Refractive Indices and Ophthalmic Lens Materials

Colour legend: Plastic Glass Organic Ceramic Other
Name of Material N (index of refraction)
(Nd = 589 nm (sodium) or
Nd = 587.6 nm (helium)
(US Standard)) 		Abbe Value Specific Gravity
grams/cm3		 Speed of Light in (miles/second) Comments
Vacuum 1.00 186,000.00 Empty space. The speed of light is 186,282.397 miles per second or 299,792,458 meters per second. It is typically rounded to 186,000.00.
Air (rounded) 1.000293 (usually rounded to 1.00) 186,000.00 Although rounded to 1.00 refractive index, it still has a value greater than 1.00. The perturbations in the atmosphere are a result of the refractive index not being exactly 1.00 and different pockets of heat that expand the air differently. This is why the Hubble telescope is able to gather pictures so clearly. No atmosphere allows for better astronomy. Adaptive optics attempt to compensate for these perturbations by using a deformable mirror in land based astronomy.
Water 1.33 139,849.62
Aqueous Humor 1.336 139,221.56 Provides nutrition to the cornea.
Vitreous Humor 1.336 139,221.56 A gelatinous, transparent mass that fills the vitreous chamber of the eye.
Cornea 1.376 135,766.42 Composed of 5 layers (Epithelium, Bowman's membrane, Stroma, Descemet's membrane, and Endothelium).
Crystalline Lens 1.42 (avg. over life span) 130,985.92 As one gets older, the ability for accommodation decreases in what is known as presbyopia. Eventually some type of reading assistance, usually in the form of multifocal lenses, is required.
CR-39 1.50 (1.498) 56.8 1.32 124,000.00 (124,165.55) One of the most common lens materials available.
Crown Glass 1.523 58.6 (60) 2.54 122,127.38 The most common form of glass available. Optically the best in terms of dispersion (also called Abbe Value or Nu Value).
PGX/PBX 1.523 57.0 2.41 122,127.38 Photo-grey / Photo-brown
Old Crown Glass 1.530 121,568.63 The Geneva Lens Measure (lens clock) is calibrated to this material.
Phoenix (Trivex) < 1.53** 43-45 1.11 > 121,568.63 Developed by Pittsburgh Plate Glass. Lightest ophthalmic lens available.
Spectralite 1.54 47.0 1.21 120,779.22 Made by Sola. Very popular mid-index lens.
Ormex 1.56 37.0 1.36 119,230.77 Available from Essilor.
Sunsensors 1.56 1.17 119,230.77 Made by Corning. Material is lighter than polycarbonate.
Barium 1.58 52.1 2.96 117,721.52 Uses barium instead of lead.
Polycarbonate 1.586 30.0 1.20 117,276.17 Developed originally by Gentex. The most impact resistant lens on the market. Blocks 99% of all UV light.
Finalite 1.60 42.0 1.22 116,250.00 Made by Sola.
Thin & Lite 1.6 1.60 32.0 1.36 116,250.00 Blocks 100% of UVA & UVB. Available from Essilor.
PGX-16/PBX-16 1.6005 42.0 2.73 116,213.68 Photochromic.
Dense Flint 1.61 36.8 3.60 115,527.95 Contains lead.
Barium (bartya) 1.616 48.2 3.12 115,099.01 Uses barium instead of lead.
Barium 1.65 42.3 3.26 112,727.27 Uses barium instead of lead.
Seiko 1.67** 1.67 32.0 1.36 111,377.25 Blocks 100% of UVA & UVB. Available from Seiko. Made from MR-10 Resin.
Thin & Lite 1.67 1.67 111,377.25 Blocks 100% of UVA & UVB. Available from Essilor (aka Stylis).
Extra Dense Flint 1.69 30.9 4.23 110,059.17 Contains lead.
Hi-Lite 1.70 31.0 2.99 109,411.76
Teslalid 1.71 36.0 1.41 108,771.93 Made by Hoya.
Profection 1.71 36.0 1.41 108,771.93 Made by Hoya.
Hyper 1.74 1.74 33.0 1.47 106,896.55 Made by Optima.
Fusio 1.74 106,896.55 Made by Essilor.
Index 8 1.812 102,649.01 Made in Branchburg NJ by the O'Hara Lens Company.
Zeiss Lantal 1.90 30.0 3.37 97,894.74 Made by Zeiss.
Lumicera 2.082 30.4 7.50 89,337.18 Currently being considered for use as camera lenses. Made by Casio & Murata.
Diamond 2.419 22.73* 3.52 76,891.28 Not a len$ material for obviou$ rea$on$.
Lead Sulfide Nano-crystals 3.91 47,570.33 Currently being considered for use in optical networks.
* Not sure about this one ** tested using green light (546nm) instead of the US industry standard

Notes

Corrected Curve Lenses: lenses which were designed with a different base curve for every Rx.

PALs: Progressive Addition Lens.

Multi-Layer Anti-Reflective Coatings: allows 99.5% percent of light to pass through the lens as opposed to about 93% without the anti-reflective coating. Developed by the Nazis in order to hide the reflection of binoculars.

Transitions: a joint venture between Essilor and Pittsburgh Plate Glass. Transitions are a plastic photochromic.

Glass Making Process

  • The process takes about 20 hours.
  • Materials: cullet (waste glass), soda lime, silica sand, potassium oxide, arsenic.
  • 1st Melt (7-8 hours): debris rises to the top and is skimmed off.
  • Fining: after another 7-8 hours, glass is stirred continuously with clay rods to produce a homogenous mixture.
  • Glass is poured into blank molds.
  • Glass is then allowed to anneal.
  • Annealing: controlled cooling down to room temperature. It reduces the strain in glass.
  • Can be made by continuous flow method for large quantities of the same lens material, or individual batch method for small quantities of glass, usually for specialty lenses.