OPT505 Clinical Skills: Complex Lenses Quiz

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Questions and Answers

What is the first choice when designing lenses for high minus prescriptions that exceed -22.00D?

Reducing lens aperture (correct)

Improving lens coatings

Using low refractive index materials

Increasing the lens diameter

Which type of aberration is NOT typically associated with spherical lenses?

Oblique astigmatism

Lens distortion (correct)

Spherical aberration

Transverse Chromatic Aberration

What does the term 'decentration' primarily refer to in lens design?

The curvature of the lens surface

The refractive index adjustments

The lens thickness variations

The alignment of the optical center (correct)

Which lens design focuses on minimizing tangential errors for better optical performance?

Minimum Tangential Error Form Signup and view all the answers

When considering high refractive index lenses, what is the most crucial factor in lens performance?

The frame size and suitability Signup and view all the answers

What is the correct cylinder measurement for the left eye in the provided prescription?

-3.50 Signup and view all the answers

Which type of prescription is mentioned in the content?

Aphakic Rx Signup and view all the answers

What specific lens type is recommended for minimizing decentration?

1.74 Aspherics or Blended Lentics Signup and view all the answers

Which factor is NOT required for a comprehensive prescription analysis?

Diameter Signup and view all the answers

What is a suggested characteristic of the frame for the prescription provided?

Plastic, small frame with similar PD to box centre distance Signup and view all the answers

What does the near vision effectivity error (NVEE) represent?

The difference between actual vergence and expected vergence from a near object Signup and view all the answers

Which type of lens is expected to have the least vergence change for near objects?

Meniscus lens Signup and view all the answers

In the provided prescription analysis, what is the primary concern associated with high myopia?

Increased lens thickness leading to distortions Signup and view all the answers

What is a recommended material for lenses in high myopia prescriptions?

Aspheric plastic to reduce weight Signup and view all the answers

When analyzing frame options for high myopia, which feature is least desirable?

Large frame size Signup and view all the answers

Which of the following is NOT a consideration listed for the prescription analysis?

Base curve of the lens Signup and view all the answers

For achieving the best cosmetic appearance in high myopia correction, what should be minimized?

Lateral decentration of the lenses Signup and view all the answers

Which prescription feature is common in both provided analyses?

Addition of +3.00D Signup and view all the answers

What is the effect of increasing the lens size from 40mm to 50mm on edge thickness and weight for a -10.00D lens power?

Edge thickness increases by 40% and weight doubles Signup and view all the answers

Which of the following statements is NOT true about aspheric lenses?

They generally have a thicker edge compared to spherical lenses. Signup and view all the answers

What is a characteristic feature of free-form surfacing?

It allows for better control of aberrations. Signup and view all the answers

What defines lenticular designs in lenses?

They feature reduced aperture lenses with flattened edge thickness. Signup and view all the answers

Which statement accurately describes the challenges associated with high plus lenses?

They result in reduced fields of view and generally have thick center substance. Signup and view all the answers

In calculating the field of view for a +5.00D hypermetrope lens, what key variable is defined as 'y'?

It is the distance from the center of rotation of the eye to the lens. Signup and view all the answers

What happens to the edge thickness of a -10.00D lens made from CR39 glass compared to a 1.9 glass lens?

The edge thickness in CR39 is typically greater than in 1.9 glass. Signup and view all the answers

Which mathematics expression is used to determine the tangents in the calculation of field of view based on given 'y' values?

tanθ = y(40-F) Signup and view all the answers

What is the primary reason for suggesting a smaller frame to complex Rx patients?

To keep decentration to a minimum Signup and view all the answers

What is the result of the deforming a conicoid surface in higher-order aspherics?

A polynomial surface Signup and view all the answers

What correction is typically needed for an aphakic eye previously deemed emmetropic?

+9.00D to +14.00D Signup and view all the answers

What does decentration refer to in the context of lens fitting?

The distance between the optical center and the pupil Signup and view all the answers

In the calculation of the apparent field, what is the value of $tanθ'$ for a lens with a 32.5 mm distance and a distance factor of 40?

1.3 Signup and view all the answers

Why might a congenital cataract extraction be left aphakic until the eye is fully developed?

To avoid surgery complications Signup and view all the answers

What is a significant effect of using higher-order aspherics over traditional lenses?

Reduction in the jack-in-the-box effect Signup and view all the answers

What is the primary disadvantage of aphakia when the eye is left without a replacement lens?

Loss of near vision accommodation Signup and view all the answers

What happens if the frame BVD does not match the trial frame BVD?

The Rx may need to be compensated. Signup and view all the answers

In the formula for effectivity calculation, what does 'd' represent?

The change in vertex distance. Signup and view all the answers

How is the new prescription (Rx) calculated if the vertex distance increases?

Add the change in distance to the original power. Signup and view all the answers

What is the result of not amending the Rx when moving to a new BVD?

The Rx will be overpowered. Signup and view all the answers

Why are lenses of the same power not interchangeable for near vision?

Due to variations in lens form and thickness. Signup and view all the answers

What does the Back Vertex Power (BVP) refer to in distance vision?

The vergence of light from the back surface of a lens. Signup and view all the answers

What is a possible consequence when different lens forms are used for the same Rx in near vision?

The resultant Rx will differ from each form used. Signup and view all the answers

In the given example, what is the front curve of a +10.00D lens made with a -3.00D base curve when used for near vision?

+12.06D Signup and view all the answers

Study Notes

OPT505 Clinical Skills and Refractive Management: Complex Lenses

The course code is OPT505
The lecturer is Claire Wright FBDO
The one-time code is NS-HU-FJ

Core Competencies

Ability to advise, order and dispense suitable optical correction considering durability, comfort, appearance, age and lifestyle
Ability to adjust spectacle frames to optimise physical and optical performance
Ability to measure and verify optical appliances adhering to relevant standards

Learning Outcomes

Recap lens design
Understand dispensing options for high minus and high plus lenses
Understand lenses used for near vision
Define decentration
Understand vertex distance

Lens Form and Optical Performance

Visual comparisons of different diopter lenses (+4.00D and -4.00D) are presented
Lens form affects optical performance, shown through visual examples

Aberrations

Material and lens form can cause aberrations.
Types of lens form aberration include: spherical aberration, coma, oblique astigmatism, curvature and distortion

Spectacle Lens Design

Ideal lenses produce point images of point objects at the far-point sphere
Key designs include Point Focal, Percival Form and Minimum Tangential Error Form

High Minus Lenses

No significant optical challenge until the prescription exceeds -22.00D
Lenses typically have thick edges
Reducing lens aperture (smaller frames) is a common solution
Increasing refractive index is a preferred option

High Refractive Index

Increasing refractive index is an option if a suitable frame is available.
Increased lens size may lead to a double weight and 40% increased thickness increase
Lenses with higher refractive index have thinner edges than similar power lenses in lower refractive index materials.

Aspheric Lenses

Lenses are non-spherical and non-cylindrical
They eliminate oblique astigmatism and reduce distortion
Lenses tend to be thinner, lighter and result in less magnification

Free-form Surfacing

Allow more complex designs
Powers are digitally mapped across the lens
Control of aberrations is improved
Designs are more variable and offer thinner lenses with good optics
The front and back surfaces can be shared in bi-concave or convex designs
Current designs are limited to approximately +8.00DS

Lenticular Designs

Reduced aperture lenses
Edge thickness is reduced or flattened (think of a fried egg shape, inverted for minus lenses)

Lenticular Lenses

Visual representation of lenticular lens types are shown

High Plus Lenses

Spherical surface use results in an optical challenge when the prescription exceeds +7.00D
Lenses have thick centers
Reduced field of view
Increasing refractive index is less effective

Ring Scotoma

The angle subtended by the effective diameter of the lens at the point conjugate with the centre of rotation is called the real field of view

Real and Apparent Field of View Calculation

Calculations are given for calculating the Real and Apparent fields of view, specifically a +5.00D Hypermetrope wearing a lens with 65mm diameter at a distance of 25mm from the centre of rotation of the eye

Higher-order Aspherics

Obtained by deforming a conicoid with a polynomial surface.
Surface power reduces from the centre to the edge
Main benefit is the absence of ring scotoma
Providing a smaller field and requiring more head movement

Aphakia (Px is Aphakic)

Eyes develop cataract
Crystalline lens may be surgically removed.
A new plastic replacement lens (“pseudo-phakic”) is implanted.
Power is calculated for 'emmetropic' vision
No accommodation, so add is needed to address working distance

Aphakia (Different Scenarios)

Before the Pseudo-phakic lens, the eye may have been left without replacement ("aphakic")
This can lead to a distance prescription ranging from +9.00D to +14.00D where previously there may have been no prescription.

Aphakia (Prescription Examples)

Sample prescriptions and data are presented including Sph, Cyl, Axis, Base, and ADD values.

Aphakia (Lens Methods)

Before aspherics, lenticular lenses offered a method for reducing lens weight/thickness

Complex Rx and Frame Choice

Smaller frames are advisable to manage weight, reduce thickness, minimise oblique astigmatism, and keep lens decentration to a minimum.

Decentration

The amount the lens needs to move to ensure the optical centre is in front of the patient's pupil.

Vertex Distance

Distance from the visual point of a lens to the corneal apex
British standards recommend it when power exceeds +/– 5.00D
Measurements can be taken using a ruler or special calliper
Frame BVD should match trial frame BVD for accurate prescription.

Vertex Distance rules

Rules for how to understand the affect of BVD measurements for lenses with high diopters.

Effectivity Calculation

Calculations are presented, including a formula and examples showing how to work out new prescriptions given changes in vertex distance

Lens Form and Near Vision

Near Vision Effectivity Error leads to not all lens forms being interchangeable when assessing near vision and requires BVP.

Near Vision Effectivity Error (NVEE)

Same power lenses can be made with different forms
Different forms provide various results for near vision because the light source used for near vision is a finite point.
Distance vision forms may differ when assessing for near vision.

NVEE (Example)

Detailed example of a +10.00D lens and its NVEE measurement calculations

NVEE (General Points)

Strong positive curved lenses provide less vergence change than bi-convex or plano-convex forms for near vision.
This is significant to single vision assessment due to multifocal segments.

Prescription Analysis

Example prescriptions and their analysis are presented.
Analysis of the prescriptions given covers different situations and various forms of consideration, namely; whether the Rx meets British Standards, Rx type, lens options, frame options and required measurements.

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Description

Test your knowledge on complex lenses and refractive management in the OPT505 course. This quiz covers lens design, dispensing options for various lens types, and the impact of lens form on optical performance. Assess your understanding of critical competencies related to optical correction and aberrations.