The Kestenbaum capillary number index is defined as the number of capillaries observed on the optic disc. It was first described in 1947 by Alfred Kestenbaum as a method to quantify the degree of optic atrophy.
The normal count is about 10. In optic atrophy, it decreases to fewer than 6; if it exceeds 12, optic dischyperemia is suggested.
Kestenbaum’s sign is a quantitative measurement of the vascular profile of the optic disc and is used for:
Quantifying the degree of optic atrophy
Assisting in the diagnosis of borderline optic atrophy
Simple clinical evaluation of the optic disc in glaucoma
QCan the Kestenbaum index be measured without pupil dilation?
A
Yes. In the original method, it is stated that usually 9 large vessels and about 10 small vessels can be observed without dilation. However, for more accurate assessment, observation under dilated pupils with magnified stereoscopic view is recommended.
The Kestenbaum index is a diagnostic indicator, so there are no subjective symptoms associated with the index itself. Depending on the cause of the underlying optic atrophy, symptoms such as decreased visual acuity, visual field abnormalities, and color vision abnormalities may occur.
Measurement method: Starting from the 12 o’clock position, count all vessels crossing the optic disc margin. Count arterioles, venules, and small vessels individually. “Small vessels” refer to vessels that cannot be identified as either arteries or veins.
Findings in normal eyes: Without dilation, usually 9 large vessels (4-5 veins, 4-5 arteries) and about 10 small vessels are observed. The course from the arterioles on the disc surface to the peripapillary retinal capillaries is clear.
Severe atrophy cases: A score of 1 indicates severe optic atrophy. Borderline cases: Even if the optic disc appears normal, if only 2-3 small vessels can be counted, it is significantly below the normal level of 9-10, suggesting atrophy.
Optic atrophy occurs as a result of axonal degeneration at the optic disc. The following are representative diseases that cause a decrease in the Kestenbaum index.
Glaucomatous Optic Neuropathy
Chronic open-angle glaucoma: One of the most common causes. Disease progression is associated with vascular dysregulation.
Findings of glaucomatous optic neuropathy: Characteristic features include vertical cup enlargement, thinning of the neuroretinal rim, NFLD, disc hemorrhage, and nasal displacement of disc vessels 2).
Diagnostic criteria: A vertical cup-to-disc ratio of 0.7 or more and a rim-to-disc ratio of 0.1 or less warrant further examination. A cup-to-disc ratio of 0.9 or more may be diagnostic of glaucoma based on optic disc findings alone 4).
Other Causes
Optic neuritis: One of the main causes of optic atrophy. It is known to be associated with multiple sclerosis.
Ischemic optic neuropathy: Optic atrophy due to anterior ischemic optic neuropathy (AION).
QIf the Kestenbaum index is low, is it necessarily glaucoma?
A
No. A decrease in the Kestenbaum index suggests the presence of optic atrophy, but the cause is not limited to glaucoma. Optic atrophy can occur in many diseases such as optic neuritis, ischemic optic neuropathy, compressive optic neuropathy, and traumatic optic neuropathy. Differential diagnosis requires a comprehensive evaluation combining medical history, visual field testing, and imaging studies.
Observe the optic disc with an ophthalmoscope (direct ophthalmoscope or slit-lamp biomicroscope with a pre-corneal lens) and count the vessels crossing the disc margin clockwise from the 12 o’clock position. Mydriasis is not essential, but observation with magnified stereoscopic view is recommended 1).
Measurement of the Kestenbaum index is performed as part of a comprehensive evaluation of the optic disc. The ISNT rule (rim width: inferior > superior > nasal > temporal) can be a reference for rim width assessment, but it has been reported that less than 45% of normal eyes follow this rule 3).
Main findings of glaucomatous optic neuropathy include vertical enlargement of the cup, diffuse or focal thinning of the neuroretinal rim, disc hemorrhage, nasal displacement of disc vessels, exposure of circumlinear vessels, and diffuse or focal thinning of the RNFL2).
In differentiating glaucomatous optic atrophy from non-glaucomatous optic atrophy, rim pallor (non-glaucomatous) and rim loss (glaucomatous) are the most effective distinguishing features. The cup in non-glaucomatous optic atrophy is shallow and relatively smooth, and decreased rim color precedes cup enlargement.
The healthy optic disc surface contains numerous capillaries that originate from branches of the retinal arterioles and continue to the peripapillary retinal capillaries. These are supplied by the central retinal artery unless a cilioretinal artery is present, which occurs in 5–40% of patients.
In optic atrophy, capillaries on the disc surface disappear along with axonal degeneration. In glaucomatous eyes, as cupping progresses, capillaries within the disc are lost, and dropout of radial peripapillary capillaries is observed in areas corresponding to NFLD.
The progression of chronic open-angle glaucoma is associated with vascular dysregulation such as local vasospasm and systemic hypertension. The Kestenbaum index provides findings that support the involvement of vascular etiology in the end stage of optic atrophy.
OCTA enables non-invasive observation of intra- and peripapillary vascular structures in glaucomatous eyes 4). It is known that superficial retinal blood flow decreases with advanced glaucoma4). Although the correlation of the Kestenbaum index with these quantitative imaging techniques has not yet been validated, it is expected to serve as a simple preliminary assessment.
Even as the role of advanced imaging diagnostics increases, counting Kestenbaum capillary numbers can be introduced to strengthen or weaken suspicion of optic disc abnormalities in borderline cases. It remains useful as a rapid preliminary assessment of the optic nerve, especially in settings where imaging equipment is not available.
QCan the Kestenbaum index replace OCT?
A
The Kestenbaum index cannot replace OCT. OCT objectively and quantitatively measures retinal nerve fiber layer thickness and allows comparison with a normative database. However, the Kestenbaum index is a simple evaluation method that requires no special equipment and can be performed with only an ophthalmoscope. It is valuable in situations where imaging equipment is unavailable or as a screening aid.
