Contact Lens Fitting and Assessment
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Questions and Answers

What is the ideal condition for fluorescein pooling under a lens?

  • Fluorescein uniformly distributed across the lens
  • Fluorescein pooling under the center of the lens (correct)
  • Fluorescein accumulation at the edge of the lens
  • Complete absence of fluorescein under the lens

What is indicated by a lens that is described as having 'low riding' lid interaction?

  • The lens is positioned too low in the interpalpebral space (correct)
  • The lens is centered perfectly on the cornea
  • The lens is positioned high above the upper lid
  • The lens is adhered to the upper eyelid

During a dynamic fit assessment, what does 'quantifying movement in mm' refer to?

  • The amount of lens shift during a blink (correct)
  • The degree of lens rotation
  • The thickness of the lens material
  • The diameter of the lens

Which type of lens movement is most likely to occur with very flat lenses on a toric cornea?

<p>Arcuate movement (B)</p> Signup and view all the answers

What factor significantly affects the centration of a lens in relation to the cornea?

<p>Lid geometry (C)</p> Signup and view all the answers

What does a narrow, even band of edge clearance indicate in lens fitting?

<p>Good alignment and fit (A)</p> Signup and view all the answers

What pattern is observed when using fluorescein to assess static fit in the mid periphery?

<p>Touch, pooling, or alignment (A)</p> Signup and view all the answers

Why does a steep fit lens retain a similar fluorescein pattern for a longer duration?

<p>It maintains a stable fit with minimal movement (C)</p> Signup and view all the answers

What is the best course of action when unsure about the alignment of a lens fit?

<p>Use a steeper lens to confirm alignment (A)</p> Signup and view all the answers

Which condition requires the consideration of a toric lens?

<p>Corneal astigmatism greater than 2.00D (B)</p> Signup and view all the answers

What problematic issue can arise from excessive edge clearance in the steeper meridian?

<p>Unwanted lid interaction with the lens (C)</p> Signup and view all the answers

What occurs when the lens fits poorly on with-the-rule corneas?

<p>Lens rocks along the steeper meridian (B)</p> Signup and view all the answers

How can lens flexure become an issue with toric corneas?

<p>It decreases comfort for the wearer (C)</p> Signup and view all the answers

Which fitting option minimizes edge clearance in the steeper meridian?

<p>Reducing the total diameter of the lens (A)</p> Signup and view all the answers

What is a potential outcome of using a spherical center with a toric periphery design?

<p>Effective when the peripheral cornea is more astigmatic (B)</p> Signup and view all the answers

What effect does narrowing the edge lift have when using aspheric RGP lenses?

<p>Minimizes edge clearance in the steeper meridian (D)</p> Signup and view all the answers

What effect does a steep lens with poor edge clearance have on fluorescein penetration?

<p>Fluorescein may not be able to pass under the lens. (A)</p> Signup and view all the answers

What could be a reason for misinterpretation of fluorescein patterns?

<p>Assessing a decentred lens. (C)</p> Signup and view all the answers

What is the typical measurement of vertical movement in a fluorescein pattern?

<p>7.5 mm (B)</p> Signup and view all the answers

What phenomenon occurs in a static fit when a steep RGP lens is used?

<p>Negative staining of the epithelium. (B)</p> Signup and view all the answers

What constitutes the typical characteristics of a 'steep' fluorescein pattern?

<p>Central touch with very narrow edge clearance. (D)</p> Signup and view all the answers

During which type of fit assessment is lid interaction primarily evaluated?

<p>Dynamic fit assessment. (B)</p> Signup and view all the answers

To amend a lens fit, which data should be combined with observations?

<p>Dynamic and static fit observations. (B)</p> Signup and view all the answers

In a fluorescein pattern, what does 'dimple veiling' indicate?

<p>Interaction between the lens and cornea. (B)</p> Signup and view all the answers

What is a key characteristic of a Bicurve lens design?

<p>Features a sharp transition between central and peripheral curves (A)</p> Signup and view all the answers

Which factors are primarily responsible for controlling the design of RGP lenses?

<p>Center of gravity and edge shape (B)</p> Signup and view all the answers

What advantage does a high refractive index material provide in lens design?

<p>Allows for a thinner lens while maintaining power (C)</p> Signup and view all the answers

In the context of RGP lens fitting, what does 'edge clearance' refer to?

<p>Distance between lens edge and eye surface (C)</p> Signup and view all the answers

Which type of lens design consists of a central radius and three peripheral curves?

<p>Tricurve (A)</p> Signup and view all the answers

What is the primary purpose of using prism ballast in RGP lens design?

<p>To ensure proper lens centration (C)</p> Signup and view all the answers

What does a Tricurve lens typically feature in comparison to a Bicurve lens?

<p>Two peripheral curves instead of one (A)</p> Signup and view all the answers

How does capillary attraction influence RGP lens fit?

<p>Good alignment results in enhanced stability (B)</p> Signup and view all the answers

In RGP lens fitting, what signifies an 'alignment fit'?

<p>Smooth vertical movement with blink and no limbal overlap (A)</p> Signup and view all the answers

What aspect of lens design can impact the comfort and removal of RGP lenses?

<p>The smoothness of the edge shape (A)</p> Signup and view all the answers

What does an increase in aqueous component do to the tear film during RGP lens wear?

<p>Decreases centration ability (A)</p> Signup and view all the answers

Which lens design results in minimized thickness for high power prescriptions?

<p>Multicurve (D)</p> Signup and view all the answers

What is the effect of using a steeper lens design on a contact lens fit?

<p>Creates negative pressure for alignment (C)</p> Signup and view all the answers

What is indicated by a fixed power in lens fitting?

<p>Limited adaptability to different corneal shapes (B)</p> Signup and view all the answers

Flashcards

Centration

The position of the center of the lens compared to the center of the cornea.

Edge clearance

A narrow, even band of clearance around the lens edge, typically 0.5mm wide.

Lens movement on blink

The way the lens moves on the eye during blinking, including direction, speed, and type of movement.

Fluorescein pattern

The pattern of fluorescein pooling or clearance under the contact lens, indicating the fit.

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Mid peripheral alignment

A type of lens fit where the lens edge touches the cornea evenly, indicating a good fit.

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Dynamic fit assessment

An assessment of how the contact lens moves on the eye during eye movements and blinks.

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Apical clearance

The fit of a contact lens where the central area is slightly higher than the cornea.

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Steep fit

The fit of a contact lens that's slightly too steep, resulting in pooling of fluorescein under the lens.

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Single curve lens

The design where the lens has a single curve.

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Bicurve (C2) lens

The design where the lens has a central curve and one flatter peripheral curve. It is characterized by a sharp transition between the curves.

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Tricurve (C3) lens

The most common RGP lens design, it has a central curve and two flatter peripheral curves. The final peripheral curve is much flatter than the first.

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Center of gravity

The center of mass of the lens plays a role in its stability on the eye. It is affected by the lens power and the lens material.

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Frictional forces

This force influences lens stability, and is affected by the tear film viscosity.

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Capillary attraction

This force helps hold the lens in place. Good alignment results in good capillary attraction leading to stability.

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Specific gravity

This refers to the lens' density compared to the tear film. A lens that is denser than the tear film may be more prone to dropping.

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Thickness and lenticulation

Refers to the thickness of the lens, thinner lenses are more comfortable, thinner lenses can also be lenticulated.

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Refractive index of materials

Refers to the material the lens is made of, and the overall lens design. This affects the lens weight and wearer comfort

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Edge clearance (EC)

The gap between the back surface of the lens and the cornea, measured during fluorescein fitting. EC is observed.

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Edge lift (EL)

A design characteristic of the lens. Radial edge lift is measured along the radius of the lens, while axial edge lift is measured along the axis of the lens. Rel refers to the flattening of the lens.

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Edge shape

A design feature of the RGP lens that can impact comfort, removal, and overall alignment.

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Alignment fit

This refers to the overall fit and positioning of the lens on the eye. Good centration means the lens is centered over the pupil and there is no limbal overlap.

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The RGP Fit

The overall performance of the lens on the eye, including comfort, centration, tear exchange, and visual acuity.

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Recap

The RGP lens design is a complex area. Lens fit involves careful consideration of multiple factors that influence how a lens functions on the eye.

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Fluorescein dye movement under a lens

The ability of fluorescein dye to pass under the edge of a contact lens is influenced by the lens's steepness and the clearance between the lens edge and the cornea. Steeper lenses with poor edge clearance make it more difficult for fluorescein to pass underneath.

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Misinterpreting Fluorescein Fit

A flat, decentered lens can appear similar to a steep lens during fluorescein staining. To avoid misinterpretations, ensure the lens is properly centered before evaluating the fluorescein pattern.

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Steep Lens Fluorescein Pattern

A pattern of central pooling of fluorescein, with very narrow edge clearance, indicates a steep lens fit.

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Fluorescein pattern recording

Recording fluorescein patterns during contact lens examinations is crucial for monitoring lens fit and identifying potential issues. Documentation should include detailed drawings and labels of the observed patterns.

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Static contact lens fit assessment

Static fit evaluation involves examining the fluorescein pattern after the lens has been removed. The lens's impression on the corneal epithelium can reveal the extent of the fit and any potential issues.

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Dynamic contact lens fit assessment

Dynamic fit assessment involves analyzing the lens movement, centration, lid interaction, and edge position while the contact lens is worn.

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Fluorescein pattern analysis

The center, mid-periphery, and periphery of the fluorescein pattern provide information about various aspects of the lens fit. Evaluating each area helps determine the overall fit characteristics.

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Fit Conclusion and Adjustments

By combining observations from both the dynamic and static fit assessments, a comprehensive conclusion about the contact lens fit can be reached. This information guides any necessary adjustments to the lens specifications for optimal comfort and lens wear.

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Dynamic fit

A type of fit assessment that evaluates the lens's movement and interaction with the eyelids during blinking.

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Static fit

A type of fit assessment that evaluates the lens's position and alignment when the eye is still.

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Edge clearance in the steeper meridian

Refers to the amount of space between the lens and the cornea in the steepest meridian of a toric cornea.

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Corneal moulding

The process of bending a lens to shape the cornea.

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Toric RGP

A rigid gas permeable lens with a toric (curved) surface designed to fit toric (astigmatic) corneas.

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Spherical center, toric periphery RGP

A type of toric lens with a spherical center and toric periphery, used when the astigmatism is mainly in the peripheral cornea.

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Lens flexure

Refers to the lens's tendency to flex or bend under the pressure of the eyelid.

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Lens rocking

The movement of the lens along the steeper meridian of a toric cornea, leading to instability and poor centration.

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Study Notes

RGP Lens Design and Fitting

  • RGP stands for rigid gas permeable lenses.
  • The presentation discusses the impact of lens design on fitting.
  • Factors influencing RGP fitting include design principles, fitting sets vs empirical fitting, and forces controlling lens design.

Principles of RGP Design

  • Single curve: First lens design (1947), PMMA material, fit 0.3mm flatter than the flattest K reading. Limited success due to physiological issues, lenses didn't fit properly. The cornea isn't spherical, increasing flattening towards the limbus. Improvements by adding peripheral curves to the lens.
  • Bicurve (C2): Consists of a central radius and one flatter peripheral curve. Example: 7.80/8.60/-3.00D. A sharp transition between curves.
  • Tricurve (C3): Central radius and flatter peripheral curves. Example: 7.70 / 8.50 / 9.65 /-3.00D. Modern lenses feature a final peripheral curve flatter than the first peripheral radius.
  • Tetracurve/Multicurve (C4): Combination of multiple curves
  • Aspheric: Advanced designs
  • Constant Axial Edge Lift (CAEL): A specific design characteristic

Fitting Sets vs Empirical Fitting

  • Fitting Sets: Fitted on the spot in one session, limited BOZR (0.10), usually fixed power and base curve.
  • Empirical Fitting: Orders are made to suit specific patient needs, more than one session, various BOZRs (0.05), and various TDS, adjustable power.

Forces Controlling Lens Design

  • Center of gravity: Affects lens centration.
  • Frictional forces: Viscosity of tear film, thinning or increase in aqueous component, reduces centration ability.
  • Capillary attraction: Good alignment leads to capillary attraction/stability. Flat lenses have reduced capillary attraction. Steep lenses achieve a negative pressure (suction effect) by creating more capillary attraction. Tear meniscus helps lens centration, larger meniscus aids better centration.
  • Specific gravity: Lenses' different densities can affect fitting and placement, gravity can pull lenses down
  • Thickness and lenticulation: Adjusting thickness controls the mass and profile, lenticulation controls zone diameter.
  • Refractive index of materials: Higher index materials result in thinner lenses. Example materials include PMMA (1.49), CAB (1.47), and Silicone (1.43).
  • Edge shape: Smooth and well-finished edge helps in comfort and removal.

RGP Lens Design

  • Edge clearance (EC): Gap between the cornea and the back surface of the peripheral curve (observed during fluorescein fit).
  • Radial edge lift (REL): Measured along radius.
  • Axial edge lift (AEL): Measured along axis of lens.

Static and Dynamic Fit Assessment

  • Static fit (Fluorescein patterns): Assess with fluorescein and cobalt blue or Burton lamp; central, mid-periphery, periphery are assessed, checking for pooling or other issues.
  • Dynamic fit: assesses centration, lid interaction, movement on blink, and edge position.

Toric Corneas

  • Toric corneas have varying curvature in different meridians.
  • Considerations include comfort, edge clearance, centration, type of contact lens. Options include altering BOZR, adjusting TD, using aspheric and toric lens design, changing the type of lens.

Fit Conclusion

  • Important to carefully evaluate the fluorescein fit, deciding if the lens is flat, aligned, or steep
  • Recommendations on how to amend the fitting or select new lens specifications.

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RGP Lens Design Impact on Fit (OPT506) 2024-25 PDF

Description

This quiz covers essential concepts related to contact lens fitting, including fluorescein pooling, lens movement, and the impact of corneal shape on lens centration. Ideal for those studying optometry and lens assessment, it addresses common challenges and considerations when fitting lenses to different corneal types.

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