Contact lens complications

Suchecki JK, Donshik P, Ehlers WH. Contact lens complications. Ophthalmol Clin North Am 2003 16 471-484. 

C. Complications of Contact Lens Wear and the Need for Care Products... 

Patients with severe keratoconjunctivitis sicca are at definite risk of this complication, and the addition of phosphate-containing eye-drops tilted the precariously balanced situation toward precipitation of calcium in the cornea and bandage contact lens. Acetate-containing rather than phosphate-containing glucocorticoid eye drops may be a safer alternative in patients with such predisposing factors. 

Clinicians should ask about past and current eye disease as well as past ocular trauma. Practitioners should inquire about a history of contact lens wear. Many topically applied medications can cause corneal complications when used in the presence of soft contact lenses. Obtaining a history of current ocular medications is essential. If their continued use is necessary, the old and... 

Bartlett JD. Medications and contact lens wear. In Silbert J, ed. Anterior segment complications of contact lens wear, ed. 2. Boston Butterworth-Heinemann, 2000. 

Although practitioners are under no legal duty to contact patients who fail to keep appointments, there are circumstances under which follow-up may be wise. For example, a patient who is undergoing treatment with therapeutic agents and who is in need of further evaluation faces a much higher risk of complication than a daily wear contact lens patient who fails to keep a 6-month recall appointment. Follow-up in the former case may prevent an injury—and a lawsuit. 

Conjunctivitis caused by toxic agents can occur as either a primary or a secondary finding. Toxicity most commonly results from exposure to medications, contact lens care products, or cosmetics. However, any agent can cause a toxic response. Toxic conjunctivitis may have a wide variety of presentations. When superimposed over infection or allergic reaction, toxicity to a medication may complicate the diagnosis. 

Contact Lens-Related Potential Complications and the Associated Signs and Symptoms... 

Liquid water on one side of a silicone contact lens permeates through the lens by a solution-diffusion mechanism and evaporates on the other side quickly according to the permeability of water, whereas the solubility of water in silicone polymer is low [1]. The high water vapor permeability was speculated to be one of the reasons causing the suction cup effect that makes the lens stationary on one spot and tenaciously stick to the cornea this may damage the corneal epithelium and result in other complications. However, the high permeability per se cannot be the reason for the suction cup effect if the exterior surface is covered by the tear film, i.e., if there is no driving force for water permeation. 

Components of the tear attach to contact lenses by electrostatic and van der Waals forces and build up to form deposits. Deposits on the surface and in the lens matrix may result in reduced visual acuity, irritation, and in some instances serious ocular complications. The composition of deposits vary because of the complexity of an individual s ocular physiology-pathology. Lysozyme is a major component of soft lens deposits, especially found on high-water-content ionic lenses [312]. Calcium [313] and lipids [314] are infrequent components of deposits, occurring as inorganic salts, organic salts, or as an element of mixed deposits, or as a combination thereof [315,316]. 

The actual form of lenses of non-spreading liquids on the surface of another immiscible liquid has been recently studied by Lyons3 and Langmuir.4 Langmuir shows that, in addition to the surface tension, if the lens is not of very large size, the linear tension / at the curved line of contact between the two liquids makes an appreciable difference to the thickness of the lens. The actual shape of the lenses is dependent on a rather complicated balance between the spreading coefficient the densities of the liquids, and the linear tension / round the perimeter of the lens, whose radius is R. If Dlt Z>2 are the densities of the lower and the upper liquids, respectively, the thickness t of a lens so large that its upper surface may be taken as flat, in the centre, is... 

Contact lenses are made of polymeric materials designed and fabricated to correct vision. Because these lenses are removed from the eye after a prescribed wear time, lens care products are required to clean, disinfect and rinse them prior to reinsertion to avoid ocular infections and other complications. Lens care products are also required to enhance the comfort of lens wear. 

This basic concept applies to our technique as well. In microsphere nanoscopy, microspheres are in direct contact with objects, which forms a Particle-on-Surface (POS) system, as illustrated in Fig. 8(a). It is this POS system that effectively interacts with the near-field evanescent waves, decouples and turns them into propagating wave that would reach the objective lens in the far-field. Like in NSOM, such interaction are quite complicated and only takes place in the proximity of the interface of particle and substrate, which was indicated by the shadow zone in Fig. 8(a). The characteristic thickness of the evanescent waves scattering zone, dg, could be decided by ... 

A nice article that describes the importance of oxygen diffusion for silicone-based soft contact lenses may be found online http //www.clspectrum.com/article.aspx7article=12953 Note if the lens contains a hydrophobic surface, it will disrupt the tear flow that results in the deposition of an albumin film on the lens. Not only will this reduce the effectiveness of the lens to correct optical aberrations, but will also cause infection/irritation. Eor more details regarding the lens surface and eye complications, see Rao, J. B., Saini, J. S. Complications of Content Lenses in Contact Lenses. Aquavella, J. V., Rao, G. N., eds. Lippincott Williams and Wilkins Philadelphia, PA, 1987. 

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