frame measurements and materials

• parts of a metal frame

  • sides -2x (not arms or legs) and 1x front
  • dowel screw- connects the sides to front
  • bridge- sits across Px nose
  • lugs 2x - connects the front to hinge near the px temples

  
• what are the types of bridge in a metal frame

  • nose pads
  • comfort bridge
  • strap bridge
  • w bridge
• what are nose pads (metal frame)

  • silicone
  • either push in or screw in
  • are fully adjustable
• what is a comfort bridge (metal frame)

  • built into frame
  • made of silicone
  • spreads weight of spec across the nose bridge
  • has metal insert for stability
• what is a strap bridge (metal frame)

  • either push in or screw in
  • good for px with shallow bridge
  • patients who have down syndrome
  • can replace nose pads
• what is a W bridge (metal frame)

  • no pads
  • bridge follows contour of nose
  • unusual
• types of bridge for plastic frame

  • fixed pad bridge
  • kehole bridge
  • regular bridge
  • asian fitting
• what is a fixed pad bridge (plastic frame)

  • fixed pads part of the frame so cant be adjusted; ensure fit at time
  • most common
• what is a keyhole bridge (plastic frame)


  • useful if px finds bridge fit uncomfortable
  • more of a fashion statement
• what is a regular bridge (plastic frame)


  • no pads
  • bridgr follows contour of the nose
  • unusual
• what is an asian fitting bridge (plastic frame)


  • pads part of the plastic front
  • better for those with a lower crest (flatter noses)
• eye size


  measured across the lens at widest point
• DBL (distance between lenses)

  horizontal measurement across bridge at the narrowest point- nasal edge of right lens to nasal end of left lens
• frame PD


  eye size + DBL
• Maximum diameter


  longest diameter measurement across the lens
• boxed lens size (H and V)

  size of rectangle containing lens shape formed by horizontal and vertical tangents and lens shapes
• distance between centres

  distance between the geometrical centres of the 2 lenses
• length to bend

  distance between dowel point and ear point
• length of drop

  distance from ear to the tip of the side
• front to bend

  distance between the lug point and the ear point (total length of side= length to bend add the length of drop)
• box centre

  geometric centre of the lens

  • the geometric centre is the half way point on the midline of the lens
• 3 numbers on the side of the frames

  • eyesize
  • DBL
  • total length of side
• the boxing system


  definitions

  
• horizontal lens size and vertical lens size

  • distance between vertical sides of the boxed rectangle
  • distance between the horizontal sides of the boxed rectangle
• horizontal centre line (HCL)

  • an imaginary line drawn through the geometric centres of the rectangular boxes
• bridge width and bridge width line

  • minimum distance between the pad surfaces of the frame measured along the bridge width line
  • bridge width line is the line parallel to and 5mm below the HCL
• bridge height, projection and crest height

  • vertical distance from the bridge width line to the intersection point of the vertical symmetry axis with lower edge of the bridge (crest height plus 5mm)
  • minimum horizontal distance from the back plane of the frame to the entre of the back of the bridge
  • vertical distance from HCL of the front to the midpoint of the lower edge of the bridge
• distance between rims (DBR)

  horizontal distance between the nasal surfaces of the rims measured at a stated distance below the midpoint of the lower edge of the bridge eg DBR 20 at 10 below crest
• apical radius 


  the radius of the arc forming the lower edge of the bridge viewed perpendicularly to the back plane of the front
• frame temple width and frame head width

  • distance between the sides 25mm behind the back plane of the frame front
  • distance between the sides at the ear points
• dowel point and ear point

  • centre of the bottom of the dowel hole
  • of a drop end side = midpoint of the arc of contact between the bend of side and circle which fits it , of a curl side= point on the lower edge of the side at the beginning of the curl, of a straight side= the point on the lower edge of the side which is assumed to make contact with the ear
• line of side, angle of let back and angle of side

  • straight line through dowel and ear points
  • horizontal angle between the inner surface of the fully opened side next to the joint and normal to the back plane of the frame front
  • vertical angle between a normal to the back plane of the front and the line of side when fully opened
• side view measurements

  length to bend and length to tangent

  
• birds eye view frame measurements

  head and temple width

  
• box measurements 


  ...

  
• the fitting triangle


  bridge of nose to points on ear

  
• what should you insure from the front when fitting frames

  • ensure frame is level 
  • Sits comfy on the nose
  • Nose pad is in contact with nose
  • Lower rims don’t rest on cheeks 
• what should you ensure from the sides when frame fitting

  • LTB correct - sides long enough to rest on ears with sides just past the top of ears 
  • Length to drop not too long , should be between 35-40mm for adults 
  • Pantoscopic tilt - angle of side with front - should be angle inwards of 5-10 degrees
  • BVD is correct - correct away from eye so not wearing on nose ; equal on both sides 
• what should you ensure from above when fitting frames

  • slight bow to the front of frame following curve of head
  • Frame should not be twisted so one lens is closer to face than other otherwise wrong BVD
  • Temple width is correct - sides grip heads snuggly - not too tight or loose 
• thermoplastics


  • can be reformed with heat
  • soften on heating
  • long chain linear
  • by addition polymerisation
  • can be reshaped and reused
  • soft, weak and less brittle
  • soluble in organic solvents
  • reclaimed for wastes