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SPHERE, CYLINDER, AXIS, and ADD Power, Exams of Ophthalmology

Kentucky Community and Technical College SystemOphthalmology

CYLINDER = correction only PART of the eye needs; patient has astigmatism ... power is only in one meridian of lens ... OS: +2.75 SPH.

Typology: Exams

2021/2022

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2/5/2018
1
UNDERSTANDING A PRESCRIPTION
Speaker: Michael Patrick Coleman, COT & ABOC
SPHERE, CYLINDER, AXIS, and ADD
Power: Why these four variables?
•Example Prescriptions:
+2.50 SPH
Simple SPHERICAL Rx
PL +1.75 X 090
Simple CYLINDRICAL Rx
-2.00 +1.25 X 180
SPHEROCYLINDRICAL Rx
+1.50 +1.00 X 045 ADD +2.00
MULTIFOCAL Rx
SPHERE, CYLINDER, AXIS, and ADD Power: Why these
four variables? (cont.)
•SPHERE = correction the WHOLE eye needs;
power is ‘everywhere’ in the lens
•CYLINDER = correction only PART of the eye
needs; patient has astigmatism (distortion);
power is only in one meridian of lens
•AXIS = location (meridian) in lens the cylinder
power will be oriented to ‘fix’ astigmatism
•ADD = ‘plus’ sphere power “added” to the distant
Rx to MAGNIFY objects & change the FOCAL
LENGTH of the lens (for near work)
SPHERICAL LENSES
Have the same power EVERYWHERE in lens…
SPHERICAL LENSES (cont.)
Have the same power EVERYWHERE in lens…
SPHERICAL LENSES (cont.)
Form a POINT focus…
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UNDERSTANDING A PRESCRIPTION

Speaker: Michael Patrick Coleman, COT & ABOC

SPHERE, CYLINDER, AXIS, and ADD

Power: Why these four variables?

  • Example Prescriptions:  +2.50 SPH Simple SPHERICAL Rx  PL +1.75 X 090 Simple CYLINDRICAL Rx  -2.00 +1.25 X 180 SPHEROCYLINDRICAL Rx  +1.50 +1.00 X 045 ADD +2. MULTIFOCAL Rx SPHERE, CYLINDER, AXIS, and ADD Power: Why these four variables? (cont.)
  • SPHERE = correction the WHOLE eye needs; power is ‘everywhere’ in the lens
  • CYLINDER = correction only PART of the eye needs; patient has astigmatism (distortion); power is only in one meridian of lens
  • AXIS = location (meridian) in lens the cylinder power will be oriented to ‘fix’ astigmatism
  • ADD = ‘plus’ sphere power “added” to the distant Rx to MAGNIFY objects & change the FOCAL LENGTH of the lens (for near work)

SPHERICAL LENSES

Have the same power EVERYWHERE in lens… SPHERICAL LENSES (cont.) Have the same power EVERYWHERE in lens… SPHERICAL LENSES (cont.) Form a POINT focus…

SPHERICAL LENSES (cont.)

  • Used to correct SIMPLE MYOPIA (SM) Example Rx: OD: -1.00 SPH OS: -2.50 SPH SPHERICAL LENSES (cont.)
  • Used to correct SIMPLE HYPEROPIA (SH) Example Rx: OD: +1.25 SPH OS: +2.75 SPH SPHERICAL LENSES (cont.) People that only need a SPHERICAL lens are often said to have a cornea that is shaped like a BASKETBALL (has the same curve everywhere!) SPHERICAL LENSES (cont.)
  • Store bought reading glasses (‘magnifiers’) are just PLUS (+) SPHERE lenses!

CYLINDRICAL LENSES

  • Have a meridian of MAXIMUM power and - ninety (090) degrees away - a meridian of ZERO power… CYLINDER LENSES (cont.)

SPHEROCYLINDRICAL LENSES (cont.)

  • When you combine a SPHERICAL lens with a CYLINDRICAL lens, you get a lens that forms TWO LINES of FOCUS, ninety (90) degrees away from each other, and separated by some distance (dependent on the lens power.) SPHEROCYLINDRICAL LENSES (cont.)
  • Spherocylindrical lenses are used for people who are not only NEARSIGHTED or FARSIGHTED, but who also have a ‘distortion’ (ASTIGMATISM) in their vision, requiring a slightly different correction than the rest of the eye needs.
  • These people would be diagnosed with one of the following refractive errors:
  • Compound Myopic Astigmatism (CMA)
  • Compound Hyperopic Astigmatism (CHA)
  • Mixed Astigmatism (MA); this means part of the eye is MYOPIC & part of the eye is HYPEROPIC! SPHEROCYLINDRICAL LENSES (cont.) An example of a SPHEROCYLINDRICAL Rx would be something like this: OS: +1.25 +2.50 X 180 (this would fix CHA)

-3.00 +2.00 X 175

(this would fix CMA) SPHEROCYLINDRICAL LENSES (cont.) COMPOUND MYOPIC ASTIGMATISM (CMA)

COMPOUND HYPEROPIC

ASTIGMATISM (CHA)

SPHEROCYLINDRICAL LENSES (cont.)

  • What about “Mixed Astigmatism” (MA)? The Rx would look something like this:

-2.00 +3.00 X 155

SPHEROCYLINDRICAL LENSES (cont.)

MIXED ASTIGMATISM (MA)

SPHEROCYLINDRICAL LENSES (cont.)

  • The area between the two focal lines produced by a SPHEROCYLINDRICAL lens is called STURM’S CONOID (or the Conoid of Sturm)
  • Within that zone is a place where the light rays are relatively focused (but not quite); it is called the CIRCLE OF LEAST CONFUSION SPHEROCYLINDRICAL LENSES (cont.) If you’ve ever calculated a “SPHERICAL EQUIVALENT”, you figured out what power SPHERICAL lens will focus light rays @ the CIRCLE of LEAST CONFUSION in the eye!

ADD POWER

  • It is all about the SPHERE!
    • The “ADD” of an Rx gets ‘added’ to the DISTANT SPHERE POWER; cylinder & axis remain same!
    • The “ADD” is always a PLUS (+) number!
    • Plus MAGNIFIES & Plus SHORTENS Focal Length

EXAMPLE: PL +0.50 X 090 ADD +2.

  • The DISTANT Rx will be PL +0.50 X 090
    • This will be good for Pt from 10 feet to infinity
  • The NEAR Rx will be +2.50 +0.50 X 090
    • This will be good for Pt @16” ADD POWER (cont.)
  • Bifocal
  • Top of lens for DISTANCE (or Intermediate range - about 30” - if it’s an ‘Office Lens’)
  • Bottom of lens for NEAR
  • Trifocal
  • Top of lens for DISTANCE
  • Middle lens is for INTERMEDIATE
  • Bottom of lens for NEAR
  • Progressive Add Lens (PAL)
  • Top of lens for DISTANCE
  • As you go LOWER in lens, it gradually gains more “plus” SPHERE power; the NEAR Rx is at the very bottom ADD POWER (cont.) EXECUTIVE BIFOCAL 7 X 25 TRIFOCAL PROGRESSIVE ADD LENS (PAL)

MYOPES NEED MINUS

  • Q: Where is the focal point? A: Before (in front of) the MACULA
  • Q: How do we change the focal point? A: Minus lenses!

PRESBYOPES NEED ADD POWER (cont.) PRESBYOPES NEED ADD POWER (cont.) PRESBYOPES NEED ADD POWER (cont.) PRESBYOPES NEED ADD POWER (cont.)

PRESBYOPES NEED ADD POWER (cont.) WHAT IS UP WITH PRISM?!

  • When a Pt sees double (usually a “tropia”) or ‘blurred’ vision not due to a refractive error (usually a large “phoria”) doc will prescribe PRISM
  • The prism will “shift” where the image appears to the patient

WHAT IS UP WITH PRISM?! (cont.) Light going through a PRISM is ALWAYS DEVIATED TOWARD THE BASE! WHAT IS UP WITH PRISM?! (cont.) The IMAGE being viewed through the prism is always deviated toward the APEX! WHAT IS UP WITH PRISM?! (cont.)

  • Prism has a BASE & an APEX
  • When it is prescribed, the doctor will identify which way the BASE should be oriented: - UP (BU), DOWN (BD), IN (BI), or OUT (BO)
  • Ironically, it is the APEX that “points” in the direction of the “problem”. For EXAMPLE: - Patient has an EXOTROPIA (eye turning out) - Doctor wants the APEX pointing toward problem (i.e., w/the APEX pointing out) - To accomplish that, the patient will be prescribed BASE IN prism WHAT IS UP WITH PRISM?! (cont.) This Patient has an ESOTROPIA (in this case, the RIGHT EYE deviates INWARD) Doctor will point the APEX of PRISM toward the problem – so APEX goes IN, just like the eye does! That means the BASE of the PRISM will be OUT; Doctor will Rx BASE OUT (BO) PRISM WHAT IS UP WITH PRISM?! (cont.) Every millimeter of deviation = approximately 15 diopters of prism! Pt will need about 30 prism diopters (Δ) of BASE OUT (BO) PRISM to ‘fix’ deviation (Specs will be made w/15Δ BO in OD & 15Δ BO in OS) WHAT IS UP WITH PRISM?! (cont.)
  • When prism is put in a prescription, it is usually “split” between the two eyes
  • For example, the doctor wants to give Pt 8 prism diopters (Δ) of BASE OUT (BO); Rx written like this:

OD PL SPH 4 Δ BO

OS PL SPH 4 Δ BO

  • If doctor wanted to give Pt 6 prism diopters (Δ) of BU prism in RIGHT EYE (OD); Rx written like this:

OD PL SPH 3 Δ BU

OS PL SPH 3 Δ BD