Choosing between eye chart types is really two decisions made at once. The first is the format: a printed (usually back-lit) chart, a chart projector with a screen, or a digital LCD chart. The second is the layout on that chart: the classic Snellen design or a logMAR layout of the Bailey-Lovie / ETDRS family. This guide compares the main types of eye charts side by side for practice owners and lane planners, with the specs that matter when you are equipping a room, and links to the visual acuity charts and systems we carry and support in the US.
If your question is about room length, mirror lanes or how to calibrate a chart to the distance you actually have, our companion guide to Snellen chart distance and exam lane setup covers that geometry. Here we stay on the buying decision: which kind of chart, and which layout.
Shopping for visual acuity charts & systems? US Ophthalmic is a direct provider of visual acuity charts & systems to eye care practices across the US. Tell us how your lane is set up and we will come back with the configurations that fit, plus current availability and lead times.
The two decisions: format and layout
Format determines how optotypes reach the patient: ink or film lit from behind, an image thrown onto a screen, or pixels on a monitor. It drives footprint, illumination, upkeep and how much flexibility you have to change what is shown. Layout determines what the patient is asked to read: how many letters sit on each line, which letters are used, and how size steps from one line to the next. Every format can carry either layout to some degree, but the formats differ a lot in how easily they switch between layouts, optotype sets and letter sequences.
Snellen vs logMAR: what actually differs on the chart
Snellen layout
Snellen built his optotypes on a 5×5 grid, with the letter five stroke-widths tall and wide. The common printed Snellen chart has eleven lines, starting with one large letter, and the standard chart uses a limited set of nine letters (C, D, E, F, L, O, P, T, Z). Because the chart is rectangular, the number of letters per line varies "as the space allows," and the size progression between lines is irregular: Precision Vision notes the step can range from 14 percent (20/70 to 20/80) to 100 percent (20/100 to 20/200 to 20/400).
The design limitations usually cited for Snellen charts are design facts rather than opinions: inconsistent size progression from line to line, letters of unequal legibility, unequal spacing between letters and rows, and large gaps between acuity levels at the low-acuity end of the chart (20/80 to 20/400).
LogMAR layout (Bailey-Lovie and ETDRS)
Ian Bailey and Jan Lovie-Kitchin designed the logMAR chart in 1976 at the National Vision Research Institute of Australia. Their stated principles: letters of equal legibility, the same number of letters on each row, uniform between-letter and between-row spacing, and a logarithmic progression of letter size. In practice that means five letters per line and size steps of 0.1 log unit, with spacing that scales with letter size, which gives the chart its familiar inverted-triangle shape.
In 1982, Ferris and colleagues at the National Eye Institute combined that layout with the ten Sloan letters (C, D, H, K, N, O, R, S, V, Z) to produce the ETDRS charts: five Sloan letters per line, lines of equal difficulty, a geometric size progression, and charts with different letter sequences for right and left eyes. The NEI protocol set the viewing distance at 4 meters "to have a more manageable chart size." Scoring is per letter: each letter is worth 0.02 log units, so a full five-letter line represents 0.1.
What the measurement standard asks for
The International Council of Ophthalmology's 1984 Visual Acuity Measurement Standard reads like a spec sheet for chart buyers. It asks for optotype sizes in a constant-ratio (0.1 log unit) progression, constant space-to-size ratios across the chart, spacing between adjacent optotypes of at least one optotype width, and at least five optotype presentations of each size, "randomly ordered." It suggests 4 meters as the standard distance, accepts 5 and 6 meters, and accepts mirror systems. It also notes that five-per-size "may not be practical in certain projection devices when testing with large letter sizes," which is one of the clearest format trade-offs on record.
| Design feature | Typical Snellen chart | LogMAR / ETDRS chart |
|---|---|---|
| Letters per line | Varies with line (1 at the top, more lower down) | Same on every line (5) |
| Size progression | Irregular, roughly 14% to 100% per step | Constant 0.1 log unit per line |
| Spacing | Not tied to letter size | Proportional to letter size |
| Letter set | Nine letters on the common chart | Ten Sloan letters |
| Scoring unit | Line (Snellen fraction, e.g. 20/20) | Letter (0.02 logMAR each) |
| Usual design distance | 20 ft / 6 m, with 10 ft / 3 m half-size versions | 4 m, with 2–3 m versions |
For reference, 20/20 (6/6) corresponds to logMAR 0.00 and 20/200 (6/60) to logMAR 1.00, so the two notations convert cleanly. The practical buying question is which layout your lane needs to present, and whether you want to switch between them.
Printed and back-lit charts
A printed chart is the simplest format: a fixed panel, usually translucent and lit from behind so the whole surface sits at an even luminance. Modern cabinets use LED light; Good-Lite, for example, describes its ESC2000 ETDRS cabinet as 3.0 inches deep against 8 inches for traditional fluorescent cabinets, and its ESV3000 as self-calibrating to preset levels of 3, 85 or 160 cd/m².
In our range, the Luxvision CP-4000 vision chart is an LED back-lit distance chart for a 3-meter (10-foot) test distance, 580 × 520 × 18 mm, which can stand on a table or hang on a wall. The CP-5000 is the 5-meter (16.4-foot) version at 280 × 845 × 19 mm, a tall, narrow panel. Both run from a 12 V DC adapter.
Where printed charts fit: screening rooms, satellite or secondary lanes, pretest areas, and any space where you want a reliable chart with no software, no setup menu and nothing to calibrate beyond placement.
Trade-offs: the letter sequence is fixed. Repeat patients see the same lines, which is why the ETDRS protocol uses different sequences for each eye and why printed ETDRS sets are sold as alternate forms, which Precision Vision recommends using "in rotation to eliminate learning effects across repeat visits." A printed chart is also built for one design distance, so it is matched to the room rather than the other way round, and swapping optotype families means buying another panel.
Chart projectors
A chart projector throws the chart onto a screen at the end of the lane and changes it by remote control. That makes it a natural fit for lanes that already have a screen, mirror geometry or a projector mount, and for practices that want many charts and masking from one compact unit beside the patient chair.
The Luxvision LCP-7800 chart projector carries 41 test charts and 34 masks (horizontal lines, vertical lines or single characters), with red/green and polarizing filters. Charts can be called up randomly or through two user-defined programs of up to 30 charts each. It uses a semi-permanent LED light source, projects over 2.5 to 8 m (8 m screen optional) at 30× magnification at 5 m, changes charts in an average of 0.15 seconds, and switches itself off after 10 minutes. It can also be networked with a digital refractor, lensmeter and autorefractor/keratometer for a connected lane.
For context on the wider category, the Essilor CP 550 is sold with a projection screen and stand, uses LED illumination and supports 2 to 7 m, while the older Topcon ACP-8R design uses a 12 V 50 W halogen lamp, with a polarized metal screen offered as an accessory. The LED versus lamp question is mostly an upkeep question: the ICO standard asks manufacturers to provide guidance on when lamps should be changed, and LED sources largely take that task off the list.
Trade-offs: a projected image is only as good as the screen and the room light. The ICO standard specifically flags that for projected charts, "degradation of contrast by ambient light should be avoided or at least minimized," so plan lighting and screen placement together. Large-letter lines may also carry fewer than five optotypes, as noted above.
Digital LCD charts
A digital chart is a dedicated monitor running acuity software. Its main advantages are flexibility and calibration: optotype size is calculated from the test distance you enter, letter sequences can be randomized so patients cannot read from memory, and one screen can hold Snellen, ETDRS-style, number, Landolt C and pediatric charts along with binocular and color tests.
The Ezer EDC-BH is a 23-inch Full-HD (1920 × 1080) medical monitor with Landolt ring, astigmatism fan and block, ETDRS-style letter and number charts and more. Charts resize automatically to the working distance you enter, from 1.0 to 6.0 m; black-and-white charts can be reversed; and images or video (AVI, MPEG, MP4, MKV) can be loaded by USB or microSD. The Luxvision LDC-2600 is a 21-inch LCD chart with line, column and single-letter masking, number, Snellen-letter and children's-figure acuity charts, and automatic calibration to working distances from 2 to 6.5 m (the maker lists 2.5 to 6 m as the best range). Its software lives on a replaceable SD card.
Across the category, feature lists look similar. Topcon's CC-100 series, for example, lists optotype randomization, masking, inversion and mirror modes, logMAR single-letter scoring and a testing distance of 2.0 to 9.0 m in 0.1 m steps; Reichert lists the ClearChart 4 as a 24-inch, 1920 × 1080 LCD with 85 cd/m² photopic and 3 cd/m² mesopic settings for lanes of 6 to 24.6 feet. Those are reasonable benchmarks when comparing any digital chart, including ours. For a ranked comparison of digital systems, see our digital LCD acuity chart buyer's guide.
Trade-offs: a digital chart needs correct setup. The distance entered must match the real lane (or the mirror path), and at very short distances the monitor's resolution can limit how finely the smallest optotypes are drawn. Mounting height and cable runs also need planning before installation day.
Head-to-head: printed vs projector vs digital
| Factor | Printed / back-lit chart | Chart projector | Digital LCD chart |
|---|---|---|---|
| Letter sequences | Fixed; alternate forms need separate panels | Many charts; random selection on some models | Randomization standard on most systems |
| Snellen and logMAR on one device | No (one layout per panel) | Depends on the chart set loaded | Yes, typically several layouts and optotype families |
| Distance flexibility | Built for one distance | Wide range (e.g. 2.5–8 m on the LCP-7800) | Calibrates to entered distance (e.g. 1.0–6.0 m on the EDC-BH) |
| Masking | None, or manual | Line, column and single letter | Line, column and single letter |
| Illumination | Back-light; LED models are even and low-upkeep | Projected; sensitive to room light and screen | Self-lit monitor |
| Hardware at the far end | The chart panel | A screen (projector sits near the chair) | The monitor |
| Setup and upkeep | Minimal | Aim, focus and screen; lamp or LED source | Distance entry, mounting, software updates |
| Best fit | Screening, pretest, secondary lanes | Lanes already built around a screen or mirror | Primary refraction lanes; short or unusual rooms |
How to choose: a checklist for your lanes
- Measure the lane first. Real eye-to-chart distance (or the full mirror path) decides whether a fixed printed chart works or whether you need a format that calibrates to distance.
- Decide which layout you need to present. If you want logMAR or ETDRS-style lines alongside Snellen, a digital chart is the simplest route; a printed setup needs separate panels.
- Count repeat-visit patients. If the same patients are retested often, randomized sequences (digital) or alternate forms (printed) matter more.
- Check luminance and ask for the data. The ICO standard recommends at least 80 cd/m² and notes US practice of 85 cd/m²; it also asks makers to supply expected luminance and calibration data. Ask for it whatever the format.
- Plan the room light. Projected charts are most affected by ambient light; back-lit and LCD charts less so.
- Think about the whole lane. If you are building toward a connected lane, check whether the chart can link with your refractor (the LCP-7800 networks with a digital refractor, lensmeter and autorefractor/keratometer).
- Budget the install, not just the device. Wall mounts, screen placement, cable runs and who calibrates on day one are part of total cost of ownership. Ask us to include them in your quote.
Every chart we supply is backed by US Ophthalmic's in-house tech and spare-parts department and US warranty and service. Browse the full visual acuity collection, or request a quote with your lane length and the layouts you need, and we will recommend a format that fits the room.
Ready to spec your visual acuity charts & systems?
Send us your requirements and our equipment specialists will come back with a configuration built around how your practice actually works — including availability and lead time. US Ophthalmic is a direct provider to eye care practices nationwide.
Frequently asked questions
What are the main types of eye charts?
By format there are three: printed (usually LED back-lit) charts, chart projectors that throw the chart onto a screen, and digital LCD charts. By layout, the two main families are the Snellen chart and logMAR charts such as Bailey-Lovie and ETDRS. Optotypes include letters, numbers, Landolt C, tumbling E and pediatric symbols.
What is the difference between a Snellen chart and a logMAR chart?
A Snellen chart has a varying number of letters per line and irregular size steps. A logMAR chart has five letters on every line, a constant 0.1 log unit size step, and spacing proportional to letter size, and it is scored per letter (0.02 logMAR each). 20/20 equals logMAR 0.00.
Is a digital eye chart better than a chart projector?
Neither is better for every lane. Digital charts calibrate to the entered distance, randomize letters and switch between layouts easily, which suits primary refraction lanes and short rooms. Projectors suit lanes already built around a screen and keep the hardware beside the chair, but they are more sensitive to room light.
What luminance should an eye chart have?
The ICO 1984 standard recommends a test chart luminance of not less than 80 cd/m² for clinical purposes and records 85 cd/m² as US practice, with 120 cd/m² in the UK and 300 cd/m² in Germany. Ask the manufacturer for its luminance and calibration data.
Can I use a 10-foot eye chart in a short exam room?
Yes. Half-size charts designed for 3 m (10 ft), such as the CP-4000, are one option; digital charts that calibrate to the distance you enter are another. Our exam lane setup guide covers mirror lanes and distance calibration in detail.
Should I buy a new or refurbished eye chart?
US Ophthalmic sells new equipment, not refurbished or used units. If budget is the priority, check our open-box units: demo, display and lightly handled items that are inspected and function-checked, with warranty terms that vary by unit.
