2026 ICD-10-CM Diagnosis Code H16.329Diffuse interstitial keratitis, unspecified eye

ICD-10-CM Codes›H00–H59›H15-H22›H16

ICD-10-CM H16.329
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

H16.329 is a billable ICD-10-CM diagnosis code for diffuse interstitial keratitis, unspecified eye. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 124 through 125. Coders also document this condition as Cogan's syndrome. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Cornea and external disease.

Code Identity

ICD-10-CM Code
H16.329
Billable Status
Yes — Valid for Submission
Code Describes
Diffuse interstitial keratitis, unspecified eye
Short Description
Diffuse interstitial keratitis, unspecified eye
Same as the full description in the CMS dataset.
Parent Code
H16.32
Diffuse interstitial keratitis

Code Classification

ChapterH00–H59Diseases of the eye and adnexa
SectionH15-H22Disorders of sclera, cornea, iris and ciliary body
CategoryH16Keratitis
This CodeH16.329Diffuse interstitial keratitis, unspecified eye

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Cogan's syndrome
  • Diffuse interstitial keratitis

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR EYE001
Cornea and external disease
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Corneal Disorders

Your cornea is the outermost layer of your eye. It is clear and shaped like a dome. The cornea helps to shield the rest of the eye from germs, dust, and other harmful matter. It also helps your eye to focus. If you wear contact lenses, they float on top of your corneas.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert H16.329 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
370.52 Diffus interstit keratit
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About H16.329Overview

Is H16.329 (Diffuse interstitial keratitis) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report diffuse interstitial keratitis, unspecified eye on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does H16.329 group to?

When diffuse interstitial keratitis, unspecified eye is the principal diagnosis on an inpatient stay, it groups to MS-DRG 124, 125, with relative weights from 0.7678 to 1.3231 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of H16.329?

Under the General Equivalence Mappings, diffuse interstitial keratitis, unspecified eye converts to ICD-9-CM 370.52 (diffus interstit keratit). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.