What Is ABS?

What Is ABS, Exactly?

ABS stands for Applied Basic Science, and in the context of optometric licensure it refers specifically to NBEO Part I, the first exam in the three-part series administered by the National Board of Examiners in Optometry (NBEO). NBEO is headquartered in Charlotte, North Carolina, and delivers Part I ABS as a one-day, computer-based exam at Pearson VUE test centers around the country. If you are searching for a plain-language definition, this is it: Part I ABS is the gateway exam that tests whether an optometry student has mastered the foundational scientific knowledge required before advancing toward independent clinical practice.

This exam is not optional. It is required for licensure in all 50 states, the District of Columbia, and Puerto Rico. No matter which state a candidate eventually practices in, Part I ABS sits at the start of the path. For a broader look at how this credential fits into the profession, see our overview of ABS Certification.

Why Part I ABS Exists in the Licensure Sequence

Optometric licensure in the United States is built on a three-part NBEO series, and Part I ABS is the entry point. Rather than testing clinical decision-making directly, it verifies that a candidate has internalized the scientific building blocks - anatomy, biochemistry, pathology, optics, and pharmacology - that every later clinical judgment depends on. Think of it as the checkpoint that confirms readiness to reason about disease, refraction, and treatment before those skills are assessed in later parts of the series.

Because it is the first hurdle, many candidates underestimate how comprehensive it is. It is worth reading a dedicated breakdown of how hard the ABS exam actually is before assuming a light review will suffice.

Exam Format, Sessions, and Question Style

Part I ABS contains 370 total items: 350 scored questions and 20 unscored pre-test items that are indistinguishable from scored content. The exam is split into two sessions of 185 items each, with 4 hours allotted per session. The first session includes an additional 15 minutes for a tutorial and a nondisclosure agreement, and candidates may take an optional break of up to 45 minutes between the two sessions.

Most items are single-best-answer multiple choice, but approximately 10 to 15 percent are multiple-response questions. These items explicitly state how many selections are required - 2, 3, or 4 - and they are scored as entirely correct or entirely incorrect. There is no partial credit, which means a candidate who selects 3 of 4 correct options on a required 4-select item receives zero credit for that question. This scoring rule alone makes multiple-response items disproportionately risky and worth specific practice.

One stylistic detail that surprises some candidates: eponymous terms (named after a person) appear in non-possessive form throughout the exam - a convention worth noting so unfamiliar phrasing doesn't cost time during the real test.

The Five ABS Content Domains

NBEO organizes Part I ABS content into five domains, each weighted differently. Understanding these weights is the single most useful piece of information for allocating study time. A full breakdown of each domain, including subtopics, is available in our ABS Exam Domains Guide, but here is the core structure:

NBEO also cross-maps content into two condition blocks that run alongside the five domains: Refractive Status, Sensory Processes and Oculomotor Processes at 122 items, and Normal Health, Disease and Trauma at 228 items - within which Systemic Health alone accounts for 55 to 75 items. This dual structure means a single question can be tagged both to a domain (like Pathology) and a condition block (like Normal Health, Disease and Trauma), so studying by domain alone may leave gaps in how conditions present clinically.

How ABS Is Scored

Raw scores on Part I ABS convert to a scaled score ranging from 100 to 900, with 300 set as the pass-fail cutoff. Individual sections are reported separately on a 0 to 99 scale, with 75 as the section-level cutoff. NBEO does not grade on a curve, meaning the standard is fixed rather than relative to how other candidates in your administration performed. For the exact mechanics of what this means for your target score, see our dedicated explainer on the ABS Passing Score.

Score reports post approximately seven weeks after the full administration - a longer wait than many candidates expect, so plan residency or job-search timelines accordingly.

Historical first-time pass rates give useful context: 68.7% for the March 2024 administration across 1,541 first-time takers, following 67.1% in March 2023 and 65.3% in March 2022. These numbers, along with what they imply about difficulty trends, are analyzed further in our ABS Pass Rate breakdown.

Registration, Fees, and Scheduling

The fee for Part I ABS is $1,490 for examinations administered from August 2026 onward, an increase from $1,445 for prior administrations. Candidates who register late face a non-refundable $400 late registration fee, and NBEO does not guarantee Pearson VUE seat availability for late registrants - a real risk if you wait too long to lock in a testing window. For the full cost picture, including how these fees compare across the licensure sequence, review our ABS Certification Cost guide.

Because seat availability is not guaranteed for late registrants, checking testing windows early matters. Our ABS Exam Dates article covers testing windows and deadlines in detail so you can register with margin to spare.

Who Takes ABS and Why It Matters

Every candidate pursuing licensure as an optometrist in the United States must pass Part I ABS. It is typically taken by optometry students at a defined point in their academic program, before moving on to the clinically oriented parts of the NBEO series. Because licensure boards in all 50 states, DC, and Puerto Rico rely on this exam as a gatekeeping credential, there is no state-by-state substitute - passing Part I ABS is a shared requirement across the entire profession.

This universality is part of why the exam carries weight beyond the test itself. Employers, residency programs, and licensing boards treat a passing score as confirmation of foundational competency. If you're weighing how this credential affects your career trajectory, our analysis on whether the ABS Certification is worth it and our ABS Salary Guide both go deeper into long-term implications, while ABS Requirements covers eligibility and prerequisites before you can even sit for the exam.

How to Approach Preparation

Given that Optics alone represents up to 35% of the exam, and Immunology/Microbiology/Pathology represents up to 30%, these two domains together can account for well over half of all scored items. A study plan that treats all five domains equally is likely to under-prepare for the areas most likely to determine your scaled score.

A reasonable approach is to sequence review so that Optics and Pathology receive the earliest and most repeated attention, with Anatomy, Biochemistry/Physiology, and Pharmacology layered in as supporting review once the two largest domains feel solid. Using timed blocks that mimic the two 185-item, 4-hour sessions - rather than untimed review - also helps build the pacing needed for exam day, since each session leaves roughly 1.3 minutes per item on average.

For a complete week-by-week strategy, our ABS Study Guide lays out a fuller plan for passing on the first attempt, and a condensed reference for last-minute review is available in the ABS Cheat Sheet. You can also build timed-practice habits directly on our practice test platform, which mirrors the two-session, multiple-response format described above.

Frequently Asked Questions