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Soft Lens Fitting and Evaluation: Comprehensive Guide

by Brianna Cuenca on October 25, 2024

General Characteristics of Soft Contact Lenses

Soft contact lenses are semi-scleral or corneoscleral lenses that cover both the cornea and sclera. Due to the hydrated plastic material they are made from, they are gas permeable, allowing the cornea to breathe primarily through the lens matrix and, to a lesser degree, via the tear pump action during blinking. Unlike rigid lenses, soft lenses move less on the eye, though thicker lenses may increase movement. Typically, they provide more comfort than hard lenses, especially when there is no compression along the limbal area.

Eye Adjustment limbal area

Soft lenses offer a wide field of view and prevent issues like fogging or slipping, unlike traditional glasses. The oxygen permeability of the materials helps maintain eye health and comfort during wear.

Soft Lens Fitting

Fitting Goals for Soft Lenses

The primary goal is to avoid a tight fit, which can result in pain, redness, and compression of the limbal vessels due to tissue edema. 

The lens must also center well, covering the limbus entirely during blinking.

When using spin-cast lenses, they are typically 2 mm larger than the horizontal visible iris diameter (HVID).

The lens should remain on the eye for at least 15 minutes to allow it to adjust to the eye’s pH, temperature, and osmolarity. Even a small bubble or tear collection at the apex of a newly inserted lens can temporarily affect its curvature.

Keratometry readings, although not as important as with hard lenses, should nonetheless be taken in all cases. It provides a baseline measurement of corneal curvature which may need to be referenced in future follow-up visits. Also, keratometry will provide at least a rough idea as to whether a flatter or steeper lens should be tried first. The base curves available will vary depending on the manufacturer. Generally, soft lenses are available in three base curves, which will be suitable for the majority of corneas due to the flexible nature of the material. Base curves may be indicated in millimeters of radius of curvature or simply as median, flat, and steep, or as Vault I, Vault II, and Vault III.

The main takeaway point is, as an optician you need to work with your patient and understand that the lens should not be fit too tight. A tight fit could result in pain and redness within just a few minutes since it causes the limbal vessels to become compressed due to tissue edema at the edge of the lens. In addition, the lens should center well, allowing the limbus to be completely covered at all times during blinking.

When spin cast lenses are used, they are generally fit about 2 mm larger than the HVID, horizontal visible iris diameter.

Fitting Goals

Spherical Equivalent
Spherical soft lenses are often fit even when a relatively low amount of astigmatism is manifest. When presented with a spectacle prescription of -3.50 -0.50 x 180, for example, a spherical soft contact lens with a power of -3.75 could be indicated. This power is known as the spherical equivalent and is derived by algebraically adding half the cylinder power to the sphere.

Understanding Different Types of Soft Contact Lenses

  • Daily Disposables: Ideal for those who want fresh lenses daily, eliminating the need for cleaning solutions.
  • Extended Wear Lenses: Worn continuously for several days, even overnight, but must be monitored to prevent complications.
  • Toric Lenses: Designed for astigmatism, offering different powers across various meridians.
  • Multifocal Lenses: Suitable for those needing different prescriptions for distance and near vision, often favored by individuals over 40.

Characteristics of a Good-Fitting Lens

Good Fitting Lens

A well-fitting soft lens should demonstrate three-point touch, lightly resting on the apex and peripheral cornea.

The following factors indicate a good fit:

  • Centration: After blinking, the rim of the lens should be evenly distributed around the cornea.
  • Movement: A standard-thickness lens should move about 0.5 to 1.0 mm after blinking. Thinner lenses fit tighter but still permit some movement due to their higher oxygen permeability.
  • Stable Vision: Visual acuity should remain sharp before and after blinking.
  • Crisp Retinoscopic Reflex: A lens fits well if the retinoscope streak is sharp both before and after blinking (see first illustration below).
  • Clear Keratometry Mires: These mires should remain undistorted before and after blinking (see second illustration below). 

Retinoscopic Reflex

Retinoscopic Reflex

The retinscopic reflex shown in figure A illustrates a good fit. It is as sharp and crisp as if no lenses were being worn both before and after blinking.

Figure B to the right illustrates a steep fitting lens where the streak spreads centrally while in the rest position. It will clear after a blink due to the flattening out of the apical vault by the action of the upper lid.

Figure C shows a flat fitting lens which is blurry immediately after the blink. It may ride low before the blink causing distorted reflexes.

Keratometry Mires

Keratometry Mires

Distortion of mires can indicate a poor fit, such as too steep (Figure B) or too flat (Figure C).

The Importance of a Comprehensive Eye Exam

Before fitting contact lenses, a thorough eye examination is crucial. This exam serves multiple purposes:

  1. Determining Prescription: The eye doctor assesses the patient’s vision to establish the correct prescription for glasses, which serves as a baseline for contact lenses.
  2. Identifying Eye Health Issues: An eye exam can uncover various conditions such as dry eyes, infections, or corneal irregularities that may affect contact lens wear.
  3. Assessing Tear Film Quality: A healthy tear film is essential for comfortable contact lens wear, making this evaluation critical.

The Eye Examination Process

During the comprehensive eye exam, several tests are conducted:

  • Visual Acuity Test: Measures how well the patient can see at various distances.
  • Refraction Assessment: The doctor uses a phoropter to determine the exact prescription needed for optimal vision.
  • Slit Lamp Examination: This allows the doctor to view the front structures of the eye, including the cornea and conjunctiva, in detail.

These tests provide valuable insights that guide the fitting process for soft contact lenses.

Initial Consultation and Fitting Process

Once the eye exam is complete, the next step involves a consultation focused on contact lens fitting. This stage is essential for ensuring that the lenses chosen align with the patient’s lifestyle and preferences.

Lifestyle Considerations

During the consultation, the practitioner will discuss various lifestyle factors that can influence lens choice:

  • Daily Activities: Understanding how and when the patient plans to wear lenses helps determine the best type.
  • Aesthetic Preferences: Some patients may be interested in colored lenses or specific designs that enhance their appearance.
  • Health Considerations: If the patient has existing eye conditions, the doctor should be consulted to recommend lenses that minimize risks.

Lens Type Selection

After discussing lifestyle needs, the practitioner will explain the advantages and disadvantages of different lens types, including:

  • Soft vs. Rigid Gas Permeable (GP) Lenses: While soft lenses are generally more comfortable, GP lenses may provide sharper vision for some individuals.
  • Multifocal Options: For those requiring bifocals, the specialist will discuss multifocal lenses or monovision strategies.

This dialogue ensures that patients make informed decisions about their contact lens options.

Measuring for the Perfect Fit

An accurate fit is vital for comfort and effective vision correction. Several measurements are taken during the fitting process to ensure the proper lens selection.

Key Measurements

  1. Corneal Curvature: Using a keratometer, the practitioner measures the curvature of the cornea. This measurement is crucial for selecting the appropriate lens curve. Diameter might also be taken.
  2. Pupil and Iris Size: The size of these structures influences lens design, especially for GP lenses. Measurements may be taken with a biomicroscope or ruler.
  3. Tear Film Evaluation: Adequate tear production and tear film quality tests are  necessary to ensure comfortable lens wear. Tests may involve placing dye in the eye for the tear break up test, which tests the quality of the tear. Paper strips to assess moisture levels which indicates the tear quantity.

These measurements help in determining the best lens size and design for optimal comfort and performance.

Trial Lenses

In many cases, trial lenses are used to confirm the fitting choice. The practitioner will place these lenses on the patient’s eyes and assess their position and movement during blinking and eye movement.

  • Assessment Duration: Patients typically wear trial lenses for at least 15 minutes to allow for stabilization of the tear film.
  • Comfort Evaluation: The practitioner will inquire about the patient’s comfort level and any sensations experienced during wear.

This hands-on approach ensures that the selected lens meets the patient’s needs before finalizing the prescription.

Follow-Up Visits: Ensuring Optimal Fit and Comfort

After the initial fitting, several follow-up visits are necessary to confirm that the lenses are continuing to fit properly and that the patient’s eyes are tolerating them well.

Monitoring Eye Health

During follow-up appointments, the eye care professional will:

  • Evaluate Lens Fit: Using a slit lamp, the practitioner checks for any signs of irritation or improper fit.
  • Assess Tear Film: A dye may be used to evaluate whether the lenses are causing dryness or damage to the cornea.
  • Identify Potential Issues: Regular check-ups allow the practitioner to catch problems early, often before the patient is aware of them.

Adjustments and Recommendations

If issues arise during follow-up visits, the practitioner may suggest various solutions:

  • Lens Material Change: Switching to a different lens type or material may alleviate discomfort.
  • Wearing Schedule Adjustments: Modifying how long the lenses are worn each day can help the eyes adapt better.
  • Care Routine Modifications: Recommendations for cleaning and storing lenses may also be provided.

These proactive measures are crucial for maintaining eye health and ensuring a positive contact lens experience.

Understanding Your Contact Lens Prescription

Once the ideal lens has been identified, the eye care professional will provide a detailed contact lens prescription. This document is essential for obtaining lenses that fit and function well.

Key Components of a Prescription

A contact lens prescription typically includes:

  • Lens Power: The corrective strength needed for clear vision.
  • Base Curve: This measurement indicates the curvature of the lens, ensuring it fits the cornea properly.
  • Diameter: The overall size of the lens, which affects how it sits on the eye.
  • Lens Brand and Manufacturer: Specific details about the lens type chosen for the patient.

Understanding these components helps patients make informed choices when purchasing their lenses.

Routine Eye Exams for Contact Lens Wearers

Regardless of how frequently or for how long contact lenses are worn, regular eye examinations are essential. These visits help monitor eye health and ensure that lenses continue to fit properly.

Frequency of Exams

  • Annual Check-Ups: Most eye care professionals recommend an eye exam at least once a year for contact lens wearers. Some lens types may require more frequent check-ups.
  • Additional Visits: Patients experiencing discomfort or changes in vision should schedule appointments sooner.

Regular exams are vital for detecting any potential issues early and ensuring long-term eye health.

The Role of Technology in Lens Fitting

Advancements in technology have significantly improved the fitting process for soft contact lenses. These innovations allow for more precise measurements and better overall outcomes.

Corneal Topography

This advanced technique creates a detailed map of the cornea’s surface, allowing practitioners to:

  • Identify Irregularities: Any irregularities can be addressed with specialized lens designs.
  • Enhance Fitting Accuracy: Detailed mapping leads to more accurate lens selections, improving comfort and vision.

Digital Measurement Tools

Modern tools enhance the fitting process by providing:

  • Automated Measurements: Devices that automatically gather data streamline the fitting process.
  • Real-Time Feedback: Technology allows for immediate adjustments based on patient responses during fittings.

These innovations contribute to a more efficient and effective lens-fitting experience.

Addressing Common Concerns in Lens Fitting

Despite the advantages of soft contact lenses, some patients may have concerns regarding their use. Addressing these issues is crucial for ensuring a positive experience.

Discomfort and Irritation

Many individuals report discomfort when first wearing lenses. Common causes include:

  • Improper Fit: A lens that is too tight or loose can cause irritation.
  • Dry Eyes: Insufficient tear production can lead to discomfort during wear.

Solutions

To alleviate discomfort or irritation, practitioners may recommend:

  • Re-evaluating the Fit: Adjusting the lens size or design can improve comfort.
  • Using Hydrating Drops: Artificial tears can help maintain moisture and comfort during wear.

Vision Changes

Patients may also experience changes in vision when wearing contact lenses. This can be due to:

  • Lens Quality: Lower-quality lenses may not provide the clarity needed.
  • Changes in Prescription: Regular adjustments to the prescription may be necessary.

Proactive communication with the eye care professional can help address these issues effectively.

OTI Take Away Points 

Soft lens fitting and evaluation are critical components of successful contact lens wear. From the initial comprehensive eye exam to ongoing monitoring, each step plays a vital role n ensuring comfort, safety,  and optimal vision. With the right approach and modern technology, patients can enjoy the benefits of soft contact lenses while maintaining their eye health. Regular check-ups and open communication with eye care professionals are essential for a positive and satisfying contact lens experience. If you are preparing for ABO/NCLE exam this module/guide on soft lens fitting is important