4.1.5 Dispenses a range of lens forms to include complex lenses, multifocals and high corrections, and advises on their application to specific patients’ needs

Question 1

Paediatric (4 or under)

Name some designers of childrens glasses

Answer 1

• Tomato glasses
• Erins world frames

Question 2

Paediatric (4 or under)

Best How to Adjust paeds frames?

Answer 2

Make sure tips of ear points of frame do not stick out as this will push on the ear and cause the ears to look bigger as the cartillage reforms itself into this position

Drop of side should be somewhat long to keep it hooked but not excessive!

As long as px looks through middle of frame, heights don’t need to be taken even with high Rxs as the likelehood of differential prism is small as a result. Also, if the Rx is equal or very similar between both eyes but still a large Rx, it will still induce less differential prism

Question 3

Paediatric (4 or under)

Is an MAR worth it for a child?

Answer 3

Parent may want AR coat but not needed as can become stratched easily and children don’t need them but if parent wants coating then write advise you gave them

Question 4

Paediatric (4 or under)

Frame selection: Two most important aspecs?

Answer 4

1. Needs to ensure lenses sit in front of the eyes i.e. in centre as much as possible, so tilt normally zero degrees
2. Should be comfortable, stable and not damage developing features

Question 5

Paediatric (4 or under)

Frame selection: What type of frame?

Answer 5

• Remember: small eye size means less thick!
• Hyperope - round, Myope - rectangular
• Material - plastic & wide sides best for durability
• Choose frame where px looks right in the centre
• Sprung hinges work well/durable hinges
• TYPES: Loop end sides, Curl end sides

Drop end sides are standard sides. Ensure bend at px ear point & drop along px head. Take away excessive drop (cut down in metal but not plastic)

(see image in notes)

Question 5

Paediatric (4 or under)

Frame selection: What frame measurements are we concerned with?

Answer 5

• Crest Height (smaller) - if negative, may mean bridge needs to be set below HCL to position pupils centrally
• Splay Angle (larger)
• Frontal Angle (larger)
• Bridge Projection (smaller)
• Head Width (smaller)
• Angle of Side (smaller)
• Length to Bend (smaller)
• Vertex Distance (smaller)

(see notes for image)

Question 6

Paediatric (4 or under)

Frame selection: What type of bridge?

Answer 6

• For babies & DS, comfort bridges work well:

Comfort bridge

W bridge good option as follows nose curvature

• For plastic, fixed or keyhole bridge works best so long as it fits the nose

(see notes for images)

Question 7

Paediatric (4 or under)

Frame selection: Fitting triangle?

Answer 7

Frame fits at 3 points: The crest of the nose & the R+L ear points. Observe this with each frame chosen

Question 8

Paediatric (4 or under)

Frame selection: What is special about Erin’s world frames?

Answer 8

Erin’s World frames designed for those with DS or atypical faces. In the pic, wide lugs and bridge lower to adjust for crest height. ( Or tomatos)

Question 9

Paediatric (4 or under)

Lens selection: What is the criteria?

Answer 9

• Impact resistant & durable
• Thin & light
• UV protection - disimilar protection to adults, should be at up to 380nm

Question 10

Paediatric (4 or under)

Lens selection: Lens materials?

Answer 10

o CR39
o Polycarbonate
o Trivex
o High index plastic
o Glass lenses should never be dispensed to a child!!
o All lenses should be scratch resistant

Question 11

Paediatric (4 or under)

Properties of CR39?

Answer 11

o Good impact resistance
o Sharp fragments on impact
o Inherent scratch resistance
o Protects against UV to 355nm
o RI = 1.498
o Abbe no. = 58

Question 12

Paediatric (4 or under)

What are the different methods of taking PD?

Answer 12

• Corneal Reflexes - For pxs who struggle with fixation, can use pentorch to locate corneal reflexes, measuring distance between nasal and temporal corneal-scleral margins or distance between nasal and temporal pupil edges
• Pupil centre to pupil centre for those who can fixate
• Canthus - The distance measurement between the nasal canthus of one eye to the temporal canthus of the other
• Strabismus - If child has a strabismus, each eye must be occluded in turn, and the measurement taken monocularly
• Parent should stand behind you so child looks at you when you take measurement. You need to be eye level. Use colourful pens or toys!

Question 13

Paediatric (4 or under)

What needs to be measured/considered with curl sides?

Answer 13

• Length to tangent (downel point to the tangent) and total length of of side, (don’t want the curl to be longer than back of ear. Should be about 3 qouters if longer than needed, then ear can grow outwards & over it! Ears are made of cartilage
• Sides must stop just short of ear lobe

Question 14

Paediatric (4 or under)

How & who to dispense a bif/vari to in terms of children?

Answer 14

• Convergence excess, juvenile stress myopia and Down’s syndrome
• D28 segments usually dispensed to have a harsh line between distance and near. Add is normally +2.50
• Heights set between pupil centre and lower pupil margin. Starts on centre then lowered as px ages
• Vari may be for those with congenital cataracts removed
• PPLs fitted as standard; larger frames needed as Adds can be +3D
  
  • Compact design not ideal as pxs need intermediate correction

Question 15

High Rx (+/-10D or >)

What differences between frame PD and px PD is important?

Answer 15

Frame PD = Px PD to reduce decentration

Question 16

Varifocal

Advantages vs disadvantages

Answer 16

Advantages
- Clear vision at all distances
- More convenient than using 2/3 separate pairs
- Cosmetically, they look like single vision lenses i.e.. no visible dividing line
- No image jump occurs as the patient looks down the lens
- Accommodation does not need to fluctuate as vision goes from one zone to another

Disadvantages
- Distortions in the periphery
- Smaller NV area cf. BIFs
- Narrow IV area cf. TRIFs
- Intermediate and reading areas in a varifocal will always be smaller than those in a bifocal
- Period of adaption required
- Transition between distance and near is narrow so accurate centration is required
- Usually no control of inset hence more horizontal head movement needed
- Cost
- More horizontal movement needed when reading

Question 17

Varifocal

Hard Vs Soft Vs Supersoft designs

Answer 17

Hard Design:

• Large distance area, narrow intermediate corridor and wider reading area
• Aberrational astigmatism confined to limited nasal and temporal areas
• Distance virtually aberration-free
• Good for previous bifocal wearers
• e.g. Sola Graduate and Kodak Elegance

Soft Design:

• Distortion extends to distance area which affects peripheral vision
• Patient will have to move head more when viewing objects at periphery
• Larger intermediate zone
• Narrower reading area
• Good for first time presbyopes (especially VDU users)
• e.g. Varilux Liberty and American Optical PRO 15

Firm (supersoft) Design:

• Offers larger distance, intermediate and reading areas
• Ideal for all presbyopes, previous bifocal wearers and those who are non-tolerant to other PPL designs
• e.g. Varilux Physio and Zeiss Gradal Top

Question 18

Varifocal

Relationship of Add and surface astigmatism

Answer 18

The surface astigmatism of a varifocal (PPL) is proportional to the Add power.

For example, the unwanted cylinder power of a +3.00 lens is roughly three times the cylinder power of a +1.00 Add lens.

Advice for patient – The higher the add the more distortion. So keeping with the same design after each eye exam may result in a smaller reading area (assuming add increases after each eye exam, which it will in cases of presbyopia)

Question 19

Varifocal

Measurements needed

Answer 19

Adjust spex so it sits straight & px happy. Tell px to bring their chair forwards then sit back & relax to get them into their habitual posture. When they sit back, ensure their head is tilted so that it is straight on with you. Make sure your chair is the correct height.

Measure Mono pds, heights to pupil centre, Pantoscopic tilt of 10 degrees

Depth ofstandard lenses from pupil to bottom of lens needs to be approx. 18-20mm – allows for a useably long enough corridor to be put into the lens

• Compact lenses require depth from pupil to bottom of lens to be at least 14mm
• Height from pupil to top of lens to be 10mm

Question 20

Varifocal

What markings are apparent on a varifocal lens?

(refer to notes)

Answer 20

a) Distance checking area (inked). The focimeter is aligned here to measure the distance power. The power in this region is stable as it lies beyond the progression zone.

b) Reference marks (engraved).
These can be circles, squares, triangles, company logos etc. They are always 34 mm apart along the 180 meridian. Their purpose is to allow re-marking of the inked markings and to verify the horizontal alignment of the lens.

c) Reading checking area (inked). The focimeter is aligned here to check the reading power. The Add of the lens is the difference between the front vertex power readings taken at ‘a’ and ‘c’. The reading checking area is usually inset 2.5mm in from the fitting cross.

d) Manufacturer’s mark (engraved). This may be the manufacturer’s logo or an identification for a particular model of progressive lens (especially if markings ‘b’ are the company logo). This mark is always below the nasal reference mark. e) Add power (engraved). This is usually a 3-digit number without a plus sign or a decimal point. The Add in this illustration is +2.25. This mark is always below the temporal mark.

F) Fitting cross (inked). This mark should be aligned with the centre of the pupil. The fitting cross position varies in different lens designs from 0 to 6 mm above the prism reference point.

g) Prism reference point (inked). This lies exactly between the reference engravings b. The focimeter is centred on this point to measure prescribed prism and prism thinning. This point is also regarded as the optical centre of the lens and is usually where the progression starts (which is why the distance power has to be measured elsewhere). In many designs this point is pre-decentred nasally- in lens catalogues the blank size will have two numbers e.g. 75m/m = 80 m/m. This means that the blank’s actual diameter is 75mm but because the optical centre has been decentred from the geometrical centre (2.5 mm nasally in this case), the lens will glaze into frame/centration combinations requiring a conventional 80 mm diameter blank
In addition, there are usually some horizontal line segments inked onto the lens to verify horizontal alignment.

Question 21

Varifocal

Prism thinning:

Answer 21

PPLs prism thinned to reduce thickness & hence improve cosmesis. Base Up removed once upper edge of lens thinned. This effectively leaves 2/3 Add as Base Down
PPLs should be checked for prism at PRP
Problems may arise if px has Odd Adds

Question 22

Varifocal

Why use freeform?

Answer 22

To accurately produce a lens with the desired power in the right places on the lens

Question 23

Varifocal

Difference between freeform & traditional surfaced varifocals?

Answer 23

• Traditionally, the front surface of the varifocal is moulded with a varifocal design & the back surface has the sphere & toric power glazed into it
• Freeform can manipulate both the front & back surface power to get desired final power. It uses special machinery to take specific measurements & will plot the power using thousands of sag points to a 0.01D accuracy!

Question 24

Varifocal

What measurements does eyecode take/consider?

Answer 24

BVD, Mono PDs, Fitting height, Eye rotation centre etc

Considers eyestrain, head posture & movement, diplopia, eye movement when reading etc