2: Prescription writing .

R: -1.00 / -0.50 × 180

L: -1.25/ -0.75 × 175

R:

-1.00 means spherical power of the lens. Small amount of hsort sightedness as only -1.00

-0.50 means cylinder power. Used to correct astigmatism

180 is axis, the orientation of the cylinder

ALWAYS WRITE TO 2 DECIMAL PLACES

R: plano / -1.00 × 90 

L: +0.25 / -1.50 × 175 

R:

Plano means no power, so no spherical power , just -1.00 astigmatism on an axis of 90 

L: 

+0.25 spherical power and -1.5 cylider power on an axis of 85 

R; +1.25 DS

L; +1.00 / + 0.25 × 90

R:

+1.25 DS means patient has just a spherical presciption. No cylinder power

L:

cylinder is positive

R: +9.00 / -1.25 × 180 BVD= 12mm

L: + 8.75 / +0.25 × 90

R:

BVD= back vertex distance. This is the distance between the rear surface of the spectacle lens at the visual point and the cornea.

Tells you how far away from the persons eyes the spec lenses need to go.

if a prescription is more than 4 dioptres a BVD is needed

R:

the 2 with the triangle means prism: prismatic power, means image needs to be moved with a prism. 2 prism dioptres needed. Up tells you where the base of the prsim is so its saying up so at the top

L:

spherical only

1. wrong as its not to 2 decimal places 

2. DC and DS is not needed 

3. no plus or minus signs written

4. no BVD for the +9.00 prescription 

5. no DS written for the left eye  

sphero-cylindrical transpostion

first one i a sphero-cylindrical prescription in the negative cylinder fomr

second one is a sphero-cylindrical power in the positive fomrm

the prescriptions are the same power just written differently

rules for transposing between positive and negative cylinder forms 

1. Add sphere and cylinder powers tpgether to make new sphere power 

2. change sign of cylinder. Leave cylinder power the same 

3. turn the cylibder axis through 90 degrees 

so, 

for the prescription -5.00 / -1.00 × 175

1. -5.00 + -1.00 = -6.00

2. -1.00 = +1.00 

3. 175 - 90 = 85 

usually minus 90 if over 100 and add if less than 100 

so new prescipt is -6.00 / +1.00 × 85

eg: +3.00 / +1.00 × 5

+4.00 / -1.00 × 95

+5.00 / -0.50 × 180

+4.50 / +0.50 × 90

+2.00 / -4.50 × 45 

-2.50 / +4.50 × 135

crossed cylinder notation is of the form:

instead of a sphere and a cylinder its 3 cylinders crossed at 90 degrees

+1.00 × 90 / +1.50 × 180

conversion to spherocylindrical form in negative form 

+1.50 / -0.50 × 90 

conversion to sphero cylinder in positive 

+1.00 / + 0.50 × 90  :  

another e.g.       -5.00 × 85 / -4.25 × 175 

negative cylinder form when converting to sphero cylinder 

-4.25 / -0.75 × 85 

positive cylinder form 

-5.00 / + 0.75 × 175 

prescription analysis

eg:

R: -5.00 / -2.00 × 90

L: -5.50 / 2.25 × 85

its not a complete prescripton as theres no BVD

myopia present and astigmatism

myopic as lens is negative so the eye focuses light in front of the retina so distant objects appear blurry but near objects are clearer

astig as the cylinder is not 0, so astig is present .

rule for astigmatism

if the cylinders are minus, and the axis is vertical (90 degree), then thats against the rule of astigmatism

if axis horizontal then with the rule

140 degrees means oblique

sphere power and severity 

anthing -0.75 - -2.00 is mild myopia 

-4.25 to -6.00 is very high myopia 

compound myopic astigmatism

where both meridians are myopic as focal points are in front of the retina

simple myopic astigmatism

one focal point is in front of the retina and one is on it

only one eye is myopic

R: -5.00 / -2.00 × 180 

L: -5.50 / -2.25 × 180 

axis flipped to 180 

compound myopic astigmtism but with the rule of astigmatism 

R: +6.00 / -2.00 × 180

L: +4.00 / -2.25 × 180

not complete prescription as no BVD

hypermyopia

compound hyperopia astig with the rule as cyl is minus and horizontal

R: +13.00 / -3.50 × 70 

L: +12.50 / -3.25 × 50 

myopia 

oblique is an axis between 50-70 or 120-150 means that the irregular curvature of your eye isnt vertical or horizontal but at a diaganol angle 

R: +2.00 / -3.50 × 180 

L: +2.50 / -3.25 × 165 

plus in one meridium and minus in the other showing mixed astigmatism 

no BVD as powers arent bigger than +2.50  

axis horzontal

R: -4.50 / -0.50 × 180 

L: -1.50 / -0.75 × 175 

no BVD 

both myopic but right eye is more short sighted than the left called anisometropia 

R: +1.50 / -0.50 × 180 

L: -1.50 / -0.75 × 175 

onse sphere is plus other is minus. Called anti mytropia 

additions

positive spherical power added to the distance prescription for near or intermediate vision as a remedy for presbyopia

presbyopia means eye loses abiloty to focus on close objects as lens stiffens, so distance prescription is for seeing far away clearly. To help see up close optometrists add a small plus number on top of the distance prescription to let eyes focus on nearer objects

e.g of addition

distance prescription : -2.00 D for myopia

add for near : +1.50 D

Near presciption is -0.50 D

range of powers for additions

+0.75 DS to +2.75 DS. sometimes higher

higher additions are sometimes prescribed for special purposes eg very close working distances and to patients with low vision

e.g

R: +1.50 / -0.50 x 180 Add +2.25 DS

L: +2.25 / -0.75 × 175 Add +2.25

power of the near prescription

R: +3.75 / -0.50 × 180

L: +4.50 / -0.75 × 175

additions: expected value

the age at which the first near addition is prescribed can vary. Depends on:

• rate of decline in amplitude of accomodation

• the near tasks that the patient does eg: occupational and recreational

• critical near task will increasethe need for an addition

• physical size and working distance eg patient with shorter arms will probably need an addition sooner than the patient with longer arms

• depth of focus eg related to pupil size, smaller pupil lessens need for addition

• health : poor health can affect accomodation

• medication: some meds particularily with an anti muscarinic effect can reduce the amplitude of accom

amplitude of accom 

Duane Hoffstetter formulae 

max amplitude = 25.0- 0.4 x age 

average amplitude = 18.5 -0.3 x age 

min amplitude = 15.0 -0,25 x age 

expected values of addition   

addition= working distance (in D) -0.5*amplitude of accom 

eg if the working distance is 40 cm and the amplitude of accom is 3.5 D;

Addition= ( 1/0.) - ( 0.5 × 3.5 )

0.75 DS 

additions- range of clear vision

range of clear vision in the near add is defined as:

near point in the add- far point in the add

eg:

R: +1.00 DS add +1.75 DS

L: +1.00 DS add +1.75 DS

Amplitude of accom 2.50 D

far point in the add ( with accom relaxed) = 1/1.75 = 0.57 m = 57 cm

nearpoint in the add ( max accom) = 1 / (1.75 + 2.50)= 0.2 m = 24 cm

so total range of clear vision will be 54cm to 24 cm

mre on range of clear vision

range gets smaller as the add goes up

total range of clear vision through distance prescription 

far point in the distance prescription = infinity 

near point in the distance prescription = 1/ amp of accom 

so for patient with 2.50 D amp of accom, and working distance of 0.4 m:

infinity ti 1 / 2.50 = 0.4 m = 40 cm 

as amplitude of accom declines..

the addition power needs to increase. This will work against the patient to reduce the range of clear vision. eg:

R: +1.00 DS add +2.75 DS 

L: +1.00 DS add +2.75 DS 

amplitiude of accom 1.00 D 

far point in the add = 1/ 2.75 =  36 cm 

near point = 1/2.75 + 1) = 26 cm 

total range in the add will be 36 to 26 cm 

sustainable range of clear vision ( from eg above )

youd use 0.5 x amp of accom, would be:

far point = 1/2.75 = 36 cm

near poinit with 0.5 accom exerted= 1/ (2.75 +0.50) = 31cm

so sustainable range of clear vision in the add will be 36 cm to 31cm

intermediate additions 

as accom declines and the required near addition increases, an intermediate addition can be very usefulfor arms length tasks and computer use etc 

intermed add usually between 50 5 and 70% of the near addition