Plasticlens material

Becker L-L, Dafsari HS, Schallner J, et al. The clinical-phenotype continuum in DYNC1H1-related disorders-genomic profiling and proposal for a novel classification. J Hum Genet. 2020;65:1003–17.

Glass spectacle lenses – i.e. lenses made from natural glass according to their professional classification – used to be the norm. They still have their place in optometry today thanks to their exceptional scratch resistance. Consumers will also like the fact that they are also less expensive than comparable plastics. In cases of severe ametropia, they can also provide the correction needed with relatively thin lenses – an aesthetic aspect that is not to be underestimated.

Acrylic lens vs polycarbonate lens

Plastic glasses – also known as organic glass – are used today for all types of spectacles and are also best for sports and children’s glasses.

The greater the refractive index range (also called the refraction index) of the spectacle lens material, the thinner the finished glass. For high dioptric values, it is therefore advisable to use a lens material with a high refractive index, as this will reduce the thickness of the lenses and thus the weight of the spectacles. For example: A lens with a refraction index of 1.6 is always thinner than one with a refraction index of 1.5 for an identical dioptric value. Natural glass has a clear advantage here: Its refractive index range extends from 1.5 to 1.9, while the refractive index range of organic glass (= plastic) is only 1.5 to 1.74. Natural glass also has a greater density than plastic.

The advantage of natural glass: It produces considerably weaker colour fringes even when the refractive index is identical to that of plastic lenses.

Plasticlens vs glass lens

The result: Even when the refraction index is the same, spectacle lenses made of glass are always thinner than those made of plastic – but they are also substantially heavier.

Nearly one-third of patients may have impaired cognition and behavioral abnormalities; however, these are unrelated to neuromuscular weakness [3]. Other findings that may be observed are cortical migration anomalies, refractory epilepsy, ocular features such as congenital cataract strabismus, etc. [2,3,4].

Scoto M, Rossor AM, Harms MB, et al. Novel mutations expand the clinical spectrum of DYNC1H1-associated spinal muscular atrophy. Neurology. 2015;84:668–79.

Wander, A., Meena, A.K., Ghanghoriya, P.K. et al. Spinal Muscular Atrophy with Predominant Lower Extremity (SMA-LED) with Intellectual Disability and Dysmorphism. Indian J Pediatr 91, 414 (2024). https://doi.org/10.1007/s12098-023-04878-1

Plastic opticsstock

Another advantage of plastic: While natural glasses can only be tinted in a few colours and at a relatively high cost, plastic glasses are easy to treat with virtually all tints. Plastic is the first choice for those who want spectacles with coloured lenses as a fashion accessory.

Plasticlenses vs polycarbonate

Amabile S, Jeffries L, McGrath JM, et al. DYNC1H1-related disorders: a description of four new unrelated patients and a comprehensive review of previously reported variants. Am J Med Genet A. 2020;182:2049–57.

To the Editor: DYNC1H1-related diseases have variable phenotypes, affecting the function of either the central or peripheral nervous system or sometimes both. Spinal muscular atrophy with predominant lower extremity (SMA-LED) is an autosomal dominant disease characterized by non-progressive early onset lower limb predominant weakness and wasting, mostly due to variants of the tail domain of the DYNC1H1 gene [1,2,3,4]. We present a case of 10-y-old girl with SMA-LED. Patient presented with a history of lower limb weakness noticed since early infancy. Childbirth was uneventful. The child had a history of global development delay. The patient had facial dysmorphism (Supplementary Fig. S1) and significant lower limb weakness and wasting of distal muscles of the foot. Power in the lower limb muscles was 3/5. Deep tendon reflexes were absent in the lower limbs. There was no upper limb or facial muscle weakness. The patient had a positive Gowers sign (Supplementary Fig. S1). The patient's creatinine phosphokinase (CK) enzyme level was 167 U/L. Brain magnetic resonance imaging (MRI) was suggestive of dilated ventricles (Supplementary Fig. S1). On electromyography (EMG), there were signs of chronic denervation. With physical examination and electrodiagnostic findings, the possibility of type 3 SMA was kept. MLPA for SMN1 was negative. Whole-exome sequence analysis revealed a pathogenic heterozygous missense mutation c.9142G > A (p. Glu3048Lys) detected in the DYNC1H1 gene in exon 47.

This fundamental question is asked every time a pair of spectacles is purchased: Do you prefer plastic or glass lenses? When you decide, remember that your glasses should be sturdy, attractive, shatter-resistant, comfortable – and, last but not least, easy to wear. The following holds true for both plastic and glass: Choosing the most suitable material hinges on individual factors such as visual acuity and personal taste.

Plasticlens manufacturer

PlasticOptical Lenses

Disadvantage: Compared to natural glasses, plastics have a low scratch resistance. As a result, they are more sensitive and require additional maintenance. A special coating can be applied as a remedy, for instance one that repels dirt or hardens the material (such as ZEISS DuraVision Platinum).

Natural glass is also recommended for bifocal or trifocal lenses because various materials can be melted together without forming a noticeable cutting edge. In principle, the increased thickness of the material makes it optically purer; the glasses appear cleaner and are free from disruptive colour fringes (so-called dispersion). When light strikes a spectacle lens, it is broken and dispersed into its component parts. This creates a disruptive visible colour spectrum, similar to a prism. The intensity of this effect, known as dispersion, depends on the condition of the material used: high-quality material = minimal dispersion. The colour fringe effect is measured based on the so-called Abbé number: The higher the Abbé number for a spectacle lens material, the lower the dispersion.

Congenital myopathies and muscular dystrophies should be kept as differentials. Although no cure is currently available, we advise that management be guided by presenting symptoms; each patient should receive a careful clinical evaluation for both the central and peripheral nervous systems.

Poirier K, Lebrun N, Broix L, et al. Mutations in TUBG1, DYNC1H1, KIF5C, and KIF2A cause malformations of cortical development and microcephaly. Nat Genet. 2013;45:639–47.