OPTICAL PRESCRIPTION

Question 1

Optical Prescriptions

Answer 1

Optical prescriptions are very important. They tell us a lot about the refractive errors of a particular patient. And patients use the optical prescription given to them to get glasses or contacts to help them see.

Question 2

There are several components to an optical prescription. Based on the prescription, we should be able to answer all of the following questions

Answer 2

Is the patient myopic or hyperopic? How myopic or hyperopic are they? Do they have astigmatism? If so, how much and at what axis? Do they have prism in their glasses? Do they need help with reading?

Question 3

THE LAYOUT AND INFORMATION ON AN OPTICAL PRESCRIPTION IS BASICALLY ALWAYS THE SAME. WE WILL TALK ABOUT SPHERE, CYLINDER, AND AXIS TODAY. THE OTHER COMPONENTS WILL BE COVERED LATER ON IN THE SEMESTER and next semester.

Answer 3

Question 4

If a patient has ONLY myopia or hyperopia and their cornea has the same curvature in all meridians what does that mean?

How can we correct that?

Answer 4

(NO ASTIGMATISM), we can correct this with a spherical lens.

Question 5

Spherical lenses

Answer 5

have a spherical curved surface and, therefore, the same power in all meridians. This makes sense since we are using a spherical lens for a “spherical” cornea.

Question 6

Since the power is the same in every meridian of a spherical lens, all light rays will converge or diverge equally.

Answer 6

Because light rays in spherical lenses either converge or diverge equally, images produced by spherical lenses form a point focus (as opposed to a line focus, which we will discuss later) at the focal point of the lens.

Question 7

Minus lense is to corerct what

Answer 7

Myopia

Question 8

plus lense is to correct what?

Answer 8

Hyperopia

Question 9

Myopic eye has too much plus or minus power?

what type of lense?

Answer 9

Remember… a myopic eye has excessive plus power that needs to be decreased. We accomplish this with a minus spherical lens.

Question 10

Whats the prescription for mypia?

Answer 10

For myopia, you may see a prescription anywhere from -0.25 to -19.00 or possibly even greater. A “high myope” describes someone who has a prescription of -6.00 D or more.

FOR EXAMPLE:

OD: -6.00

OS: -5.50

THIS PRESCRIPTION SHOWS THAT THIS PATIENT IS MYOPIC IN EACH EYE. HOWEVER, THIS PRESCRIPTION IS NOT COMPLETE! IT DOES NOT TELL US WHETHER OR NOT THE PATIENT HAS ASTIGMATISM.

Question 11

If you have a patient who is ONLY myopic or hyperopic, then their prescription is said to be

Answer 11

“spherical”. This MUST be included in the Rx and NOT assumed. Sph is usually used as an abbreviation for sphere.

EXAMPLE:

OD: -6.00 SPH

OS: -5.50 SPH

THIS IS THE DEFINITIVE WAY TO state that SOMEONE DOES NOT HAVE ASTIGMATISM. IF SPH IS NOT INCLUDED IN THE RX, IT COULD BE POSSIBLE THAT THE ASTIGMATISM POWER WAS omitted accidentally.

Question 12

For hyperopia, you may see a prescription from

Answer 12

+0.25 to +15.00 or possibly higher.

FOR EXAMPLE:

OD: +2.50 SPH

OS: +3.25 SPH

Question 13

For Spherical lenses how many parameters?

Answer 13

So remember, spherical lenses only have one parameter which is power (D).

Spherical lenses can be plus or minus and will display characteristics of those lenses (image movement, magnification, central or peripheral thickness, convergence or divergence, etc).

Question 14

But what do we do when someone has astigmatism?

Answer 14

Question 15

What can we all to the lenses for regular astigmatism

Answer 15

We can add cylindrical lenses to a prescription to correct for any type of regular astigmatism. This is usually shortened to cylinder or cyl

Question 16

Similar to a spherical lens

Answer 16

Similar to a spherical lens, a cylindrical lens is measured in diopters. A higher dioptric power means a person has more astigmatism. Cylinder can be anywhere from 0.25 D to 6.00 D or more

Question 17

which one are more complex? Spherical or Cynlindrical

explain both?

Answer 17

Cylindrical lenses are slightly more complex than spherical lenses.

Unlike spherical lenses which refract light rays equally in all meridians, cylindrical lenses refract light only along one axis. This is because cylindrical lenses have 2 optical surfaces – a flat one and a curved one.

Question 18

That should make sense when we think about what astigmatism is (a cornea with a steeper curve or more power in one meridian and a flatter curve in another meridian).

Answer 18

reAD

Question 19

The plane surface of a cylindrical lens has what?

Answer 19

has no curvature and no power. It is called the cylinder axis and it is 90 degrees away from the curved surface.

Question 20

The curved surface has what?

what is it called?

the image forms a focal point? what does it form and which shape does it apply to?

Answer 20

has curvature and power;

it is called the power meridian.

Its image does not form a point focus (focal point) like a spherical lens,
but rather a line focus
(focal line) along the
cylinder axis.

Question 21

Therefore, if a cylinder lens is placed with its axis at 90, its full power is provided at axis 180. The cylinder is oriented so that its axis is along the steeper meridian of the cornea. It effectively increases the power of the flatter meridian so that it equals that of the steeper meridian. This neutralizes the effect of the astigmatism.

Answer 21

Therefore, if a cylinder lens is placed with its axis at 90, its full power is provided at axis 180. The cylinder is oriented so that its axis is along the steeper meridian of the cornea. It effectively increases the power of the flatter meridian so that it equals that of the steeper meridian. This neutralizes the effect of the astigmatism.

Question 22

AT WHAT AXIS WILL A CYLINDER LENS OF THE APPROPRIATE POWER BE ORIENTED TO PROVIDE CORRECTION ALONG AN AXIS OF 65 DEGREES?

Answer 22

CYLINDER POWER REQUIRED AT AXIS: 65

CYLINDER SHOULD BE ORIENTED 90 DEGREES AWAY:

65 + 90 = 155

Question 23

AT WHAT AXIS WILL A CYLINDER LENS BE ORIENTED TO PROVIDE CORRECTION ALONG AN AXIS OF 120?

Answer 23

CYLINDER POWER REQUIRED AT AXIS: 120

CYLINDER SHOULD BE ORIENTED 90 DEGREES AWAY:

120-90 = 30 DEGREES

Question 24

How many cylindrical lenses have?

Answer 24

Remember, cylindrical lenses have 2 parameters, power and axis, which are 90 degrees away from each other. There must always be an axis if there is cylinder power!

Question 25

Cylindrical lenses can be recorded either as a plus lens or a minus lens.

Answer 25

++++++++++++++++++++++

Question 26

They are referred to as plus cylinder or minus cylinder.

Answer 26

OD: +0.75 +1.50 X 075

OD: +1.25 +0.50 X 120

OD: +1.00 -1.00 X 090

OS: +0.25 -1.00 X 090

Question 27

Let’s review astigmatism one more time.

Answer 27

The cornea has one meridian with a flatter curve and one with a steeper curve. Either the steeper curve has too much power, or you could say the flatter curve has too little power. Thus, the light rays are not coming to a single focal point

Question 28

A minus cylinder can be used, oriented in the opposite direction as the steeper curve. This would reduce the power 90 degrees away from that (at the steeper curve). Or, a plus cylinder can be used. A plus cylinder is oriented in the same meridian as the steeper curve. This would increase the power of the flatter meridian. The end result would be the same.

Answer 28

A minus cylinder can be used, oriented in the opposite direction as the steeper curve. This would reduce the power 90 degrees away from that (at the steeper curve). Or, a plus cylinder can be used. A plus cylinder is oriented in the same meridian as the steeper curve. This would increase the power of the flatter meridian. The end result would be the same.

Question 29

Optometrists tend to write optical prescriptions in

Answer 29

in minus cylinder form.

Question 30

Ophthalmologists write their prescriptions in

Answer 30

plus cylinder form.

Question 31

Lenses are generally made with

Answer 31

a minus cylinder ground into the lens.

Question 32

Cylinder lenses are used to correct

Answer 32

astigmatic errors in which only one meridian needs to be corrected and the other is plano (pl). Plano is the same as “zero” spherical power. Cyl is used to correct simple myopic and simple hyperopic astigmatism

Question 33

If a patient has simple hyperopic astigmatism in both eyes their prescription may look like this…

Answer 33

OD: pl +1.00 x 045

OS: PL +0.75 X 120

The PL Indicates THAT THERE IS NO (ZERO) SPHERICAL POWER!

Question 34

PLANO

Answer 34

IS ZERO

Question 35

A MYOPIC PRESCRIPTION

Answer 35

WOULD BE A SINGLE POINT ON THE NEGATIVE SIDE OF THE NUMBER LINE (A MINUS PRESCRIPTION IS NEGATIVE).

Question 36

A HYPEROPIC PRESCRIPTION

Answer 36

IS A SINGLE POINT ON THE POSITIVE SIDE OF THE NUMBER LINE (A PLUS PRESCRIPTION IS POSITIVE).

Question 37

IF A PATIENT HAS ASTIGMATISM, THERE WILL BE

Answer 37

2 POINTS ON THE NUMBER LINE, ONE FOR THE SPHERICAL POWER AND ONE FOR THE CYLINDER POWER. THESE POINTS CAN FALL ANYWHERE ON THE NUMBER LINE. IF IT IS A SIMPLE ASTIGMATISM IN PLUS CYLINDER, ONE OF THE POINTS ON THE NUMBER LINE MUST BE ZERO AS THERE IS ZERO SPHERICAL POWER!

Question 38

How many powers the cornea has

Answer 38

2 different powers

THE CORNEA HAS 2 DIFFERENT POWERS. THE AMOUNT OF CYLINDER IS ACTUALLY THE DIFFFERENCE BETWEEN THESE 2 POWERS.

THE AMOUNT OF CYLINDER (IN DIOPTERS) TELLS US HOW FAR WE WOULD TRAVEL ON THE NUMBER LINE TO GET TO THE 2ND POWER READING. YOU CAN THEN DETERMINE WHAT KIND OF ASTIGMATISM THE PATIENT HAS.

Question 39

IN OUR EXAMPLE OF SIMPLE HYPEROPIC ASTIGMATISM, WE STARTED AT 0 D IN THE RIGHT EYE. WE WILL THEN TRAVEL IN THE PLUS DIRECTION (AS INDICATED BY THE + IN FRONT OF THE CYLINDER) ON THE NUMBER LINE BY 1.00 D. WE END UP ON +1.00. FOR THE LEFT EYE, WE STARTED AT 0 D. WE MOVE IN THE PLUS DIRECTION 0.75 D. WE END ON +0.75 D.

Answer 39

OD: pl +1.00 x 045

OS: PL +0.75 X 120

Question 40

Since our first number was “0”,

Answer 40

and we ended on the positive side of the number line, that tells us that this prescription is correcting simple hyperopic astigmatism.

Question 41

What happens when a patient is myopic or hyperopic WITH astigmatism?

Answer 41

spherocylindrical

In that case, a spherocylindrical lens is used. As the name implies, it is a combination of a spherical lens and cylindrical lens. Thus, spherocylindrical lenses have 2 meridians, one of maximum power and the other of minimum power.

Question 42

Spherocylindrical lenses

Answer 42

are used to correct compound myopic and compound hyperopic astigmatism as well as mixed astigmatism.

Question 43

IMAGINE A SPHEROCYLINDRICAL PRESCRIPTION TO BE 2 POINTS ON A NUMBER LINE

Answer 43

ONE POINT IS FOR THE SPHERICAL POWER, AND THE OTHER POINT IS FOR THE CYLINDRICAL POWER. NEITHER POINT CAN BE ZERO.

IF BOTH POINTS FALL ON THE NEGATIVE SIDE OF THE NUMBER LINE, THAT WOULD BE COMPOUND MYOPIC ASTIGMATISM.

IF BOTH POINTS FALL ON THE POSITIVE SIDE OF THE NUMBER LINE, THAT WOULD BE COMPOUND HYPEROPIC ASTIGMATISM.

IF ONE POINT IS ON THE NEGATIVE SIDE, AND ONE IS ONE THE POSITIVE SIDE, THAT WOULD BE MIXED ASTIGMATISM.

Question 44

If a patient has compound myopic astigmatism, their prescription may look like this…

Answer 44

OD: -2.50 +1.75 X 002

OS: -4.25 +0.25 X 178

Question 45

If a patient has compound hyperopic astigmatism, their prescription may look like this…

Answer 45

OD: +2.00 +1.00 X 095

OS: +1.75 +1.25 X 085

Question 46

If a patient has mixed astigmatism, their prescription may look like this…

Answer 46

OD: -2.00 +3.00 X 075

OS: -4.00 +5.00 X 070

Question 47

QUICK REFERENCE GUIDE FOR TYPE OF ASTIGMATISM

Answer 47

Question 48

Aside from the “normal” changes a patient may have in their prescription, there are several conditions that can cause a shift in an optical prescription.

Answer 48

SOME EXAMPLES INCLUDE…

• CATARACTS
• RETINAL PATHOLOGY
• DIABETES
• CORNEAL PROBLEMS
• PREGNANCY

Question 49

Cataracts can cause a myopic shift in a prescription. The hardening of the lens centrally can increase the dioptric power. Remember, higher power means a shorter focal length. The focal point is shifted closer to the lens.

Answer 49

Question 50

RETINAL PATHOLOGY

Answer 50

IN ADDITION TO DECREASED VISION, RETINAL PATHOLOGY CAN CAUSE A HYPEROPIC SHIFT IN THE PRESCRIPTION OF AN EYE. IF A PATIENT HAS MACULAR SWELLING OR FLUID, THE RETINA IS PUSHED FORWARD. THIS ELEVATION DECREASES THE AXIAL LENGTH OF THE EYE. AND A SHORTER EYE IS OF COURSE MORE HYPEROPIC

Question 51

DIABETES

Answer 51

PATIENTS WITH UNCONTROLLED DIABETES MAY EXPERIENCE A MYOPIC SHIFT IN THEIR PRESCRIPTIONIN ADDITION TO A NUMBER OF OTHER EYE PROBLEMS (SUCH AS DIABETIC

RETINOPATHY). THERE IS A COMPLEX

PROCESS INVOLVED, BUT HIGH BLOOD

SUGARS CAN LEAD TO SWELLING OF

THE FIBERS INSIDE THE LENS OF THE

EYE. THIS CAUSES AN INCREASE IN

THE POWER OF THE LENS AND

THUS A MYOPIC SHIFT.

Question 52

CORNEAL PROBLEMS

Answer 52

ANYTHING THAT DISRUPTS THE SURFACE OF THE CORNEA CAN AFFECT THE PRESCRIPTION OF THE EYE. THIS INCLUDES SCARRING FROM INJURY OR CORNEAL DISEASE, PTERYIGUMS, DRY EYES, ETC. SHIFTS CAN BE MYOPIC, HYPEROPIC, OR INDUCE ASTIGMATISM.

Question 53

PREGNANCY

Answer 53

PREGNANCY CAN ALSO AFFECT THE PRESCRIPTION OF THE EYES. THIS COULD BE THE RESULT OF ANY NUMBER OF THINGS SUCH AS HORMONE CHANGES, FLUID RETENTION, CHANGES IN CIRCULATION OR METABOLISM. IN THE CASE OF FLUID RENTENTION, INCREASED FLUID IN THE CORNEA AND/OR LENS CAN CHANGE THE THICKNESS AND CURVATURE. THIS TYPICALLY RESULTS IN A MYOPIC SHIFT BUT HYPEROPIA AND ASTIGMATISM CAN ALSO OCCUR.

Question 54

these chages can be temporary

Answer 54

These are just a few examples of situations where a change in an optical prescription can occur. It is important to consider the possible cause of a refractive change in a patient because some of these changes could be temporary!

Question 55

Can Astigmatism be in both eyes

Answer 55

Remember, astigmatism can occur by itself or with myopia or hyperopia. It can be corrected with a cylindrical lens or a spherocylindrical lens. And a patient does NOT always have astigmatism in both eyes or the same amount (D) or axis in both eyes!