OPTOMETRY

2. History of Contact Lenses

3.  Leonardo da Vinci (1508)is often claimed to
be the first to describe a ‘contact’ lens.
 His sketches of a schematic eye (with an iris
diaphragm and an artificial crystalline lens)
and the head immersed in water have been
used to illustrate the concept of a refractive
system in ‘contact’ with the eye.

4.  Understood that better vision could be
achieved by enlarging the retinal image
Sketched an elongated tube filled with water
placed against an eyeball Demonstated the
principal of the telescope, not the contact lens.

6.  Herschel, an English astronomer, was
interested in the correction of corneal
astigmatism by a spectacle lens.
 Herschel was probably the first person to
describe the concept of cosmetic lenses.
 Herschel can be considered the ‘father of
contact lenses’.

7.  Described the following:
• Need to correct irregular cornea
• Contact with the eye
• Eye impressions
• Need for a transparent medium
• Combining a soft material with a rigid
overlying material

8.  First person to apply a therapeutic contact
device
 Used gelatin square soaked in mercury
chloride
 First drug delivery system

9.  Devised the first contact lens for keratoconus
 Wanted to remodel the corneal curvature by
using glass contact shells as splints
 Resulted in substantial visual improvement

10.  Used glass shells on rabbit corneas.
 Trials using glass as lens material.

11.  1934 – PMMA material patented – John
Crawford and Rowland hill.
 Development of PMMA material.
 1937 – CAB lenses.
 1948 – kevin Tuohy – 12 mm corneal lenses.

12.  1961 – HEMA patented
 1970 – Hydrogels era – rapid developments
in design.
 1972 – First RGP lens – silicone acrylates
 1981 – First cosmetic extended wear
(HEMA)
 1984 – Disposable lenses (Orlando Battista –
gave the concept of 1st collagen lens.)

13.  1989 – Hybrid – soft perm lenses
 1994 – Daily Disposable lens
Newer & newer designs of hydrogels – toric
/bifocal/multifocal.
 2000 – Continuous wear lens material –
Siloxane containing hydrogels.

14. Types of Contact Lens

15. Contact lenses can be classified
 By the nature of the material from which they
are made
 By their wearing schedule
 By their purpose
 By their design.

16.  Hard - PMMA
 Rigid Gas Permeable- CAB,Silicone
acrylate
 Hydrogel - HEMA
 Hybrid - - combination of both
Hard and Soft.

17.  Daily wear – removed daily and not utilized
during sleep.
 Continuous or extended wear – utilized both
during waking and sleep hours for a specified
number of days continuously .These lenses are
generally made from high water content or
high DK material.
 Flexible wear – utilized during the day and
occasionally overnight.

18.  Traditional / conventional :replaced annually.
 Disposable or planned replacement :
discarded after a specified wearing period. Can
be disposed of daily ,weekly biweekly,
monthly, bimonthly or quarterly.
 Occasional – occasional use ,eg., athletics or
social activities.

19.  THER APEUTIC : for protection or healing
of the cornea.
 Cosmetic - for modification of the colour
of the eye or to improve the appearance of a
disfigured eye.
 Optical : for correction of refractive error
and or regularization of the corneal surface.

20.  Spherical - having anterior and posterior
spherical surfaces.
 Aspheric – different radii of curvature in the
center and periphery ,simulating the structure
of the cornea.
 Toric – two principal meridians have different
radii of curvature.

21.  Bifocal
 Progressive
 Multicurve
 Reverse curve – a central posterior curve
,which is flatter, utilized primarily for fitting
after refractive surgery for myopia or ortho K

22. CONTACT LENS TERMINOLOGY

23.  Blank : or the button from which the rigid or a soft
lens is fabricated by lathe.
 Semi finished Blank: - a blank where base curve
is pre generated.
 Semi finished lens: a lens that has the back and
the front curve cut. The peripheral curves and the
edges is not yet fabricated.
 Finished lens: a lens ready to be worn on the eye.

24.  Base curve
 Power
 Lens diameter
 Peripheral curves
 Optic zone
 Central thickness
 Edge Design

25.  BC is also called as BOZR –Back optic zone
radius ,BCOR – Back central optic radius or
CPC – central posterior curve.
 This is the back curve of the CL ,which
contours the front surface of the eye. To
achieve a proper fit the base curve of the CL
should be aligned with the curvature of the
cornea.

26. BC is expressed in mm (milimeters)
Example – 8.1 mm,8.3 mm ,8.6 mm etc..
8.1 mm is a steeper BC than 8.3 mm and 8.3
mm is steeper than 8.6 mm .So a longer BC
produces flatter base curves.

27.  BC can be spherical or aspheric .
 An aspheric base curve as the name suggests
flattens from center to periphery and matches
the corneal Asphericity.
 The Asphericity is specified by e –value
Zero spherical
Between 0-1 elliptical
1.0 parabolic
>1.0 hyperbolic

28.  The length of the lens across its widest
diameter is called the overall diameter or lens
diameter.
 It is specified in mm.
 A soft lens is usually 12-15 mm and a rigid
lens is of 8 to 10 mm diameter.

29.  DIAMETER depends up on the corneal
diameter and the palpebral aperture.
 Larger the corneal diameter greater is the
overall diameter of the lens required.

30.  Monocurve lens– single BC
 Bicurve lens – two BC
 Tricurve lens - three BC
 Multicurve – more than three curve
 Secondary curve or intermediate curve.

31.  The junction b/w the base and the peripheral
curves are blended properly to give a smooth
transition and junction.

32.  The peripheral and intermediate curve have a
fixed width or size.
 It is usually 0.3 to 0.5 mm wide.
 Depends up on optic zone diameter and the
overall diameter.

33.  The central optic portion, which carries the base curve
of the BC of the lens, is called the optic zone.
 It is the central circular portion of the lens where the
power of the lens is located.
 The average size of the optic zone is 7 to 8.5 mm in
case of rigid lens and 7 to 12.0 mm in case of soft
lenses.

35.  It is grounded on the front surface of the lens.
 A plus lens will be thicker in the central a d minus lens
will be thicker in the periphery.