360° Meridian Analysis
Evaluates oblique power across all 360 individual meridian angles, pin-pointing the exact maximum edge thickness axis, minimum edge axis, and safety bevel margins.
Pupil Decentration Physics
Accurately models monocular PD and segment height offsets relative to the frame boxing geometric center (GC), capturing temporal edge thickening.
Multi-Index Comparison
Directly benchmarks standard CR-39 (1.50) against Trivex (1.53), Polycarbonate (1.59), High-Index 1.60, 1.67, and Ultra-High Index 1.74 for weight and millimeter savings.
Clinical Ophthalmic Dispensing & Edging Guide
1. Understanding Minus vs Plus Lens Geometries
In ophthalmic optics, minus lenses (prescribed for myopia) have a steeper concave ocular surface curve than front convex base curve. Consequently, center thickness is thin, while edge thickness increases quadratically with radial distance from the optical center (OC). Conversely, plus lenses (hyperopia/presbyopia) are thickest at the optical center and taper toward thin knife-edges along the periphery.
2. The Decentration Penalty & Monocular PD
When the patient's pupillary distance is narrower than the frame optical center distance (Frame PD = (A + DBL) / 2), the lens must be decentered nasally. In minus lenses, this shifts the thick peripheral edge further outward toward the temporal frame corner, dramatically increasing maximum visible edge thickness.
3. Astigmatism & Cylinder Axis Orientation
In astigmatic prescriptions (sphero-cylindrical), maximum minus power occurs 90 degrees away from the specified cylinder axis according to Martin's oblique power law: F(θ) = Fsph + Fcyl · sin2(θ - α). A cylinder axis of 90° concentrates maximum edge thickness horizontally along the 180° temporal edge.
4. Frame Mounting Safety Limits (ANSI Z80.1)
Optical edging standards require minimum physical thickness thresholds depending on frame mounting style: Full-rim plastic and metal frames require a minimum 1.0mm edge; semi-rimless nylon cord frames require 1.8mm to 2.0mm to support the mechanical groove; rimless drill-mounts require 2.0mm to 2.2mm of high-tensile material (1.60, 1.67, or Trivex) to resist screw-torque cracking.
Frequently Asked Questions (Ophthalmic Optics FAQ)
When should 1.74 ultra high-index be chosen over 1.67?
1.74 ultra high-index is recommended for prescriptions stronger than -6.00D or +5.00D, or when mounting large frame eye sizes (A > 54mm). For moderate prescriptions between -3.00D and -5.50D, 1.67 offers an optimal balance of thickness reduction, optical Abbe clarity (Abbe 32), and value.
Do anti-reflective (AR) coatings make lenses physically thinner?
AR coatings do not reduce the physical millimeter thickness of the lens substrate. However, AR coatings eliminate internal reflections and white "power rings" visible along thick edges, creating a cosmetically thinner, clearer appearance.
What is the Minimum Blank Size (MBS) needed for edging?
Minimum Blank Size (MBS) represents the smallest uncut lens disc diameter required by an optical lab generator: MBS = Effective Diameter (ED) + 2 · Total Decentration + 2mm (edging allowance).