 |
|
Bringing Expertise Back into Soft Contact Lens Fitting
 Is it about time that we recognize that soft contact lens fitting takes skill and expertise. I trust that most people reading this perspective will understand and practice at this level already; but, the sale of soft contact lenses by novelty shops (such as for Halloween) and internet suppliers (which, although they legally can only supply to patients with a valid prescription, a recent student project suggests 60% seek no proof of this) suggests otherwise, and many eye care practitioners treat soft contact lenses as a commodity that will just 'work' if you can get them onto the ocular surface. However, to 'work,' they need to fit appropriately, provide optimum vision, be virtually 'invisible' in terms of discomfort and cause no complications. Lens fitting expertise was 'dumbed-down' with the understandable reduction in soft contact lens SKUs to one or two for mass-produced contact lens designs. However, defining these lenses in terms of [central] base-curve and diameter implies that these are the principal drivers of lens fit. Recent research has shown that this is not the case; soft lens fit is predicted by more peripheral characteristics of the ocular surface such as the horizontal visible iris diameter and corneo-scleral junction. In addition, more complex elements of the lens shape profile and ocular anatomy interaction must influence lens fit, as changing from one lens design to another does not have a systematic effect on lens fit even in the majority of patients. Eye care practitioners should also be able to offer optimum vision to all patients, not just to those whose eyes can achieve an acceptable fit with the current (limited) range of mass-produced contact lens designs. 'Speciality' soft contact lenses designed to fit eye shapes beyond the 'norm' should be in the remit of all contact lens fitting professionals.
James S. Wolffsohn BSc(Hons) PgCertHE PgDipAdvClinOptom MBA PhD PFHEA FRSB FCOptom FAAO-Dipl CCLRT FIACLE FBCLA
Deputy Dean, Life and Health Sciences, Professor of Optometry, Aston University (UK)
Adjuct Professor of Optometry, University of Houston (USA)
|
 
Soft Lenses with Positive Spherical Aberration for Myopia Control
Positive Spherical Aberration, Axial Lenth, Cycloplegic Autorefraction
The purpose of this study was to determine whether soft contact lenses with positive spherical aberration can slow myopia progression. Eligible subjects (n=127, primarily Asian) aged 8 to 11 years were randomized to wear either control (spherical design) or test (with +SA) soft daily disposable contact lenses for a minimum of 1 and up to 2 years (treatment phase). Subjects from the initial cohorts (n=82) were then followed for an additional 1.5 years while wearing a marketed spherical daily disposable contact lens (withdrawal phase). Axial length and spherical equivalent cycloplegic autorefraction were measured at baseline and every 6 months in both phases. Eyes wearing test lenses increased in length by 0.11 (65.3%) and 0.14 (38.6%) mm less than eyes wearing control soft lenses at 6 and 12 months, respectively. The investigators conclude that soft contact lenses with positive spherical aberration slowed axial growth of the eye, although this did not translate into a sustained statistically significant effect on cycloplegic autorefraction. The majority of the treatment effect occurred in the initial six months of wear. No evidence of rebound effect was observed after ceasing treatment.
|
Drug Delivery with Contact Lenses - A Review
Drug Release, Soft Lenses, Water Content, Silicone Hydrogels, Tear Film
Contact lenses for ophthalmic drug delivery have become very popular and are regularly covered in this newsletter. Due to their unique advantages such as extended wear and more than 50% bioavailability, soft lenses may have an advantage. To achieve controlled and sustained drug delivery from contact lenses, researchers are working on various systems such as polymeric nanoparticles, microemulsion, micelle, liposomes, use of vitamin E, etc. Numerous scientists are working on different areas of therapeutic contact lenses to treat ocular diseases by implementing techniques like the soaking method, molecular imprinting, entrapment of drug-laden colloidal nanoparticles, drug plate/film, ion ligand polymeric systems, supercritical fluid technology, etc. Though sustained drug delivery was achieved using contact lenses, the critical properties such as water content, tensile strength (mechanical properties), ion permeability, transparency and oxygen permeability were altered, which limit the commercialization of therapeutic contact lenses. Also, issues including drug stability during processing/fabrication (drug integrity test), zero order release kinetics (prevent burst release), drug release during monomer extraction step after fabrication (to remove unreacted monomers), protein adherence, drug release during storage in packaging solution, shelf life study, cost-benefit analysis, etc. are still to be addressed. This review provides an expert opinion on different methodologies to develop therapeutic contact lenses, with special remarks of their advantages and limitations. A recent study by Lasovski in the April issue of Optometry & Vision Science came to the conclusion that silicone hydrogel materials have the potential to deliver drugs for over 2 weeks without compromising lens properties. This could potentially overcome the need for regular drop instillation and allow for the maintenance of drug concentration in the tear film over the period of wear. This represents a potential option for treating a host of ophthalmic disorders in children including myopia and retinoblastoma, the article states.
|
Eyeblink Movevent & Push-Up
Soft Lens Movement, Initial Fit, End of the Day Fit, SiHy, HEMA
To investigate how HEMA and silicone-hydrogel (SiHy) contact lenses initially fit on insertion, a study was performed in Birmingham (UK) involving 30 participants (aged 22.9�4.9 years). The aim was to see how the initial fit informs prescribing decisions and reflects end-of-day fit. Subjects were contralaterally fit with HEMA and SiHy contact lenses. Corneal topography and tear break-up time were assessed pre-lens wear. Centration, lag, post-blink movement during up-gaze and push-up recovery speed were recorded after 5min, 10min, 20min and 8h of contact lens wear by a digital slit-lamp biomicroscope camera. Comfort and centration were similar with the HEMA and SiHy lenses, but comfort decreased with time whereas centration remained stable. Movement-on-blink and lag were greater with the HEMA than with the SiHy lens, but movement-on-blink decreased with time after insertion whereas lag remained stable. Push-up recovery speed was similar with the HEMA and the SiHy lens 5-20min after insertion, but was slower with the SiHy after 8h of wear. Lens movement-on-blink and push-up recovery speed after 10-20min of SiHy wear was predictive of the movement after 8h of wear; this was also the case after 5 to 20min of HEMA lens wear. In conclusion, the authors state that a HEMA or SiHy contact lens with poor movement-on-blink/push-up after at least 10min following insertion should be rejected.
|
Advances in Soft Lens Materials and Designs
Soft Lens Material Properties, Lens Surface Wettability and Lubricity
Ongoing research and development efforts strive to improve soft lens comfort and health. Soft lens discomfort remains the primary reason for lens wear discontinuation, despite decades of contact lens development and improvement. Today, new lens materials and designs focus primarily on improving the soft lens surface, as bulk lens properties (e.g., oxygen permeability) have been thoroughly addressed over the years. Current thinking among contact lens researchers is that improved soft contact lens surface wettability provides better pre-lens tear film stability and, consequently, improves lens comfort. In addition to providing better pre-lens tear film stability, a strongly hydrophilic surface likely promotes high soft lens lubricity (i.e., low soft lens-sliding friction). Over the past several years, significant effort has been directed toward quantifying and reducing lens-sliding friction in vitro. It is unclear at this point, however, whether such improvement in surface properties will improve lens comfort and to what degree. Standardized in-vitro procedures for assessing surface properties, along with prospective, randomized, controlled clinical studies, are warranted to definitively correlate soft lens surface properties with soft lens wearing comfort, the paper states.
|
Red-Tinted Lenses & Quality of Life in Retinal Disease
Centrally Red-tinted Soft Lenses, Photophobia, Vision Function
To determine the benefits provided by centrally red-tinted contact lenses on visual acuity, contrast sensitivity (CS), photophobia, and quality of life in patients with degenerative retinal diseases, investigators from Israel evaluated nine patients (aged 15 to 22 years) with severe photophobia and poor visual acuity. Each patient underwent a full eye examination with and without contact lenses, including visual acuity at distance and near, CS, eye movement recording for nystagmus, refraction, and a fundus examination. All patients completed a low-vision-adapted VFQ 25-Version 2000 quality-of-life questionnaire. Seven of nine patients demonstrated improvement in binocular visual acuity as well as improvement in CS with the tinted contact lenses. Subjectively, all patients described a major improvement in their photophobia both outdoors and indoors as well as a marked improvement in quality of life. Red-tinted contact lenses may improve visual functions, outdoor performance, and quality of life of patients suffering from retinal diseases, the investigators say - and these lenses should be a part of the regular assessment in specialty clinics treating patients who have low vision, glare, and photophobia, it was stated.
|
Soft Lens Fitting using Corneo-Scleral Topography
CASE REPORT
Soft specialty lenses for keratoconus can be manufactured in either hydrogel or silicone hydrogel materials, and these lens designs are typically fit using diagnostic lenses. The goal of this methodology is to match up the sagittal depth of the specialty soft lens with the sagittal height of the eye for the chord diameter of the lens. This is a trial and error process that is more art than science. Diagnostic lens fitting of these patients can challenge and frustrate even the most experienced practitioner. However, corneo-scleral topography will revolutionize the fitting process. Software from corneo-scleral topography can produce a three-dimensional model of a measured eye. Sagittal height data can be calculated and then used to manufacture a custom-designed lens. This ensures an ideal fitting relationship that is determined from one measurement. Power is calculated from refraction or over-refraction of a diagnostic lens. According to the author, corneo-scleral topography will revolutionize the way that we fit specialty contact lenses. The process will become science-based and will eliminate the frustration of the diagnostic lens fitting process.
|
Masking Corneal Irregularities with Soft Lenses
CASE REPORT
Three cases are presented by Lefteris Karageorgiadis, from Greece, regarding aligning soft lenses with the challenging cornea and masking (blending) of the irregular surface. A relatively central keratoconus, a moderate keratoconus and an advanced keratoconus are fitted with specialty lenses. In conjunction with the soft lens materials' low modulus, the availability of higher-Dk materials for specialty soft lenses offer an advantageous alternative to other, more rigid, lens options. Moreover, due to lens design, fit and material selection, corneal warpage can be avoided, offering an additional viable lens modality option for the eye care practitioner. Following insertion of the diagnostic lens, topography can be performed over the lens to immediately visualize the homogenization of the front optical surface of the eye-lens system. In addition, over-refraction techniques such as PSF (Point spread function) used in wavefront aberrometry can minimize practitioners' chair time and can be of great help in the fitting process, the author states. Aberrometry performed with the diagnostic lens on the eye can show the reduction in main high-order aberrations that reduce vision, such as coma, spherical aberration and trefoil. The same measurements are advised with the final lenses on the eye to double-check the end-result.
|
|
 |
This Newsletter is Kindly supported by: 
|
| |
|
|
|
|
