Understanding Types of Glaucoma

When coding glaucoma, terms such as primary, open angle, closed angle, primary angle closure, and narrow angle can leave a coding professional confused and frustrated.  These terms seem to be used interchangeably within the documentation and from one provider to another.  Therefore, it is helpful to gain a better understanding of the clinical picture of glaucoma.


In a normal eye aqueous humor flows through the trabecular meshwork between the anterior and posterior chambers in the anterior segment of the eye.  Glaucoma may be primary when the cause is unknown or secondary when the underlying condition is known. Glaucoma is increased pressure in the eye caused by excess aqueous humor.  This typically occurs because there’s a blockage somewhere in the drainage system also known as trabecular meshwork and canal of Schlemm.  Basically, there are two different types; open angle and primary angle closure.  Open angle, the most common, occurs when the angle between the cornea and iris is open but the meshwork is blocked.  Primary angle closure occurs when the angle between the cornea and iris is so tight or narrow that the fluid is blocked.


Open angle glaucoma is also known as wide angle or chronic glaucoma and develops slowly over time. Open angle glaucoma is identified by code category H40.1- and requires documentation of the stage (mild, moderate, and severe). Indeterminate stage must be based on physician documentation as this option is when the stage cannot be clinically determined.  The open angle codes include N40.12- low-tension also known as normal tension because the intraocular tension may be normal but the meshwork is blocked.  Pigmentary glaucoma is coded N40.13-.  This type occurs when portions of the iris break off and clog up the meshwork.  Pseudoexfoliation glaucoma is coded H40.13- occurs when proteins in the eye build up over time and get trapped in the trabecular meshwork.


Narrow angle or angle closure glaucoma is less common and develops very quickly and requires immediate medical attention.  The codes for narrow angle are H40.2- and identify acute attacks, chronic angle-closure, and intermittent attacks.  Because narrow angle glaucoma comes on suddenly symptoms are more dramatic such as pain, redness, blurred vision, nausea, and headaches.


The code category H40.0- glaucoma suspect is for patients who are pre-glaucoma or showing signs of possible glaucoma but have not been diagnosed.  In these codes the patient is assessed if they are at low-risk or high-risk for the development of open angle glaucoma.  For example: H40.023 Open angle with borderline findings, high risk, bilateral.  


Understanding the different types and causes of glaucoma is important for proper coding and reporting.  Our coders are provided both clinical and coding education through our LMS (learning management system) to help them to maintain exceptional coding skills and prevent over-coding or under-coding commonly seen among inexperienced coders.  We have the workforce solutions to assist with all of your HIM coding needs.