~allows clinical measurement of the pupil 

~Instrumentation- defining acceptance cone of light to instrument or system

~Instrumentation-  determines the defining cone of light producing the image and thus the brightness of the image

~telescopes and field of view

Defined by the angle that the marginal ray from the exit pupil makes with the axis. 

~NA is proportional to the square of image brightness. 

~depends on the refractive index of the media of image space 

*** it defines image brightness

Formula: N.A = n' sin u'

ie half the angular subtense of the exit pupil 

~dft distances in image space

~The range over which the image screen can be moved with acceptable clarity 

~the range over which the obj can be moved and imaged with acceptable clarity 

~dft distances from camera (eye) in obj space 

~small amt of blur being ok 

~inversely proportionate to N.A

~no consideration for diffraction effects 

~stops within the system that limit off axis points 

~Limits the extent of the object that is imaged 

~may be a physical stop or a lens in the system 

~If placed at the image plane there is a sharp cut off in intensity at the image edge 

~the extent of the obj that the system images

~Can be specified by actual size or angle between extreme rays 

~vignetting occurs 

~image brightness fades gradually towards more off axis points of image

NOTE: **** often used to optical designers to control the image quality even if the image is not so bright 

~field stop may be an actual aperture or may be a lens in the system 

~only the most extreme point reaches the image 

(ie bright at the axis and darker the further away you go)

~Tries to make the retinal image size as large as possible. (this could be achieved by bringing the obj

as close as possible but you would also get defocus)

~Assumes the near point is 250mm

NOTE: *** if the obj is placed at the first principle focus of a magnifiying positive lens the intermediate image is formed at infinity and this acts as an obj for the eye. (It can be viewed by the emmetropic eye or the corrected eye w.o accommodation)

M= angle subtended by the magnified image /angle subtended by direct view of the obj

M= w'1/w'2 = (h/f') x(-q/h) = -q/ f'= 250/f' 

TF

~ M=F/4

TRUE

note:*** near may be better for increased field of view

IF the Image is formed NEARER than infinity than the position of the lens compared to the eye matters. 

~ there is a fixed distance so px does not need to steadily hold it at a fixed distance 

~this is good bc many ppl that need magnifiers are elderly (may fatigue easily)

~the distance btw f' of the objective lens and the f of the eyepiece 

**** by convention 160mm

~it magnifies the image formed by the objective lens and places it at infinity (typically)

Me= -q/-fe' =250/-f'e

1. Astronomical (Keplerian)

2. Terrestrial (Galilean)  

~positive eyepiece

~distant obj produces an image at f'o(objective lens 2nd focal pt), which is coincient with fe (primary focal pt of the eyepiece), bc the distance btw the eyepeice and the objective lens is (f'o -fe), this produces a longer telescope

NOTE **** GIVES A REAL INVERTED IMAGE 

prisms are used to re invert the image

~make the lens bigger, heavier and thicker

~may touch cheeks 

1. tighten all screws

2. adjust bridge of frame

3. frontal hinge angle

4. 4 point touch (affects pantoscopic angle)

5. temple tips

6. nose pads if applicable 

****all steps must be done in order 

when worried about pantoscopic tilt, if a person has low ears what kind of temple shoudl you choose in frame selection?

high ears?

mid to low temple 

high temples for high ears

~Crown glass & CR 39

~very heavy lens

~near OC segment line (no jump)

~one piece design (both lens materials)

~CR- 39 and crown glass

~2nd most common 

~Near OC at centre of segment 

~available 22, 24, 25 segments

~adds available up to+30.00D in CR-39 

(+0.25D steps up to +15D)

(+0.5D steps up to +30D)

Available in 22, 25, 28, 35, 40 and 45 mm segments,

measured across full width of the segment, not line

-Adds available to +8.00D -Most common bifocal design - Near OC at 5mm below seg line

-Available in (fused) glass, (one piece) CR39, polycarbonate and some high index lens materials

Near OC is below the seg line, OC setting is dependant on bifocal style

When neutralizing the add the near OC will not centre in the lensometer redicule

The lower the OC in the bifocal, the more “prismatic jump” the image will have

␣

~Do not try to centre the lensometer target when neutralizing the add power

Worn line bifocal in the past

 Has an rx outside of PAL range

 Cannot adapt to PAL

 Has vocation or avocation needing specific Rx ranges

 Add power is usually for 40cm but could be adjusted for special circumstances*

*Tall people can need a full add at 60cm due to longer arms!! Check during the eye exam!!

 normal: 1.48 - 1.54 

mid: 1.54 -1.64 

high: 1.64- 1.74 

very high: >1.74

1. hard: hard design short corridor most of distortion is below 180 

2. Soft: longer corridor, some distortion in the distance area

*** can have long or short corridors 

myopes may tend to prefer hard style bc they are more dependent on their distance rx 

~adds up to +4 

~distance rx: +13.00D to -18D (-6D cyl) available in every lens material index

On a PAL lens what is located under the temporal etching? nasal etching?

how far apart are the etchings?

temporal: add power 

nasal: manufacturer

The etchings are always 34mm apart (prism pt is exactly btw these 2 pts)

1. corneal vertex distance 

2. pantiscopic tilt

3. faceform angle 

4. monocular IPD's (distance and near)

NOTE **** fit frame before you take any PAL measurements 

~symmetry of the frame 

~measurement of E.D(effective diameter)

~consider frame edge style during frame selection 

~frame size 

choose small symmetrical lenses

~fit lenses nearer to the eye (eye lashes allowing)

~may also optimizes retinal image size

~spherical lenses it will depend on frame shape

~spherocyl lens it will depend on shape of frame and toric powers 

~also dependent on E.D 

1.small, dark and close  

2.regular shape, metal or plastic  

3.check vertex distance 

4.thicker full eyewire with a hide a bevel 

5.small eye size 

6.nose pad / guard arm clearance

7.discourage rimless

1. As vertex distance increase, F.O.V decreases

2. As the size of the lens increases, F.O.V decreases

1.small eyesize 

2.little or no decentration

3.short vertex distance

4regular shape (more round)

5.adjustable nosepads

6.cable temples or tight fitting skulls temples

7.no rimless

Long lashes 

~high cheek bones

~high rx

~face wrap

~flat bridge 

~frames with no nose pads

what is the formula for decentration?

MBS formula 

Decentration = (frame pd - px pd)/2

MBS= E.D + 2 decentration(per eye)

-12.00D

~myodisc 

~blended lenticular 

~ single vision glasses and readers 

~single vision glasses tilt head down to continue looking through optical centre 

~bifocal CL's, monovision, or CL and readers

~slab off prism 

HIGH RX’S -­ CONSIDERATIONS

Things to always consider with high Rx’s

-­ Frame selection – frame pd = patients pd, rounded shapes, nosepads with good guardarms, add nosepads?, wider hinges for minimum eyesize and best fit

-­ Lens selection – hi index and/or aspheric, AR a must!

-­ Photochromic, a good option – check availability

-­ Measurements – monocular pds, pupil height, vertex distance, base curves

-­ Counselling – even small changes are an issue: change of frame size, lens index and vertex should be discussed when ordering not on delivery

-­ Listen to client concerns, be realistic and honest

1. spherical aberration

2. coma 

3. oblique (off axis) astigmatism

4. curvature of field 

5.distortion 

****** assume spherical surfaces 

~square of aperture (pupil radius)

~ LSA decreases as refractive index increases

~LSA varies as a factor of F^3

~LSA increases as the square of pupil radius 

~LSA varies with obj position 

TRUE or FALSE 

spherical Aberration can be completely eliminated by changing the lens form 

FALSE 

~it can be reduced but not completely eliminated

~ variation of magnification btw the peripheral and the paraxial rays 

~depends on square of the aperture and the height of the object 

~coma is 0 when shape factor =0.8

(OAE) is difference between tangential and sagittal foci

~the inability of a lens to form a pt image of a pt obj

~depends on the square of the object height and the pupil diameter

~CR-39

NOTE:*** polycarb and some high index materials are hard to tint 

~some SRC are non tintable 

~CAN NOT TINT OVER AR COATINGS EVER

~CR-39 

***** NO UV coating available for glasse lens materials 

Also new high index lenses already have UV 400 protection built into lens 

TRUE OR FALSE 

no lens is scratch proof but can be scratch resistant 

~cold bright weather/climate

~will not become as hard in warmer climate 

NOTE: this type does NOT darke  behind the windshield 

Transitions XtrACtive

~also has a slight tint when indoors(15%)

TRUE

*****BUT They are consider “safe” because the lenses “stick” to the polarized film if the lens is chipped, cracked or broken.

1.Avoidance: Isolate hazard from worker, physical barrier 

2. shielding: personal protection equipment, No contact while in presence of hazard 

3. Maximum permissible exposure: when PPE can not prevent hazard, limited exposure,

MPE= total exposure vs dose rate 

1.Safety spectacles including side shields

2. goggles

3. visors

4. helmet

5. respirator facepieces

CSA Z94.3

~rx and non rx safety glasses

class 1. safety glasses

class 2. goggles

class 3. welding helmets 

class 4. welding hand shields

class 5. Non rigid helmet hood

 class 6. face shield

class 7. respirator facepieces

What are the types of hazards 

list the classes

A: Flying objects 

B: flying particles (dust, wind)

C: Heat sparks Molten Splash 

D:Acid splash, Chemical burns 

E. Abrasive blasting materials 

F: glare, stray light 

G: injurious optical radiation 

H: injurious optical radiation 

!  Desirable features

!  headband

!  shock absorbing foam pads

!  smooth edges

!  no scotoma

!  good optical quality

!  protection from front and side

! 1. Failure to prescribe materials

!  what is most appropriate for the hazard? !  2.Failure to warn

!  what are the limitations of the protector? !  3.Failure to inspect materials

!  have you determined the protector is free of defects?

!  4.Failure to provide appropriate follow-up !  is the protector being used properly?

1.Check transcription frm RX file (very common mistake)

2. Lab error (check lab form vs. order form)

3. +ves and -ves are incorrect

4. re take all measurements 

5. retake measurements on patient to verify

6. Neutralize RX from original rx 

7. base curve change?

8. index change?

9. lens warpage?

10. If high Rx- vertex distance problem

11. missing info frm original order (individualized lens)

12. balance lens 

Heat tempering:

~fast individual process

~not for design lens with surface discontinuity

~up to 600micron compression layer

~polariscope test proof of treatment 

Chemical tempering:

~slow batch process

~temperature and purity sensitive

~any design 

~100 micron compression layer 

Hertizian fracture 

~small high speed missile

~front surface simple elastic denting 

(ie where the missile hits is not the area of the break, rather the area of the lens at the edge of the missile is where the fracture occurs)

~compound flexure 

~slower larger missile on minus lens 

~star pattern to fragments

This is called simple flexure

~slow larger missile on plus lens 

~tends to fail on minor axis of the lens 

~elastic shock wave 

~shock wave focused by Griffith flaw at edge or bevel

~spalling (edge chips)

Ballistic testing 

(CR-39)

dress lenses 2mm 

~no failures at 18m/s

~90% survive 50 trials 

~all fail at 46.5m/s

3mm 

~no failures at 18m/s

~no failures at 46.5m/s 

~failures from 48 -68 impact speed

1. Solid state lasers: Nd YAG lasers

2. GAS: argon, HeNe, Krypton, excimer

3. semi conductors: small low powered lasers   

Temporal mode:

1. continuous 

2. pulse(ms)

3. Q switched (ns)

4. Mode locked (ps)

Spatial Mode:

1. transverse - limited coherence and focusability

2. Longitudinal- frequency and coherence

What is the formula for acceptable emmission limit

Nominal Hazard Zone (NHZ)

 The space within which the level of direct, reflected or scattered radiation during normal operation exceeds the MPE

~the dioptric distance btw the far point sphere and the petzval surface 

image shell error = FPS -Petz

The inability of a lens to form a image of the same shape as the object   

depends on h^3 (obj size cubed)

NOTE: can be reduced with a spheric surface