The American Medical Association CPT code book has had consistent language defining new or established patients for many years.

This was the case even prior to evaluation and management (E/M) changes in 2021 stating that referrals within a group practice are billed as established patient codes (99212-99215) when the physicians are the “exact same specialty and subspecialty.”

What Are Ophthalmic Subspecialties? 
Although AMA has a specific definition, the payer actually defines what a subspecialty covers. The Centers for Medicare & Medicaid Services (CMS) does not always follow AMA rules and has published its own specialty codes, including any recognized subspecialties.
All ophthalmology subspecialties, even those with specific taxonomy codes, are included in a single specialty code (18). This is unlike other subspecialties with separate codes like neuromuscular (25), neurology (13), orthopedic (20) and hand surgeon (40).

The Medicare Provider and Supplier Crosswalk database links the specialty code for ophthalmology (18) to the following code sets (aao.org/taxonomy):

207WX0120X for cornea specialist; 
207WX0009X for glaucoma specialist; 
207WX0109X for neuro-ophthalmology;
207WX0200X for oculoplastics specialists;
207WX0110X for pediatric ophthalmology and strabismus specialist; 
207WX0107X for retina specialists;
207WX0108X for uveitis and ocular inflammatory disease.

For CMS, all ophthalmic subspecialties would consider internal referrals established patients if an ophthalmologist in the same group has seen them within the past three years.

A physician’s specialty and taxonomy are designated during credentialing. For Medicare, the specialty is identified on form 855i (single specialty for ophthalmology) and the taxonomy in the National Plan and Provider Enumeration System (NPPES) linked to the national provider identifier (NPI).

Some payers may follow Medicare's rules and others may publish unique taxonomy/specialty code mapping, which provides guidance and may still designate ophthalmology as one specialty.

Practices may identify varied payer policies. However, receiving payment for a new patient visit does not necessarily confirm the payer’s policy. It may be subject to recoupment. Confirm the payer's policy related to specialty codes, the physician’s specialty designation during credentialing and the taxonomy code submitted on the claim for accuracy.

Neuro-Ophthalmology, Dual Specialties
Some payers may allow designating neurology (13) as the only specialty code during credentialing when meeting their requirements (e.g., neurology board certification). In this unique case, the payer may recognize the different specialty from ophthalmology and allow you to bill internal referrals as a new patient.