Summary of Contact Lens Fitting and Management
Contact Lens Fitting and Management: A Student's Guide
Introduction
Contact lens fitting is a clinical process that matches lens design and material to a patient's ocular anatomy, refractive needs, lifestyle and ocular health. This guide focuses on clinical management: selecting contact lens modality, fitting rigid gas-permeable (RGP) and soft lenses, managing astigmatism and irregular corneas (including keratoconus), and practical decision-making during consultations and fittings.
Definition: Contact lens fitting is the clinical assessment and selection of lens type, parameters and care plan to achieve optimal vision, comfort and ocular health for an individual patient.
1. Initial consultation and preliminary evaluation
History and motivation
- Ask reasons for contact lens wear: cosmesis, sports, recreation, occupation, inconvenience of spectacles.
- Assess motivation and likelihood of compliance (work/lifestyle, willingness to attend follow-up).
- Medical/ocular history: allergies, dry eye symptoms, systemic disease (diabetes), medications (antihistamines, anticonvulsants), pregnancy.
Objective assessments
- Refractive status (subjective refraction)
- Keratometry and corneal topography
- Tear film evaluation: tear meniscus height, TBUT (Lissamine Green), Schirmer or Phenol Red
- Slit-lamp exam: corneal staining, neovascularization, microcysts, scars, epithelial changes
Definition: Tear breakup time (TBUT) is the interval in seconds between a blink and the first appearance of a dry spot on the cornea measured with fluorescein or lissamine green.
2. Choice of contact lens modality
Use a decision framework combining refractive error, corneal shape, ocular surface, lifestyle and risk factors.
Table: Modality comparison
| Feature | Soft lenses | RGP (GP) | Specialty (scleral, custom GP) |
|---|---|---|---|
| Initial comfort | +++ | + | + |
| Vision for irregular cornea | + | +++ | +++ |
| Stability for astigmatism | ++ (toric) | +++ | +++ |
| Risk of hypoxia (daily wear) | depends on material | depends on Dk | depends on design |
| Ease of handling | +++ | ++ | + |
Practical examples
- Young athlete wanting minimal lens dislocation: consider soft daily disposable or high-Dk soft lens.
- Irregular cornea/keratoconus: RGP or scleral lens preferred for better optics and masking irregularity.
3. Basic contact lens optics and magnification
- Spectacle magnification depends on spectacle vertex distance and lens power; contact lenses reduce spectacle-induced magnification because of proximity to the eye.
Definition: Calculated Residual Astigmatism (CRA) is the difference between refractive astigmatism and corneal astigmatism and helps predict which lens type will best correct astigmatism.
Use these formulas when planning lens type:
- For RGP lenses: $\mathrm{CRA} = \mathrm{Refractive,astigmatism} - \mathrm{Corneal,astigmatism}$
- For soft lenses: $\mathrm{CRA} = \mathrm{Refractive,astigmatism}$
Example: Spectacle Rx $-2.25-1.50\times180$, Ks $43.25@180/44.50@090$.
- For RGP: $\mathrm{CRA} = -1.50\times180 - (-1.25\times180) = -0.25\times180$.
- For soft lens: CRA equals refractive astigmatism $-1.50\times180$ so soft lenses may neutralize corneal astigmatism differently.
4. GP fitting: design, evaluation and troubleshooting
Lens design choices
- Standard (manufacturer-design) vs. custom: custom gives practitioner control of center thickness (CT), peripheral curves and optical zone diameter (OZD).
Base curve and OZD selection
- Typical starting OAD/OZD: average 9.4/8.0 mm, larger corneas 9.8/8.4 mm, smaller corneas 9.0/7.6 mm.
- Adjust base curve relative to OZD: flatten BCR 0.25 D for each increase in OZD of 0.50 mm; steepen BCR 0.25 D for each decrease in OZD of 0.50 mm.
Fit patterns with fluorescein
- Steep fit: central pooling, mid-peripheral touch, minimal ed
Zaregistruj se pro celé shrnutíAlready have an account? Sign in
Contact Lens Fitting — Clinical Management
Klíčové pojmy: Perform thorough history and tear film evaluation before selecting lens modality, Use CRA to decide between RGP and soft lenses: $\mathrm{CRA} = \mathrm{Ref\,astig} - \mathrm{Corneal\,astig}$ for RGP, GP fluorescein patterns: steep = central pooling; flat = central touch; alignment = target fit, Start GP OAD/OZD around 9.4/8.0 mm and adjust BCR by 0.25 D per 0.50 mm OZD change, Select trial toric axis as refractive axis + $10^{\circ}$ and sphere within $\pm2.00$ D of refraction, Prefer RGP/scleral lenses for keratoconus and irregular astigmatism for improved optics, Choose lens material based on water content, modulus and patient symptoms (dry eye, deposits), Empirical fitting with topography data reduces chair time for specialty lenses, Soft toric: front-surface torics for near-spherical corneas, back-surface for more cylindrical corneas, Monitor for complications: GPC, deposits, neovascularization and modify modality as needed