Rigid Gas Permeable Lenses Overview

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Questions and Answers

What is the typical size range of epithelial microcysts?

10-50 um (correct)

100-200 um

1-10 um

50-100 um

Which condition can lead to the formation of epithelial microcysts?

Increased humidity

Increased visual acuity

Chronic hypoxia (correct)

Ocular surface injury

What is the typical appearance of new endothelial bedewing?

Brown and irregular

Whitish and round (correct)

Yellow and elongated

Transparent and symmetrical

What immediate action should be taken if a patient experiences intolerance to contact lens wear due to endothelial bedewing?

Reduce wearing time or cease wear Signup and view all the answers

What is a distinguishing feature of endothelial blebs compared to corneal guttata?

Irregular shaped black zone Signup and view all the answers

What is the first step in the RGP fitting process?

General eye examination Signup and view all the answers

Which parameter should always be adjusted if there is excessive movement in lens fitting?

Lens diameter Signup and view all the answers

What should be monitored for during the preliminary fitting assessment?

K-reading and pupil size Signup and view all the answers

What is the maximum wear time for a new contact lens wearer on the first day?

3 hours Signup and view all the answers

Which of the following is NOT part of the lens care and maintenance instructions?

Use tap water for rinsing Signup and view all the answers

What happens if the corneal cylinder is slightly smaller than the ocular cylinder?

A thinner lens is used with more flexible material. Signup and view all the answers

What effect does eyelid force have on RGP lenses?

Lid opening lifts the lens during blinking. Signup and view all the answers

Which factor is considered helpful in stabilizing a lens during a blink?

Edge clearance of the lens. Signup and view all the answers

How does wider edge surface tension affect RGP lenses?

It allows for better surface tension. Signup and view all the answers

What is the primary challenge of using spherical lenses when residual physiological astigmatism is high?

They can compromise vision. Signup and view all the answers

What is a potential negative effect of lens rotation on vision?

Degraded vision quality. Signup and view all the answers

Why is a significant astigmatism challenging when fitting lenses?

It often results in visual distortion. Signup and view all the answers

What is a disadvantage of using a spherical lens to correct astigmatism?

They may not effectively address lens rotation issues. Signup and view all the answers

What is the primary purpose of using cosmetic contact lenses?

To enhance or alter the appearance of a normal eye. Signup and view all the answers

Which design type of contact lens has a central curve that is relatively flatter than the peripheral corneal curve?

Reverse Geometry Design Signup and view all the answers

What adjustment should be made if there is inadequate vault at the limbal zone during fitting?

Increase the chord diameter or steepen curves. Signup and view all the answers

Which type of contact lens is specifically used to improve the appearance and help correct vision of a disfigured eye?

Prosthetic CL Signup and view all the answers

What is a characteristic of the zonal specific scleral lens?

It vaults the entire cornea. Signup and view all the answers

What is the goal for central vaulting during corneal zone fitting?

Aim for 100 - 400 um. Signup and view all the answers

Which type of tint is used in contact lenses to improve visibility but does not change eye color?

Visibility tints Signup and view all the answers

What is a potential issue when using enhancement tints in certain occupations?

They can lead to color deficiency issues. Signup and view all the answers

What is the primary consequence of overdenture syndrome on the cornea?

Decreased oxygen supply leading to edema Signup and view all the answers

What is the typical recovery time for overdenture syndrome after ceasing lens wear?

Within 24 hours Signup and view all the answers

What should be done first in case of tearing and moderate-to-severe irritation or discomfort with contact lenses?

Remove, clean, rinse, and reinsert the lenses. Signup and view all the answers

Which factor increases the risk of developing corneal warpage syndrome?

Long-term wear of poorly fitted RGP lenses Signup and view all the answers

During fitting assessment, what is assessed with white light to ensure proper lens centration?

Whether the pupil is within the Back Optical Zone Diameter (BOZD). Signup and view all the answers

Which of the following symptoms is NOT typically associated with overdenture syndrome?

Improved vision Signup and view all the answers

What is a key management strategy for corneal warpage syndrome?

Cease contact lens wear Signup and view all the answers

What does a normal lens movement indicate when checking a patient's blink?

The lens drops smoothly and vertically to its original position. Signup and view all the answers

What is the grading system for endothelial polymegethism based on cell size irregularities?

0 - 4 Signup and view all the answers

If there is excessive lens tearing, what action should be taken regarding its settling time?

Allow 10 minutes or longer, depending on the tearing. Signup and view all the answers

Which interaction type is least likely to produce corneal edema when assessing lid-lens relationships?

Inter-palpebral interaction. Signup and view all the answers

What might indicate a potential issue if contemplating extended wear lenses?

Increased age Signup and view all the answers

What is the suggested action to take until abrasions are treated in overdenture syndrome?

Cease lens wear Signup and view all the answers

What should be observed when assessing the fluorescein pattern during fitting assessment?

Edge clearance on the top of the RGP lens. Signup and view all the answers

What indicates a flat lens during lens movement assessment?

Quick movement with apical rotation. Signup and view all the answers

What should be done if the lens is decentered during the fitting assessment?

Move it back to center using the aid of the lids. Signup and view all the answers

Study Notes

Rigid Gas Permeable Lenses (RGP)

RGP lenses are made of silicone, fluorine, and PMMA (Fluorosilicone acrylate) or silicone acrylate
These materials improve oxygen permeability and wettability, which improves comfort and reduces complications like keratitis
Larger diameter lenses lead to less movement, and better optical quality than scleral contact lenses (SCL)
RGP lenses may stain more easily than PMMA
RGP initial discomfort is common initially due to a transition from PMMA
Indications for wearing RGP include increased corneal astigmatism, distorted or irregular corneas, or corneal scarring. RGPs are less suitable for patients with eyelid problems that do not cover the superior and inferior limbus. Other conditions for RGP use may require assessment of the individual situation.
Parameters such as Total Diameter (TD), and Peripheral curves (PC) can affect the lens fit and comfort
Aspheric lens design may enhance tear flow and reduce lens sensation
Toric lenses provide astigmatism correction, and can be used in conjunction with Spherical RGP lenses
Radial (normal to lens edge) and Axial (parallel to primary axis of lens) parameters are used to compare the fitting of the lens against the corneal topography
Edge lift is a critical consideration: Steeper BOZR results in greater edge lift

Fitting Philosophies & Assessment of Fitting

Fitting goal: good alignment and slightly flatter than the central touch
Assess pupil coverage, comfort and vision
Central touch assessment of lens fitting
Edge clearance, if too steep, may cause excess tear pooling and/or lens displacement; conversely, a flat fit may lead to central pooling
Lid & Lens movement during blinking is evaluated
Fitting process (wearing): clean and insert to locate any issues or difficulties. Check for trapped bubbles
Check lens centration (using white light) and effect of lid interaction after checking blinking and movement

RGP Considerations

Ask the patient to blink naturally, observe any movement
Lens movement (norm = 1.5-2.0mm) and speed (medium to fast) should not excessively deviate from the limbus.
Flat lenses move quickly and remain at the corneal apex after movement, causing it to not drop down. Steep lenses cause a jerky movement and remain at the corneal apex, thereby leading to no drop-down.
Evaluate and assess the cornea; a good fit is one that does not induce pain or alter visual acuity after wear.
Evaluate the lens fit, centration, and overall comfort. Factors such as tear exchange and edge pressure should be assessed.
Analyze blinking using blue light for lens centration evaluation: If decentration observed, reposition the lens to correct the issues
Consider peripheral cornea fit as well as the central cornea fit

Fitting Assessments

Assess lens fitting/fitting strategies on a range of variables using fitting goals, testing and assessment techniques/methods.
Evaluate and consider additional factors
Evaluate the lens parameters, including the total diameter, peripheral curves, and others, to determine if the fit and centration are acceptable
Evaluate any symptoms and evaluate and consider appropriate actions
Evaluate tear exchange adequacy (assess the tear film in the upper and lower areas of the lens)
Ensure lens stability, including any movements, during various movements of the patient’s head or eyes
Evaluate lens fitting and visual acuity. Appropriate actions or next steps for the fitting.

Considerations for Extended Wear (EW)

Higher Dk lenses are ideal to reduce corneal complications of EW
Increased risk factors for microbial keratitis in EW lenses, thus proper hygiene and cleaning methods are necessary for effective use. Proper instruction to the patient is needed, as well as proper aftercare.

Complications

Potential complications of CL wear include corneal edema, epithelial microcysts, endothelial bed-weeping, corneal infiltrates, and associated CL-associated capillary conjunctivitis
Other factors that can cause complications are environmental factors & microbiological factors
Other potential causes of CL-associated complications include improper lens fitting or maintenance, lens material properties, and underlying medical conditions.
Symptoms of complications may include pain, irritation, discomfort, reduced visual acuity, and dryness, as well as tearing

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Description

This quiz explores Rigid Gas Permeable (RGP) lenses, including their materials, benefits, and indications for use. Learn about their comfort levels, fitting parameters, and differences compared to other lens types. Ideal for students and professionals in optometry.