You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Combining structure and function to evaluate glaucomatous progression: implications for the design of clinical trials. The selection of a suitable method for assessment of glaucomatous progression and estimation of rates of change is an essential component of the design of clinical trials investigating neuroprotective therapies for the disease. Due to the limitations of currently available tests, approaches combining structural and functional tests are essential in order to provide reliable detection of endpoints. This could also potentially enable shorter clinical trials with relatively smaller sample size requirements. A recent approach for estimating rates of retinal ganglion cell loss using a combination of structural and functional tests has been shown to perform better than isolated parameters from conventional tests for diagnosing, staging and detecting glaucoma progression and may prove useful as an outcome measure in clinical trials of the disease.
{"Chemical": []}