Toric, Multifocal, Aspheric, Hybrid, Scleral, Orthokeratology & Quadrant-Specific

Toric, Multifocal, Aspheric, Hybrid, Scleral, Orthokeratology & Quadrant-Specific Designs

Quick Answer: Lens design matches ocular geometry and visual demand. Toric designs use stabilization features to keep astigmatic correction on-axis. Multifocals use simultaneous or alternating vision. Specialty designs — hybrid, scleral, ortho-K, quadrant-specific — solve irregular-cornea, dry-eye, and myopia-control problems conventional soft lenses cannot.

Toric Lens Designs

Soft toric lenses correct ≥0.75 D of astigmatism. Because a soft lens drapes over the cornea, rotation must be controlled for the cylinder axis to align. Stabilization methods:

• Prism ballast — thicker, heavier bottom edge; gravity pulls it inferiorly
• Truncation — bottom edge cut flat to sit on the lower lid
• Double slab-off — thin top and bottom zones, thick mid-periphery; lids squeeze the lens into place
• Peri-ballast — thick zones nasal and temporal to the optical zone, thin top and bottom (reduces prism-induced vertical imbalance)

LARS (Left Add, Right Subtract): when a toric lens rotates, adjust the axis by the rotation amount — Add for left rotation, Subtract for right rotation. Observe the slit-lamp rotation marker (typically a laser-engraved line at 6 o'clock). A lens rotated 10° to the patient's right → subtract 10° from the manifest cylinder axis on reorder.

Multifocal Designs

Two functional classes:

Simultaneous vision — both distance and near images are presented to the retina at the same time; the visual cortex selects the in-focus image.

• Concentric (annular) rings — alternating distance/near zones
• Aspheric — power progresses from center to periphery (or periphery to center)
• Diffractive — fine concentric grooves create simultaneous near and distance foci

Aspheric sub-types:

• Center-near — add increases toward center (popular for early presbyopia, computer users)
• Center-distance — distance in center, add in periphery (better distance in low light, mature presbyopia)

Alternating / Translating — the lens physically shifts with down-gaze (reading), moving the near zone over the pupil. Truncated bottom edge rests on lower lid. Better for high add and mature presbyopia; requires lid interaction and lens movement.

Modified monovision — one eye distance, one multifocal — is a common compromise for patients who fail full bifocal fit.

Aspheric Lenses

Aspheric designs progressively flatten (or steepen) from center to periphery, reducing spherical aberration. Positive spherical aberration in conventional lenses reduces image quality in low light (large pupil). Aspheric surfaces improve contrast and reduce halo. The same aspheric geometry is used in multifocal designs and in single-vision lenses for high-quality vision.

Hybrid Lenses

Hybrid lenses combine an RGP center with a soft hydrogel or silicone hydrogel skirt. Examples: ClearKone, SynergEyes, Duette.

Indications:

• Irregular cornea (keratoconus, post-LASIK ectasia, post-PK) where RGP optics are needed but comfort is poor
• Athletes who need RGP-quality vision but cannot risk lens dislodgement
• Patients with RGP intolerance

Fitting matches the soft skirt to the scleral sag and the RGP zone to the cone; the skirt vaults the limbus. Hybrid lenses are a bridge between RGP and scleral options.

Scleral Lenses

Scleral lenses vault the entire cornea and land on the sclera. Diameter 14.5–16.0 mm (mini-scleral) to 18.0+ mm (full-scleral).

Indications:

• Keratoconus and other ectasias
• Post-penetrating keratoplasty (post-PK)
• Severe dry eye (Sjögren, GvHD) — the vaulted tear reservoir bathes the cornea
• Irregular cornea (scarred, post-refractive, post-corneal surgery)
• Ocular surface disease requiring mechanical protection

Fitting keys: vault (sagittal depth) over cornea and limbus, landing zone on sclera without compression or blanching, edge lift for tear exchange. Over-vaulting risks corneal edema; under-vaulting compresses the conjunctiva and causes vascular engorgement. Scleral lenses should show central clearance of ~150–250 µm at insertion, settling to ~50–150 µm after several hours.

Orthokeratology (Ortho-K)

Ortho-K uses a reverse-geometry RGP lens worn overnight to flatten the central cornea, temporarily reducing myopia. The lens creates a central flat zone with a steep "return curve" and a peripheral landing zone, producing corneal epithelial redistribution (central thinning, mid-peripheral thickening).

Indications:

• Myopia ≤ −5.00 D (best results at ≤ −3.00 D)
• Astigmatism ≤ −1.50 D (with-the-rule is easiest)
• Myopia control in children — multiple studies show 40–60% slowing of axial elongation versus single-vision spectacles

Lenses removed on waking; effect lasts 1–2 days. Patient must wear nightly to maintain unaided daytime vision. Corneal warpage is reversible, but discontinuation returns the eye to baseline within 1–2 weeks.

Quadrant-Specific Designs

Quadrant-specific (or quadrant-asymmetric) lenses vary geometry across quadrants to match asymmetric corneas — post-LASIK with nasal steepening, pellucid marginal degeneration, post-PK with suture-induced astigmatism. Each quadrant can have independent sagittal depth, tangent, or eccentricity. Used in specialty RGP, scleral, and hybrid designs.

Lenticular Designs

Lenticular designs reduce thickness in high Rx lenses:

• Plus lentic — thinned mid-periphery to reduce center thickness and mass in high-plus (aphakic) lenses
• Minus lentic — thinned edge zone to reduce edge thickness in high-minus lenses

Reducing thickness raises Dk/t, improves comfort, and reduces lid interaction — critical for high Rx patients who would otherwise suffer hypoxic and mechanical complications.

Design Selection Cheat Sheet