Optic Cup Size In Relation to The Optic Disc Size
Pearls
Optic cup size or border is determined by contour and NOT by color.
Must be examined stereoscopically.
Similar to optic disc size and neuroretinal rim area, there is considerable normal interindividual optic cup size variability.
The size of the optic cup is proportional to the size of the optic disc.
The cup- disc ratio (CDR) can range from 0.0 to 0.9 in the normal population with significant overlap between normal patients and glaucomatous patients.2
Small CDR in smaller nerves, large CDR in larger nerves—both normal.
The larger the optic disc, the larger the optic cup.
Caution with overdiagnosing large CDRs in large discs.
A large optic cup in a large optic disc should not automatically be diagnosed as glaucomatous, especially if the other optic nerve features (i.e., neuroretinal rim shape, retinal nerve fiber layer, etc.) are normal.
Risk for overtreatment.
Caution with underdiagnosing/misdiagnosing average CDR in small discs with or without ocular hypertension.
Early or moderate glaucomatous optic nerve damage may erroneously be overlooked in small discs because of “ pseudo-normal” appearance.
Risk for undertreatment.
Carefully examine the parapapillary region for decreased retinal nerve fiber layer visibility (diffuse or focal), decreased arteriole diameter (diffuse or focal), and parapapillary chorioretinal atrophy.
Constant in size after first years of life.
Unlike glaucoma, the optic cup does not significantly enlarge and therefore the neuroretinal rim will not significantly decrease.
The increase in cup area is an important marker to differentiate between glaucomatous and nonglaucomatous optic nerve damage.
The neuroretinal rim does not significantly decrease in eyes with nonglaucomatous optic nerve damage.
The size of the optic cup may be more predictive of future functional progression than the amount of remaining neuroretinal rim.3
The amount of remaining neuroretinal rim may correlate better with the patient’s current level of functional status.
