Crystal's Coder Hub👁️ CPT 92100 — Serial Tonometry With Multiple Measurements of Intraocular Pressure, Interpretation and Report, Same Day
“Serial tonometry (separate procedure) with multiple measurements of intraocular pressure over an extended time period with interpretation and report, same day (eg, diurnal curve or medical treatment of acute elevation of intraocular pressure)”
Quick Reference
wRVU: 0.52 | Global Period: 000 | Assistant Payable: No | Bilateral Indicator: 2
Rule: The bilateral indicator of 2 means the payment is already based on the assumption that both eyes may be measured; modifier -50 is not applied because pricing already reflects a bilateral service. The global period of 000 means there is no postoperative period — only the day of the procedure is bundled. No pre-op or post-op visits are included in the allowable. This code is designated as a “separate procedure,” meaning it should not be billed when it is an integral part of a more comprehensive ophthalmological service performed on the same day without a distinct, separately documented medical necessity.1
📋 Clinical Description
CPT 92100 describes serial tonometry, a diagnostic ophthalmological procedure in which intraocular pressure (IOP) is measured multiple times (typically a minimum of three) over an extended period — generally six or more hours — all within the same calendar day, with a written interpretation and report by the physician.1 Unlike a single tonometry reading performed incidentally during a standard eye exam (which is bundled into 92002–92014), serial tonometry captures the diurnal variation in IOP that is clinically critical for managing conditions such as glaucoma and ocular hypertension. The procedure generates a diurnal curve — a graphical or tabular representation of how IOP fluctuates throughout the day — which helps the provider optimize timing and dosing of glaucoma medications or assess the urgency of surgical intervention2
This code also applies when a provider monitors and treats an acute elevation of IOP — such as during an acute angle-closure glaucoma attack — by re-checking pressure at intervals after administering hypotensive therapy (e.g., topical beta-blockers, alpha-agonists, oral acetazolamide, or mannitol). The repeated measurements document both the severity of the acute episode and the clinical response to treatment, which distinguishes this service from a routine single IOP check. Because CPT 92100 requires a separate written interpretation and report (not just a notation in the chart), thorough documentation is essential to support the billing.3
This procedure may be performed in the following clinical contexts:
- Diurnal IOP curve for glaucoma management — A patient with known primary open-angle glaucoma presents for a full-day IOP monitoring session to determine whether IOP spikes occur at specific times of day, guiding adjustment of topical glaucoma medication schedules.
- Acute angle-closure glaucoma treatment monitoring — A patient presents with sudden severe eye pain, halos, nausea, and markedly elevated IOP; the physician initiates emergent hypotensive therapy and serially measures IOP every 30–60 minutes to document response and determine whether surgical intervention (e.g., laser peripheral iridotomy) is immediately required.2
- Ocular hypertension surveillance — A patient with documented ocular hypertension and a thick cornea (confirmed on pachymetry via 76514) undergoes serial tonometry to establish a pressure baseline and evaluate fluctuation risk before initiating prophylactic treatment.
- Suspected normal-tension glaucoma workup — Serial measurements help document that IOP remains within statistically normal limits throughout the day in a patient with suspicious optic nerve cupping and visual field defects, supporting the low-tension glaucoma diagnosis.3
- Post-medication adjustment monitoring — After switching a glaucoma patient to a new prostaglandin analog or combination drop, serial tonometry is used to document the new IOP range and confirm therapeutic efficacy within the same clinic day.
🔬 Anatomical & Procedural Considerations
| Variant | Mechanism | Key Notes |
|---|---|---|
| Goldmann Applanation Tonometry (GAT) | A slit-lamp-mounted prism flattens the corneal apex; the force required to applanate a 3.06 mm circle of cornea is converted to mmHg. This is the gold-standard technique and the most commonly used for serial measurements in an office setting. Topical anesthetic (e.g., proparacaine) and fluorescein dye are required. | GAT readings are influenced by central corneal thickness (CCT); artificially high readings may occur in thick corneas and artificially low readings in thin corneas. Corneal pachymetry (76514) is frequently ordered in conjunction with serial tonometry to contextualize results. Each measurement must be documented separately with time stamps. |
| Non-Contact Tonometry (NCT / Air-Puff) | A controlled puff of air deforms the cornea momentarily; the instrument detects the milliseconds it takes to applanate and back-calculates IOP. No anesthetic or dye required; lower risk of cross-contamination between measurements. Less precise than GAT but appropriate for rapid serial screening. | While convenient for serial monitoring across multiple time points in a busy clinic, NCT is generally considered less accurate than GAT for documenting acute IOP elevations. Technicians may perform the measurements, but the interpreting physician must personally review all readings and produce a written report for 92100 to be billable. |
| Rebound Tonometry (iCare) | A small magnetized probe makes brief contact with the cornea and rebounds; the deceleration of the probe is analyzed to determine IOP. Requires no anesthetic, minimal patient cooperation, and can be performed in non-traditional settings. | Particularly useful in pediatric patients or patients who cannot tolerate slit-lamp examination. For serial tonometry billing purposes, the same documentation rules apply: minimum three readings with time stamps, extended time period, physician interpretation, and formal report. |
Clinical Pearl
Medicare and most commercial payers require at least three separate IOP measurements performed over six or more hours to justify billing CPT 92100 — a single “check-in-check-out” IOP pair is not sufficient.1 Each measurement should be documented with the exact time it was obtained, the technique used, the eye(s) tested, and the resulting IOP value in mmHg. The final interpretation and report must be a separate, signed physician note — not simply the time-stamped values alone. Failure to include a formal written interpretation is the single most common reason for claim denial and audit recoupment on this code.3
✅ Procedure Includes
- All individual IOP measurements performed during the session — Every tonometry reading taken throughout the extended monitoring period is bundled into the single unit of CPT 92100; you do not report multiple units of this code regardless of how many measurements are taken.1^
- Topical anesthetic administration — If applanation tonometry is used, the instillation of anesthetic drops (e.g., proparacaine, tetracaine) is considered integral to the procedure and is not separately billable.
- Fluorescein dye application — When GAT is performed, fluorescein is required to visualize the applanation mires and is bundled into 92100.
- Technician-assisted IOP measurements — Staff-obtained readings that are subsequently reviewed, interpreted, and reported by the supervising physician are included; the physician’s formal report is what validates the 92100 billing.
- Written interpretation and report — The formal written summary of all IOP values over time, physician analysis of the diurnal curve or treatment response, and clinical conclusions constitute a required component of this code — not a separately billable service.2
- Any repeat measurements needed for accuracy — Re-checking a reading due to patient movement or instrument error does not create a separately reportable event; all readings on the day are part of the single 92100 service.
❌ Excludes / Do Not Report Together
| Code | Description | Relationship |
|---|---|---|
| 92002 | Ophthalmological services: medical exam & evaluation, new patient, intermediate | Tonometry performed as part of a standard intermediate or comprehensive eye exam (92002–92014) is incidental to the exam and is not separately reportable as 92100. If you are billing a full eye exam on the same day, 92100 should only be additionally reported if there is a distinct, separately documented medical necessity for the serial measurements beyond the routine exam IOP check.1^ |
| 92012 | Ophthalmological services: medical exam & evaluation, established patient, intermediate | Same bundling logic applies as with new patient exams. The IOP check during a standard established-patient visit is bundled; 92100 requires separate documentation justifying the serial nature and extended time period of measurement.1 |
| 92140 | Provocative test for glaucoma with interpretation and report | CPT 92140 is a distinct provocative glaucoma test (e.g., dark-room prone provocative testing for angle-closure) and should not be reported on the same day as 92100 without clear documentation that entirely separate clinical indications justify each procedure. Bundling edits may apply depending on payer. |
| 76514 | Corneal pachymetry; unilateral or bilateral (with interpretation and report) | Pachymetry is separately reportable when a thorough evaluation of corneal thickness is performed and documented with its own interpretation and report. However, do not reflexively add 76514 every time 92100 is billed — it must be independently medically necessary and documented.3 |
Bundling Alert
Because CPT 92100 carries a global period of 000, there is no post-op period to navigate, but the “separate procedure” designation in the CPT descriptor is a critical audit flag. CMS and commercial payers may bundle 92100 into a same-day comprehensive eye exam code (92004 or 92014) absent a modifier and distinct documentation of medical necessity. If serial tonometry is performed on the same day as a billable eye exam and there is a clearly separate reason for the extended IOP monitoring (e.g., acute glaucoma attack management), append modifier -25 to the E/M or eye exam code — not to the 92100 — to signal that the evaluation was a significant, separately identifiable service beyond the decision to perform serial tonometry. Failure to properly document the separate medical necessity is the top audit risk for this code pairing.1 2
🌳 Code Tree — Medicine: Ophthalmology — Special Ophthalmological Services
CPT 92002–92499 Medicine: Ophthalmology
│
├── 92002–92014 General Ophthalmological Services (Eye Exams)
│ ├── 92002 Ophthalmological services, new patient, intermediate
│ ├── 92004 Ophthalmological services, new patient, comprehensive
│ ├── 92012 Ophthalmological services, established patient, intermediate
│ └── 92014 Ophthalmological services, established patient, comprehensive
│
├── 92015–92099 Special Ophthalmological Services
│ ├── 92015 Determination of refractive state (Global: 000)
│ ├── 92025 Computerized corneal topography, unilateral or bilateral (Global: 000)
│ ├── 92060 Sensorimotor examination (Global: 000)
│ ├── 92081 Visual field examination, unilateral or bilateral (limited examination) (Global: 000)
│ ├── 92082 Visual field examination, unilateral or bilateral (intermediate examination) (Global: 000)
│ ├── 92083 Visual field examination, unilateral or bilateral (extended examination) (Global: 000)
│ ├── ▶▶ 92100 ◀◀ Serial tonometry (separate procedure) with multiple measurements of IOP over an extended time period with interpretation and report, same day ← YOU ARE HERE (Global: 000)
│ ├── 92120 Tonography with interpretation and report (not to include provocative tests) (Global: 000)
│ └── 92140 Provocative tests for glaucoma with interpretation and report (Global: 000)
│
└── 92230–92287 Posterior Segment Ophthalmology Services
├── 92230 Fluorescein angioscopy with interpretation and report
└── 92250 Fundus photography with interpretation and report
💰 RVU & Reimbursement Profile
| Component | Value |
|---|---|
| Work RVU | 0.52 |
| Global Period | 000 |
| Bilateral Indicator | 2 — Already priced as bilateral; do not append modifier -50 |
| Assistant Surgeon | Not applicable |
| Co‑Surgeon | Not applicable |
| Team Surgery | Not applicable |
| PC/TC Split | 0 — No professional/technical split; service is reported as a whole |
| Modifier -51 Exempt | No |
| Anesthesia | Not applicable for this diagnostic procedure |
Bilateral Billing Rules
CPT 92100 carries a bilateral indicator of 2, which means the Medicare fee schedule payment amount already accounts for bilateral performance — i.e., the physician is measuring IOP in both eyes, and the fee schedule rate reflects this. You should never append modifier -50 (Bilateral Procedure) to CPT 92100, as it will result in incorrect payment and potential overpayment recoupment. Do not append -RT or -LT either, as this is not a unilateral procedure by definition. If the procedure is performed on only one eye due to an unusual clinical circumstance, the guidelines do not provide for a reduced payment modifier in this scenario for bilateral indicator 2 codes — the full bilateral rate is payable regardless.1
🏷️ Modifier Reference
| Modifier | Name | When to Apply |
|---|---|---|
| -25 | Significant, Separately Identifiable E/M Service | Append -25 to the eye exam or E/M code (not to 92100) when an eye examination is performed on the same day as serial tonometry and represents a significant, separately identifiable service beyond the decision to perform the tonometry. Documentation must support both services independently.2 |
| -59 | Distinct Procedural Service | Use modifier -59 (or an appropriate X{EPSU} modifier) on 92100 if a payer-specific bundling edit flags it against another diagnostic code performed the same day and the services are truly distinct with separate documentation. Use sparingly and only when clinically justified. |
| -76 | Repeat Procedure by Same Physician | Rarely applicable for 92100 since the code inherently includes multiple measurements; however, if payer policy requires separate claims for a repeated extended monitoring session initiated for a new acute clinical event on the same day, -76 may be applicable per payer-specific guidance. |
| -GQ | Via Asynchronous Telecommunications | Applicable if serial tonometry results are transmitted and interpreted via store-and-forward telehealth in states/payers that allow this for ophthalmology.3 |
| -GT | Via Interactive Audio and Video | Used when telehealth modality applies per applicable payer and CMS rules; verify telehealth eligibility for 92100 under current CMS telehealth list. |
| -52 | Reduced Services | If fewer than the standard number of measurement intervals were completed due to patient or clinical circumstances, -52 may be appropriate with documentation of the reason. Expect reduced reimbursement. |
| -53 | Discontinued Procedure | Use if the serial monitoring session was initiated but had to be discontinued prior to completion due to a significant clinical event (e.g., patient needed emergency transfer). |
Modifiers NOT applicable to 92100
🩺 Common ICD‑10‑CM Pairings
Primary Diagnosis Group
| ICD‑10 | Description | HCC? | Notes |
|---|---|---|---|
| H40.1111 | Primary open-angle glaucoma, right eye, mild stage | No | Most common pairing; serial tonometry used to establish diurnal IOP curve for medication titration. Confirm laterality and staging from documentation — codes range from H40.1111–H40.1134 by eye and stage.3 |
| H40.1121 | Primary open-angle glaucoma, left eye, mild stage | No | Mirror code for the left eye; always code to the most specific laterality and stage documented by the provider. |
| H40.2110 | Acute angle-closure glaucoma, right eye, unspecified stage | No | High-acuity pairing when 92100 is used to monitor acute IOP elevation and treatment response during an angle-closure attack. Stage specificity is required when documented. |
| H40.051 | Ocular hypertension, right eye | No | Common pairing for diurnal curve testing in patients with elevated IOP but no confirmed glaucomatous damage yet; helps risk-stratify for prophylactic treatment.2 |
| H40.1211 | Low-tension glaucoma, right eye, mild stage | No | Serial tonometry helps confirm IOP remains in normal range throughout the day, supporting this diagnosis when optic nerve changes suggest glaucoma. |
Secondary Group
| ICD‑10 | Description | HCC? | Notes |
|---|---|---|---|
| H40.001 | Preglaucoma, unspecified, right eye | No | Used when a patient has risk factors and borderline findings warranting serial IOP monitoring but does not yet meet full glaucoma criteria. |
| H40.031 | Anatomical narrow angle, right eye | No | May warrant serial tonometry to evaluate IOP fluctuation in an eye predisposed to angle closure, often as a precursor to prophylactic iridotomy. |
Etiology / Complication
| ICD‑10 | Description | HCC? | Notes |
|---|---|---|---|
| H40.031 | Anatomical narrow angle, right eye | No | Structural predisposition may be an underlying etiology when serial tonometry is ordered to evaluate angle-closure risk. |
| H44.511 | Absolute glaucoma, right eye | No | End-stage glaucoma with no light perception; serial tonometry may still be performed to guide pain management decisions in blind painful eyes. |
Coding Specificity Reminder
Nearly all glaucoma ICD-10-CM codes require four levels of specificity: (1) type of glaucoma, (2) laterality (right, left, bilateral), (3) stage (mild, moderate, severe, indeterminate, unspecified), and (4) in some categories, a fourth character for additional detail. Always code to the highest level of specificity documented in the medical record — do not default to “unspecified” if the provider has clearly documented the stage and laterality. For acute angle-closure glaucoma (H40.211–H40.213), stage is expressed in the 7th character. Review the most recent ICD-10-CM tabular carefully, as glaucoma staging codes are among the most complex in Chapter 7 and are a common specificity audit finding.3
🏥 MS‑DRG Considerations
CPT 92100 is a Medicine/diagnostic procedure code and does not function as an operative procedure that would drive MS-DRG assignment in the inpatient setting. In the rare event that serial tonometry is performed on a hospitalized patient (e.g., a patient admitted for acute angle-closure glaucoma attack under MDC 02 — Diseases and Disorders of the Eye), the DRG assignment is driven by the principal diagnosis and any surgical procedures performed — not by the diagnostic tonometry itself. As an inpatient profee coder, you would capture CPT 92100 on the professional claim for the ophthalmologist’s services; the facility claim would use ICD-10-PCS to capture any therapeutic interventions (e.g., laser iridotomy). DRGs most commonly associated with glaucoma-related admissions include DRG 124 (Other Disorders of the Eye with MCC), DRG 125 (Other Disorders of the Eye with CC), and DRG 126 (Other Disorders of the Eye without CC/MCC), all within MDC 02. Serial tonometry in isolation does not elevate DRG complexity.4
🔧 ICD‑10‑PCS Equivalents
Note
CPT 92100 is a diagnostic measurement procedure (tonometry). ICD-10-PCS captures measurement functions under Section 4 (Measurement and Monitoring). There is no direct single-code PCS equivalent that maps perfectly to “serial” tonometry — ICD-10-PCS would typically capture a single measurement or monitoring event. The closest PCS root operations are Measurement (single-point) and Monitoring (repeated over time), both in the Central Nervous System and Anatomical Regions body system for sensory functions.
| PCS Code | Full Description | Modality |
|---|---|---|
| 4A07XBZ | Measurement of Eye, Pressure, External Approach | Tonometry — single measurement, no device |
| 4A17XBZ | Monitoring of Eye, Pressure, External Approach | Monitoring — serial/repeated pressure assessment over time; closest PCS equivalent to the “serial” component of 92100 |
| 4A07XVZ | Measurement of Eye, Ophthalmologic, External Approach | Broader ophthalmologic measurement — less specific than pressure-only |
| 4A17XVZ | Monitoring of Eye, Ophthalmologic, External Approach | Broader ophthalmologic monitoring — applicable when documentation supports ongoing multiparameter eye monitoring |
PCS Character Analysis (using 4A17XBZ as primary example)
| Position | Character | Value | Definition |
|---|---|---|---|
| 1 | Section | 4 | Measurement and Monitoring — captures diagnostic data-gathering procedures that assess physiological parameters. |
| 2 | Body System | A | Physiological Systems — the visual system falls under this body system classification for measurement/monitoring purposes. |
| 3 | Root Operation | 1 | Monitoring — defined as determining the level of a physiological or physical function repetitively over a period of time; this distinguishes serial tonometry (monitoring) from a single IOP check (measurement, root op 0). |
| 4 | Body Part | 7 | Eye — encompasses the entire globe including the aqueous humor compartments responsible for IOP generation and drainage. |
| 5 | Approach | X | External — tonometry is performed on the external surface of the cornea without incision, puncture, or insertion of instrumentation through the skin. |
| 6 | Device | Z | No Device — no implantable or inserted device is involved in tonometry; the instrument contacts the eye transiently. |
| 7 | Qualifier | B | Pressure — specifies that the physiological parameter being monitored is intraocular pressure specifically, as opposed to other ophthalmologic parameters. |
Root Operation Comparison
- Measurement (root op 0) vs. Monitoring (root op 1): Use Measurement (4A07XBZ) when a single IOP reading is taken as part of a routine examination — this parallels the tonometry bundled into an eye exam (92002–92014). Use Monitoring (4A17XBZ) when IOP is assessed repeatedly over time — this parallels CPT 92100’s serial nature. The distinction in ICD-10-PCS mirrors the CPT distinction precisely.
- PCS Section 4 vs. Section 8 (Other Procedures): Tonometry always belongs in Section 4 (Measurement and Monitoring) — do not confuse with Section 8, which captures miscellaneous procedures not classifiable elsewhere. Section 4 is specifically designed for non-invasive physiological measurement procedures like tonometry, spirometry, and ECG monitoring.
- Inpatient applicability: ICD-10-PCS tonometry codes would only appear on a UB-04 (facility claim) if the procedure is performed in the inpatient setting and the facility chooses to report it. Many facilities do not report diagnostic measurement PCS codes separately from the DRG bundling unless required by payer contract or internal coding policy.
📝 Coding Examples
Example 1 — Diurnal Curve for Glaucoma Medication Adjustment
Clinical Scenario:
A 67-year-old established patient with known bilateral primary open-angle glaucoma, moderate stage (documented by the ophthalmologist), presents to the office at 8:00 AM for a scheduled full-day diurnal curve. The patient’s current regimen of a prostaglandin analog and a beta-blocker has been in place for six months. The ophthalmologist suspects IOP is spiking in the late morning based on the patient’s progressive VF changes. IOP is measured by GAT at 8:00 AM, 10:00 AM, 12:00 PM, 1:30 PM, and 3:00 PM. An intermediate ophthalmological examination is also performed at the 8:00 AM visit, during which cup-to-disc ratio and posterior segment findings are documented. The physician reviews all five IOP values, identifies a peak of 26 mmHg OU at 10:00 AM, documents a formal written interpretation, and adjusts the medication timing accordingly.
| Field | Code | Rationale |
|---|---|---|
| CPT 1 | 92012-25 | Intermediate established patient eye exam; modifier -25 appended to signal a significant, separately identifiable service beyond the decision to perform serial tonometry. The exam included posterior segment evaluation and clinical decision-making independent of the tonometry. |
| CPT 2 | 92100 | Serial tonometry with five time-stamped GAT measurements over seven hours, physician-written interpretation, and report documenting the diurnal curve and medication adjustment decision. Billing a single unit of 92100 regardless of the number of individual readings.1 |
| PDx | H40.1121 | Primary open-angle glaucoma, left eye, moderate stage (H40.1122 for right eye — both coded; see note). |
Note
When POAG is bilateral, code both lateralities (H40.1121 for left, H40.1122 for right) per ICD-10-CM convention — there is no “bilateral” POAG code. Modifier -25 must be on the eye exam code, not on 92100. Ensure the medical record clearly documents that the examination included findings and clinical decision-making separate from the serial IOP monitoring itself.3
Example 2 — Acute Angle-Closure Glaucoma Treatment Monitoring
Clinical Scenario:
A 58-year-old patient presents to the ophthalmology office as an urgent walk-in with sudden onset right eye pain, blurred vision, halos around lights, nausea, and a red eye beginning two hours prior. On examination, the right cornea is hazy, the anterior chamber is shallow, and IOP by GAT measures 52 mmHg in the right eye. The physician diagnoses acute angle-closure glaucoma, right eye, and immediately initiates treatment with topical timolol, brimonidine, and oral acetazolamide. IOP is re-checked at 30 minutes (44 mmHg), 60 minutes (32 mmHg), and 90 minutes (21 mmHg). The physician documents a formal interpretation noting the acute episode, treatment administered, serial IOP values with timestamps, and a plan for urgent laser peripheral iridotomy. A comprehensive new patient eye examination is also performed and documented separately.
| Field | Code | Rationale |
|---|---|---|
| CPT 1 | 92004-25 | Comprehensive new patient eye exam; modifier -25 required because the comprehensive exam represents a significant, separately identifiable service from the acute glaucoma management and serial tonometry. |
| CPT 2 | 92100 | Serial tonometry with four GAT measurements (initial + three follow-up) over 90 minutes monitoring response to emergent hypotensive therapy. The “extended time period” requirement should be verified against payer policy — some Medicare contractors require 6 hours for the diurnal curve indication but allow shorter intervals for acute IOP management.1^2^ |
| PDx | H40.2110 | Acute angle-closure glaucoma, right eye, unspecified stage. |
Warning
Some Medicare Administrative Contractors (MACs) publish LCDs specifying that serial tonometry for acute IOP management may have different time-interval requirements than serial tonometry for a diurnal curve. Always verify with your MAC’s LCD (if one exists) before billing 92100 for the acute-elevation-of-IOP indication. Absence of a formal written interpretation and report — separate from the exam note — is the most common denial reason.2
Example 3 — Ocular Hypertension Workup, No Concurrent Exam
Clinical Scenario:
A 45-year-old patient with recently diagnosed ocular hypertension, right eye, returns specifically for a full diurnal tonometry curve per the physician’s instructions at the conclusion of last week’s comprehensive exam. No examination is performed today — the patient checks in, has IOP measured by a trained technician at 9:00 AM, 11:00 AM, 1:00 PM, and 3:00 PM, and returns at 3:30 PM for the physician to review all values and document a written interpretation. Peak IOP is 24 mmHg at 11:00 AM. The physician concludes that IOP fluctuation does not meet the threshold for initiating prophylactic treatment at this time and documents the clinical reasoning.
| Field | Code | Rationale |
|---|---|---|
| CPT | 92100 | Serial tonometry only — no concurrent eye examination is being billed today. Four GAT readings over six hours, technician-performed, physician-reviewed with formal written interpretation and report. Single unit reported regardless of number of measurements.2^ |
| PDx | H40.051 | Ocular hypertension, right eye — the primary indication driving the medical necessity for the diurnal curve today. |
Global period reminder
CPT 92100 has a global period of 000, which means only the day of service is included in the procedure payment — there is no post-op period. If this patient had undergone a laser iridotomy or other ophthalmologic procedure within the past 10 or 90 days, check the global period of that procedure before billing 92100. If 92100 falls within the global period of a prior procedure performed by the same provider, a modifier (-79 for unrelated procedure, or -24 for unrelated E/M) may be required depending on the situation. Since 92100 has its own 000 global period, it generally does not restrict subsequent service billing.4
⚠️ Common Coding Pitfalls
- Pitfall 1 — Billing 92100 for a single tonometry reading: CPT 92100 requires multiple measurements over an extended time period with interpretation and report. A single IOP check during a glaucoma visit — even if documented — does not meet the definition of serial tonometry. Billing 92100 for one or two readings is considered upcoding and is an active audit target. Most payers require a minimum of three readings; many Medicare MACs specify at least three measurements over six or more hours for the diurnal curve indication.1
- Pitfall 2 — Missing written interpretation and report: The CPT descriptor explicitly requires “interpretation and report.” A simple IOP notation in the exam note does not satisfy this requirement. The physician must produce a separate, dated, signed written summary that analyzes the serial values, discusses the clinical significance, and outlines the management implication. Absent this document, the claim is not supportable and is subject to recoupment.3
- Pitfall 3 — Appending modifier -50, -RT, or -LT: Because CPT 92100 carries a bilateral indicator of 2, the fee schedule payment already reflects bilateral performance. Appending -50 would result in a payment at 150% of the bilateral rate — which is incorrect and constitutes an overpayment. Similarly, -RT and -LT are not appropriate for bilateral indicator 2 codes. This is a frequent error in practices that apply laterality modifiers reflexively.1
- Pitfall 4 — Failing to append modifier -25 to the same-day E/M or eye exam: If a comprehensive or intermediate eye exam (92002–92014) is billed on the same day as 92100, modifier -25 belongs on the exam code, not on 92100. Many practices incorrectly append -25 to the procedure code rather than the evaluation code, which may cause claim rejections or improper payment. The exam must be documented as a significant, separately identifiable service beyond the decision to perform tonometry.2
- Pitfall 5 — Billing multiple units of 92100: Some coders bill multiple units of 92100 when numerous measurements are taken throughout a long day, reasoning that each set of readings represents a separate service. This is incorrect — CPT 92100 is reported once per day, regardless of how many individual IOP readings are documented. Reporting multiple units will result in claim rejection or overpayment and is a clear coding error.1
- Pitfall 6 — Ignoring MAC-specific LCD requirements: Not all MACs have published an LCD for serial tonometry, but those that have may specify additional documentation requirements (e.g., minimum number of readings, minimum time span, clinical indications). Always verify with your regional MAC’s coverage determinations before billing, especially for the acute angle-closure management indication where the time-interval requirements may differ from the diurnal curve indication. Coding without checking applicable LCDs is a compliance risk.3