishing the rate of change in patients condition; this information assists in assuring that the patients treatment is rational and effective.
