2026 ICD-10-CM Diagnosis Code A50.31Late congenital syphilitic interstitial keratitis

ICD-10-CM Codes›A00–B99›A50-A64›A50

ICD-10-CM A50.31
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

A50.31 is a billable ICD-10-CM diagnosis code for late congenital syphilitic interstitial keratitis. 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. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Cornea and external disease, Perinatal infections, and Sexually transmitted infections (excluding HIV and hepatitis).

Code Identity

ICD-10-CM Code
A50.31
Billable Status
Yes — Valid for Submission
Code Describes
Late congenital syphilitic interstitial keratitis
Short Description
Late congenital syphilitic interstitial keratitis
Same as the full description in the CMS dataset.
Parent Code
A50.3
Late congenital syphilitic oculopathy

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA50-A64Infections with a predominantly sexual mode of transmission
CategoryA50Congenital syphilis
This CodeA50.31Late congenital syphilitic interstitial keratitis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Bilateral interstitial keratitis of eyes
  • Bilateral keratitis of eyes caused by bacteria
  • Interstitial keratitis due to congenital syphilis
  • Interstitial keratitis due to late congenital syphilis
  • Interstitial keratitis of bilateral eyes due to congenital syphilis
  • Interstitial keratitis of left eye due to congenital syphilis
  • Interstitial keratitis of right eye due to congenital syphilis
  • Keratitis due to syphilis
  • Keratitis of left eye caused by bacteria
  • Keratitis of right eye caused by bacteria
  • Syphilitic interstitial keratitis

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)
      • in (due to)
        • syphilis
    • Keratitis(nodular) (nonulcerative) (simple) (zonular)
      • interstitial (nonsyphilitic)
        • syphilitic (congenital) (late)
    • Keratitis(nodular) (nonulcerative) (simple) (zonular)
      • punctata
        • syphilitic (profunda)
    • Keratitis(nodular) (nonulcerative) (simple) (zonular)
      • syphilitic (congenital) (prenatal)
    • Syphilis, syphilitic(acquired)
      • congenital
        • interstitial keratitis
    • Syphilis, syphilitic(acquired)
      • congenital
        • late, or 2 years or more after birth NEC
          • interstitial keratitis
    • Syphilis, syphilitic(acquired)
      • keratitis (congenital) (interstitial) (late)

Clinical ClassificationClinical

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

CCSR EYE001
Cornea and external disease
Default principal diagnosis: inpatient No · outpatient No
CCSR PNL009
Perinatal infections
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR INF010
Sexually transmitted infections (excluding HIV and hepatitis)
Default principal diagnosis: inpatient No · outpatient No

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 A50.31 to ICD-9-CMHistory

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

ICD-9-CM
090.3 Syphilitic keratitis
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 A50.31Overview

Is A50.31 (Late congenital syphilitic oculopathy) a billable code?

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

What MS-DRG does A50.31 group to?

When late congenital syphilitic interstitial keratitis 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 A50.31?

Under the General Equivalence Mappings, late congenital syphilitic interstitial keratitis converts to ICD-9-CM 090.3 (syphilitic keratitis). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.