Contact lenses offer a convenient and often preferred alternative to spectacles for many individuals. Effective Contact Lens Fitting and Management is crucial for patient comfort, vision, and ocular health. This comprehensive guide covers the essential steps and considerations for students and practitioners, from initial evaluation to advanced fitting techniques and patient education, ensuring optimal outcomes for contact lens wearers.

Understanding Contact Lens Fitting and Management: The Initial Steps

The journey of contact lens fitting begins with a preliminary evaluation to gather essential patient information and assess ocular health. This foundational step ensures a safe and successful fitting process.

Initial Consultation and Patient History

During the initial consultation, a thorough history is taken, focusing on the patient's motivations and health:

Reasons for Contact Lens Wear: Patients often seek contact lenses for cosmesis, sports, recreation, inconvenience of glasses, improved vision, or occupational needs.
Medical & Ocular History: It's vital to inquire about medications, symptoms like itching, burning, or tearing, sinusitis, seasonal or chronic allergies, dry mouth, convulsions, fainting, and diabetes (Type I, II).
Previous Contact Lens Experience: If applicable, details on rigid or soft lenses, satisfaction, symptoms, lens replacement schedule, and solutions used are important.

Anatomical Measurements and Refractive Status

Accurate measurements and refractive assessment are critical for selecting appropriate lens parameters:

Anatomical Measurements: These include blink rate, Horizontal Visual Iris Diameter (HVID), palpebral aperture/lid position, and pupil diameter.
Refractive Status: This involves subjective refraction, keratometry (or corneal topography for more detail), and calculating the Calculated Residual Astigmatism (CRA).
For RGP lenses: CRA = Refractive astigmatism - Corneal astigmatism.
For soft lenses: CRA = Refractive astigmatism.
If CRA is > -0.75, fitting a spherical RGP lens may compromise visual acuity (VA). For example, with an Rx. -3.00 and K's 43.75/44.75 @ 180, CRA is -1.00x180 for RGP, but 0 for soft, suggesting soft lenses are better.

Ocular Health and Tear Film Evaluation

Assessing the health of the eye and the tear film is paramount for contact lens wear:

External Appearance: Check for pterygium, ectropion, entropion, trichiasis, blepharitis, and meibomianitis.
Conjunctival Evaluation: Examine the tarsal, bulbar, and palpebral conjunctiva.
Cornea: Look for edema, microcysts, stromal striae, neovascularization, scars vs. infiltrates, and the health of the epithelium/endothelium. A 30 y/o patient wearing lenses for 12 years with increased wear time to 17-20 hours, reporting irritation and redness, with microcystic edema, conjunctival injection, and superior incipient neo-vascularization upon lens removal, indicates significant issues likely due to hypoxia or overwear.
Tear Film Evaluation: This detects borderline dry eyes. Insufficient tear prism (using fluorescein) indicates aqueous deficiency. Other tests include Tear Meniscus evaluation (with Rose Bengal), Tear Breakup Time (TBUT, with Lissamine Green), Schirmer Tear Test, and Phenol Red Test. Wait 1-2 minutes before evaluating fluorescein patterns.

Contact Lens Fitting: Rigid Gas Permeable (GP) Lenses

GP lenses, also known as Rigid Gas Permeable lenses, offer excellent vision for many patients, especially those with astigmatism or irregular corneas. Understanding their fitting principles is key.

GP Lens Design and Selection

GP lenses can be standard or custom-designed:

Standard Lens Design: Less time-consuming, manufacturer uses their design for center thickness (CT), peripheral curves, and overall zone diameter (OZD). Takes some control away from the practitioner.
Custom Lens Design: Practitioner has control over parameters, making lens modification easier.

Base Curve and Overall/Optical Zone Diameter Selection

Diagnostic Base Curve Selection: Based on corneal astigmatism and refractive error.
Corneal Cylinder 0.00-0.50 D: 0.50-0.75 D flatter than K (FTK).
Corneal Cylinder 0.75-1.25 D: 0.25-0.50 D FTK.
Corneal Cylinder 1.50 D: "on K".
Corneal Cylinder 1.75-2.00 D: 0.25 D steeper than K (STK).
Overall/Optical Zone Diameter (OAD/OZD):
Rule of thumb: Select OZD equal to the base curve radius (BCR) in millimeters (e.g., 8.09mm BCR = 8.1mm OZD).
Average values: 9.2-9.4mm for OAD, 7.6-8.0mm for OZD.
Good starting points: 9.4/8.0 (average), 9.8/8.4 (larger), 9.0/7.6 (smaller).
Consider pupil size (OZD larger than pupil in dim illumination), corneal curvature (larger OAD with flatter curvature, smaller with steeper), and refractive error (larger with hyperopes, smaller with myopes).
Base Curve Selection Tip: Use a steeper-than-K base curve or larger OZD for positive lenses to improve lens centration. Flatten BCR by 0.25D for each 0.50mm increase in OZD. Steepen BCR by 0.25D for each 0.50mm decrease in OZD.

GP Lens Evaluation

Evaluating the lens fit is crucial for comfort and vision:

Lens Evaluation: Assess centration and fluorescein pattern using a Wratten #12 yellow filter.
Fit Types:
Steep Fit: Lens is tight, central pooling, mid-peripheral touch, minimal edge clearance. Does not move on blink, blanching of conjunctival vessels.
Flat Fit: Loose lens, central bearing or touch, mid-peripheral pooling, excessive edge lift, lens decentration. Lens is displaced, moves too much, or has edge lift.
Alignment Fit (Desired): Minimal central clearance, mid-peripheral alignment, adequate edge lift, centered lens. Centers well, moves easily with blink.

Power Selection for GP Lenses

Once the base curve is determined, calculate the contact lens power:

Use SAM (Steeper Add Minus), FAP (Flatter Add Plus) acronym if needed for power changes due to BC. This appears to be misremembered from original, which just says to use it without explanation.
Calculate Predicted Over Refraction (POR) = Contact Lens Power - Diagnostic Lens Power.
Perform an over-refraction (OR).
Final CL Rx = OR + Diagnostic Lens Power.

Soft Contact Lens Fitting

Soft contact lenses are popular for their comfort and ease of adaptation. Their fitting involves understanding material properties and proper base curve selection.

Material Properties of Soft Lenses

Soft lenses are made from polymers with varying characteristics:

Polymer Component: Stable, can absorb or bind with water, has pores allowing water to enter. Consists of monomers that determine water content, refractive index, hardness, mechanical strength, and oxygen permeability.
Water Content: Amount of water absorbed. < 4% hydrophobic, > 4% hydrophilic. Increased water content generally increases Dk, increases fragility, and can lead to deposit formation.
Oxygen Permeability/Transmission (Dk and Dk/t): Depends on water content; higher Dk allows more oxygen to reach the cornea.
Transparency: Clarity of material, typically 92%-98%.
Tensile Strength: How much stretching force before breaking.
Hardness and Stiffness: Degree of flexibility. More flexible for better comfort; stiffer for easier handling and better VA.
Modulus of Elasticity: Ability to keep shape under stress. Lower modulus = less resistant; higher modulus = resists stress, holds shape, better VA.
Refractive Index: Related to water content; increasing water content reduces refractive index.
Wettability: Aids lid closure over lens, improves comfort, creates stable tear film, optimizes vision, and resists deposits.
Ionic Charge: Materials can be ionic (negative charge, more reactive with acidic solutions, prone to deposits) or non-ionic (electrically neutral, less reactive to tears, more deposit resistant).

FDA Lens Groups

Soft lenses are classified into four FDA groups based on material and water content:

Group I: Non-ionic, low water content.
Group II: Non-ionic, high water content.
Group III: Ionic, low water content.
Group IV: Ionic, high water content.

Soft Lens Construction and Material Selection

Construction: Lathe cut, spin cast, or cast molded.
Material Selection:
Borderline dry eye: Low water content.
Occasional use: Daily disposable lenses, preferably Group I.
Seasonal allergies: Daily disposable lenses.
Case Example: An 18 y/o desiring occasional wear with little care due to a busy lifestyle, with concerns of compliance, would benefit greatly from daily disposable lenses.
Case Example: A 26 y/o pregnant female, otherwise a soft CL candidate, should be carefully evaluated, as pregnancy can affect tear film and corneal sensitivity.

Base Curve Selection for Soft Lenses

Unlike GPs, keratometric readings are less predictive for soft lens fit:

Average K's (42.00-45.00 D): Start with a medium base curve (8.6, 8.7).
Flatter K's (<42.00 D): Flatter base curve (8.8, 8.9, 9.0).
Steeper K's (>45.00 D): Steeper base curve (8.3, 8.4).
Movement Evaluation: Wait 5-10 minutes for the lens to equilibrate. Evaluate centration and movement. Movement should be 0.5-1.0mm in primary gaze, up to 2.0mm in superior gaze.
If the lens doesn't move: Select a flatter base curve.
If the lens moves too much: Select a steeper base curve.
If movement is adequate: Stay with the selected base curve.

Advantages and Disadvantages of Soft Lenses

Advantages: Comfort, ease to fit, fewer base curves, good for sports, less lens dislocation, cosmetics (can change eye color).
Disadvantages: More susceptible to complications (e.g., Giant Papillary Conjunctivitis (GPC) development), lens tears, deposits, infections. A 22 y/o female prone to jelly bumps and deposits, with issues persisting despite care regimen changes, needs material or modality change, potentially to daily disposables.

Correcting Astigmatism with Contact Lenses

Correcting astigmatism, especially irregular astigmatism, has become more manageable with advanced contact lens technology.

Soft Toric Contact Lenses

Soft toric lenses are no longer a challenge, thanks to better designs and more available parameters. A step-wise, logical approach is required.

Does this patient require toric correction? Yes, if cylinder power is greater than 1/4 - 1/3 of the spherical power (e.g., Rx: -1.00-1.25x180; -3.50-0.75X090; -6.50-1.50X090). A soft toric lens is often the best alternative for residual astigmatism.
Which type of soft toric is appropriate? Consider lens stabilization for rotation.

Lens Stabilization: Prism ballast (better for WTR astigmatism), thin zones (better for ATR astigmatism).
Lens Bending: More stable lens with less bending. Front surface toric for more spherical corneas; back surface toric for more cylindrical corneas. Larger diameter lenses (14.5mm, 15.0mm) are generally more stable, especially for more toric corneas.

Which trial lens parameters should be selected?

Begin by looking at the cylinder power axis: Select axis + 10 degrees from refractive astigmatism.
Check cylinder power: If exact power isn't available, choose the closest but smallest power available.
Choose the sphere power: Should be within +/- 2.00D of the refractive sphere power.
Example: Spec. Rx: -1.75-1.75x090, K's: 44.5/45.50 @ 180. Trial lens selection: Sphere -1.75 + 2.00 = +0.25 (then adjust to closest trial lens sphere, e.g., -3.00), Cylinder -1.75, Axis 090 + 10 = 100. So, TL: -3.00-1.75x100.

Does the lens fit? Lenses need orientation marks (10°, 20°) to evaluate position. Evaluate centration and movement after 5-10 minutes of equilibration. If it centers well, moves easily with blink, fully covers the cornea, and does not rotate more than 20°, then it's a good fit.
What power should I order?

If astigmatism is fully or closely corrected with the trial lens, perform a spherical over-refraction.
If VA is not within one line of best acuity with OR, check lens rotation. Compensate for rotation if it's less than 20° using LARS (Left Add, Right Subtract): Left = clockwise rotation, Right = counterclockwise rotation.
Resultant Cross Cylinder: If a spherical OR does not provide acceptable vision, perform a sphero-cylindrical over-refraction and check for resultant cross cylinder. Measure the combined power of trial lens cylinder and OR cylinder with a lensometer.
Procedure: Set the trial lens cylinder power and axis on a frame. In front of that, place the OR cylinder power at its correct axis. Measure the two-lens combination with a lensometer.
To obtain total spherical power, add sphere values from the trial lens, OR, and lensometry measurement. For example, if combined power reads -0.25-2.25x010, and trial lens was -2.50-1.75x180, OR +0.50-1.00x030, then the ordered sphere might be [(-2.50)+(+0.50)+(-0.25)] = -2.25 combined with –2.25x010. The lens dispensed should provide good visual correction with the same fitting characteristics as the trial lens.

Specialty Lenses for Astigmatism and Irregular Corneas

Identifying patients who require specialty lens fits is important:

High Corneal Astigmatism (CA > 2.00 D): Use back surface toric GP lenses or bi-toric GP lenses.
Induced Cylinder: Use aspheric GP lenses (e.g., for ATR astigmatism).
Residual Astigmatism (Low CA with High Refractive Astigmatism): Front surface toric GP lenses, often with prism ballast.

Managing Irregular Astigmatism and Keratoconus

Irregular astigmatism, often caused by conditions like keratoconus, presents unique fitting challenges.

Irregular Astigmatism

Contact Lens Fitting: Improves vision better with RGP lenses than with spectacles or soft lenses. There are no set rules; fitting is often trial and error, as each cornea is unique. General methods aid the fitting process.
Causes: GP lenses are used for keratoconus, pellucid marginal degeneration, post-graft, and post-refractive surgery.

Keratoconus: Diagnosis and Management

Keratoconus is a progressive, non-inflammatory, bilateral (96% of cases) corneal thinning disorder.

Etiology: Not exactly known, but heredity, nutritional factors, atopic factors (hay fever, asthma, eczema in 50% of patients), and possibly contact lenses (due to mechanical pressure and hypoxia) are suggested factors.
Early Detection & Symptoms: Thorough history is crucial. Early signs include monocular diplopia or "ghost" images, frequent changes in Rx, asthenopic complaints (photophobia, halos), and gradual decrease in VA. "Scissors-like" motion in retinoscopy is also a key finding.
Diagnosis Methods:
Keratometry: Lack of parallelism in mires, distorted mires, impossible to overlap (+) and (-) signs, increased and shifting corneal astigmatism to an oblique axis.
Corneal Topography: Most valuable tool. Provides curvature of entire cornea, from limbus to limbus. Color-coded maps indicate curvature changes, help educate patients on corneal shape and fitting difficulty. Can localize cone apex and areas of steepening.
Slit Lamp: Essential for diagnosis. Clinical signs include Vogt's striae (stretching of posterior stroma/Descemet's membrane), Fleischer's ring (hemosiderin deposits in deep epithelium outlining the cone base, in 50% of cases), corneal thinning, increased visibility of nerve fibers at the corneo-scleral junction. Corneal hydrops (in severe cases, secondary to Descemet's rupture) may also be present.
Ophthalmoscopy: Circular, oblong shadow against the red retinal reflex (may be confused with cataract). Fundus details are difficult to observe. Photodiagnosis can monitor cone size, shape, and location.
Munson's Sign: External finding, corneal protrusion on downgaze.
Classification (Progression):
Stage 1: Correctable with spectacles, slight increase in refractive astigmatism, mild scissors reflex, slight or no keratometric mire distortion. Difficult to diagnose.
Stage 2: Corneal distortion and irregular astigmatism, increase in myopia and refractive astigmatism, 1-4D keratometric steepening.
Stage 3: Decreased best corrected VA with spectacles, difficult to get accurate "K" readings, increased irregular astigmatism, Vogt's striae, Fleischer's ring, corneal thinning.
Stage 4: Corneal steepening > 55D, apical corneal scarring, Munson's sign.
Classification (Shape and Size): Nipple cone (3-4mm, round, inferior to infero-nasal), Oval cone (5-6mm, oval, infero-nasal to infero-temporal), Globus cone (>6mm, infero-temporal).
Differential Diagnosis: Corneal Warpage Syndrome (reversible, caused by long-term CL wear, no keratoconus slit lamp signs), Pellucid Marginal Degeneration, Keratoglobus.
Management: Spectacles or contact lenses. GP lenses, hybrid lenses, scleral lenses, or specialty soft lenses are used.

Basic Contact Lens Principles and Magnification

Understanding how contact lenses affect magnification is key for optimal vision correction.

Magnification (Relative Spectacle Magnification - RSM)

RSM is the ratio of image size in the corrected eye to the image size of the standard emmetropic eye. It varies based on whether the ametropia is axial or refractive.

Axial Ametropia with Spectacle Correction: RSM = 1 if spectacle Rx. is placed at the anterior focal length of the eye.
Axial Ametropia with CLs: Magnification will occur, but the percentage is low, making CLs a good choice. Both refractive and axial ametropes benefit from CLs.
Refractive Ametropia: RSM will be similar to spectacle magnification.
Spectacle Magnification: (Shape factor) x (Power factor).
Shape factor: Influenced by the lens's shape and material.
Power factor: Influenced by the lens power. e = distance between the back surface of the lens and the entrance pupil (3mm).

Contact Lens Care and Patient Education

Proper lens care and patient education are paramount for maintaining ocular health and prolonging lens wear success.

Insertion and Removal Techniques

Patients must be able to perform insertion and removal before leaving the office. Provide several ways:

Insertion: Hold both upper and lower lids. Place the lens on the fingertip of the dominant hand. Place directly onto the cornea or slightly inferior. Pull back the finger once in the eye. Keep the upper lid grabbed and move the eye until the lens centers. Release the upper lid. If air bubbles are present, close the eye and gently roll or massage the lids lightly.
Removal: Look up. With the middle finger, hold down the lower lid. Use the forefinger to slide the lens to the lower part of the eye. Pinch the lens with the thumb and forefinger and remove without excessively folding it.

Care Regimen and Solutions

Patients must understand the function of solutions and the importance of proper and regular disinfection. Noncompliance can lead to serious problems, as demonstrated by the patient with increased wear time and corneal neo-vascularization.

Cleaning:
Nonabrasive Surfactants: Found in most GP cleaners. Remove mucoproteins, lipids, and debris. Digital pressure is important for effectiveness.
Abrasive Surfactants: Effective for mucoproteinaceous deposits. More effective than non-abrasive but can cause lens scratches or induce minus lens power. Can be minimized with small-particle abrasive cleaners.
Surfactant Soaking Solutions & Enzymes: Also used for cleaning.
Wetting and Soaking Solution Functions: Enhance lens surface wettability temporarily, maintain hydration, disinfect, and act as a mechanical buffer between the lens, cornea, and lids.
Preservatives (Most Common): Provide disinfection without toxic reactions, compatible with lens material and tear film.
Thimerosal: Organic mercurial compound. Sensitivity in hydrogel wearers, slow-acting, rarely toxic with GP wearers. Used with other preservatives for optimal effectiveness.
Chlorhexidine: Bactericidal, limited binding with GPs, ineffective against yeast, fungi, and Serratia. Used in 0.0005% in hydrogel disinfecting solutions.
Ethylenediamine Tetraacetate (EDTA): Not a true preservative. Chelating agent. Used with other preservatives to enhance antibacterial action against Pseudomonas.
Benzyl Alcohol: Solvent for CL materials. Low molecular weight, bipolar, water-soluble. Negligible binding to GPs, good antimicrobial activity.
Benzalkonium Chloride (BAK): Quaternary ammonium compound (often 0.004%). Often combined with EDTA. Toxic with hydrogel lenses.
Polyaminopropyl Biguanide (PAPB): Low sensitivity with hydrogel patients, great antimicrobial activity (especially against Serratia). Possible toxic reaction in rigid lens solutions at certain concentrations.
Wetting Agents:
Polyvinyl Alcohol: Water-soluble, non-viscous, non-toxic to ocular surface, good spreading and wettability.
Methylcellulose: May retard regeneration of corneal epithelium. Successful in more viscous GP solutions.
Care Regimen: Includes wetting and soaking solutions, cleaning, laboratory cleaners.

Final Consultation and Long-Term Management

The final consultation is an opportunity to reinforce patient education and ensure understanding of the management plan.

Final Consultation: Discuss lens care, replacement schedules, and what to do in case of issues.
Patient Motivation: Assess the patient's motivation for contact lens wear, comparing benefits against spectacles.
Contact Lens Modality: Confirm the choice between rigid vs. hydrogel (soft) lenses based on the patient's needs and clinical findings. For example, a 10 y/o myope, responsible and active in sports, with normal tests and motivation, is an excellent candidate for soft lenses.

Frequently Asked Questions about Contact Lens Fitting and Management

Students often have specific questions about contact lens practice. Here are some common inquiries.

What are the key steps in a preliminary contact lens evaluation?

A preliminary evaluation involves a comprehensive patient history (medical, ocular, CL experience), anatomical measurements (HVID, lid position), refractive status assessment (subjective refraction, keratometry, CRA), and a thorough ocular health check, including slit lamp examination and tear film evaluation.

How do you determine if a soft contact lens fits correctly?

After allowing 5-10 minutes for the lens to equilibrate, evaluate centration and movement. A good fit means the lens centers well, moves easily (0.5-1.0mm) with blinking, fully covers the cornea, and does not rotate more than 20 degrees. If it's too tight, it won't move; if too loose, it will displace or have excessive edge lift.

What is keratoconus and how is it managed with contact lenses?

Keratoconus is a progressive, non-inflammatory thinning of the cornea causing irregular astigmatism. Diagnosis involves keratometry, corneal topography, and slit lamp findings like Vogt's striae and Fleischer's ring. Management often involves specialty contact lenses like rigid gas permeable (GP) lenses, hybrid lenses, or scleral lenses, which can provide better vision than spectacles or soft lenses by masking the irregular corneal shape.

Why is patient education on contact lens care so important?

Patient education is vital because improper lens care, such as noncompliance with disinfection regimens or extended wear, can lead to serious complications like infections, corneal inflammation, microcystic edema, and neovascularization. Patients must be proficient in insertion/removal and understand the function of solutions and the risks of misuse to maintain ocular health and extend comfortable lens wear.

Contact Lens Fitting and Management