CPT Code 66999: Unlisted Procedure, Anterior Segment of the Eye

What is an unlisted anterior segment procedure?

The 66999 CPT code refers to an unlisted procedure involving the anterior segment of the eye, typically used when no specific CPT code accurately describes a surgical procedure performed on a patient. It’s often reported for combined glaucoma procedures, like minimally invasive glaucoma surgery (MIGS) performed alongside cataract surgery, or for newer techniques involving devices such as the Xen gel stent or iris expansion devices.

Since these unlisted procedures fall outside existing Category III codes, thorough documentation is crucial to support medical necessity, especially for cases involving complex cataract surgery, micro invasive glaucoma surgery, or concomitant cataract removal.

Unlisted anterior segment procedures may also be necessary for advanced conditions like primary open-angle glaucoma, where conventional or MIGS techniques are applied. In some instances, these unlisted procedures may include both cataract and MIGS components, particularly when standard codes fail to reflect the full scope of care.

Because CPT code 66999 serves as a placeholder rather than a clearly defined procedure, it's essential to describe any manual or mechanical techniques, the use of an intraocular lens prosthesis, or steps like anterior capsulotomy. This flexibility allows providers to document innovative or atypical procedures of the anterior segment that lack a current procedural terminology match, helping ensure reasonable and necessary services are appropriately billed and reimbursed.

Documentation requirements

Extensive documentation is required and should include:

• Detailed description of the procedure and clinical indications: Define what was done and why, since CPT 66999 is a catch-all unlisted procedure without a defined description.
• Justification for using an unlisted code: Explain why an existing Category I or III CPT code doesn’t apply (e.g., new or hybrid procedures involving MIGS, Xen stents, or ECPC).
• Intraoperative technique and equipment used: Include specific tools, implants (e.g., intraocular lens, iris expansion device), and whether a manual or mechanical technique was performed.
• Surgical site, laterality, and anesthesia: Required to provide a complete clinical picture. Supports proper modifier usage and medical necessity documentation.
• Comparable procedure(s) and relative complexity: Payers often require a reference code (like 66984 for routine cataract surgery) to assess reimbursement. Complexity comparisons are also important.

A separate cover letter or statement of medical necessity is usually necessary for payer review. Strongly recommended and often required by Medicare and commercial payers, especially for prior authorization and claims processing of unlisted codes.

Billing guidelines

Follow these guidelines for accurate billing and appropriate reimbursement:

• Requires manual pricing along with a clear fee rationale to support the billed amount.
• Standard modifiers like -TC (technical component) and -26 (professional component) may be used if the payer accepts them for unlisted codes. Avoid using modifier -50 (bilateral) unless explicitly allowed.
• Prior authorization is strongly recommended to determine whether the unlisted procedure anterior segment is medically necessary and meets payer criteria.
• Coverage may be denied without adequate supporting documentation, including FDA approval, published clinical studies, or evidence of clinical efficacy for minimally invasive glaucoma surgery (MIGS) or micro-invasive procedures. May not be covered without supporting literature, FDA status, and evidence of clinical efficacy.
• Providers may indicate increased procedural services when submitting 66999 to reflect the additional complexity or duration of the surgical technique.

Before reporting the 66999 CPT code, confirm that the service isn't more accurately represented by an existing code, such as:

• 66982 – Complex cataract surgery
• 66984 – Routine cataract removal with intraocular lens prosthesis

Other relevant CPT codes

• 66984 – Cataract surgery with IOL, standard
• 66982 – Complex cataract surgery
• 65855 – Laser peripheral iridotomy