An Analysis on Forecasting Progress with Silicone – YDROGEL Contact Lenses: Methodological Considerations

Contact lenses have been created for more than a hundred years and advances in Contactology are astounding. The development of knowledge in corneal and ocular surface physiology led in parallel to impressive advance concerning contact lenses, permitting conveyance of this type of optical rectification and treatment in an extensive populace and of any age. Development of delicate contact lenses in the 70s, was a standout amongst the most huge disclosures of the most recent century, an immense territory that as of now incorporates more than 140 million wearers around the world. In the mid 80's specialists started utilizing more slender materials to make lenses with a high water content, expanding oxygen transmissibility and permeability level keeping in mind the end goal to enhance the physiological reaction of the cornea. Additionally around then it was set up the request of oxygen at the corneal level and the base oxygen level that a contact lens must give while wearing amid day or night keeping in mind the end goal to dispense with the corneal edema. After this it took one more decade for the business and staff to build up the primary delicate contact lens with high oxygen permeability. This accomplishment was relatively mysterious in light of the fact that specialists have struggled for quite a long time to figure out how to consolidate in silicone elastomer in the hydrogel polymer. The principal investigate the physiological advantages of the silicone-hydrogel contact lenses was introduced in 1995 at ARVO meeting - Association for Research and Vision in Ophthalmology and after an additional 3 years the main silicone-hydrogel lenses showed up.

trailed by suitable suggestions on the type of contact lens, multipurpose arrangements, how to wear and substitution and furthermore aversion and early location of conceivable complications. Eye mind professionals are in charge of suggesting contact lenses considering every one of the variables included, attempt to create with alert the signs for optical rectification and therapeutic with delicate contact lenses, particularly silicone-hydrogel and to basically assess clinical their performance to validate their helpfulness for the advantage of the wearer. Various investigations have been directed to date to decide the impact of contact lenses on the cornea and front section. On account of the potential danger of genuine complications prompting visual impairment, looks into have concentrated on corneal diseases, especially identified with the expanded port, which were related with a more serious hazard for microbial keratitis. Daytime wearing remains the primary method for wearing contact lenses hydrogel and silicone-hydrogel even with high permeability for oxygen, regardless of whether the last ones were initially presented for expanded port. Albeit corneal damage other than microbial keratitis, isn't undermining to vision misfortune, such circumstances can cause the wearer uneasiness and discontent, which in the end prompt relinquishment conduct. Silicone-hydrogel lenses were related with superior epithelial arcuate lesions (SEALs), papillary conjunctivitis induced by contact lenses CLPC, and other mechanical complications. All silicone-hydrogel contact lenses influences the ocular surface, corneal homeostasis is slow, smooth connections happen between the surface of the eye and contact lens material and the tear film structure and its physiology is modified. A considerable lot of these impacts are opened up by wearing amid rest, when the eye is in a genius inflammatory status, is more delicate to hypoxia induced by contact lenses and have nearer connection with palpebral conjunctiva, yet is completely reversible when waking, without neurotic circumstances. Silicone-hydrogel lenses join the advantages of delicate hydrogel lenses with high oxygen transmissibility, giving wearers greater adaptability in wearing and longer wearing period, with noteworthy clinical advantages. A significant number of lenses accessible today, as we have found in the examination, are giving ideal stream of oxygen lessening the hypoxic push and having an essentially littler impact on corneal homeostasis. Be that as it may, broadened wear silicone-hydrogel refractive blunders, which are fitted in thicker lenses and subsequently a lower oxygen transmissibility. Here and now impacts of silicone-hydrogel lenses on tear film are irrelevant, however we should consider any individual varieties. Future examinations should survey the more extensive effect of silicone-hydrogel lenses on tear film, for longer timeframes and to explain singular contrasts that impact achievement in fitting and wearing methodology. Research proposes roughly 50% of ebb and flow contact lens wearers experience the ill effects of dryness and inconvenience, especially towards the finish of the day. The symptoms portrayed by these people are fundamentally the same as dry eye sufferers, prompting this condition being named contact lens induced dry eye (CLIDE). This unavoidably prompts disappointment and is the best reason for cessation of lens wear. Preceding fitting their patients with contact lenses there are various tests accessible to the professional to survey the quality and amount of tears, to enable counsel to be given on a person's appropriateness for contact lenses and to prescribe the most proper methodology. Generally these tests have included non-invasive separation time (NIBUT), invasive fluorescein tear separation time (TBUT), corneal and conjunctival staining, tear crystal stature estimation, phenol red test and different symptomatology questionnaires. Bulbar and limbal hyperaemia can give a sign of ocular surface health and all the more as of late the degree of both lid parallel conjunctival collapsing (LIPCOF) and lid wiper epitheliopathy (LWE) have been added to the rundown of potential markers of dry eye. LIPCOF evaluated at any rate review 2 is probably going to be related with dry eye symptoms. Early silicone-hydrogel contact lenses caused little yet measurably noteworthy changes in ocular physiology and symptomatology in new contact lens wearers more than year and a half wear, yet these were clinically inconsequential. In any case, no investigations have analyzed the impact of consequent ages of silicone-hydrogel materials in contact lens amateurs. Pult and associates (2008) analyzed 61 experienced contact lens wearers and inferred that those with dryness symptoms showed essentially more LWE and LIPCOF. LIPCOF total seriousness scores were the most prescient of symptoms. A further report by these specialist in 2011 reasoned that NIBUT, tear meniscus tallness (TMH), phenol red string test, LIPCOF, and LWE were altogether, yet decently, identified with OSDI scores; the most grounded relationship was accomplished by joining NIBUT with nasal LIPCOF. Various investigations have discovered a relationship

wearing either hydrogel and silicone-hydrogel contact lenses. In any case, it is as yet not clear which clinical measures foresee those new patients that will drop-out of contact lens wear.

The most recent decade has been unfathomably noteworthy for the improvement of contact lens (CL) materials. The dispatch of the primary silicone hydrogels (SiHs) in the late 1990's spoken to a noteworthy point of reference in CL material science. The drive behind the development of CL materials was identified with the need to upgrade patient solace and vision, while enhancing biocompatibility and limiting the effect of the material on corneal physiology. Hydrogel CLs offer a material that has great wettability, vision and beginning patient solace. In any case, in spite of many advances in hydrogel material properties, there has dependably been a cutoff to the level of oxygen accessible to the cornea. Furthermore, patient symptoms, for example, uneasiness and end of day dryness keep on being an issue. SiHs join the underlying solace of a delicate lens material with generous changes in oxygen performance. There is additionally developing proof to help the way that some SiHs can offer expanded happy with wearing time, with reduced symptoms of end of day dryness. This has brought about changing states of mind to clinician's contact lens endorsing propensities and proceeded with development of the SiH advertise. The primary SiH lenses enabled adequate oxygen transmissibility to meet corneal oxygen needs amid overnight wear (ON). Be that as it may, persistent wear (CW, or ON wear for up to 30 evenings) has not demonstrated as well known as anticipated, especially in the UK and other European markets; this methodology as of now represents just 7% of new fits and 13% of refits in the UK. This not as much as expected development is in all likelihood because of alert with respect to the specialist, remembering that the danger of corneal inflammatory occasions and microbial keratitis stay higher when patients rest in their lenses, both generally and with present day materials, despite the fact that buyer hesitance to grasp this methodology may likewise be a factor. As SiH lenses set up themselves inside the market, it turned out to be evident that the properties of these materials offered benefits for wearers well beyond their utilization for ON wear. Oxygen performance is helpful to any patient who wears lenses for extended periods, or for those with higher or more intricate medicines and subsequently thicker lenses. Therefore, the materials began to discover a place as perfect lenses for refitting daily wear (DW) patients with indications of hypoxia, and furthermore as first decision for some utilization of SiH materials for more "normal" DW fits and in the meantime endeavors were being made by makers to address a portion of the confinements of the principal SiH materials, by finding an ideal adjust of oxygen conveyance, mechanical performance and wettability. From 2004 there has been a consistent increment in the quantity of SiH lenses accessible, with these newer materials basically went for DW or incidental overnight utilize. Not at all like traditional hydrogel materials where the oxygen performance is identified with, and constrained by, the water content, the manner by which oxygen is transported through silicone hydrogels is extraordinary and isn't subject to water content alone. In SiHs, the oxygen is transmitted essentially through the silicone-based segment of the lens material, which enables tremendous enhancements in oxygen performance to be acquired contrasted with hydrogel materials. A current survey of the writing was completed to find out whether symptoms of dryness and distress experienced by a few wearers of regular hydrogel lenses may be associated with the level of accessible oxygen. The survey inferred that a great part of the distributed writing proposes that patient signs and symptoms seen with hydrogel lens wear might be because of an inflammatory reaction identified with incessant or intense hypoxia and that clinical investigations including highly oxygen porous SiH materials bolster an association between enhanced solace and dryness and the level of accessible oxygen. All the more as of late presented lenses don't generally need to depend on surface treatment techniques to upgrade the material wettability. Galyfilcon An and senofilcon An utilization innovation to render the lens wettable without the requirement for surface treatment. The materials contain a moisture-rich wetting agent, high molecular weight polyvinyl pyrrolidone (PVP), which accomplishes a highly wettable, smooth lens. The wetting agent ingests moisture and furthermore limits on-eye lack of hydration amid wear. Comfilcon An and a two-week by week substitution SiH lens for DW (accessible in the US), AvairaTM with enfilcon An, utilization innovations to create a normally wettable material, again without the requirement for surface treatment. Air Optix Aqua is plasma-covered lotrafilcon B and employs a hydrophilic moisture agent that is guaranteed to tie to the lens surface, said to improve comfort on inclusion. It is said to have a lower starting contact angle than the first lotrafilcon B lens.

A wide assortment of conditions can profit by the utilization of contact lenses. These may change from 'bandage' applications, where the therapeutic impact is either to enhance comfort or ensure the cornea amid recuperating, to circumstances where the optical impacts of the lens can enhance vision, (for example, keratoconus). Mechanical insurance might be fitting where conditions, for example, trichiasis happen either with age-related entropion (when lens wear might be here and now preceding surgery) or trauma (where lens wear may be on a long haul premise). In bullous keratopathy, assurance of the corneal nerve endings through a bandage lens may have a critical effect on comfort while the bullae resolve. Following corneal surgery, the bandage properties of the lens may help with securing the influenced cornea and in addition giving insurance to keep mechanical trauma from fastens in full thickness unites. In corneal epithelial dystrophies and recurrent erosions, a bandage contact lens may improve comfort by securing uncovered nerve endings while the lens may likewise help avert consequent epithelial misfortune by preventing the lid from holding fast to as of late re-joined epithelial cells amid rest, when the tear film turns out to be less fluid. Much of the time on lid opening, inadequately joined territories of epithelium are 'ripped off' by the lid causing a further scene of trauma and torment. In different conditions, the lens will either work to enhance comfort or to offer security to a generally uncovered corneal surface, while in instances of obsessive dry eye, a contact lens may help counteract corneal drying up. In the last case, silicone elastomer lenses are frequently favored because of their absence of water content which anticipates drying out, yet silicone hydrogels may likewise be of esteem given their low water content and relative thickness. In instances of corneal inconsistency from trauma or conditions, for example, keratoconus, a contact lens may reestablish a uniform optical surface, altogether enhancing visual performance. While the major point of the therapeutic lens is to help the recuperation of the cornea from the condition under treatment or to improve symptoms, the lens ought to likewise have insignificant effect on corneal physiology. High Dk lenses are to be favored since they reduce hypoxic stretch and are particularly shown in situations where mending is required, since epithelial recuperating is advanced within the sight of typical levels of oxygen. A further necessity is that mechanical trauma to the cornea ought to be insignificant and, beyond what many would consider possible, the lens should act to make a steady, very much dispersed tear film. patients in light of the Holden-Mertz rule for both daily and overnight wear. The low water content of the lens and surface treatment both add to excellent wetting with an insignificant open door for lack of hydration since parchedness is water content ward. The higher modulus (stiffness) of these materials ought not be an immediate reason for concern albeit any propensity to make epithelial part or the development of mucin balls ought to be checked painstakingly. Given the high Dk and high modulus of silicone hydrogel lenses, they may have a place for more extraordinary fitting prerequisites. Westerhout provided details regarding a blend framework utilizing a medium or high water content delicate lens with an unbending lens of 9.00-10.00mm breadth fitted over the best. In any case, the unbending lens frequently rode low and there can be confirmation of confined hypoxia even with high Dk RGP lenses in such lens blends. In any case, others have along these lines likewise utilized this approach. In comparative fittings utilizing silicone hydrogel lenses, the enhanced unbending nature and upgraded oxygen transmission may enhance the achievement and results have been as of late announced. In different conditions, therapeutic contact lenses have been utilized to convey medications to the foremost ocular surface. Take-up and arrival of medications is an element of water content and lens thickness which together decide the repository accessible to take up the medication and after that discharge it onto the eye. High water content lenses take up and discharge medicates substantially more rapidly than low water content materials. While silicone hydrogels have been appeared to be fit for taking up and discharging drugs in-vitro, there is little confirmation of this being connected in a therapeutic setting.

Tear exchange behind adaptable contact lenses (CLs) was verifiably considered to have little significance, on the grounds that early examinations showed that tear exchange is probably not going to contribute extraordinarily to enhanced corneal oxygenation. At present, in any case, enhanced materials are accessible that have defeated hypoxia identified with adaptable lens wear, yet complications remain.

imperative in keeping the amassing of flotsam and jetsam, cellular material, and metabolites behind a delicate lens. Mertz and Holden6 exhibited the main direct proof that the postlens flotsam and jetsam acquired from a patient with an inflammatory response from an expanded wear lens was made out of bodily fluid, epithelial cells, and neutrophils. They guessed that the nearness of the flotsam and jetsam may impel an inflammatory response that ends up noticeably intense if the garbage stays in situ for a managed period. All the more as of late, the expanded danger of corneal disease related with overnight lens wear has again been accounted for, affirming that there has been no lessening in the hazard related with hydrogel lenses in the course of recent years. Constrained tear exchange has been refered to as a key factor in the pathogenesis of CL-related disease. Later in vitro and ex vivo information investigations of bacterial destructiveness recommend that postlens tear stagnation, maybe identified with lacking tear exchange, may incline the cornea to Pseudomonas aeruginosa contamination. Cytotoxic strains of P. aeruginosa cause epithelial cell interruption and demise with delayed cell contact. Different strains of P. aeruginosa cause epithelial cell attack following 3 hours of contact. It is possible that impaired tear exchange delays the removal of infected corneal epithelial cells and gives the premise to bacterial intrusion of corneal tissue. In outline, tear exchange may have importance to effective adaptable lens wear without hypoxia, albeit guide proof of causal relationships to disease and aggravation has not been found. Before examination of these relationships, exact and dependable systems for estimating tear exchange are required. There are few finished reports of postlens tear exchange, especially in connection to current hydrogel materials. In two early reports, a fluorescent tracer (Fluorexon; molecular weight 710; Dioptic Laboratories, Markham, Ontario, Canada) was utilized to appraise tear exchange. In consequent examinations, the tracer measure was expanded to 4.4 kDa (FITC-dextran). Fluorexon is retained into a hydrogel lens inside 10 minutes, which likely happens amid the 8-to 12-minute estimation time of the analyses. Besides, Fluorexon likely entered the cornea, since substantially bigger fluorescent mixes, for example, FITC-dextrans have exhibited rabbit scleral entrance in vitro. Tissue entrance overestimates the end rate (ER) by as much as 25% contrasted and a nonpenetrating color.

Since the approach of silicone hydrogel (SiHy) contact lenses (CLs), numerous bothersome clinical complications coming about because of CLinduced hypoxia have been dispensed with. Be that as it may, a CL on an eye unavoidably upsets the ocular surface by mechanical communications—the back lens surface is in close contact with the whole cornea, limbus, and surrounding bulbar conjunctiva, though the foremost surface cooperates with the palpebral conjunctiva and upper/bring down lid margins. In this way, it isn't shocking that mechanically determined occasions consistently and unavoidably happen with SiHy CLs, in light of the fact that these lenses can't really copy the ocular surface. Mucin balls, superior epithelial arcuate lesions, corneal erosions, and papillary conjunctivitis are a few cases of mechanically determined complications related with CL wear. Since the underlying dispatch of SiHy CLs, these unfavorable occasions have been broadly talked about in distributed survey articles. This article gives reports on these themes from the previous decade and discourses identified with newer discoveries on complications, for example, conjunctival epithelial flaps, lid wiper epitheliopathy (LWE), and meibomian organ dropout. This article additionally plans to recognize the regions of research that warrant promote examinations that may help limit the event of these mechanically induced complications amid SiHy lens wear.

Mucin balls are round and translucent or opalescent bodies sandwiched between a CL and the cornea that can be seen inside minutes after lens inclusion. They are made fundamentally out of mucin, and their sizes have been accounted for to go in the vicinity of 20 and 200 mm in distance across. Since they can be essentially bigger than the thickness of the postlens tear film8– 11 or the corneal epithelium, it isn't shocking that some mucin balls can turn out to be profoundly installed into the cornea. They can be squinted away or leave sorrows on the corneal epithelium on lens removal. These despondencies are best seen with fluorescein instilled in the eye as the color pools in the engraved territories and are generally settled inside 24 hrs. Mucin balls and mucin ball– induced melancholies are not related with diminished lens-wearing solace or traded off vision, and patients are normally asymptomatic. A current report announced that the nearness of mucin balls is altogether connected with a diminished

thick bodily fluid layer, which keeps the upregulation of the safe reaction against bacterial ligands. Without a doubt, mucin balls result from the mechanical collaborations between the lens surface and the postlens tear film; nonetheless, its clinical centrality stays hazy. Some may contend that the mucin balls are not an unfriendly occasion. Regardless, future examinations are expected to give confirmation to its clinical irrelevance to order them as lens-induced changes rather than an antagonistic occasion.

Superior epithelial arcuate lesions (SEALs) were first described in the 1970s as a complication of conventional soft CL wear. The SEALs can be full-thickness lesions located 1 to 3 mm from the superior limbus between the 10- and 2-o‘clock meridians on the cornea. Depending on the distance from the limbus, they have been described as limbal or paralimbal SEALs. Patients with paralimbal SEALs are more symptomatic and may complain of foreign body sensation or irritation, whereas those with limbal SEALs may be asymptomatic. Most cases are unilateral. On slitlamp examination, the lesion, which is usually 0.1 to 0.3 mm wide and 1 to 5 mm in length, often appears with raised and irregular edges, separated from the limbus by a clear region. The lesion stains intensely with sodium fluorescein but may not be apparent after resolution. The lesion may also be accompanied by subepithelial infiltrates either immediately beneath or surrounding the lesion. Paralimbal SEALs are more likely to provoke an infiltrative response and are found to be associated with back-surface deposition. Patients diagnosed with a SEAL should be instructed to discontinue lens wear until staining and infiltration are resolved (between 1 and 7 days). To prevent recurrence, patients may be refitted into a different lens type (i.e., material or design) or instructed to change wearing modality (e.g., from EW to daily wear [DW]) and monitored closely. One study showed a 63% rate of recurrence of SEALs, where 50% did not suffer a third episode after being refitted into another lens type or lens care system and 13% continued to have recurrence regardless of any changes made. Refitting into a rigid gas permeable lens should be considered if the recurrence persists (generally three times). Corneal epithelial erosions related to CL wear are epithelial defects with a wide range of clinical presentations. In general, they can be characterized as localized, well-circumscribed lesions that can be as small as 0.1 mm in diameter or encompass a much larger area of the cornea. They can present anywhere on the cornea, but 87.5% have been found inferiorly and, more commonly, near the vertical midline just below the pupil. The lesions can be superficial, affecting only the first one to three layers of the epithelium or deep into the basement membrane, and stain with sodium fluorescein with no underlying infiltrates. Alternatively, the epithelium may become detached centrally but remain adherent at the border, representing an early stage of development. There is no mucopurulent discharge, and there may be localized limbal and bulbar conjunctival injection. Patients may be asymptomatic or experience foreign body sensation, especially on awakening if lenses are worn overnight, or sharp pain exists on lens removal. Although the aim of management is to reduce pain, prevent infection, and promote reepithelialization, there is no consensus on how best to do so. In general, lens wear discontinuation, ocular lubricants in the form of drops, gels, or ointments, and prophylactic antibiotics are all believed to help with the healing process. Bandage CLs are avoided in cases of CL-induced erosion to reduce the risk of infection.

Contact lens–induced papillary conjunctivitis (CLPC) is an inflammation of the upper palpebral conjunctiva and is one of the main reasons for CL discontinuation. It is characterized by enlarged papillae (.0.3 mm), hyperemia, and mucus strands. Two presentations of CLPC have been described: local and general. When the upper tarsal conjunctiva is divided into 5 discrete zones, local CLPC is described as being confined to 1 or 2 zones and general CLPC is described as being scattered across 3 or more zones. Patients who have CLPC can be asymptomatic or experience acute ocular discomfort with complaints of itching, mucus or ropy discharge, lens awareness, and blurred vision, which are the results of increased front-surface lens deposits and excessive lens movement. The CLPC is managed by frequent cleaning and replacement of lenses, reducing wearing time, changing in lens-wearing modality to DD wear, and refitting into a different lens type or material. On discontinuation of the lens, there is usually a rapid relief in symptoms, with ocular signs dissipating over the course of several days, sometimes longer.

Conjunctival epithelial flaps (CEFs) were first reported with SiHy CLs in CW in 2005. Conjunctival epithelial flaps are bulbar conjunctival lesions that are best observed with fluorescein dye under cobalt blue light with a yellow filter. In 65% of cases, they occur bilaterally and are most often located in the superior quadrant of the bulbar conjunctiva, followed by the inferior and temporal quadrants. The size of CEFs vary based on the lens-wearing modality with SiHy CLs, ranging from 0.1 to 0.5 mm during DW to approximately 9.0 mm during CW. The CEFs have been reported with DW and CW of SiHy and with CW of GP CLs. A recent study reported that the probability of developing a CEF is significantly greater in CW than in DW, especially after a minimum of a week of CW with SiHy CLs and 3 weeks with GP lenses. The CEFs with SiHy CLs occur at approximately 3% with DW and approximately 8% to 37% with CW, in contrast to 26% with GP CW. This condition has no age, gender, or ethnicity predilection.

Silicone hydrogel lenses have been produced to address the real issues of overnight wear. High levels of oxygen transmission, alongside excellent surface wetting, add to noteworthy wearer benefits. While considering therapeutic uses, the requirement for overnight wear without additionally bargain to an effectively unhealthy cornea, recommends that silicone hydrogel lenses could offer a huge advance forward. An audit of the most recent decade of mechanically induced unfavorable occasions related with SiHy CL wear has yielded intriguing patterns identified with lens materials, wearing modalities, and length of wear. Albeit original SiHy lenses wiped out numerous unwanted CL-induced hypoxia complications, it missed the mark in some different classifications. Contrasted and traditional hydrogel lenses, original SiHy CLs are related with more noteworthy seriousness of mucin balls and higher frequency of corneal disintegration. As a rule, many mechanically induced complications seen with SiHy CLs are the aftereffect of not as much as perfect arrangement between a CL and ocular surface ebbs and flows. This jumble might be exacerbated in certain CL wearers if their lids create higher degrees of shear constrain applied on the ocular surface amid flickering. Studies have proposed that, notwithstanding lens attributes, patient ocular qualities are likewise basic to great arrangement between the CL and ocular surface. Alastair K, Dennistan O, Philip I. (2006). Oxford handbook of Ophthalmology, Oxford Medical Publications, pp. 158-159 Anthony J. Phillips and Lynne Speedwell (2007). Contact lenses – fifth edition, Elsevier, pg. 21-50 Buckley, R. (2002). Therapeutic applications in Contact Lens Practice. Ed. Efron, N, Butterworth Heinemann, Oxford, pp. 325-331. Dart JKG, Stapleton F, Minassian D. (1991). Contact lenses and microbial keratitis. Lancet ; 338: pp. 650–653. Douglas J. Coster (2002). Cornea-Fundamentals of Clinical Ophthalmology series, BMJ Books 2002 Efron N., Morgan P.B., Cameron I.D. et. al. (2007). Oxygen permeability and water content of silicone hydrogel contact lens materials. Optom Vis Sci 2007; 84; 4: pp. 328-37. Helton, D.O. and Watson, L.S. (1991). Hydrogel contact lens dehydration rates determined by thermogravimetric analysis. CLAO J. 17 (1): pp. 59-61. Ilene K. Gipson (2007). The Ocular Surface: The Challenge to Enable and Protect Vision, The Friedenwald Lecture Invest. Ophthalmol. Vis. Sci. October 2007 vol. 48 no. 10, pp. 4391-4398 Jalbert, I., Sweeney, D.F. and Holden, B.A. (2001). Epithelial split associated with wear of a silicone hydrogel contact lens. CLAO J. 27 (4): pp. 231-3. Levy B., Comstock T., Cresciullo T., et. al. (2000). Randomized controlled clinical trial of silicone hydrogel contact lens for 30 days of continuous wear [ARVO abstract]. Invest Ophthalmol Vis Sci.; 41(4):S74. Abstract nr 387. Millar T.J., Papas E.B., Ozkan J., et. al. (2003). Clinical appearance and microscopic analysis of mucin balls associated with contact lens wear. Cornea 2003; 22: pp. 740–745. Morgan P.B., Efron N. (2008). Demographics of UK contact lens prescribing. Contact Lens Ant Eye 2008; 31: pp. 50-1.

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