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Contact Lens > test 1 > Flashcards

test 1 Flashcards

1
Q

What are the 2 types of lenses?

A

Scleral and cornea l

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2
Q

What is a scleral lens?

A

a lens that is extends beyond the diameter of the cornea

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3
Q

What are some examples of a scleral lens?

A

soft lenses and haptic lens

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4
Q

what is a corneal lens?

A

a lens that is the same diameter as the cornea

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5
Q

what is an example of a corneal lens?

A

rigid lenses

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6
Q

how are corneal lenses supported?

A

with fluid retention AND OR the lid

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7
Q

In what year and what concept did Leonardo Da Vinci come up with?

A

a very basic optical system where the cornea is neutralized through contact with an optical medium. 1508

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8
Q

What did Rene Discartes come up with and when?

A

sketched an elongated tube filled with water and at the end had a glass the same shape as a cornea. 1636

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9
Q

Thomas Young

A

understood how to neutralize cornea, but did not think of CLs. 1801

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10
Q

Sir John F. W. Herschel

A

1823, described the elements of a CL more precisely but did not put into practice

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11
Q

Adolf Fick

A

1888, A contact spectacle. Described the first contact lens with refractive power known to have actually been worn.

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12
Q

What was the very first contact lens?

A

a thin glass bowl invented by adolf fick in 1888. can wear it for 2 hrs without irritation but it had no power.

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13
Q

what was the second CL to be developed?

A

made with a glass blower. bi-curve lens of 14mm in diameter. This was used in irregular astigmats and they had visual improvement.

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14
Q

What were the first cosmetic lenses?

A

lenses painted with irises on them to avoid enucleating eye

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15
Q

Eugene Kalt

A

1888, made the first CL to tx keratoconus. and first cosmetic lens

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16
Q

August Muller

A

1889, structured lenses so that posterior surface could be held in place by cappillary attraction. anterior surface would correct refractive error. used cocaine as anesthesia. did fittings on himself to neutralize his -14.00 D myopia.

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17
Q

who created the lift off on the cornea?

A

August muller because he saw that tears were important to prevent corneal edema.

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18
Q

Karl Zeiss

A
  1. Developed the first trial lens made of glass..was very heavy and not successful.
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19
Q

spin casting

A

uses liquid polymer which is spun to create the correct curvature

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20
Q

cast molding

A

uses liquid polymer filled in a mold, most disposable lenses are cast in mold

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21
Q

lathe cutting

A

uses solid polymer that is cut and polished to the power required

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22
Q

Muller Co.

A

made lenses from blown glass on individual basis in the presence of the patient in an attempt to correct his ocular irregularity. had smooth edges and regular curvature.

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23
Q

ptosis crutch

A

ridges were upper eyelid can rest. caused DES bc patient had difficulty blinking.

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24
Q

joseph dallos.

A

emphasized fitting lens with slight difference bw. lens and cornea to allow tears to flow unnderneath. noticed central cornea spherical and peripheral was flatter.

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25
Q

william feimbloom

A

1936, the first to use plastic to capture the advantage of low specific gravity. hybrid lenses.

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26
Q

J. Teissler

A

1937, made corneo-scleral lenses shell from cellulose acetate plastic (first gas permeable lens)

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27
Q

Rhom and Haas Co.

A

1936, introduced to the US a transparant material known as PMMA

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28
Q

PMMA

A

dominated CL field for 4 decades.

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29
Q

John Mullen and Theodore Obrig

A

1938, developed techniques for making scleral lenses from PMMA (found CL could be made thinner but still had difficulty with oxygen delivery.

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30
Q

Kevin Tuohy

A

developed the first corneal CL that has became a practical device for correction. 1946, technician cut erroneously and created RGP. found these lenses eliminated the symptoms of halos.

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31
Q

George Butterfield

A

1950, – Recognized that by adding various peripheral curves to the posterior surface of the lens central curve could nearly match the radius of curvature of the cornea.
• This represented the first introduction of the modern term of fitting “on K” or contouring the cornea.

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32
Q

Otto Wichterle

A

1952, synthesized HEMA, produced hydrogel lenses of different degrees of water content. in 1961, created more casting machines.

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33
Q

C lenses

A

first lenses introduced by B&L was barely successful.

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34
Q

N lenses

A

2nd lenses introduced by B&L, was significantly more popular.

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35
Q

what did Vistakon do?

A

introduced the first disposable lenses. (Acuvue)

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36
Q

Cellulose Acetate Butyrate

A

was gas permeable but poor physical stability and warped easily

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37
Q

Norman Gaylord

A

1971, invented silicone methacrylate RGP material. permeability was similar to CAB and it was more stable.

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38
Q

how did intro of fluoride help?

A

increased Dk of lens. FS/A

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39
Q

function of tear film?

A

maintain hydration of soft lenses and cornea. anterior refractive surface.

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40
Q

what is the most commonly used CL?

A

Silicone hydrogel

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41
Q

high wetting angle

A

the higher the angle, the less tearsthat is spread over surface

42
Q

components of tear

A

Mucous (basal layer)
Aqueous layer
Lipid layer

43
Q

what glands produce mucus in tears

A

goblet cells, glands of moll and krause

44
Q

glands that produce aqueous layer in tears

A

lacrymal gland, accessory gland of zeiss

45
Q

glands that produce lipid layer

A

meibomian glands. this prevents evaporation

46
Q

what does TBUT measure?

A

mucus layer, when that evaporates, water touches cornea and cornea is hydrophobic and the water breaks.

47
Q

what is n of cornea?

A

1.376 and power of 45D

48
Q

what is the thickness of the cornea

A

0.52 in the center and 0.97 in periphery

49
Q

5 layers of the cornea

A 
epithelium with basement membrane
bowman's zone
stroma
descemet's membrane
endothelium
50
Q

epithelium of cornea

A

50 um in thickness, 10% of total corneal thickness. 5-6 layers basal, wings and surface cells

51
Q

glycocalyx

A

helps mucin to adhere to corneal epithelial cells.

52
Q

how fast are small corneal abrasions healed?

A

24 hours

53
Q

what attaches epithelium to basement?

A

hemidesmosomes

54
Q

how long does basement take to heal?

A

months

55
Q

what makes up 90% of corneal thickness?

A

bowman’s zone (part of stroma)

56
Q

descemet’s membrane

A

is elastic but consists of collagen

57
Q

to avoid corneal edema how should the lens be fitted?

A

1.50D flatter than the flattest corneal meridian

58
Q

what percent of the stroma is water?

A

78%

59
Q

how much of tears is NaCL?

A

.91%

60
Q

When the eye is open, tear osmolarity is ______________ due to evaporation into the atmosphere.

A

higher

61
Q

When the eyes are closed the tear osmolarity is ___________ and hence a slight corneal thickness is produced

A

lower

62
Q

__________ use when corneal oxygen supply is deficient.

A

anaerobic glycolysis

63
Q

________ used 15% of the glucose in the cornea but produces three times the total corneal energy.

A

aerobic glycolysis

64
Q
  1. During sleep, the oxygen supply to the cornea comes from the
A

palpebral conjunctiva

65
Q
  1. _____________ is the primary source of oxygen in the endothelium
A

aqueous humor

66
Q
  1. At 0% of oxygen level the cornea swells 8% in 3 hours.
A

this is maximum corneal swelling

67
Q
  1. A contact lens worn overnight, under experimental extended wear conditions, show a corneal swelling of about
A

12- 13 %

68
Q
  1. Low transmissibility lenses provide an additional ____________ oxygen from transmission, which in most patients reduces any corneal swelling to less than 1%.
A

3-6 %

69
Q
  1. Medium transmissibility lenses provide oxygen levels of ____________ and eliminate clinical edema in daily wear patients
A

5-8%

70
Q
  1. High transmissibility lenses provide levels of ______________.
A

8 - 16%

71
Q
  1. A practical clinical description of the oxygen tension produced in the pre-corneal film by transmission through a contact lens
A

Equivalent oxygen percentage

72
Q
  1. Which of the following material has the ability to transmit and increase oxygen level in the cornea?
A

silicone

73
Q
  1. It’s termed the permeability of a contact lens material. It is an intrinsic characteristic of the material which is not related to its thickness.
A

Dk value

74
Q

is termed the lens oxygen transmissibility. This measure is inversely proportional to lens thickness.

A

Dk/t

75
Q

Low transmission material cause a corneal swelling of ______.

A

6- 8 %

76
Q

Medium transmission material cause a corneal swelling of ______

A

2-4 %

77
Q

High transmission material cause a corneal swelling of ______.

A

0-2%

78
Q
  1. Developed with optical power with the help of a glass blower. Bi curve lens of 14mm in diameter. Was tried in 6 patients with irregular astigmatism due to scaring.
A

second lens

79
Q

A thin, glass bowl, was worn for 2 hours, the shell stabilized well but had no
power.

A

first lens

80
Q

previous tx of keratoconus was

A

d. Cauterization of cone with silver nitrate, instillation of myotics and application of pressure dressing.

81
Q

Dk/t

A

D= diffusion
k= solubility
t= thickness
minimum is 24

82
Q

F1

A

front surface power (n’-n)/ r1

83
Q

F2

A

back surface power (n-n’)/ r2

84
Q

Fv

A

front vertex power

[F2/1- (t/n)(f2)] + F1

85
Q

Fv’

A

back vertex power

[F1/ 1-(t/n)(F1)] + F2

86
Q

F1 with F2 and Fv’ given

A

(Fv’ - F2) / 1 + (t/n) (Fv’ - F2)

87
Q

n of a keratometer

A

337.5

88
Q

plus lenticular

A

for negative power lenses greater the 5.00 D it minimizes problems associated with thick edges.

89
Q

minus lenticular

A

used to increase edge thickness in plus lenses and minus lenses up to -1.50 D

90
Q

what effect does a spectacle corrected myope have?

A

Bi object appears further away

91
Q

what effect does a spectacle corrected hyperope have?

A

bo, objects appear closer

92
Q

who has more complaints with CLs at near?

A

exo myopes and eso hyperopes

93
Q

Effective power

A

Ep= Fv’/1-d(Fv’)

94
Q

Vergence F

A

(100/l) + Fv’

95
Q

EpV effective power vergence

A

= VerF/ 1-d(VerF)

96
Q

accommodation

A

EpV- Ep

97
Q

how to calculate accommodation with spectacles?

A

1st calculate d

2nd: Ep
3: VeF
4: EpV
5: EpV - Ep

98
Q

How to calculate accommodation in CLs

A

1st: now, lens is at cornea plane so distance of object is l+vd
Ex. L=40cm, VD=12mm so new distance is 41.2cm
2nd: calculate power of the CL at the corneal plane (Epcp) using just the vertex distance
3rd: calculate vergence power leaving CL
4th: calculate the effective power of that vergence at the principle plane
5th: calculate accommodation, where Epv-Ep (Ep, as in what was calculated for spectacles (at the principle plane) using d)

99
Q

mag of spectacle wearing hyperopic aphakic patient

A

50-60%

100
Q

mag of CL wearing hyperope aphakic patient

A

3%

Contact Lens (1 decks)

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