2026 ICD-10-CM Diagnosis Code H16.399Other interstitial and deep keratitis, unspecified eye

ICD-10-CM Codes›H00–H59›H15-H22›H16

ICD-10-CM H16.399
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

H16.399 is a billable ICD-10-CM diagnosis code for other interstitial and deep 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 focal stromal keratitis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Cornea and external disease.

Code Identity

ICD-10-CM Code
H16.399
Billable Status
Yes — Valid for Submission
Code Describes
Other interstitial and deep keratitis, unspecified eye
Short Description
Other interstitial and deep keratitis, unspecified eye
Same as the full description in the CMS dataset.
Parent Code
H16.39
Other interstitial and deep keratitis

Code Classification

ChapterH00–H59Diseases of the eye and adnexa
SectionH15-H22Disorders of sclera, cornea, iris and ciliary body
CategoryH16Keratitis
This CodeH16.399Other interstitial and deep keratitis, unspecified eye

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Focal stromal keratitis
  • Idiopathic linear interstitial keratitis
  • Infectious crystalline keratopathy
  • Lipid keratopathy

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Keratitis(nodular) (nonulcerative) (simple) (zonular)
      • deep
        • specified type NEC

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 H16.399 to ICD-9-CMHistory

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

ICD-9-CM
370.59 Interstit keratitis NEC
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 H16.399Overview

Is H16.399 (Other interstitial and deep keratitis) a billable code?

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

What MS-DRG does H16.399 group to?

When other interstitial and deep 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 H16.399?

Under the General Equivalence Mappings, other interstitial and deep keratitis, unspecified eye converts to ICD-9-CM 370.59 (interstit keratitis NEC). 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.