Measuring visual acuity at distance alone gives an incomplete picture of how a patient actually sees. A 55-year-old with 20/20 distance acuity may be completely unable to read a menu without holding it at arm's length. A 30-year-old with good near acuity may struggle to see road signs. Distance and near acuity measure related but distinct visual capabilities, and both are essential components of a comprehensive examination.
As a paraoptometric, you will perform both measurements regularly and need to understand not just the mechanics of each test but why the results matter clinically. The CPO and CPOA exams test your knowledge of testing protocols, recording conventions, and the significance of discrepancies between distance and near findings. This guide covers the practical and conceptual foundations for both.
The key distinction comes down to accommodation. Distance acuity is measured at optical infinity (20 feet or 6 meters), where the eye is in a relaxed state. Near acuity requires the eye to accommodate -- the crystalline lens changes shape to focus on objects at reading distance. Any condition that impairs accommodation, from presbyopia to medication side effects, will affect near acuity while potentially leaving distance acuity intact.
Distance Acuity: Principles and Protocol
Distance acuity is the foundation of visual acuity testing. At 20 feet, light rays from the chart are essentially parallel when they enter the eye, meaning accommodation is not required to bring the image into focus. This gives you a true measure of the eye's refractive state -- the combination of corneal curvature, lens power, and axial length that determines where light naturally focuses.
Distance Acuity Quick Reference
When the exam lane is shorter than 20 feet, there are two common solutions. A mirror placed at 10 feet from the patient effectively doubles the optical distance to 20 feet (the patient looks at the chart reflected in the mirror). Alternatively, projector charts and electronic acuity systems can be calibrated for shorter lanes -- the letter sizes are adjusted so that they subtend the same visual angle at the reduced distance. In either case, the numerator of the Snellen fraction should still be recorded as the actual testing distance, and the chart must be calibrated for that distance.
Near Acuity: Charts, Notation, and Protocol
Near acuity is tested at 14 to 16 inches (35-40 cm), which approximates a normal reading distance. Unlike distance testing, the eye must actively accommodate to focus at this range. This makes near acuity a compound measurement that tests both the optical quality of the eye and the accommodative system.
Jaeger Notation (J System)
The oldest near acuity notation, using J numbers from J1 (smallest, roughly 20/20 equivalent) through J16+ (very large print). While widely used, Jaeger values are not perfectly standardized -- J1 from one manufacturer may not match J1 from another. This imprecision is a known limitation. J1+ is the smallest size, J1 through J3 represent normal near acuity, and J5 or worse is considered reduced.
Rosenbaum Pocket Card
A handheld card with rows of numbers, letters, or symbols in decreasing sizes. It includes both Jaeger and Snellen-equivalent notation, making it the most practical near card for clinical use. The card is designed to be held at exactly 14 inches (36 cm) from the patient. Some cards include a string or cord of the correct length to ensure proper distance.
Reduced Snellen Near Cards
These cards use standard Snellen notation (20/20, 20/40, etc.) calibrated for 14-16 inches rather than 20 feet. This allows direct comparison between distance and near acuity using the same notation system, which simplifies clinical interpretation. If a patient is 20/20 at distance and 20/60 at near with correction, the discrepancy is immediately apparent.
M-Unit Notation
M-units (metric units) are the most precise near acuity notation. 1M print subtends 5 minutes of arc at 1 meter. The print size is physically measured and metrically defined, eliminating the variability of Jaeger notation. M-units are particularly important in low vision rehabilitation and are increasingly preferred in standard clinical practice. Convert to Snellen equivalent using: testing distance (meters) / M-unit = decimal acuity.
Near Acuity Testing Protocol
Ensure proper lighting
Near acuity is significantly affected by illumination. Use good, even overhead or task lighting directed at the near card. Dim lighting artificially reduces near acuity, especially in older patients. Avoid glare on the card surface. The room does not need to be bright, but the card itself should be well-lit.
Position the card at 14-16 inches
The patient holds the card or it is placed on a stand at the specified distance. If a cord is attached, have the patient hold the end against their cheekbone while holding the card at the other end. Watch for patients who instinctively move the card closer -- this is common and must be corrected. If the patient holds the card at 10 inches instead of 14, the measurement is invalid.
Test with near correction in place
For patients over 40, near acuity is typically tested with their reading glasses or bifocal/progressive add in place. You may also test without correction to assess unaided near function. The doctor's protocol will specify which conditions to measure. Always document whether the test was performed with or without near correction.
Test each eye, then both eyes
Follow the same OD, OS, OU sequence used for distance testing. Occlude one eye at a time with a paddle or tissue. Near binocular acuity is particularly important because most reading and near work is done with both eyes open.
Record using the card's notation system
Document the smallest line read correctly using whatever notation the card provides: J number, Snellen equivalent, M-unit, or point size. Always note the testing distance, correction status, and any observations about the patient's behavior (e.g., "patient held card at 10 inches despite instruction").
Practice acuity testing questions for your exam
Opterio covers distance and near acuity protocols, notation systems, and clinical interpretation.
Presbyopia and Age-Related Near Vision Changes
Presbyopia is the progressive loss of accommodative ability that begins in the early 40s and continues through the mid-60s. The crystalline lens gradually stiffens, losing its ability to change shape for near focus. This is universal -- every human will develop presbyopia if they live long enough. It is not a disease but a normal part of aging.
A typical 45-year-old has about 3.50 diopters of accommodation remaining, barely enough for comfortable reading at 14 inches. By age 55, accommodation is usually 1.50 diopters or less. By 65, it is essentially zero. This is why near acuity testing becomes increasingly important as patients age -- their distance vision may remain stable while their near vision steadily declines.
Clinical Significance
Patients often present complaining that their "arms are not long enough." They hold reading material farther away to bring it into focus, which works until the material is too far to read even at arm's length. This is the classic presbyopia presentation. Near acuity testing quantifies the deficit and guides the add power prescription.
When Distance-Near Discrepancies Matter
The most clinically useful information from near acuity testing comes from comparing it to distance acuity. Certain patterns of discrepancy point to specific conditions that the doctor needs to evaluate further.
Good distance, poor near (with proper near correction)
If distance acuity is 20/20 but near acuity is significantly reduced even with appropriate reading correction, suspect macular pathology. The macula is responsible for fine central detail, and macular disease (AMD, diabetic macular edema, epiretinal membrane) preferentially affects near tasks that demand high-resolution central vision.
Poor distance, good near (in younger patients)
A younger patient with reduced distance acuity but normal near acuity is likely myopic (nearsighted). Myopic eyes naturally focus well at near distances because the focal point falls in front of the retina. The near test distance may fall within their clear range even without correction.
Both distance and near reduced equally
When both distance and near acuity are reduced by roughly the same amount, consider media opacity (cataract), optic nerve disease, or other pathology that affects all visual function regardless of working distance. A pinhole test helps differentiate refractive from pathological causes.
Fluctuating near acuity
If near acuity varies significantly between visits or even during the same exam, consider uncontrolled diabetes (blood sugar fluctuations change lens hydration and refractive power), dry eye (unstable tear film causes transient blur), or accommodative spasm. Document these fluctuations and alert the doctor.
Near Acuity Notation Conversion
You may encounter multiple notation systems on the same card or across different cards in the office. Understanding the approximate equivalents helps you communicate findings clearly and answer exam questions that test cross-system knowledge.
Approximate Near Acuity Equivalents
| Jaeger | Snellen Equivalent | Point Size | M-Units |
|---|---|---|---|
| J1+ | 20/20 | ~3 pt | 0.4M |
| J1 | 20/25 | ~4 pt | 0.5M |
| J2 | 20/30 | ~5 pt | 0.6M |
| J3 | 20/40 | ~6 pt | 0.8M |
| J5 | 20/50 | ~8 pt | 1.0M |
| J7 | 20/70 | ~10 pt | 1.4M |
| J10 | 20/100 | ~14 pt | 2.0M |
Note: Jaeger values are approximate and may vary between card manufacturers. Snellen and M-unit values are standardized.
Documentation Best Practices
Complete Near and Distance VA Documentation
Distance VA (cc, habitual Rx):
OD: 20/20 OS: 20/20 OU: 20/20
Near VA (cc, bifocal add):
OD: J2 @ 14" OS: J1 @ 14" OU: J1 @ 14"
Near VA (sc):
OD: J7 @ 14" OS: J5 @ 14" OU: J5 @ 14"
Always note the testing distance, correction status, and notation system used. If the patient could not maintain the standard distance, note the actual distance tested.