Formulas

What is the formula for calculated AC/A?

AC/A = PD(cm) + NFD(m)(Pn - Pf)

The amount of hyperopia the pt can't neutralize with accommodation is called?

Absolute hyperopia

An uncorrected 2D myope can see clearly from 33cm to 1m in front of his eyes. First find the linear depth of field, and then find the dioptric depth of field.

As a 2D uncorrected myope, his focal point is at 1/2m = 50cm in front of his eyes

What is the equation to calculate contrast?

Contrast = (target luminance - background luminance)/(background luminance)

A lens system in air consists of a +4.00 diopter lens and +6.00 diopter lens separated by 10 cm. What is the equivalent power of this optical system?

De = D1 + D2 - (t/n) x D1D2

The amount of hyperopia the pt can neutralize with accommodation is called?

Facultative hyperopia

What is the refractive index formula?

Index is really just a ratio of the velocity or wavelength of light in air to the velocity or wavelength of light in a different material

The amount of hyperopia that can't be relaxed in routine refractive exam

Latent hyperopia

The amount of hyperopia that can be measured by relaxation of accommodation with plus lenses?

Manifest hyperopia

A lens with an index of refraction of 1.50 measures 5 mm thick at its apex, and 9 mm thick at its base. The lens also has a vertical dimension of 50 mm. Given these lens parameters, what is the amount of vertical prism that is present within the center of this lens.

P= 100g(n-1)/d

Formula for Lasik corneal thickness calculation

Pachymetry - (Flap Thickness+Ablation amount) = Residual Stromal Bed*

How can we put the circle of least confusion on the the retina on a spherocylindrical rx?

Prescribe the spherical equivalent

What is the ANSI standard for Power tolerance (sph and cyl)?

The tolerance for sphere power is higher for PALs as compared to single vision or bifocal lenses The tolerance for cylinder power is higher for PALs as compared to single vision or bifocal lenses

What is the formula for Total spectacle magnification?

Total Spec Mag = Power Mag x Shape Mag

vAn observer is looking at an object 2m away and has a DOF of +/- 0.50D (draw it out)

When the observer views an object at 2m, everything from 1m out to infinity will be clear This means that 2m is the hyperfocal point This is why Hyperfocal Point = 1/DOF -1/.50D = 2m

What is the spectacle Rx (12 mm vertex distance) for a myope who wears -7.50D contact lenses?

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low n bulging into high n is (concave or convex)

concave Don't look at the shape, consider which index is bulging into the other

high n bulging into low n is (concave or convex)

convex Don't look at the shape, consider which index is bulging into the other

Light is traveling in glass (n = 1.6) with a wavelength of 585 nm. What is the frequency of light in the glass?

freq of glass = 3.2 x 10^14 s-1

What is the formula for the relationship between the dioptric depth of field and diameter of acceptable blur circle?

h = diameter of lens

If need nD for calculation of chromatic aberration for CR-39 (495-580)

nD = 1.495

What is the formula for Far point?

see examples on slide 21 and 22

What is the formula for Near point?

see examples on slide 23 and 24

Abbe number of polycarbonate (580-300)

v = 30

What is the formula of hyperfocal point?

1/Dioptric DOF