unit 2-3 Flashcards
Myopia
Through the crystalline lens, object will focus before the retina (nearsighted) so by the time the object gets to the retina it is blurry
-Minus lens, concave lens (apex to apex)
-Nearsighted so distance objects are blurry
Hyperopia
Through the crystalline lens, object lands behind the retina (farsightedness)
-Plus lens, convex lens (base to base)
Types of astigmatism
Corneal
Lenticular; lens is irregular shape
Picture courtesy of MidShoreeye.com
Astigmatism inside a lens
With the rule
-Steeper axis at 90
-44 x 90 and 43 x 180
-More common in younger patients and myopics eyes
Lensometer
thin lines?
sphere
lensometer
thick lines
cylinder
measuring for verticle prism
- Strongest Power at 90
- Center on OC and PD
- Measure Rx and any Prism
measuring for horizontal prism
- Centre for PD and OC – without moving the table
- Neutralize the Rx
- Determine Prism
Myopic lenses perscriptions
- -0.25 -> -20.00
and beyond!
hyperopia lenses rx
- +0.25 -> +14.00
and beyond
astigmatic lenses rx
- -0.25 -> -6.00
types of progressives
- General Progressives
- Reading focused Progressives
- Computer focused Progressives
- Room focused Progressives
- Task Specific Progressives
lens clock
used to measure the base curve of the lens
-Black numbers are for convex
-Red numbers are concave
lens aligning pliers
Help you align any type of lens axis
pupilometer
Measure the pupil distance (PD) in mm
-Distance – Infinity
-Near – 40cm
-When fitting progressive you ALWAYS want monocular measurement
-Binocular is the distance from center of pupil to the other center of pupil
-Monocular is from the nose to the center of the pupil
penlight and ruler
-When measuring distant put penlight on top of the head
-When measuring near put penlight underneath chin
- Distometer & Power Wheel
Measure the vertex distance from the back surface of the spectacle lens to the cornea through a closed eyelid
lensometer
used to verify the prescription of eyeglasses
what types of lenses can we measure with a manual lensometer
Single spherical lenses
Bifocal
Trifocal
Progressive
Contact lens
What steps do we take to measure a lens?
-Firstly, focus the eyepiece to yourself (have the black lines be clear)
- Clear black lines
- Spherical- when black and green lines are all clear
- Thin lines- (sphere)
- Thick lines- (cyl)
Prentices rule
P = cF
c= distance (cm)
F= Power (D)
converting from mm to cm
divide by 10
Proper positioning of the temple bend on the ear
- When this bend is proper it starts just behind the top of the ear.
- This allows the bent down portion to be parallel with the root of the ear.
Lensometer proccess
- Focus the Black Circle lines
- Place the glasses convex side towards you, temples away on the table. Both lenses rest comfortably on the table
- Centre lens mires in the lensometer
- Power Wheel at highest expected + rx
- Determine Power at correct axis
- Determine the power at the cylinder axis
- Dot the lenses with the ink pens
- Middle dot = optical center
Measurments we need to duplicate eyeglasses
- Prescription
- Pupil Distance
- Optical centre
- Boxing system
- Vertex distance
- Base curve
- Lens thickness
- Pantoscopic tilt
- Frame wrap
boxing system
- A size
- B size
- ED measurement
- Geometric centre
wide jaw temple angling wire
adjusting the temple for frame tilt
closed temple fold
when reading a perscription in minus cylinder form
turn the power wheel in the high plus direction, now slowly turn the wheel back in the minus direction
