Optics: Splitting Prism Power

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Questions and Answers

What is the purpose of splitting prism power between a pair of eyes?

To provide balanced prismatic correction for each eye, ensuring optimal vision.

In horizontal prism splitting, if the right eye has +2.00D and the left eye has +2.00D with 4D inward, what is the result of splitting?

RE +2.00D 2D IN and LE +2.00D 2D IN.

What is the formula represented by the Prentice Rule?

P = cF, where P is prismatic power, c is the distance from the center in cm, and F is the lens power.

What happens when you have base down and base up in differential prismatic effects?

You ADD the prismatic powers together. Signup and view all the answers

How do power tolerances affect the acceptance of prescriptions in progressive lenses?

If the checked values are outside the specified power tolerances, the order is rejected. Signup and view all the answers

When given RE +1.00D with 6D down and LE +1.00D, how can this prism defect be split?

By splitting to RE +1.00D 3D UP and LE +1.00D 3D DOWN. Signup and view all the answers

In the context of power tolerances, what would be the result of comparing -3.25 / -1.00 x 90 with -3.37 / -0.75 x 90?

The result would be to reject the order due to a failure in power tolerance. Signup and view all the answers

What is the significance of converting distances between mm and cm in Prentice Rule applications?

It ensures accuracy in prismatic power calculations regardless of the unit system used. Signup and view all the answers

Based on the given measurements, what is the total horizontal displacement for the right eye (RE)?

The total horizontal displacement for the right eye (RE) is 0.75D. Signup and view all the answers

What is the total horizontal displacement for the left eye (LE) as per the provided data?

The total horizontal displacement for the left eye (LE) is 0.60D. Signup and view all the answers

If no prism was ordered and the highest principal power is -4.50D, what tolerance must be calculated?

The tolerance must be calculated based on the maximum principal power being greater than +/-3.37D. Signup and view all the answers

What is the purpose of antireflection coating on lenses?

It reduces reflection, improving lens efficiency, contrast, and visual acuity. Signup and view all the answers

How much unwanted prism is produced in total from both eyes given the final calculations?

The total unwanted prism produced in both eyes is 1.35D. Signup and view all the answers

How is horizontal prism split in optics?

The number is divided while keeping the term 'prism' the same. Signup and view all the answers

What is the individual contribution of the right eye to the total unwanted prism?

The right eye contributes 0.70 ∆ base IN to the total unwanted prism. Signup and view all the answers

What distinguishes phoria from tropia in strabismus?

Phoria is a tendency for misalignment, whereas tropia is a constant misalignment. Signup and view all the answers

In terms of base direction, how does the left eye's prism contribution compare to the right eye's?

The left eye contributes 0.90 ∆ base IN, which is more than the right eye's contribution. Signup and view all the answers

What formula can be used to calculate the induced prism for a lens, and what do its terms represent?

The formula is P = cF, where P is the induced prism, c is the distance in centimeters from the lens optical center to the line of sight, and F is the lens power in diopters. Signup and view all the answers

Explain the Prentice Rule in lens optics.

The Prentice Rule states that the power of prism in diopters equals the distance in centimeters from the optical center multiplied by the lens power in diopters. Signup and view all the answers

What are the prescribed distances for the ordered and measured pupillary distance (PD) based on the example?

The ordered PD is 32 / 32 mm, while the measured PD is 35 / 34 mm. Signup and view all the answers

Define compound myopic astigmatism.

Compound myopic astigmatism occurs when the eye has two different types of myopic prescriptions along two different axes. Signup and view all the answers

What are the common characteristics of the thin lens formula?

The thin lens formula relates the object distance, image distance, and focal length in a simple equation. Signup and view all the answers

What does the lens power represent in diopters (D)?

Lens power represents the degree of convergence or divergence of light by the lens. Signup and view all the answers

What is the effect of chromatic aberration in lenses?

Chromatic aberration causes color separation due to different wavelengths refracting at varied angles. Signup and view all the answers

Describe simple hyperopic astigmatism.

Simple hyperopic astigmatism occurs when one principal meridian is hyperopic and the other is emmetropic. Signup and view all the answers

What are power tolerances in lenses?

Power tolerances refer to the acceptable range of deviation from the prescribed lens power. Signup and view all the answers

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Study Notes

Splitting Prism

Vertical and horizontal prisms can have their power divided between the eyes to manage alignment and vision correction.
For horizontal prism: Split the prism power and retain the original direction (e.g., RE +2.00D 2D IN, LE +2.00D 2D IN).
For vertical prism: Also divide the prism power but adjust the vertical orientation (e.g., RE +1.00D 3D UP, LE +1.00D 3D DOWN).

Prentice Rule

Formula: P = cF
- P represents prismatic power in prism dioptres.
- c is the distance from the optical center in centimeters.
- F stands for the lens power in diopters.
Conversion: To change millimeters to centimeters, divide by 10; to change centimeters to millimeters, multiply by 10.

Differential Prismatic Effect Rules

Combining prism powers follows specific rules:
- Base OUT & Base OUT: ADD
- Base IN & Base IN: ADD
- Base IN & Base OUT: SUBTRACT
- Base UP & Base UP: SUBTRACT
- Base DOWN & Base DOWN: SUBTRACT
- Base DOWN & Base UP: ADD

Power Tolerances

Tolerances must ensure prescriptions align with specifications.
Example: A prescription of -3.25 / -1.00 x 90 compared to check measurements (-3.37 / -0.75 x 90) may fail tolerances.

Progressive Powers Checking

Compare ordered and measured pupillary distances (PD) and central distances (CD) to assess success.
Example: Ordered PD of 32/32 mm and Measured CD of 35/34 mm indicates a potential issue.

Unwanted Prism Calculation

Assess unwanted prism from measurements:
- Use the formula P = cF for both eyes and sum total horizontal differential prismatic effects (DPE).
- Example calculation yields Total Horizontal DPE = 1.35DIN.

Optical Cross

Visual representation to analyze lens prescriptions for astigmatism.
Essential for understanding lens power in different orientations.
Common types of astigmatism include:
- Compound Hyperopic Astigmatism
- Compound Myopic Astigmatism
- Mixed Astigmatism
- Simple Hyperopic Astigmatism

Simple Transposition

Process of converting prescriptions into alternate forms involves:
- Adjusting signs and positions of the cylindrical components.
- Important in correcting and evaluating lens prescriptions accurately.

Lens Power

Total power (F) measured in diopters (D) is determined by both the front (F₁) and back (F₂) surface powers.
Different lens types:
- Bi-convex: Both surfaces outward.
- Bi-concave: Both surfaces inward.
- Plano-convex: One surface flat, one outward.
- Meniscus: One surface concave and one convex.

Types of Strabismus

Phoria refers to a tendency for misalignment, while tropia denotes constant misalignment.
Categories include:
- Hypotropia (eye turned downward)
- Hypertropia (eye turned upward)
- Exotropia (eye turned outward)
- Esotropia (eye turned inward)

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