H57.02

H57.02 — Anisocoria

Code Overview

H57.02 is a billable ICD-10-CM diagnosis code for anisocoria — a condition characterized by unequal pupil size. It belongs to the H57.0 subcategory (Anomalies of pupillary function) within H57 (Other disorders of eye and adnexa), Chapter 7 (Diseases of the Eye and Adnexa, H00-H59).

Anisocoria is not a diagnosis in isolation — it is a clinical sign that may represent a completely benign physiologic variant or a manifestation of serious, potentially life-threatening neurological or vascular pathology. H57.02 is the appropriate code when anisocoria is the documented finding and no more specific underlying etiology code is available or has yet been established. When a specific cause is identified (Horner syndrome, CN III palsy, Adie tonic pupil, etc.), the underlying condition code is sequenced first, with H57.02 added as an additional manifestation code if still clinically relevant.

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Full Code Description

Element	Detail
Full Code	H57.02
Description	Anisocoria
Billable	Yes
Chapter	7 — Diseases of the Eye and Adnexa (H00-H59)
Block	H55-H57 — Other disorders of eye and adnexa
Category	H57 — Other disorders of eye and adnexa
Subcategory	H57.0 — Anomalies of pupillary function
Laterality	Not applicable
7th Character	Not applicable — 5-character billable code, complete as written
Chronic Condition	Not designated as chronic
Valid FY	FY2025 (Oct 1, 2024 - Sep 30, 2025)

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Clinical Description

Definition

Anisocoria (from Greek: anisos = unequal, kore = pupil) is the clinical finding of asymmetric pupil diameter between the two eyes. The difference may be as small as 0.5 mm or as large as several millimeters and may be fixed or variable. Normal pupil diameter ranges from approximately 2-4 mm in bright light and 4-8 mm in dim light. Anisocoria is detected during routine external eye examination, emergency neurological evaluation, or incidentally on photographs.

Critically, anisocoria itself is not inherently pathological — approximately 15-20% of the normal population has physiologic anisocoria of up to 1 mm (typically ≤ 0.4 mm difference) that has no underlying cause, varies day to day, and requires no treatment. The clinical significance lies in accurately determining whether the anisocoria is physiologic or pathologic, and when pathologic, identifying the responsible mechanism.

Pupillary Anatomy and Neural Control — Foundation for Understanding

The pupil is a circular aperture in the iris controlled by two opposing muscle groups:

Iris sphincter (constrictor pupillae):

• Circular smooth muscle fibers in the iris

• Innervated by the parasympathetic nervous system via the oculomotor nerve (CN III)

• Pathway: Edinger-Westphal nucleus (midbrain) → CN III → ciliary ganglion (orbital apex) → short ciliary nerves → iris sphincter

• Function: pupil constriction (miosis) in response to light, near stimulus

• Damage → dilated pupil (mydriasis), sluggish or absent light reflex

Iris dilator (dilator pupillae):

• Radially oriented smooth muscle fibers

• Innervated by the sympathetic nervous system via the cervical sympathetic chain

• Three-neuron pathway:

  • First-order neuron: hypothalamus → ciliospinal center of Budge (C8-T2 in spinal cord)

  • Second-order neuron: C8-T2 → sympathetic chain → superior cervical ganglion

  • Third-order neuron: superior cervical ganglion → follows internal carotid artery → cavernous sinus → ophthalmic branch of CN V → long ciliary nerves → iris dilator

• Function: pupil dilation (mydriasis) in darkness, sympathetic arousal

• Damage → small pupil (miosis), impaired dilation in darkness — Horner syndrome

Pathophysiology and Causes

The differential diagnosis of anisocoria is systematized by determining:

1. Which pupil is abnormal — is the larger pupil pathologically dilated (efferent/parasympathetic pathway problem) or is the smaller pupil pathologically constricted (sympathetic pathway problem)?

2. When is the anisocoria worse — greater in bright light (large pupil is the problem) or greater in darkness (small pupil is the problem)?

Anisocoria Greater in Bright Light (Large/Dilated Pupil is Abnormal)

Third Nerve Palsy (CN III Palsy):
The most concerning acute cause of a dilated, poorly reactive pupil. The parasympathetic fibers of CN III run on the outside of the nerve and are the most susceptible to compression. A pupil-involving CN III palsy (dilated, poorly reactive pupil + ptosis + down-and-out gaze deviation) is a neurological emergency until a posterior communicating artery (PCoA) aneurysm is excluded. Key points:

• Surgical CN III palsy (pupil-involving): compression of CN III by PCoA aneurysm, uncal herniation, tumor; requires urgent CTA/MRA of the circle of Willis

• Medical CN III palsy (pupil-sparing): ischemic infarction of CN III core (diabetes, hypertension); pupil typically spared because the peripheral parasympathetic fibers receive collateral blood supply

• A complete CN III palsy with pupil involvement is an emergent condition requiring immediate neuroimaging

Adie Tonic Pupil:
A benign condition caused by denervation of the ciliary ganglion (typically from a viral infection, trauma, or idiopathic cause). Presents with a unilaterally dilated pupil that:

• Constricts very slowly and tonically to sustained near stimulus (tonic near response)

• Shows sectoral iris sphincter paralysis on slit lamp (vermiform movements)

• Has light-near dissociation (sluggish to light, better response to near)

• Shows supersensitivity to dilute (0.1-0.125%) pilocarpine (denervation supersensitivity) — confirmatory pharmacologic test

• Commonly affects young women; may be associated with absent deep tendon reflexes (Holmes-Adie syndrome)

• Typically benign; not associated with serious intracranial pathology

Pharmacologic Mydriasis:
Inadvertent or intentional instillation of a mydriatic/cycloplegic agent (atropine, scopolamine, tropicamide, cyclopentolate, phenylephrine). The dilated pupil:

• Does NOT constrict to 1% pilocarpine (distinguishes from CN III palsy, which DOES constrict to 1% pilocarpine)

• History of anticholinergic medication use, transdermal scopolamine patch, or plant contact (Jimson weed, Brugmansia)

• Often incidental finding; resolves spontaneously as drug wears off

Iris Sphincter Damage (Mechanical/Structural Anisocoria):

• Posterior synechiae from uveitis pulling the pupil irregularly

• Iris trauma (traumatic mydriasis from blunt or penetrating ocular injury)

• Acute angle-closure glaucoma (mid-dilated, non-reactive pupil)

• Previous iris surgery or sphincterotomy

Anisocoria Greater in Darkness (Small/Miotic Pupil is Abnormal)

Horner Syndrome:
Interruption of the sympathetic supply to the eye at any level of the three-neuron arc. Classic triad:

• Miosis — small pupil that fails to dilate adequately in the dark; the anisocoria is more apparent in dim light

• Ptosis — partial upper lid ptosis (1-2 mm) from loss of Müller’s muscle innervation

• Anhidrosis — depending on lesion level (only with first- or second-order lesions)

• Dilation lag — the Horner pupil dilates more slowly in the dark than the normal pupil (a key sign)

Causes by neuron level:

• First-order (central): Brainstem stroke, MS, syringomyelia, hypothalamic lesion; MRI brain required

• Second-order (preganglionic): Pancoast tumor (lung apex), cervical rib, thyroid mass, lymphadenopathy at the apex; MRI neck and chest CT required

• Third-order (postganglionic): Carotid artery dissection (urgent!), cavernous sinus pathology, otitis media, cluster headache; MRA/CTA of the carotid arteries is required when carotid dissection is suspected — THIS IS AN EMERGENCY

Pharmacologic localization tests for Horner syndrome:

• Cocaine test (4-10%): Blocks norepinephrine reuptake → dilates normal pupil but NOT Horner pupil; confirms Horner syndrome

• Apraclonidine test (0.5-1%): Alpha-2 agonist; reverses pupillary inequality in established Horner (Horner pupil dilates, normal pupil constricts due to denervation supersensitivity) — preferred because cocaine is a controlled substance

• Hydroxyamphetamine (1%): Releases stored norepinephrine; dilates both pupils if third-order neuron intact; no dilation of Horner pupil if third-order neuron is damaged; localizes lesion level

Other causes of a small pupil:

• Argyll Robertson pupils (H57.01) — bilateral miosis that does not react to light but accommodates to near; classically neurosyphilis but also diabetic autonomic neuropathy, MS; coded separately from H57.02

• Anterior uveitis/iridocyclitis — inflammatory miosis from iris sphincter spasm

• Topical pilocarpine or other miotics

• Opioid-induced miosis (bilateral, non-localizing)

Physiologic Anisocoria

• Present in 15-20% of normal population

• Typically ≤ 1 mm difference (often ≤ 0.4 mm)

• Both pupils reactive to light; no ptosis; no other neurological signs

• Symmetry of reactivity is preserved; anisocoria may reverse sides on different days

• No treatment required; benign reassurance

• Documentation as “physiologic anisocoria” supports H57.02 as the appropriate final code with no further workup required

Clinical Evaluation Algorithm

Step 1 — Determine which pupil is abnormal:
Examine in both bright light and dim light. The anisocoria is greater in light → large pupil is abnormal (parasympathetic/CN III problem). Greater in dark → small pupil is abnormal (sympathetic/Horner problem).

Step 2 — Assess pupillary light reflex:

• Normal light reflex in both pupils → likely physiologic

• Sluggish or absent light reflex in the large pupil → CN III palsy or Adie tonic pupil

• Near reaction better preserved than light reaction → light-near dissociation (Adie or Argyll Robertson)

Step 3 — Assess for associated findings:

• Ptosis ipsilateral to large pupil + down-and-out gaze → CN III palsy (EMERGENCY if pupil-involving)

• Mild ptosis ipsilateral to small pupil + dilation lag → Horner syndrome

• Neck/orbital pain + Horner → carotid dissection until proven otherwise (EMERGENCY)

• Headache + CN III palsy → PCoA aneurysm until proven otherwise (EMERGENCY)

Step 4 — Pharmacologic testing when indicated:

• Dilute pilocarpine (0.1%) → constriction of Adie pupil confirms denervation supersensitivity

• 1% pilocarpine → constriction of CN III palsy pupil; NO constriction = pharmacologic dilation

• Apraclonidine → reversal of Horner confirms sympathetic pathway disruption

• Hydroxyamphetamine → localizes Horner to pre- or postganglionic

Step 5 — Neuroimaging:

• CN III palsy with pupil involvement → emergent CTA or MRA circle of Willis (exclude PCoA aneurysm)

• Horner + neck pain → urgent CTA/MRA carotid arteries (exclude carotid dissection)

• Horner without pain → MRI brain, neck, chest CT (exclude Pancoast, mass lesion)

• New anisocoria in context of trauma, altered consciousness → CT head, CT angiography

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Code Structure / Code Tree

H00-H59    Diseases of the Eye and Adnexa
  └── H55-H57    Other disorders of eye and adnexa
        └── H57    Other disorders of eye and adnexa
              └── H57.0    Anomalies of pupillary function    ◄ **SUBCATEGORY**
                    ├── [[H57.00]]    Unspecified anomaly of pupillary function
                    ├── [[H57.01]]    Argyll Robertson pupil, atypical
                    │            (Light-near dissociation; neurosyphilis / diabetic)
                    ├── [[H57.02]]    Anisocoria    ◄ **THIS CODE**
                    │            (Unequal pupil size; physiologic or pathologic)
                    ├── [[H57.03]]    Miosis
                    │            (Abnormally small or constricted pupil)
                    ├── [[H57.04]]    Mydriasis
                    │            (Abnormally large or dilated pupil, bilateral)
                    ├── H57.05    Tonic pupil
                    │     ├── [[H57.051]]    ... right eye (Adie tonic pupil)
                    │     ├── [[H57.052]]    ... left eye
                    │     └── [[H57.059]]    ... unspecified eye
                    ├── H57.09    Other anomalies of pupillary function
                    └── H57.1    Ocular pain
                          ├── [[H57.10]]    ... unspecified eye
                          ├── [[H57.11]]    ... right eye
                          └── [[H57.12]]    ... left eye

Tip

H57.02 vs H57.05 — Anisocoria vs Tonic Pupil: When the anisocoria is specifically attributed to an Adie tonic pupil (confirmed by slit-lamp signs and/or dilute pilocarpine supersensitivity), code H57.051/H57.052 (tonic pupil, right/left) rather than H57.02. Tonic pupil is a more specific code — use H57.02 when the cause of the dilated/unequal pupil is not yet identified or when the anisocoria is physiologic. When Adie tonic pupil is confirmed, H57.05x is the most specific code.

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Includes / Excludes Notes

Includes (H57.02)

Conditions appropriately captured by H57.02:

• Physiologic anisocoria (benign pupil size variation ≤ 1-2 mm in otherwise normal examination)

• Episodic anisocoria (intermittent, recurrent pupil size asymmetry without identified etiology)

• Pharmacologic anisocoria (when documented as the cause and H57.02 is used as the sign code)

• Anisocoria of undetermined etiology during the diagnostic workup phase (pre-diagnosis)

• Anisocoria documented without further specified cause

Key Coding Decision: H57.02 as Principal vs. Additional Code

H57.02 functions as a symptom/sign code in the ICD-10-CM coding hierarchy. Per Official Guidelines (Section I.C.7 and Section I.B.5):

• Use H57.02 as principal/first-listed: When the anisocoria is the reason for the visit and no definitive causative diagnosis has been established (e.g., initial evaluation encounter, workup in progress, physiologic anisocoria)

• Code the underlying cause first, H57.02 additional: When the cause is identified (CN III palsy → G52.0-, H49.01-H49.03; Horner syndrome → G90.2; Adie tonic pupil → H57.05x), sequence the causative condition first

• H57.02 alone may be appropriate long-term: For physiologic anisocoria where no further evaluation is warranted and the finding is documented as a benign normal variant

Excludes2 at H57 (May Code Together When Both Present)

Code	Description	Can Code With H57.02?
H57.01	Argyll Robertson pupil, atypical	Yes — if both conditions documented separately
H57.05x	Tonic pupil	Generally no — if Adie tonic pupil confirmed, use H57.05x instead of H57.02
G52.0-	Disorders of olfactory nerve (not relevant)	N/A
H49.0x	Third nerve palsy, right/left/unspecified	Code H49.0x as principal if CN III palsy is the established diagnosis; H57.02 may be dropped or added
G90.2	Horner syndrome	Code G90.2 as principal; H57.02 may be used additionally

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HCC (Hierarchical Condition Category) Mapping

H57.02 does NOT map to a CMS-HCC in any current risk adjustment model.

HCC Model	HCC Assignment	RAF Impact
CMS-HCC Model V28	Not assigned	No RAF
RxHCC Model	Not assigned	No RAF
HHS-HCC (ACA Marketplace)	Not assigned	No RAF

Note

Underlying cause HCC opportunity: While H57.02 itself carries no RAF, the identified underlying causes often do. Horner syndrome from a Pancoast tumor (C34.- lung cancer) carries significant HCC weight. Carotid dissection (I77.71-) or stroke (I63.-) driving anisocoria carry HCC weight. CN III palsy from an intracranial aneurysm (I67.1) carries HCC weight. Accurate identification and coding of the underlying etiology maximizes appropriate RAF capture.

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MS-DRG Mapping (Inpatient)

H57.02 as a principal inpatient diagnosis (when anisocoria alone drives admission, rare) groups to:

MS-DRG	Description	Trigger
123	Neurological Eye Disorders	H57.02 as PDx when neurological etiology documented
124	Other Disorders of the Eye with MCC	H57.02 as PDx + qualifying MCC
125	Other Disorders of the Eye without MCC	H57.02 as PDx, no MCC

When admitted under a neurological principal diagnosis with H57.02 as secondary:
The DRG is driven by the neurological principal diagnosis (stroke → DRG 061-066; aneurysm → DRG 073-075; carotid dissection → DRG 069-071). H57.02 is not a CC or MCC and will not upgrade DRG severity as a secondary code.

Note

MDC: MDC 02 — Diseases and Disorders of the Eye (when eye is the primary organ system driving the admission) or MDC 01 (Nervous System) when the neurological cause is the principal diagnosis.

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CPT Procedure Codes (Commonly Associated)

Anisocoria itself has no direct procedural intervention. All associated CPT codes relate to evaluation and diagnostic workup. Code selection depends on the clinical context (ophthalmology vs. ED vs. neurology), patient complexity, and diagnostic tests performed.

Ophthalmological Examination

CPT	Description	wRVU (approx.)	Notes
92002	Ophthalmological exam, new patient, intermediate	1.43	Initial eye exam with external, biomicroscopy, ophthalmoscopy
92004	Ophthalmological exam, new patient, comprehensive	2.67	Full new patient exam including pupillary evaluation
92012	Ophthalmological exam, established patient, intermediate	0.97	Follow-up pupillary monitoring
92014	Ophthalmological exam, established patient, comprehensive	1.50	Comprehensive dilated exam with pupil evaluation

E/M Services

CPT	Description	wRVU (approx.)	Notes
99205	New patient office visit, high complexity	3.50	Neuro-ophthalmology new patient evaluation
99215	Established patient office visit, high complexity	2.80	Complex pupil workup in ophthalmology/neurology
99283	ED visit, moderate severity	1.97	ED evaluation of new anisocoria
99284	ED visit, high severity	2.60	Concerning anisocoria (CN III palsy, Horner) in ED
99285	ED visit, high severity with threat to life/function	3.80	Pupil-involving CN III palsy, acute Horner
99221-99223	Initial hospital care	1.92-3.86	If admitted for neurological workup

Pharmacologic Pupil Testing (In-Office)

Pharmacologic pupil testing (cocaine, apraclonidine, hydroxyamphetamine, pilocarpine) does not have a standalone CPT code. It is typically included in the E/M or ophthalmological exam code for the visit. Document the specific agent used, concentration, route, and result in the clinical note.

Consideration	Guidance
Apraclonidine test for Horner	Billable as part of the E/M service; document instillation, waiting period, result
Dilute pilocarpine for Adie	Included in comprehensive ophthalmological exam
Hydroxyamphetamine for Horner localization	Included in E/M; document as a diagnostic intervention
1% pilocarpine for CN III vs. pharmacologic	Documented in visit note; part of the exam

Note

Important: Some payers may separately reimburse pharmacologic testing under specific codes. Check with payer-specific policy. Do not bill a separate drug administration CPT (e.g., 96372 subcutaneous injection) for ophthalmic drops instilled during examination.

Diagnostic Imaging (Neuroimaging for Etiology)

H57.02 is explicitly listed as a covered diagnosis for MRI/CT head and neck imaging in CMS billing articles:

CPT	Description	wRVU (approx.)	When Used
70450	CT head without contrast	1.50	Acute/traumatic anisocoria — rule out hemorrhage, herniation
70460	CT head with contrast	1.90	Suspected mass or infection
70470	CT head with and without contrast	2.00	When both phases clinically needed
70496	CT angiography, head	2.53	CN III palsy — rule out PCoA aneurysm
70498	CT angiography, neck	2.53	Horner syndrome — rule out carotid dissection
70553	MRI brain with and without contrast	2.50	Definitive brain parenchymal evaluation
70544	MRA head without contrast	2.50	Circle of Willis — aneurysm screening
70547	MRA neck without contrast	2.50	Carotid/vertebral artery evaluation (Horner)
70548	MRA neck with contrast	2.75	Enhanced cervical vascular imaging
71250	CT thorax without contrast	1.49	Horner + preganglionic — Pancoast/apex lesion
71270	CT thorax with and without contrast	2.25	Enhanced chest CT for Pancoast tumor

Note

Neuroimaging medical necessity documentation: CMS and commercial payers require specific clinical indications for head/neck imaging. H57.02 alone may not be sufficient — document the clinical concern (e.g., “new anisocoria with ptosis and ipsilateral neck pain — rule out carotid dissection,” or “pupil-involving CN III palsy — rule out intracranial aneurysm”) to support medical necessity. H57.02 is listed in the CMS MRI/CT Head and Neck Billing and Coding Article (A57215) as a covered diagnosis.

Visual Field Testing (If Optic Pathway Evaluated)

CPT	Description	wRVU (approx.)	Notes
92083	Visual field examination, extended	0.58	If optic pathway involvement suspected alongside pupil disorder
92081	Visual field, limited (Amsler, tangent screen)	0.35	Basic screening

Electrophysiology (Rare — Selected Cases)

CPT	Description	wRVU (approx.)	Notes
95930	Visual evoked potential (VEP)	0.95	If optic nerve or chiasm lesion suspected along with pupil abnormality

Assistant Surgeon Payable?

Service	Assistant Allowed?
All E/M and ophthalmological exams	No
All diagnostic imaging	No
All pharmacologic testing	No
Visual field testing, electrophysiology	No
Neurosurgical procedures (if cause requires surgery — aneurysm, tumor)	Verify per specific CPT code

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Coding Examples

Example 1 — Physiologic Anisocoria, Reassurance Visit

Clinical Scenario:
A 28-year-old female presents concerned about a friend noticing that her pupils are different sizes in photos. Comprehensive ophthalmological examination is performed. Both pupils react normally to light and near. The difference is approximately 0.5 mm and is variable — it was right > left on one exam and left > right on another. No ptosis, no diplopia, no neurological symptoms. The provider documents “physiologic anisocoria — benign normal variant.”

ICD-10-CM:

• H57.02 — Anisocoria (physiologic anisocoria — no more specific code; H57.02 is the correct final code)

CPT:

• 92004 — Comprehensive ophthalmological exam, new patient

Coding note: For physiologic anisocoria with a definitive benign determination, H57.02 is the appropriate and final code. No additional etiology code is needed; no neuroimaging is indicated.

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Example 2 — New Anisocoria with Ptosis OD, CN III Palsy Workup — ED Presentation

Clinical Scenario:
A 52-year-old male presents to the ED with sudden onset right eye ptosis and a dilated right pupil noticed that morning. He also reports a severe headache (“worst of his life”). Examination reveals complete ptosis OD, right pupil 7 mm non-reactive to light, down-and-out gaze deviation OD, and anisocoria OD > OS. Emergent CTA head is obtained showing a right posterior communicating artery aneurysm compressing CN III.

ICD-10-CM (initial ED visit — before diagnosis confirmed):

• H57.02 — Anisocoria (presenting sign driving workup)

• H49.01 — Third nerve palsy, right eye (if documented as CN III palsy in the ED note)

• G44.309 — Post-traumatic headache, unspecified (or R51.9 — headache, if CN III palsy not yet confirmed)

After diagnosis confirmed (PCoA aneurysm):

• I67.1 — Cerebral aneurysm, nonruptured (principal diagnosis once confirmed)

• H49.01 — Third nerve palsy, right eye (additional — manifestation of aneurysm compression)

• H57.02 — Anisocoria (may be dropped once H49.01 captures the pupillary abnormality; per provider preference)

CPT (ED):

• 99285 — ED visit, high severity with threat to function

• 70496 — CT angiography, head (CTA for aneurysm)

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Example 3 — Horner Syndrome with Carotid Dissection — Urgent Presentation

Clinical Scenario:
A 38-year-old female presents to neurology with left-sided neck pain and new left-sided anisocoria (left pupil smaller than right). She reports the neck pain started after a chiropractic manipulation. Examination reveals a 1 mm left pupil with dilation lag, left mild ptosis, and no anhidrosis. Apraclonidine test is positive — confirms Horner syndrome. MRA neck reveals left internal carotid artery dissection.

ICD-10-CM (final diagnoses after workup):

• I77.71 — Dissection of carotid artery (principal — underlying cause)

• G90.2 — Horner syndrome (the specific pupillary pathology — sequences before H57.02)

• H57.02 — Anisocoria (additional — the observable sign)

CPT (outpatient neurology visit):

• 99205 — New patient office visit, high complexity

• 70548 — MRA neck with contrast

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Example 4 — Adie Tonic Pupil, Left Eye — Ophthalmology Confirmation

Clinical Scenario:
A 33-year-old female presents to ophthalmology with an incidentally noted large left pupil found by her optometrist. Comprehensive eye exam reveals: left pupil 6 mm in bright light (right = 3.5 mm), near-light dissociation of the left pupil (slow tonic constriction to sustained near), sectoral iris sphincter paralysis on slit lamp (vermiform movements). Dilute 0.1% pilocarpine instilled — left pupil constricts (supersensitivity confirmed). Diagnosis: Adie tonic pupil, left eye.

ICD-10-CM:

• H57.052 — Tonic pupil, left eye (most specific code once Adie tonic pupil confirmed — use H57.05x, NOT H57.02)

Critical code switch: Once Adie tonic pupil is confirmed by dilute pilocarpine testing and slit lamp findings, H57.052 (tonic pupil, left eye) is the most specific and appropriate code. H57.02 should NOT be used when a more specific pupillary diagnosis has been established.

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Example 5 — Anisocoria During Active Neurological Workup (Undifferentiated)

Clinical Scenario:
A 65-year-old male is referred to neuro-ophthalmology for anisocoria noted by his PCP — right pupil consistently larger than left for the past 2 weeks. He has mild right ptosis and no extraocular motility deficit. Pharmacologic testing is equivocal. MRI brain and MRA head ordered; results pending. The neuro-ophthalmologist documents “anisocoria — right pupil larger — etiology under investigation; possible Horner vs. Adie vs. partial CN III palsy.”

ICD-10-CM (at this visit — workup in progress):

• H57.02 — Anisocoria (appropriate during the diagnostic workup phase when no definitive etiology has been established)

CPT:

• 92004 — Comprehensive ophthalmological exam (or 99205 if billed as E/M)

• 70553 — MRI brain with and without contrast (ordered; support with H57.02 on imaging requisition)

• 70544 — MRA head without contrast

Update code once diagnosis confirmed: At the follow-up visit when imaging results are reviewed and a specific diagnosis is established, update the code from H57.02 to the specific etiology code (G90.2 for Horner, H49.0x for CN III palsy, H57.05x for Adie tonic pupil).

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Example 6 — Pharmacologic Anisocoria — Post-Procedure

Clinical Scenario:
A 72-year-old male is evaluated by the hospitalist team. The ophthalmologist had placed tropicamide drops in the right eye for a dilated fundus exam earlier that day. The hospitalist notices right pupil dilation and documents “anisocoria OD.” The ophthalmology note is reviewed; pharmacologic dilation is the obvious cause.

ICD-10-CM:

• H57.02 — Anisocoria (pharmacologic anisocoria is an appropriate use of H57.02 as the sign code)

• Z79.899 — Other long-term drug use (only if applicable; not for a single-use mydriatic drop)

Coding note: Pharmacologic anisocoria from diagnostic mydriatics is a common incidental finding on inpatient rounds. H57.02 accurately captures the finding. No neurological workup is needed when the mydriatic history is clearly documented.

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Key Coding Pitfalls & Tips

• H57.02 is a sign code — always pursue a specific etiology. Unless the anisocoria is definitively physiologic or pharmacologic, H57.02 should prompt coding of the underlying cause when identified. Do not stop at H57.02 when Horner syndrome, CN III palsy, Adie tonic pupil, or another specific condition has been diagnosed.

• H57.02 vs H57.05x — Adie tonic pupil distinction. Once Adie tonic pupil is confirmed by dilute pilocarpine supersensitivity or slit-lamp vermiform iris movements, H57.052 (left) or H57.051 (right) is the correct code — not H57.02. H57.05x is more specific and should be used when the Adie diagnosis is established.

• H57.02 vs H57.03/H57.04 — anisocoria vs isolated miosis/mydriasis. H57.03 (miosis) and H57.04 (mydriasis) capture abnormally small or large pupils that are bilateral in the primary context. H57.02 captures the asymmetry between the two pupils. Use H57.02 when the primary finding is the size difference between eyes, not a bilateral abnormality.

• Sequence underlying cause first. If Horner syndrome (G90.2), CN III palsy (H49.0x), or another etiology is established, that code is the principal/first-listed — H57.02 is additional or may be omitted when the etiology code fully captures the clinical finding.

• Neuroimaging medical necessity requires clinical specificity. When ordering CT/MRI/MRA based on anisocoria findings, document the specific clinical concern (CN III palsy with headache → rule out aneurysm; Horner with neck pain → rule out carotid dissection) in the order and in the medical record. H57.02 alone may be insufficient for payer approval of advanced neuroimaging.

• Emergency recognition — two life-threatening causes to never miss:

  • Pupil-involving CN III palsy + headache = PCoA aneurysm until proven otherwise → CTA/MRA head emergently

  • New Horner syndrome + ipsilateral neck/face pain = carotid artery dissection until proven otherwise → CTA/MRA neck urgently

• Laterality nuance. H57.02 has no laterality specification — anisocoria involves both pupils by definition (one large, one small). Document in the clinical note which pupil is abnormal (the larger or the smaller), the degree of difference, and the lighting conditions in which it is most apparent.

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Related Codes (Cross-Reference)

Code	Description
H57.00	Unspecified anomaly of pupillary function
H57.01	Argyll Robertson pupil, atypical (light-near dissociation; neurosyphilis)
H57.03	Miosis (abnormally small pupil, may be bilateral)
H57.04	Mydriasis (abnormally large or dilated pupil)
H57.051	Tonic pupil, right eye (Adie tonic pupil confirmed, right)
H57.052	Tonic pupil, left eye (Adie tonic pupil confirmed, left)
H57.059	Tonic pupil, unspecified eye
H49.00	Third nerve palsy, unspecified eye
H49.01	Third nerve palsy, right eye
H49.02	Third nerve palsy, left eye
G90.2	Horner syndrome (sympathetic pupillary pathway disruption)
I67.1	Cerebral aneurysm, nonruptured (PCoA aneurysm causing CN III palsy)
I77.71	Dissection of carotid artery (Horner syndrome — 3rd-order neuron)
I63.-	Cerebral infarction (stroke causing central Horner or CN III palsy)
C34.-	Malignant neoplasm of bronchus and lung (Pancoast tumor — 2nd-order Horner)
H20.0-	Acute iridocyclitis (mechanical miosis/anisocoria from uveitis)
H40.21-	Acute angle-closure glaucoma (mid-dilated fixed pupil)
S05.10XA	Contusion of eyeball and orbital tissues, unspecified eye (traumatic mydriasis)
A52.11	Tabes dorsalis — associated with Argyll Robertson pupils (neurosyphilis)
Q13.2	Congenital anomaly of iris (congenital anisocoria from iris malformation — use Q13.2)
Z01.00	Encounter for examination of eyes and vision, without abnormal findings
Z01.01	Encounter for examination of eyes and vision, with abnormal findings

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Last Reviewed: 2026-02-18 | Source: ICD-10-CM FY2025, CMS MPFS, CMS MS-DRG v42.0, CMS Billing and Coding: MRI and CT Scans of the Head and Neck (A57215), StatPearls Anisocoria, EyeWiki Anisocoria, AAO Neuro-Ophthalmology Guidelines, ICD-10-CM Official Coding Guidelines FY2026