OPT505 Clinical Skills: Complex Lenses Quiz

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.

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.