Ratios in Ophthalmology

RATIO IN OPHTH

• ·         Kesten-Baum index refers to ratio of large blood vessels versus small blood vessels on the disc. Normal ratio is 4:16. This ratio is decreased in patients with optic atrophy.
• ·         Cup-disc ratio. Normal cup disc ratio is 0.3. (i) Large cup may be physiological or glaucomatous. (ii) Cup becomes full in papilloedema and papillitis.
• ·         Results of EOG are interpreted by finding out the Arden ratio as follows:

Arden ratio = (Maximum height of light peak/ Minimum height of dark trough) × 100

Normal curve values are 185 or above.

Subnormal curve values are less than 150.

Flat curve values are less than 125.

• ·         Normal arterioles are bright red in colour and veins are purplish with a caliber ratio of 2: 3. Following abnormalities may be detected:

Narrowing of arterioles is seen in hypertensive retinopathy, arteriosclerosis, and central retinal artery occlusion.

Tortuosity of veins occurs in diabetes mellitus, central retinal vein occlusion and blood dyscrasias.

Sheathing of vessels may be seen in periphlebitis retinae, and hypertensive retinopathy.