Keratometry PPO2

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What is the purpose of a keratometer?

To measure the refractive index of the cornea

To determine the axial length of the eye

To directly measure the dioptric power of the cornea

To convert the radius of curvature to the dioptric power of the cornea (correct)

What is the range within which a keratometer can measure corneal curvature without the need for auxiliary lenses?

44.00D to 60.00D

36.00D to 52.00D (correct)

30.00D to 56.00D

20.00D to 45.00D

What is a limitation of keratometry mentioned in the text?

It can only measure corneal curvature in a small region of the cornea (correct)

It ignores spherical aberrations

It does not provide accurate measurements for eye axial length

It measures the cornea only at one particular radius

What error can result from incorrect focusing while using a keratometer?

Misalignment errors Signup and view all the answers

How should the procedure for using a keratometer begin?

Disinfect the instrument and adjust the patient's position Signup and view all the answers

What should be done to the principal meridians while using a keratometer?

Make them parallel Signup and view all the answers

What is a consequence of ignoring spherical aberrations in keratometry?

Inaccurate measurements in certain cases Signup and view all the answers

What should be overlapped with the horizontal meridian wheel in keratometry procedures?

"Plus" signs Signup and view all the answers

What should be aligned with the vertical meridian wheel?

Minus signs Signup and view all the answers

When observing corneal integrity, what should be evaluated?

The mires Signup and view all the answers

What is the recommended action if irregular astigmatism is present?

Perform the horizontal meridian first Signup and view all the answers

Which type of astigmatism is characterized by principal meridians being perpendicular?

Regular Astigmatism Signup and view all the answers

In With-the-rule (WTR) Astigmatism, where is more power located?

Vertical meridian Signup and view all the answers

How should one proceed after evaluating the right eye (OD)?

Proceed with observing the left eye (OS) Signup and view all the answers

What is recorded with an amount of corneal astigmatism in diopters and an axis of -1.13x180?

-1.13x180 Signup and view all the answers

In which type of astigmatism do principal meridians not form a 90-degree angle?

'Oblique' Astigmatism Signup and view all the answers

What should you do if you are unable to locate keratometric mires?

Ensure the patient's forehead is secure against the headrest Signup and view all the answers

What can cause transient mire focus issues?

Patient's eyelid drooping Signup and view all the answers

How can extended ranges be achieved in keratometry?

Using loose lenses over the opening of the keratometer barrel Signup and view all the answers

What should be done if only 1 plus sign is visible during measurement?

Have the patient open wide Signup and view all the answers

When might a patient have irregular astigmatism affecting H&V mires measurement?

When fellow eye is not occluded Signup and view all the answers

What action should be taken if only 1 minus sign is visible during measurement?

Ensure the occluder is not obstructing view Signup and view all the answers

What are the corrective factors for increasing and decreasing diopter range in keratometry?

+9.00D and -6.00D respectively Signup and view all the answers

For K readings above 52.00D, what should be added to extend the range?

+9.00D with a +1.25D lens Signup and view all the answers

What is the correct true K value when the K reading is 49.00D and a +1.25D lens is added in front of the barrel?

58.00D Signup and view all the answers

What is the formula used to calculate the true K value after adding a corrective lens in front of the barrel?

$ ext{K value} imes ext{Correction Factor}$ Signup and view all the answers

How should mires be recorded in cases of irregular and distorted shapes?

Egg shaped Signup and view all the answers

What is the expected angular separation between the 2 principal meridians in astigmatism?

90 degrees Signup and view all the answers

For astigmatism, what is the average range for K readings according to the text?

43.00 to 44.00D Signup and view all the answers

When adding a -1.00D lens in front of the barrel, what is the new K drum reading if the initial K reading is 38.00D?

39.00D Signup and view all the answers

What is Javal's Rule primarily focused on determining?

Relationship between corneal astigmatism and refractive astigmatism Signup and view all the answers

In recording corneal cylinder (CC) data, what are the steps used for each line in the dial in diopters?

$0.25$ diopters Signup and view all the answers

What will be the refractive astigmatism when the corneal curvature is -2.00 @ 090 using Javal’s rule?

-2.50 x 090 Signup and view all the answers

If the total refractive astigmatism is -1.00 x 180, what will be the result after applying the Simplified form of Javal’s Rule?

-1.50 x 180 Signup and view all the answers

For a corneal curvature of 43.00 @ 180 and 46.00 @ 090, what is the total refractive astigmatism using Javal’s rule?

-3.75 @ 090 Signup and view all the answers

When the corneal curvature is -0.50 @ 090, what will be the predicted total refractive astigmatism using the Simplified form of Javal’s Rule?

-1.00 @ 090 Signup and view all the answers

For a corneal curvature of -1.00 @ 090 and applying Javal’s rule, what would be the total refractive astigmatism?

-1.25 @ 090 Signup and view all the answers

If the corneal curvature is -2.00 @ 180, what will be the predicted total refractive astigmatism using the Simplified form of Javal’s Rule?

-1.50 @ 180 Signup and view all the answers

What will be the refractive astigmatism when the corneal curvature is -2.00 @ 090 according to Grosvenor et al?

-2.5 x 090 Signup and view all the answers

When you have a corneal curvature of -1.50 @ 180 and apply Javal's rule, what is the total refractive astigmatism?

-1.75 @ 180 Signup and view all the answers