National Organization for Rare Disorders (NORD):  www.rarediseases.org - 

NORD is a federation of voluntary health organizations dedicatedto helping people with rare diseases.

Center for Parent Information and Resources (CPIR): http://www.parentcenterhub.org/disability-landing/  - 

CPIR has information about the category of OHI.

US National Library of Medicine (NIH): https://www.nlm.nih.gov/ - 

NIH provides links to databases and literature regarding medicalconditions and diseases.