This guide offers a step-by-step approach to successfully fitting Rigid Gas Permeable (RGP) contact lenses. This process involves thorough eye exams, lens selection, trial fittings, and precise adjustments. The aim is to ensure optimal comfort, clear vision, and promote eye health by allowing increased oxygen transmission to the cornea.
Initial Data Gathering
The first crucial step in RGP lens fitting is gathering comprehensive initial data. This involves a thorough assessment of the patient’s ocular health and visual needs. Begin by obtaining a detailed patient history, noting any prior contact lens experience, refractive errors, and relevant medical conditions. A recent refraction is essential, with careful attention to visual acuity and back vertex distance.
A full eye examination, including a slit-lamp assessment, is necessary to evaluate corneal health, tear film quality, and any potential contraindications for RGP lens wear. Keratometry readings are vital for determining corneal curvature, as these measurements guide the initial lens selection. Assess for the presence and degree of astigmatism, as RGP lenses can effectively correct this refractive error.
Evaluate the patient’s blink rate and lid position, as these factors can influence lens centration and comfort. Measure the horizontal visible iris diameter (HVID) to aid in selecting the appropriate lens diameter. Assess tear film quality, as adequate tear volume and stability are crucial for successful RGP lens wear. Document all findings meticulously to establish a baseline for future evaluations.
In cases where myopia progression control is desired, document baseline measurements to monitor effectiveness. This comprehensive data gathering lays the foundation for accurate lens selection and a successful RGP fitting process. Remember to follow all contact lens and solution insert instructions carefully.
Lens Selection Based on K Readings
Following the initial data gathering, the next critical step is selecting an appropriate diagnostic RGP lens based on the keratometry (K) readings. The K readings provide valuable information about the curvature of the cornea, which is essential for determining the base curve radius (BCOR) of the initial trial lens. Ideally, the lens BCOR should closely match the patient’s K readings to achieve a proper fit.
For spherical corneas, select a lens with a BCOR that is approximately 0.05 mm flatter than the average K reading. In cases of astigmatism, consider using the flattest K reading as a starting point for BCOR selection. It’s important to note that the goal is to achieve a comfortable and well-centered lens fit, so adjustments may be necessary based on the fluorescein pattern and dynamic assessment;
If the patient has significant astigmatism (e.g., ≥ 0.75D), consider prescribing a toric lens to compare the quality of vision with a spherical lens. If diagnostic lenses are unavailable, empirical fitting can be considered by using K readings and refraction information. When ordering empirically, aim to provide good vision after initial lens application to create a positive patient experience. Always consult with a contact lens laboratory to determine the optimal lens parameters for each individual patient.
Fluorescein Pattern Assessment
After placing the initial trial RGP lens on the eye, the next crucial step is to assess the fluorescein pattern. This diagnostic technique uses a cobalt blue light and fluorescein dye to visualize the tear film layer between the back surface of the lens and the cornea. The pattern reveals areas of bearing, clearance, and pooling, which are essential for evaluating the lens-cornea relationship.
An ideal fluorescein pattern should demonstrate minimal spherical apical clearance, indicating a slight touch in the central cornea, and adequate edge lift to allow for proper tear exchange. A central bearing pattern suggests that the lens is too flat, whereas excessive apical clearance indicates a steep lens. Areas of pooling, where the fluorescein dye gathers, show where there is excessive space between the lens and the cornea.
Evaluate the fluorescein pattern under normal room illumination and document your findings. Adjustments to the lens parameters, such as BCOR, diameter, or peripheral curves, should be made based on the observed pattern. The goal is to achieve an optimal fit that provides corneal alignment, adequate tear exchange, and minimal corneal bearing, ensuring both comfort and corneal health for the patient. Remember to read and follow all contact lens and solution inserts.
Dynamic Assessment of Lens Fit
The dynamic assessment of an RGP lens fit involves observing the lens behavior on the eye during blinking and eye movements. This evaluation provides crucial information about lens stability, movement, and interaction with the eyelids. The goal is to ensure that the lens moves adequately to facilitate tear exchange and prevent corneal hypoxia, while maintaining good centration for optimal vision.
Observe the lens movement during a blink. The lens should move slightly, typically between 0.5 to 1.5 mm, in an upward direction. Excessive movement may indicate a loose fit, whereas minimal or no movement could suggest a tight fit. Assess the centration of the lens; ideally, it should remain centered on the cornea. Decentration can cause visual disturbances and discomfort.
Evaluate the lens lag, which is the amount the lens lags behind during lateral gaze. Excessive lag may indicate a flat-fitting lens. Also, observe the lens edge lift. Excessive edge lift can lead to lid bumping and discomfort, while insufficient edge lift can impede tear exchange. Adjustments to the lens parameters, such as diameter, peripheral curves, or edge design, may be necessary to optimize the dynamic fit; Aim for a lens that moves well, centers properly, and interacts comfortably with the eyelids.
Static Assessment of Lens Fit
The static assessment of an RGP lens fit involves a detailed examination of the lens-cornea relationship when the eye is in a static, or non-moving, position. This assessment is typically performed using a slit lamp biomicroscope and fluorescein dye to visualize the tear layer between the lens and the cornea. The fluorescein pattern reveals areas of lens bearing, clearance, and pooling, providing valuable information about the overall fit.
Examine the apical zone, the central area of the cornea beneath the lens. Ideally, there should be a slight apical clearance, indicated by a thin layer of fluorescein. Excessive apical clearance suggests a steep-fitting lens, while apical bearing indicates a flat-fitting lens. Evaluate the mid-peripheral zone for a smooth transition from the apical zone. Look for an even distribution of fluorescein in the peripheral zone, indicating adequate edge lift and tear exchange.
Assess the overall fluorescein pattern to determine the lens fit category. A lens with good alignment will exhibit a thin, even layer of fluorescein throughout the central and mid-peripheral zones, with adequate edge lift. Modify lens parameters to achieve the desired fluorescein pattern.
Over-Refraction
Over-refraction is a crucial step in the RGP lens fitting process, determining the final lens power required for optimal visual acuity. This procedure is performed after a diagnostic lens has been successfully fitted and allowed to settle on the eye. It involves measuring the patient’s refractive error while they are wearing the trial RGP lens.
Begin by stabilizing the diagnostic lens on the eye. Use a phoropter or trial frame to refine the patient’s vision. Carefully add spherical and cylindrical power until the patient achieves the best possible visual acuity. Pay close attention to the patient’s responses and make adjustments accordingly. Note the over-refraction findings, including the sphere, cylinder, and axis.
The over-refraction results are then used to calculate the final lens power. Consider the vertex distance when converting the spectacle refraction to the corneal plane. Be mindful of any changes in the patient’s refractive error due to the RGP lens. Once the final lens power has been determined, it is essential to verify the visual acuity with the corrected lens. This confirms the accuracy of the over-refraction and ensures that the patient will experience optimal vision with their new RGP lenses.
Troubleshooting Common Fitting Issues
Even with meticulous fitting, RGP lenses can present challenges. Centration issues, where the lens decenters excessively, can lead to discomfort and blurred vision. Assess the lens position and movement. Flat fitting lenses often decenter inferiorly. Steepening the base curve or adjusting the edge lift might improve centration. Conversely, excessive movement may indicate a loose fit. Selecting a steeper base curve or increasing the lens diameter can enhance stability.
Poor vision can arise from incorrect power or an unstable tear film. Perform over-refraction to refine the lens power. Evaluate the fluorescein pattern for areas of excessive bearing or clearance. Adjustments to the lens design, such as aspheric optics or peripheral curves, can optimize the fit and improve vision.
Patient discomfort is another common concern. Edge awareness can be addressed by polishing the lens edges or modifying the edge lift. Corneal staining might indicate excessive bearing. Adjusting the base curve or peripheral curves can alleviate pressure points. Thoroughly educate patients on proper insertion, removal, and cleaning techniques to minimize complications and ensure comfortable lens wear.
Ordering the Final RGP Lens
After achieving an optimal fit during the trial lens assessment, the next crucial step is ordering the final RGP lens. This process involves meticulously documenting all relevant lens parameters to ensure accurate replication by the laboratory. Begin by recording the final base curve radius, which directly impacts the lens-to-cornea relationship. Specify the lens diameter, considering both corneal coverage and lid interaction. The power of the lens, as determined by over-refraction, must be accurately noted, including the sphere and cylinder components, along with the axis if applicable.
Furthermore, specify the lens material, choosing from the available options based on oxygen permeability and patient needs. Clearly indicate any peripheral curve modifications or special design features incorporated during the fitting process. Communicate any specific instructions or requests to the laboratory to ensure the final lens meets the precise requirements.
Double-check all documented parameters before submitting the order to minimize errors and delays. Provide the patient’s name and contact information for lens identification and delivery purposes. A well-documented and accurate order is essential for a successful final RGP lens fitting experience.