ABO Equations

A -4.00 D spherical lens is decentered 6mm nasally. what is the resulting prism?

2.4 base out

2.4 base in

0.67 base in

0.67 base out

2.4 base out

Prentices rule: Power x decentration. 4.00*0.6=2.4. for a minus lens decentering nasally induces out prism.

A lens has a focal length of +50cm. What is its power in diopters?

+50.00D

+5.00D

+0.50D

+2.00D

+2.00

Power (D)=1/ focal length in meters. 50cm=0.50m. Power= 1/0.5= +2.00D

A patients rx is -4.00 -1.00 x 90 what is the power in the 45th meridian?

-4.50D

-4.75D

-4.00D

-5.00D

-4.50

The reason why is (-4.00 and -5.00) the middle is -4.50

A patient looks 10mm below the optical centers of a pair of glasses: OD -5.00, OS -2.00. What is the induced vertical imbalance

3.0 base down

3.0 base up

0

7.0 Base down

3.0 based down

The reason why is -5 -2 equals -7 so 3 is remaining Or another way is 5-2 is 3 vertical means down

If a patients rx is -5.00 SPH what is the maximum acceptable power deviation according to ANSI Z80.1?

+/- 0.50

+/- 0.16

+/- 0.13

+/- 0.25

+/- 0.13

For sphere powers between +/-0 and +/- 6.50 the tolerance value is 0.13

convert the following plus cylinder rx to minus cylinder from +2.50+1.25*90:

+3.75-1.25×90

+3.75-1.25×180

+2.50-1.25×90

+1.25-1.25×180

+3.75-1.25x180

to transpose from plus to minus, add the sphere and cylinder EX: +2.50+1.25=+3.75 THEN changing the cylinder +1.25 to -1.25 and changing the axis adding 90 degrees 90+90=180 degrees. the result is +3.75-1.25x180

The add power for a patient with +1.00D distance and +3.50D near RX is

+4.50D

+2.50D

+3.50D

+1.00D

+2.50D

Add power= near power-distance power=+3.50-(+1.00) = 2.50

If a patient looks 10mm below the optical center of a +2.00 D lens, how much prism is included?

2 Prism diopters

4 prism diopters

1 prism diopters

3 prism diopters

2 prism diopters.

using prentices rule P=c*F= 1.0cm*2.00 diopter= 2.00 prism diopters

A Rx of -2.00-0.50*180 in both eyes with the optical centers decentered 3mm inward in each eye produces what prism?

no prism

0.75 prism diopters base out each eye

1.5 prism diopters base in each eye

0.75 prism diopters base in each eye

0.75 prism diopters base in each eye

when a patient has 4 prism diopters base out prescribed for the right eye and 2 diopters base out for the left eye when the total is prism effect?

2 prism diopter base out

6 prism diopters base out

no net prism

4 prism diopters base in

2 prism diopter base out

4-2=2 prism diopters base out

A patient has a rx of -8.00D measured at a 12mm vertex distance. if fitted with contact lenses (0mm vertex distance) what is the approximate effective power?

-8.50D

-7.50D

-7.25D

-8.00D

-7.25D

Using the vertex formula: F=F/(1-dF) so F=-8/ (1-0.012*-8) = -8/1.096=7.30D so approximately 7.25D to insert in the calculator of the phone is 1-(0.012*(-8))

a patient with -5.00D lenses complains of induced prism when looking away from the optical center. how much prism is induced 4mm from the optical center.

1.0D

1.25D

2.0D

2.50D

2.0D

PRENTICES RULE: P=c*F=0.4cm-5.00D=2.0

What is the prismatic effect at the reading level of a +2.00 D add bifocal if the optical center of the distance portion is 8 mm above the segment top?

0.8 prism diopter base down

1.6 prism diopters base down

1.6 prism diopter base up

no prism effect

1.6 prism diopters base down

Using Prentice's Rule: P = c × F = 0.8 cm × 2.00 D = 1.6 prism diopters. Since the optical center is above the reading level, the prism at the segment is base-down

what prism is induced when a -4.00D lens is decentered 2mm temporally?

1.6 prism diopters base temporal

0.8 prism diopters base nasal

0.8 prism diopters base temporal

no prism

0.8 prism diopters base nasal. P=0.2cm*-4.00= - 0.8prism diopters for minus lenses temporal decentration produces base nasal prism

if a patient wears -6.00D glasses at a 12mm vertex distance and switches to contact lenses what compensation is needed?

-6.50D

-5.75D

-5.50D

No changes needed

-5.50

using the vertex formula: F=F/ (1-dF) where F=-6.00 AND D\d=0.012m, so F=-6/(1-0.012*-6)=-6/1.072= -5.60D

what is the power in the 90degree meridian of a -3.00-1.50*180 rx?

-3.75D

-4.50D

-3.00D

-1.50D

-4.50D

-3.00+(-1.50)=4.50D

A -5.00 lens must be decentered by how many millimeters to induce 2 diopters of base in prism?

2mm

3mm

4mm

5mm

4mm

because every 1 diopter is induced by every millimeter

so 2diopter + 2 millimeters = 4mm

What is the total power of the rx +2.00 -2.00x 90?

plano

-2.00

+2.00

+4.00

Plano

that's because sphere + cylinder= total power

A Rx of +4.00-2.00x180 has its power of +4.00 in which meridian?

45 degrees

90 degrees vertical

180 degrees horizontal

135 degrees

90 degrees vertical

For a RX with 2 prism diopters base in OD and 2 prism diopters base out OS, the total prism effect is?

2 prism diopters convergence

0 prism (cancels out)

4 prism diopters convergence

4 prism diopters divergence

4 diopters convergence

using prentices rule what is the induced prism when a +4.00D lens is decentered 5MM?

2.50 Prism D

1.5 Prism D

2.0 Prism D

1.0 Prism D

2.0 Prism D

P= 0.50*4.00=2.00 Prism D

a patient requires 3 prism diopters base out in the right eye. if using a +6.00 D lens, How far and in which direction should the optical center be moved?

5mm out(temporal)

5mm in(nasal)

0.5 mm in(nasal)

0.5mm out (temporal)

5mm in (nasal)

using prentices rule: we need to find out how may MM, so 3/6=0.5CM = 5mm

which is the effective power of a +10.00D lens moved from 12mm to 15mm vertex distance?

+10.00D

+11.00D

+9.50D

+10.50D

+10.50D

The lens is move 3mm away from the eye (12-15=3) 3mm=0.003 so using F=F/(1-dF) is F=1/(1-0.003*10)= 10/0.97= +10.31

what is the spherical equivalent of a rx -3.00-1.50*180

-4.25D

-4.00D

-3.75D

-3.50D

-3.75D

The spherical equivalent is calculated by taking half of the cylinder power and adding it to the sphere. -3.00 (-1.50/2) = -3.00-0.75= -3.75

the near point of accommodation for a patient with +2.50D add is

20cm

25cm

50cm

40cm

40cm

the calculation of this is near point=1/F= 1/2.50=0.40

if transposing from minus cylinder to plus cylinder form, if the original axis is 45 degrees what is the new Axis?

180 degrees

45 degrees

135 degrees

90 degrees

135 degrees

45degrees +90

what prism induced when a -4.00 lens is decentered 2mm temporally?

no prims

1.6 prism diopter base temporal

0.8 prism diopters base temporal

0.8 prism diopters base nasal

0.8 prism diopters base nasal

using prentices rule P=0.2CM X-4.00= 0.8 Prism diopters. For minus lenses temporal decentration produces base nasal prism.

what is the formula for calculating decentration needed to produce a specific amount of prism

c= PXF

c= P+F

c= F/P

c= P/F

c=P/F

what is the total prism effect when a patient looks 1cm below the optical center below the optical center of a +3.00D add in the right eye and +2.00 D add in the left eye?

0.5 prism diopters vertical imbalance

3 prism diopters vertical imbalance

1prism diopter vertical imbalance

no prism effect

1 prism diopter vertical imbalance

using prentices rule for each eye P=1cm x 3 prism diopters BD. Left eye P- 1cm x 2.00 D =2prism diopters. the differential prism is 3-2=1 prism diopter vertical imbalance that the patient must overcome.

What is the prismatic effect at the reading point for an add of +2.00D if the reading segment is decentered 2mm in?

0.2 base out

0.2 base in

0.4 base out

0.4 base in

0.4 base in

equation: 2x 0.2mm= 0.4 base in

a patient with presbyopia and a +2.50 add needs to read at 40cm. what is the approximate accommodative demand for this reading distance?

+2.50D

+4.00D

+1.50D

+0.50D

+2.50D

Formula: 1/distnace

example of equation: 1/0.40m= +2.50D

a patient's spectacle rx is -10.00 at a vertex distance of 12mm. what is the approximate contact lens power needed (compensated for vertex distance)?

-8.93D

-9.50D

-11.24D

-10.00D

-8.93D

Formula is Fs/ (1-d x Fs)

Fs is spectacle power

d is the distance in meters

example of the equation: -10.00/(1-0.012x(-10.00))- -10.00/ (1+0.12)= -10.00/1.12 = -8.93D

A patient needs bifocal lenses. the distance rx is -2.00DS and the add power is +2.50. what is the net power in the bifocal segment for near vision?

+0.50D

+2.50D

-4.50D

-2.00D

+0.50D

Ex of equation-2.00 + (+2.50) = +0.50D

When neutralizing a lens on a manual lensometer you first focus the thin single mires at +2.00D with the axis wheel at 90 degrees. you then turn the power drum further into the plus to focus the thick triple mires which become clear at +3.50D. what is the correct RX in plus cyl form?

+3.50+1.50x180

+2.00-1.50x90

+3.50-1.50x180

+2.00-1.50x90

+2.00+1.50x90

READ CAREFULLY: they want the CYL in PLUS form and the axis has to be 90 degrees it says in the format

Transpose the following prescription into plus cylinder form: +1.50 -2.00 x 090

A. +1.50+2.00X180

B. -0.50+2.00X180

C. -0.50-2.00X180

D. +3.50-2.00X180

B. -0.50+2.00X180

what is the prismatic effect at a point 4mm below the optical centers of a -3.00D lens?

1.2 base up

1.2 base down

0.75 base up

0.75 base down

1.25 base up

0.4*3.00 = 1.2 base up since they are looking down

what is the power cross for the RX +2.00-1.50x90

+0.50D at 90 and +2.00D at 180

+2.00D at 90 and +0.50D at 180

-1.50D at 90 and +2.00D at 180

+2.00D at 90 and 1.50D at 180

+0.50 at 90 and +2.00D at 180

transposing the RX +3.50-2.00x45 to plus cylinder form gives

+1.50+2.00x135

+1.50+2.00x45

+3.50+2.00x135

+5.50-2.00x135

+1.50+2.00x135

45(axis)+90degrees = 135

cyl has to be changed to +2.00

subtract +3.50-2.00 = 1.50

what is the 400mm focal length lens dioptric strength?

-2.50

+2.50

+0.25

+4.00

+2.50

1/0.4=2.50

Transpose the following prescription into MINUS cylinder form: -3.00+1.25X170

A. -1.75-125X80

B. -4.25+1.25X80

C. -1.75+1.25X80

D. -3.00-1.25X80

A. -1.75-1.25X80

What is the spherical equivalent of the prescription +2.25 -1.50 x 120?

A. +0.75D

B. +3.00D

C. +1.50D

D. +2.25D

C. +1.50

+2.25+ (-1.50/2) = +2.25+(-0.75) = +1.50D

Transpose the prescription Plano +2.50 x 030 into MINUS cylinder form.

A. -2.50+2.50X120

B. PLANO-2.50X120

C. +2.50+2.50X120

D. +2.50-2.50X120

D. +2.50-2.50X120

Which of the following prescriptions is optically identical to -1.00 -1.00 x 045?

A. -2.00+1.00X135

B. PLANO-1.00X135

C. -2.00-1.00X135

D. -1.00+1.00X135

A. -2.00+1.00X135

Transpose the prescription +4.75 +0.75 x 110 into minus cylinder form.

+4.00-0.75X20

+5.50-0.75X20

+5.50+0.75X20

+4.75-0.75X20

+5.50-0.75X20

transpose the following RX into plus cylinder form: +1.50-2.00x90?

A. +1.50+2.00x180

B. -0.50+2.00x180

C. -0.50-2.00x180

D. +3.50-2.00x180

B. -0.50+2.00x180

A patient with a prescription of -4.00 DS looks 5 mm above the optical center.
How much prism is induced and in what direction?

2.0 base up

2.0 base down

0.8 base up

0.8 base down

2.0 base down

0.5cm x 4.00d = 2.0

patient is looking up so he needs to look down for it to be centered

A lens with a power of +6.00 D is decentered 3 mm nasally.
What is the resulting prism?

A. 1.8Δ Base Out

B. 2.0Δ Base In

C. 1.8Δ Base In

D. 2.0Δ Base Out

1.8 base in

0.3MM× 6D=1.8

+= BASE IN

A patient's PD is 64 mm, but their glasses were made with the optical centers at 60 mm. If the Rx is -5.00 DS in both eyes, what is the total induced prism?

A2.0Δ Base In

B1.0Δ Base Out

C1.0Δ Base In

D2.0Δ Base Out

D. 2.0 Base out

64-60 = 4mm so -5.00 × 0.4= 2.0

base out since its a minus lens

How much must a -10.00 D lens be decentered to produce 3.0Δ of prism?

Select your answer

A. 1.5 mm

B. 3 mm

C. 3.3 mm

D. 30 mm

B. 3mm

-10.00 × 0.3mm = 3 prism

A patient with Rx OD: +2.00 DS, OS: +4.00 DS looks 10 mm down to read. What is the vertical imbalance?

A1.0Δ

B2.0Δ

C4.0Δ

D6.0Δ

B. 2.0

2X0.10 = 2 ; 4X0.10= 4; SO 2-4 = 2

A patient wearing +3.50 D reading glasses holds their reading material 4 cm to the right of center. How much prism is induced horizontally?

A.1.4Δ Base Out

B.14.0Δ Base Out

C.0.875Δ Base Out

D.0Δ

D.0Δ the glasses are already in the center