Nomagram for Calculating Optic Nerve Head Rim Area Using Clinical Parameters
Purpose
Recent studies have identified several OCT optic nerve head parameters, such as rim area, that are superior to cup-to-disc (c/d) in identifying patients with glaucoma. In this study we present and validate a method for calculating optic disc rim area clinically.
Methods
We performed a retrospective chart review of patients diagnosed with primary open angle glaucoma. We validated our model for calculating rim area by using disc diameter and c/d as measured by OCT against rim area measured by OCT. We then obtained c/d and optic nerve size from the electronic medical record from one clinican. Using only these clinical parameters we calculated a predicted rim area (RAp) by applying our model. We compared RAp against rim area as measured by OCT (RAoct) using a Pearson’s correlation coefficient.
Results
In our chart review, we identified 144 eyes with primary open angle glaucoma, of which 36 had slit lamp optic disc size documented. In our validation step, our predicted rim area calculated using our model had excellent correlation with measured OCT rim area (r = 0.98, p < 0.05). Using clinical c/d, clinical nerve height and our model to calculate RAp we achieved excellent correlation with RAoct (r = 0.93, p < 0.05).
Conclusion
We present the first method that allows for calculation of nerve rim area without ancillary testing equipment. With this model we have developed a nomogram that allows clinicians to quantify rim area at the slit lamp. We hope to provide clinicians with additional information when assessing patients who have glaucoma, as well as provide access to rim area information to rural centers who do not have access to OCTs.