Advanced Contact Lenses
Specialty contact lens fitting, troubleshooting, advanced designs, and patient management.
GP Lens Design and Fitting
GP Lens Parameters:
- BOZR (Back Optic Zone Radius) — The base curve of the central optical zone. Determines the fitting relationship with the cornea.
- OZD (Optic Zone Diameter) — The diameter of the central optical zone, typically 7.0-8.5mm.
- Peripheral Curves — Secondary and peripheral curves provide edge lift for tear exchange.
- Overall Diameter — Total lens size, typically 8.5-10.0mm for corneal GP lenses.
Fluorescein Pattern Evaluation:
- Alignment (ideal) — Thin, even fluorescein layer centrally, with adequate edge clearance
- Steep fit — Central pooling (bright green), peripheral seal-off (dark ring)
- Flat fit — Central bearing (dark area), excessive edge lift (wide green ring)
- Three-point touch — Used for keratoconus: clearance over the cone, light touch on shoulders, peripheral clearance
GP Lens Modifications:
- Power changes, blend modifications, edge polishing, diameter changes
- Can be performed in-office with a lens modification unit
- Verification with a lensometer and measuring magnifier
Specialty Contact Lens Applications
Orthokeratology (Ortho-K):
- Reverse-geometry GP lenses worn overnight to temporarily reshape the corneal epithelium
- Flattens the central cornea to reduce myopia (FDA approved up to -6.00 D)
- Effect is reversible — lenses must be worn regularly to maintain correction
- Also used for myopia management in children
Scleral Lenses:
- Large-diameter GP lenses (14.5-24mm) that vault entirely over the cornea
- Rest on the conjunctiva overlying the sclera
- Fluid reservoir between lens and cornea provides comfort and corrects irregular astigmatism
- Indications: keratoconus, pellucid marginal degeneration, post-surgical irregularity, severe dry eye, Stevens-Johnson syndrome
Hybrid Contact Lenses:
- GP center for crisp optics + soft hydrogel or silicone hydrogel skirt for comfort
- Bridge the gap between GP visual quality and soft lens comfort
- Indications: keratoconus, high astigmatism, patients who cannot adapt to full GP lenses
Bandage Contact Lenses:
- Plano or low-powered soft lenses for corneal protection during healing
- Indications: corneal abrasions, post-PRK/LASEK, recurrent erosions, bullous keratopathy
Prosthetic (Cosmetic) Lenses:
- Custom-painted or stock lenses to mask disfigurements (corneal scars, iris defects, anisocoria)
- May include refractive correction
- Can reduce photophobia with an opaque iris and artificial pupil
Myopia Management with Contact Lenses
Evidence-Based Strategies:
1. Orthokeratology
- Overnight corneal reshaping creates peripheral myopic defocus
- Studies show 40-60% slowing of myopia progression
- Most effective in younger children (8-12 years)
2. Center-Distance Multifocal Soft Lenses
- Distance correction in the center, plus power (add) in the periphery
- Creates peripheral myopic defocus while maintaining clear central vision
- CooperVision MiSight — first FDA-approved soft lens for myopia management
- Shows approximately 59% reduction in myopia progression over 3 years
3. Peripheral Defocus Designs
- Custom lens designs that specifically target peripheral retinal defocus
- Based on the theory that hyperopic peripheral defocus signals the eye to grow longer
Mechanism:
All strategies work by creating myopic defocus on the peripheral retina, which is believed to slow axial elongation of the eye. The central retina receives a clear, focused image for good distance vision.
Candidate Selection:
- Progressive myopia in children/teens (typically ages 8-15)
- Family history of high myopia
- Good compliance and hygiene capability
- Cooperative patient and parents
Multifocal Contact Lens Fitting
Simultaneous Vision Designs:
Both distance and near images are present on the retina simultaneously. The brain selects the appropriate image.
Center-Near Design:
- Near power in the center, distance in the periphery
- Works well when the pupil constricts for near tasks
- Preferred for most presbyopic fits
- May reduce distance contrast sensitivity
Center-Distance Design:
- Distance power in the center, near in the periphery
- Better for patients prioritizing distance vision
- May be less effective for near tasks in low light
Concentric Ring Designs:
- Alternating rings of distance and near power
- Pupil size affects which zones are used
Monovision:
- Dominant eye corrected for distance, non-dominant for near
- Simple and effective but reduces stereoacuity
- Modified monovision: distance lens in dominant eye, multifocal in non-dominant
Fitting Tips:
- Determine ocular dominance first
- Start with manufacturer-recommended initial lens
- Allow adequate adaptation time (1-2 weeks)
- Fine-tune by adjusting add power, not just sphere
- Manage patient expectations — multifocal contacts involve visual compromise
Contact Lens Complications and Management
Corneal Staining Grading (Efron Scale):
- Grade 0: No staining
- Grade 1: Trace/mild (minimal punctate dots)
- Grade 2: Mild (scattered punctate staining)
- Grade 3: Moderate (confluent staining)
- Grade 4: Severe (deep, extensive staining)
Contact Lens-Induced Dry Eye:
- Most common reason for lens dropout
- Management: rewetting drops, reduced wear time, switch to daily disposables, silicone hydrogel materials, or lower water content lenses
- Tear film assessment: TBUT (Tear Break-Up Time), Schirmer test, meibomian gland evaluation
Microbial Keratitis Prevention:
- Extended wear increases risk 5-15x compared to daily wear
- Risk factors: sleeping in lenses, poor hygiene, swimming in contacts, using tap water
- Prevention: proper hand washing, replace cases regularly, never use water with lenses, follow replacement schedule
Over-Refraction Technique:
- Refraction performed OVER the contact lens to fine-tune the prescription
- Spherical over-refraction is most common
- Result is added to the current contact lens power to determine the new Rx
- Important for GP lens fitting where the tear lens affects power
Environmental Factors Affecting Comfort:
- Low humidity environments → increased evaporation and dryness
- Air conditioning/heating → reduced tear stability
- Extended digital device use → reduced blink rate
- Wind and dust → irritation and debris under lenses
- Air travel → low cabin humidity exacerbates dryness