Quarterly newsletter on Soft Specialty Contact Lens
Research, Developments, Designs and Materials SPRING 2013
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WORLD WIDE VISION
Drug Delivering Contact Lenses
One of the greatest opportunities for the development of "specialized" soft lenses may relate to their use as ocular drug delivery devices. The first documented report of using soft lenses to deliver drugs to the ocular surface dates back to 1970. The interest in this topic is evidenced by the fact that almost 150 peer-reviewed publications have addressed this issue since that time, with 25% in the last 3 years. The methods used to deliver the medications are many and varied, with many employing novel approaches based on nanotechnology. Considering the rapidly expanding literature in this field and the level of interest, it appears to be just a matter of time before such devices become commercially available. Logistical issues such as who would be licensed to prescribe such lenses, how the slow leakage of medications into the blister-pack solutions will limit their relevant shelf-life and regulatory approvals to decide what studies are necessary to obtain licensure remain hurdles to overcome, but despite this, research in this area continues unabated. Click here for full report.
Lyndon Jones PhD FCOptom FAAO
Waterloo - Canada
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IN THE LITERATURE
International Survey Data
Status on Contact Lens Use in 2012 and Outlook towards 2013
 The January issue of Contact Lens Specrtum featured the yearly update on the contact lens market over 2012. Jason Nichols in his annual report states that the contact lens field was healthy in 2012, with notable growth in certain lens categories and modalities. In a survey of readers, when asked which specialty lens design has the greatest potential for growth in 2013, respondents indicated 'custom soft lenses' to be number one (49%) followed by hybrids (24%) sclerals (19%) and orthokeratology (8%). Of the respondents, 64% reported using a silicone hydrogel material in 2012 for different lens modalities (spherical, toric, multifocal). This was confirmed by the International Survey Data - more than half of all contact lenses prescribed are with silicone hydrogels worldwide, representing 70% or more of all daily wear soft lens fits in Canada, Colombia, France, the Netherlands and Slovenia. See link above for full table with results of 20.566 lens fits from 36 countries. |
IN THE LITERATURE
Which Soft Lens Power is Better for Piggyback in Keratoconus?
Lens Power, Corneal Topography, Eccentricity, Higher Order Aberrations
Thirty keratoconic eyes were fitted with soft lenses powered -3.00D, -1.50D, plano, +1.50D and +3.00D. Corneal topography was performed over the lens surfaces. Negative powered and plano lenses flattened the ocular surface shape in all cases, whereas positive powered lenses did not induce any significant changes in comparison to the naked eye. Also, significant differences in corneal eccentricities were found over an 8mm cord, with a tendency for increased eccentricity with increasing lens powers. No significant differences were found in higher order aberration root mean square between the different lens powers. It was concluded that negative powered soft lenses provide a flatter anterior surface in comparison to positive powered lenses in subjects with keratoconus and thus might be more suitable for piggyback contact lens fitting.
Romero-Jiminez et al - Contact Lens & Ant Eye, February 2013
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IN THE LITERATURE
Developments in Soft Lens Options for Keratoconus
New Lens Design, Materials, Hypoxia
 To illustrate the momentum of custom soft lenses in specialty lens practices, Neil Pence in Contact Lens Spectrum describes many new lens designs specifically for keratoconus that have become available to us in recent months. 'The increased comfort and easier adaptation are generally gained at the cost of slightly reduced best visual acuity' he concludes. On a precautionary note, the author states, 'these are all very thick soft contact lenses,' and despite the availability in high Dk silicone hydrogel materials - consistant monitoring of hypoxic signs in these patients remains crucial. Photo: Greg DeNaeyer. |
IN THE LITERATURE
Simplified Recording of Soft Lens Fit
Lens Movement, Push-Up Test, Base Curve Radius, Lens Material
In the series of 'classical papers' regarding soft lens fitting, it may be good to take another look at an article by James Wolffsohn et al in Contact Lens & Anterior eye. The study aims to determine the critical fitting characteristics of modern soft contact lens fits. Soft lens behavior was analyzed with eye blinking (central and up-gaze), and excursion lag (up, down, right and left gaze), and push-up movement, centration and coverage were recorded. Lens centration was on average close to the corneal centre. Movement on blink was significantly smaller in up-gaze than in primary gaze. Lag was greatest in down-gaze and least in up-gaze. Push-up test recovery speed was 1.32±0.73 mm/s. Overall lens movement was best determined by assessing horizontal lag, movement on blink in up-gaze and push-up recovery speed. Steeper lens base curves did not have a significant effect on lens fit characteristics. Contact lens material did influence lens fit characteristics, particularly silicone hydrogels, which generally had lower centration and a faster push-up speed of recovery than HEMA lenses.
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Silicone Hydrogels - Ten Years Later
Contact Lens Induced Hypoxia, Safety, Microbial Keratitis
The January issue of Eye & Contact Lens, the journal of the Contact Lens Association of Ophthalmologists, hosts a special on 10 years of silicone hydrogels. It contains no fewer than 18 review articles on the topic. In conclusion, it can be said that hypoxia-related issues are basically resolved in cosmetic soft lens wear of silicone hydrogels. The textbooks on 'contact lens complications' can be rewritten from that standpoint, marking a major breakthrough in the history of contact lens wear. However, the main contact lens complication (microbial keratitis) seems to be present at the same magnitude with silicone hydrogel lens wear as it is with traditional lenses. It appears that hypoxia was not the main driving force behind this, as had been previously thought. 'Making sure the defense mechanisms of the eye are intact' - including the tear film, epithelium and basal membrane in particular - is of crucial importance in preventing corneal adverse events, according to Suzanne Fleiszig at the 'Contact Lens Summit.' The meetings' highlights can be found in the January supplement of Contact Lens & Anterior Eye and in Contact Lens Spectrum of late last year.
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EDUCATION
Over-Topography in Soft Lens Fit Evaluation Matt Lampa & Mark André
In this issue we discuss the importance and implications of performing corneal topography over soft contact lenses, how to interpret the results and the clinical decisions that can be made from such a measurement. When dealing with optic zones of particularly large size (traditional sphere and toric lenses), subtle differences in the centration of optics and line of sight are of minimal visual consequence. However, once the optics become more precise and complex, as in the example of soft lens multifocal optics, the potential mismatch between the patient's line of sight (center of the topographical map) and the center of the lens optics (as evidenced by the difference display) become clinically meaningful. Click here for the full report on over-topography in soft lens fit evaluation.
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