Fig. 8.1 2 × 2 table used in the deÞnition of sensitivity and speciÞcity

the source of decades-long controversy over the proper way to deÞne ischemia (see Chaps. 4 and 9).97 Measurement of macular thickness in macular edema has a reproducibility that can be quantitated by the coefÞcient of repeatability (COR). This is the difference between any two measurements above which one can be 95% conÞdent that the change is real and not due to measurement variability.9 For example, in the OCT measurement of diabetic macular edema, the COR is ±11% of the macular thickness.14 SpeciÞcally, if we suppose that a baseline macular thickness is 300 mm by time-domain OCT (TD-OCT), then we can be 95% conÞdent that a measurement of 335 mm at a follow-up visit represents a true worsening of the patientÕs macular edema (ME) because the 35 mm of extra thickening is greater than 11% of the baseline measurement. Test equipment improves all the time, therefore reproducibility depends on technology. For example, reproducibility with some spectral-domain OCT (SD-OCT) machines is better than with TD-OCT machines.