Various Vertex Decentration Price Standard values General
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Visual acuity conversion

Snellen decimal

Snellen fraction m

Snellen fraction ft

LogMAR

Fill one field and press enter.

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Snellen decimal = Snellen fraction numerator / Snellen fraction denominator. Snellen fraction = Wanted numberator / (Wanted numerator / Snellen decimal). logMAR = log10(1 / Snellen decimal). Snellen decimal = 1/10^(logMAR)

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Convert between plus-cylinder and minus-cylinder

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New sphere = old sphere + old cylinder

New cylinder = old cylinder · -1

New axis = old axis + 90, reduced by 180 if necessary

Spherical equivalent

Sphere

Cylinder

Result

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Cylinder without sign is calculated as plus-cylinder.

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Spherical equivalent = sphere + half the cylinder

Vertex calculator

Cylinder without sign is calculated as plus-cylinder.

If moved away from the eye, write a negative amount of mm.

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Vertex corrected power = 1 / (1 / Power - Distance in meters)

The calculator saves you the hassle of keeping track of the sphere and cylinder calculations. Axis added for simplicity.

Reference [3]

Vertex chart

Write only sphere, without sign. If moved away from the eye, write a negative amount of mm.

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Vertex corrected power = 1 / (1 / Power - Distance in meters)

Reference [3]

Minus

Number

Plus

Estimate prisms from decentration

Fill in prescription, then either amount of mm or desired prism. Then press enter while the field is marked.

In this calculator, any axis not close to 90° or 180° is considered oblique. With oblique axis, prismatic effect in other directions will also be induced.

For oblique axis, the calculation is based on spherical equivalent and less precise. The higher the cylinder, the less reliable the calculation.

Cylinder without sign is calculated as plus-cylinder.

The base direction is the direction the lens is thickening. For example, increasing pupillary distance will give base-out prism in a plus-powered lens and base-in prism in a minus-powered lens.

A lens with prism decentration should always be controlled manually.

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Calculated with Prentice's rule: Prism diopters = Lens power · distance in cm

If distance is supplied: Prism diopters = mm distance / 10 · Lens Power

If prisms are supplied: mm distance = Prism diopters · 10 / Lens Power

An axis of 90° contributes to horisontal prism, an axis of 180° contributes to vertical prism.

Reference [§r, §t]

Amount of mm movement for 0.5 prism diopters per eye

This section does not take into account the sum of both eyes, so calculating 0.5 prism for both eyes will result in 1.0 total prism.

In this calculator, any axis not close to 90° or 180° is considered oblique.

For oblique axis, the calculation is based on spherical equivalent and less precise. The higher the cylinder, the less reliable the calculation.

Cylinder without sign is calculated as plus-cylinder.

A lens with prism decentration should always be controlled manually.

⏷

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The basis for this calculator is the assumption that 0.5 prism diopters is a reasonable limit for acceptable decentration. This assumption is uncertain.

Prentice's rule: Prism diopters = Lens power · distance in cm

Decentration in mm to reach 0.5 prism diopters = (0.5 / Lens Power) · 10

[u] concluded 0.5 vertical prism diopters or 1.0 horisontal prism diopters are values most spectacle wearers likely can tolerate.

Reference [§r, §t, §u]

Sum all

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Cornea

[e, g, h, i, j]

Central thickness: mean from 532.1 to 563.0 µm. Standard deviation from 18.8 to 40 µm.


Keratometry: mean from 43.6 to 44.62 D. Standard deviation from 1.5 to 1.7 D.

Corneal astigmatism: mean from 0.67 to 1.06 D. Standard deviation 0.96 D.

[e]: Central corneal thickness mean 534.35 ± 36.2 µm. Both eyes of 124 Hispanic subjects, 66 female and 58 male, mean age 35 ± 15.1 years. Measured with Orbscan.

[g]: Central corneal thickness mean 534 ± 40 µm. Keratometry mean 44.26 ± 1.70 D. In women 44.62 D, in men 43.75 D. Mean 543.6 ± 19.8 µm in women and 543.6 ± 19.8 µm in men. Corneal astigmatism mean 1.06 ± 0.96 D. Chinese subjects, 28,709 right eyes of cataract surgery candidates, 59.1/40.9% female/male. Measured with IOLMaster 700.

[h]: Central corneal thickness mean 549 ± 34 µm in right eyes and 550 ± 34 µm in left eyes. In women 546 ± 35 µm in right eyes and 547 ± 34 µm in left eyes, in men 552 ± 34 µm in both eyes. Keratometry mean 44.0 ± 1.6 D in both eyes. In women 44.4 ± 1.5 D in both eyes, in men 43.6 ± 1.6 D in both eyes. Corneal astigmatism mean 0.74 D in both eyes. In women 0.81 D in right eyes and 0.80 D in left eyes, in men 0.67 D in right eyes and 0.69 D in left eyes. 3014 subjects, 1460/1554 women/men, age 58.6 ± 10.4 years. Measured in Germany.

[i]: Central corneal thickness mean 532.1 ± 18.8 µm. Used in vivo confocal microscopy through-focusing on seven human subjects.

[j]: Central corneal thickness mean 563.0 ± 31.1 µm. Used in vivo confocal microscopy on 70 corneas on 70 subjects.

[i, j, k, l]

Epithelium

Central thickness: mean from 28.6 to 53.5 µm. Standard deviation from 3.9 to 7 µm. Range from 43.5 to 63.6 µm in [l].

Mid-peripheral thickness: mean from 48 to 58.8 µm. Standard deviation from 4.6 to 7 µm.

Peripheral thickness: mean 48 µm. Standard deviation 6 µm.

[i]: Central epithelial thickness 50.6 ± 3.9 µm. |

[j]: Central epithelial thickness 28.6 ± 5.1 µm. Used in vivo confocal microscopy on 70 corneas on 70 subjects.

[k]: Central epithelial thickness 48 ± 5 µm, mid-peripheral thickness 48 ± 7 µm and peripheral thickness 48 ± 6 µm in 18 subjects who had not used contact lenses. Central thickness 41 ± 7 µm, mid-peripheral thickness 41 ± 7 µm and peripheral thickness 42 ± 9 µm in 15 contact lens users. The study used a modified optical pachymeter.

[l]: Central epithelial thickness 53.4 ± 4.6 µm, range 43.5-63.6 my. Thickness 3 mm superior of vertex 53.1 ± 4.7, 3 mm inferior of vertex 58.8 ± 4.9 µm, 3 mm temporally of vertex 53.8 ± 5.0 µm and 3 mm nasally of vertex 55.0 ± 4.6 µm. 110 eyes, 74% caucasian, 17% east indian, 5% east asian, 4% black, aged 20.5-73.5 years (mean 38.4). High amount of myopes. The study used Artemis 1 digital ultrasound.

[i, m]

Bowman's layer / Anterior limiting lamina

Mean thickness: From 8.16 to 16.6 µm.

[i]: Mean 16.6 ± 1.1 µm. Used in vivo confocal microscopy through-focusing on seven human subjects.

[m]: Mean thickness measured on two eyebank corneas 8.16 and 8.20 µm. Transmission electron microscopy was used.

[§ad]

Retinal thickness

Center: Mean 237.8 µm. Standard deviation 20.3 µm. Range from 186.7 to 296.7 µm.

Women: Mean 232.4 µm. Standard deviation 19.0 µm.

Men: Mean 240.3 µm. Standard deviation 20.4 µm.


[§ad]: .

[§ad]

Retinal thickness by the ETDRS macular grid

Center Outer superior Outer nasal Outer inferior Outer temporal Inner superior Inner nasal Inner inferior Inner temp.

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Click on a cell to see the values.

Center

Mean 237.8 µm. Standard deviation 20.3 µm. Range from 186.7 to 296.7 µm.

In women: Mean 232.4 µm. Standard deviation 19.0 µm.

In men: Mean 240.3 µm. Standard deviation 20.4 µm.

Outer superior

Mean 276.1 µm. Standard deviation 12.6 µm. Range from 227.1 to 318.7 µm.

In women: Mean 277.0 µm. Standard deviation 10.7 µm.

In men: Mean 275.0 µm. Standard deviation 13.5 µm.

Outer nasal

Mean 293.1 µm. Standard deviation 15.0 µm. Range from 239.3 to 340.1 µm.

In women: Mean 293.0 µm. Standard deviation 13.4 µm.

In men: Mean 291.0 µm. Standard deviation 15.7 µm.

Outer inferior

Mean 262.8 µm. Standard deviation 13.1 µm. Range from 218.0 to 302.3 µm.

In women: Mean 263.5 µm. Standard deviation 12.5 µm.

In men: Mean 262.5 µm. Standard deviation 13.4 µm.

Outer temporal

Mean 264.9 µm. Standard deviation 12.4 µm. Range from 227.6 to 299.3 µm.

In women: Mean 262.4 µm. Standard deviation 11.0 µm.

In men: Mean 266.0 µm. Standard deviation 12.8 µm.

Inner superior

Mean 318.3 µm. Standard deviation 14.5 µm. Range from 269.9 to 355.9 µm.

In women: Mean 314.8 µm. Standard deviation 12.8 µm.

In men: Mean 319.9 µm. Standard deviation 15.0 µm.

Inner nasal

Mean 316.8 µm. Standard deviation 15.2 µm. Range from 263.4 to 357.8 µm.

In women: Mean 311.7 µm. Standard deviation 14.4 µm.

In men: Mean 319.2 µm. Standard deviation 15.0 µm.

Inner inferior

Mean 315.2 µm. Standard deviation 14.4 µm. Range from 268.8 to 350.6 µm.

In women: Mean 311.0 µm. Standard deviation 13.0 µm.

In men: Mean 317.2 µm. Standard deviation 14.6 µm.

Inner temporal

Mean 305.4 µm. Standard deviation 14.5 µm. Range from 255.0 to 343.4 µm.

In women: Mean 300.6 µm. Standard deviation 13.3 µm.

In men: Mean 307.7 µm. Standard deviation 14.5 µm.

[§ad]: .

[h]

Intraocular pressure

Mean from 14.5 to 15.2 mmHg. Standard deviation from 2.86 to 2.98 mmHg.

[h]: Mean 14.9 ± 2.92 mmHg for right eyes and 15.0 ± 2.96 mmHg for left eyes. For women 14.8 ± 2.86 mmHg in right eyes and 14.9 ± 2.94 mmHg in left eyes, for men 14.5 ± 2.98 mmHg in right eyes and 15.2 ± 2.96 mmHg in left eyes. Non-contact tonometry, measured in Germany.


[h]

Astigmatism

Mean from 0.52 to 0.64 D. Standard deviation 0.56 to 0.71 D.

[h]: Mean 0.59 ± 0.65 D for right eyes and 0.57 ± 0.60 D for left eyes. For women 0.64 ± 0.71 D in right eyes and 0.62 ± 0.64 D in left eyes, for men 0.53 ± 0.57 D in right eyes and 0.52 ± 0.56 D in left eyes. Measured in Germany.

[b]

Orbit

Height of margin: Median from 41.08 to 42.55 mm. Standard deviation from 2.4 to 2.5 mm. Range from 38.8 to 44.8 mm.

Width of margin: Median from 35.33 to 35.86 mm. Standard deviation 2.2 mm. Range from 32.7 to 37.4 mm.

Depth: 47.73 to 48.40 mm. Standard deviation from 4.6 to 4.7 mm. Range from 38.7 to 55.7 mm.

[ac]

Optic nerve sheath diameter

3 mm posterior to the globe margin: Mean from 5.01 to 5.12 mm. Standard deviation 0.63 mm. Range from 3.85 to 6.9 mm.
For women: Mean 5.01 mm, standard deviation 0.63 mm.
For men: Mean from 5.10 to 5.12 mm, standard deviation 0.63 mm.

8 mm posterior to the globe margin: Mean from 4.35 to 4.41 mm. Standard deviation from 0.49 to 0.52 mm. Range from 3.15 to 6.40 mm.
For women: Mean 4.35 to 4.36 mm, standard deviation 0.51 to 0.52 mm.
For men: Mean from 4.40 to 4.41 mm, standard deviation 0.49 to 0.51 mm.

Snellen fraction

Visual acuity = Testing distance (m or ft) / Distance where the smallest optotype read equals 5 minutes of arc

Minimal angle of resolution (MAR)

MAR = 1 / Snellen decimal

logMAR

logMAR = log10(MAR). logMAR = log10(1 / Snellen decimal). Snellen decimal = 1/10^(logMAR)

[§r, §t]

Prentice's rule

Prism diopters = Lens power · distance in cm

Calculates the result prismatic effect from moving the center of a spectacle lens.


Far point

Far point in meters = 1 / dioptric distance power of the unaccomodating eye. Dioptric distance power = 1 / far point in meters

The point in which an eye can see most clearly without accommodation. The far point is in front of the eye for myopes and behind the eye for hyperopes.


[3]

Vergence

Vergence in diopters = 1 / object distance in meters

[3]

Vertex corrected power

Vertex corrected power = 1 / (1 / Power - Distance in meters)

Calculates the change to dioptric power from moving a lens closer to or further from the eye.

Conversion meter, feet, inches

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"

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Fill one box and press enter.

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1 meter =
    100 cm
    1000 mm
    3.28 feet
    39.37 inches

1 foot =
    12 inches
    0.3048 meters

References [v, y, z]

Weight converter

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1 kg =
    1000 grams
    2.2046 pounds

1 pound =
    16 ounces
    0.453592 kg

References [v, x, z]

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Volume converter

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Fill one box and press enter.

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1 liter =
    1000 milliliters
    1 cubic decimeter
    0.035315 cubic feet
    0.2642 gallons
    67.6 tablespoons

1 cubic meter =
    1000 liters
    1000000 cubic centimeters
    35.315 cubic feet
    264.17 gallons
    67627.9 tablespoons

1 cubic foot =
    28.317 liters
    0.028317 cubic meters
    7.48 gallons
    1915 tablespoons

1 gallon =
    3.78541 liters
    0.00378541 cubic meters
    0.133681 cubic feet
    8 pints
    16 cups
    256 tablespoons

1 tablespoon =
    14.7868 milliliters / cubic centimeters
    0.0000443603 cubic feet
    0.0591939 cups
    3 teaspoons

References [v, y, z]

Temperature converter

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Celsius to Fahrenheit: F = (C · 9/5) + 32

Celsius to Kelvin: K = C + 273.15

Fahrenheit to Celsius: C = (F - 32) · 5/9

Fahrenheit to Kelvin: K = (F + 459.67) · 5/9

Kelvin to Fahrenheit: F = K · 9/5 - 459.67

Kelvin to Celsius: C = K - 273.15

References [v, w]

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