Contact Lens Fitting Principles

Pre-Fitting Essentials - Foundation First

• History:
  • Ocular: Prior CL issues, surgery, trauma, dry eye symptoms, allergies.
  • Systemic: DM, autoimmune (Sjogren's), thyroid; meds (antihistamines, OCPs → dry eye).
• Motivation & Lifestyle:
  • Reason for wear, hygiene, environment (dust, AC).
• Refraction:
  • Accurate manifest; vertex distance correction if power > ±4.00D.
  • Astigmatism: Amount & type (corneal vs. residual).
• Ocular Exam:
  • Lids/Lashes: Blepharitis, MGD.
  • Conjunctiva: Hyperemia, papillae (e.g., GPC).
  • Cornea: Clarity, staining, neovasc; Keratometry (K-readings); Topography (if irregular).
  • Tear Film: TBUT (normal > 10s); Schirmer's (normal > 10mm/5min).
  • Pupil size (dim/bright light).

⭐ Keratometry provides average corneal curvature (K-readings), essential for initial contact lens base curve selection.

Soft Lens Fitting - Soft & Simple

• Goal: Optimal vision, comfort, ocular health.

• Initial Selection:

  • Base Curve (BC): Flatter than avg. K (e.g., avg. K + 0.8-1.0mm).
  • Diameter (Dia): HVID + 2mm (e.g., 13.8-14.5mm).
  • Power: Vertex-corrected Rx.

• Assessment (📌 CCM):

  • Centration: Good.
  • Coverage: Full corneal.
  • Movement: 0.2-0.5mm on blink.

• Fit Issues & Fixes:

  • Tight Fit: Minimal movement, discomfort. → Flatter BC (↑ radius) / ↓ Dia.
  • Loose Fit: Excessive movement, variable vision. → Steeper BC (↓ radius) / ↑ Dia.

• Over-refraction: Refine power.

⭐ Ideal soft lens movement on blink is 0.2-0.5mm, ensuring tear exchange and comfort.

RGP Lens Fitting - Rigid & Precise

• Goal: Optimal lens-cornea alignment: apical clearance or light central touch, adequate peripheral clearance for tear exchange.
• Initial Selection:
  • Base Curve (BC): From K-readings (e.g., "on K" or flatter).
  • Diameter: Typically 9.0-10.0 mm. Optic Zone Diameter (OZD) related to pupil.
  • Peripheral Curves: Ensure adequate edge lift.
• Dynamic Assessment: Movement (1-1.5 mm with blink), centration, fluorescein pattern.

• Fluorescein Patterns:

Specialty Fits & Follow-Up - Beyond Basics

• Advanced Lens Applications:
  • Keratoconus: RGP (apical clearance/touch), scleral (vault), hybrid.
  • Post-Refractive Surgery (e.g., ectasia): Reverse geometry RGP, scleral.
  • Presbyopia: Monovision, multifocal (simultaneous/alternating), aspheric.
  • Aphakia: High (+) power, extended wear options.
• Essential Follow-Up & Management:
  • Schedule: 1 wk, 1 mo, 3 mo, 6 mo, then annually.
  • Key Checks: VA, over-refraction, fit (centration, movement), corneal health (staining, edema), lens integrity.
  • Troubleshooting: Discomfort (edge, deposits), ↓VA (rotation, flexure), redness (⚠️ CLARE, CLPU, MK).

⭐ Scleral lenses are a game-changer for severe irregular astigmatism (e.g., advanced keratoconus, post-PKP) and ocular surface disease, creating a tear reservoir_._

High-Yield Points - ⚡ Biggest Takeaways

• Keratometry (K-readings) guide initial Base Curve Radius (BCR) selection.
• Soft lens BCR: typically 0.8-1.0 mm flatter than average K; OAD: 1-2 mm > HVID.
• RGP fitting: fluorescein pooling = steep fit; central touch = flat fit.
• Lens movement: 0.2-0.4 mm (soft), 1-2 mm (RGP) for tear exchange.
• Over-refraction over trial lens finalizes lens power.
• Steeper BCR (shorter radius) = tighter fit; flatter BCR (longer radius) = looser fit.