View source for Cisco OID's for Optical Receive Power

Ensure snmp is installed. If not, install the package snmp. Run the command snmpwalk -v2c -c public [ip address]. This will return a list of OID's, filter for the string of the value you are after (ie. Gi1/1 Transmit power). Take the last number from the OID and run the command snmpget -v2c -c public [ip address] 1.3.6.1.4.1.9.9.91.1.1.1.1.4.[last number]. This will return the current value. This has only been tested for a limited number of OID's. 

#NOTE Ensure SNMP agent is enabled on the Cisco device, the community string being used and any access control lists for SNMP.