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Opto Prac 2 > Keratometry > Flashcards

Keratometry Flashcards

1
Q

is an instrument used to measure the front surface curvature of the cornea

A

Keratometer

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2
Q

the approximate radius of cornea

A

3 mm

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3
Q

Informations that keratometer provide:

A

The radii of the curvature of the cornea
The degree of corneal astigmatism
Presence of corneal distortion
Direction of the principal meridian of the eye

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4
Q

Keratometry is essential in the

A

fitting of CL, evaluating patients with keratoconus, and IOP implant surgery

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5
Q

Refractive index of cornea

A

1.3375

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6
Q

Parts of keratometer

A
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7
Q

One position keratometer: measures 2 meridian at the same time

A

Bausch and Lomb Keratometer

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8
Q

Two position keratometer: measures one meridian at one time

A

Javal-Schiotz Keratometer

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9
Q

Note: difference between one position keratometer and two position is that Bausch and Lomb Ker has circles while Javal-Schiotz has rectangles and stairs

A
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10
Q

When the weakest corneal meridian is at near 180

A

WTR

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11
Q

When the weakest corneal meridian is at 90

A

ATR

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12
Q

If the principal meridian are between 30 and 60 degrees or between 120 and 150 degrees

A

Oblique

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13
Q

It determines the relationship between corneal and refractive astigmatism

A

Javal’s Rule

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14
Q

Types of astigmatism

A

Simple astigmatism
Compound astigmatism
Mixed Astigmatism
Irregular Astigmatism
Oblique Astigmatism

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15
Q

one focal line falls on the retina, the other meridian may fall in front or behind the retina

A

Simple astigmatism

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16
Q

Both focal points lie either in front or behind the retina

A

Compound Astigmatism

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17
Q

one focal point lies behind the retina, the other focal point lies in front of the retina

A

Mixed Astigmatism

18
Q

the flat and steep axes are not at right angles

A

Irregular Astigmatism

19
Q

occurs along the 45 degrees or 135 degrees meridians

A

Oblique Astigmatism

20
Q

WTR Astigmatism has ___ steepest curvature

A

Vertical

21
Q

ATR Astigmatism has ______ steepest curvature

A

Horizontal

22
Q

Manual keratometry is preferred in patients:

A

with poor fixation
Corneal abnormalities
distorted mires
when cornea is highly toric
cornea is dry

23
Q

Preferred in px with readings less than 40 D or greater than 46 D

A

Corneal topography

24
Q

used to verify no corneal abnormalities and astigmatism is regular

A

Topography

25
Q

Determines the axis and magnitude of corneal astigmatism

A

Toric calculator

26
Q

A degenerative corneal disease resulting in a generalized thinning and cone-shaped protrusion of the central cornea

A

Keratoconus

27
Q

Mild keratoconus

A

45D

28
Q

Moderate keratoconus

A

45-52D

29
Q

Advanced keratoconus

A

52D

30
Q

Severe keratoconus

A

62D

31
Q

Vertical misalignment of plus signs indicates

A

Astigmatism

32
Q

Bausch and Lomb contains how many prisms

A

2 prisms

33
Q

Procedure in using kera

A
34
Q

Determined by retinoscopy or subjective refraction

A

Refractive Astigmatism

35
Q

Due to the toricity of the back surface of the cornea and tilting of the crystalline lens with respect to the optic axis

A

Internal astigmatism

36
Q

Correct axis alignment when the horizontal lines of the plus appear

A

Continuous

37
Q

Corneal abnormalities

A

• Irregular contour or shape of cornea
•Inadequate or excessive tear film
•Ointment on the cornea
•Eyelid interference

38
Q

first to use the doubling principle

A

Helmholtz

39
Q

What did Helmholtz used

A

two small glass plates with plane parallel faces

40
Q

Javal Schiotz used what type of doubling prism

A

Wollaston prism as a doubling device.

41
Q

Chamber-inskeep ophthalmometer used what doubling prism

A

Biprism

42
Q

Clinical Use of Keratometric Information

A

■ CL fitting, choice of trial lens
■ Monitoring corneal shape
■ Verification of contact lens parameters
■ Measure corneal power

Opto Prac 2 (3 decks)

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