Quarterly newsletter on Soft Specialty Contact Lens
Research, Developments, Designs and Materials WINTER 2015
|
Contact Lens Dewetting
Assessment of Lens Biocompatibility with the Tear Film
Adequate wettability of the contact lens surface is known to be important to maintain a stable and evenly spread tear film. Contact lens manufacturers strive to develop materials that mimic the wettability of the corneal epithelium and are as biocompatible with the tear film as possible. A uniform tear film layer over a lens is essential for good vision and lubrication as well as for preventing deposit formation and infections. Apart from evaporation, dewetting - a phenomenon directly related to lens surface properties - may play a major role in this. Dewetting, by definition, describes the rupture of a liquid film and formation of droplets like the ones observed with the slit lamp biomicroscope when the light is scattered on a drying lens surface. It seems reasonable to believe that to reduce the prevalence of contact lens-related discomfort, more attention should be dedicated to the assessment of the pre-lens tear film when prescribing a contact lens. Some steps in this direction have been taken, as some commercially available videokeratoscopes have developed dedicated software for tear film surface analysis. Click here for full report.
Dorota H. Szczesna-Iskander PhD
Wroclaw University of Technology, Wroclaw, Poland
|
|
IN THE LITERATURE
Lathed Soft Toric Contact Lenses for Eyes with Intrastromal Corneal Ring Segments
Lathed Soft Toric Lenses, Intrastromal Rings, Vision, Comfort
To assess the feasibility of fitting a lathed soft toric contact lens after the implant of intrastromal corneal ring segments to treat keratoconus, Carballo-Alvarez et al conducted a study on 47 eyes of 47 patients. The soft lenses were successful in 75%, 66.66% and 0% of the intrastromal corneal ring segments implanted eyes with respectively stages I, II and III keratoconus. Lathed soft toric contact lens fitting is a feasible option in a large proportion of patients implanted with intrastromal corneal ring segments
they concluded. When these lenses are unsatisfactory, a Piggy-Back system is a good alternative the authors suggest.
Photo: Gert Vanschoenwinkel (Belgium)
|
IN THE LITERATURE
Soft Lenses versus Irregular Astigmatism
Base Curve, Lens Thickness, Lens Power, Paracentral Fitting Curve 
'Specially designed custom soft lenses can provide great vision and comfort for irregular cornea patients,' writes Joel A. Silbert in an extended coverage on the topic in the December issue of Contact Lens Spectrum. He describes several different soft lens options for keratoconus and the irregular cornea. For one of them, which may apply to others as well, he advises to:
1. Determine the central base curve based on average Ks (or Sim Ks if using topography).
2. Determine lens thickness (IT Factor): use the lowest IT Factor that produces regular mires verified by over-keratometry.
3. Determine the total lens power needed: compensate for vertex distance as well as for rotation when adding the sphero-cylindrical over-refraction to your spherical test lens.
4. Determine the para-central lens fit: excessive lens movement or edge lift requires use of a steeper fitting curve.
The gains in comfort with customized soft lenses are well worth the additional chair time spent in fitting them, Silbert writes. Good lens movement and the use of silicone hydrogel materials can help provide irregular corneas with improved metabolism and reduce the risks of vascularization. Because of the increased thickness of these materials, be prepared to see more movement than with other types of soft contact lenses (0.75mm to 1mm of movement is desirable). Greater amounts may result in increased lens awareness, although this may improve with adaptation.
|
|
IN THE LITERATURE
Soft Designs for Keratoconus
RGP Intolerance, Custom Soft Contact Lenses, Comfort, Visual Acuity
The first FDA-cleared soft contact lens for keratoconus was manufactured on Jan. 4, 1979, write Patrick Caroline and Mark André. Since then, several custom soft contact lens manufacturers have developed or distributed soft lenses for keratoconus. In the United States, these include Flexlens (X-Cel Contacts), Soft K (Advanced Vision Technologies), NovaKone (Alden Optical), KeraSoft IC (B+L) YamaKone IC (C&E Vision Services, Inc.), and Hydrakone (Visionary Optics, LLC). A 32-year-old patient was referred to them with the diagnosis of keratoconus and RGP lens intolerance. With fenestrated Soft K lenses of OD 7.60mm base curve, 14.2mm diameter, -6.50D power, 0.40mm center thickness and OS 7.90mm base curve, 14.2mm diameter, -2.25D power, 0.40mm center thickness, the patient was able to achieve all-day comfort and visual acuities of OD 20/30 and OS 20/25.
|
IN THE LITERATURE
Presbyopia I
Monovision, Multifocal Soft Lenses, Customization
A study published in Eye & Contact Lens looks at the performance of monovision versus four different soft multifocal lenses under dim and glare conditions. The outcome under these suboptimal light conditions appears to be in favor of the monovision systems. See full abstract via the link below this item. Ron Watanabe in Contact Lens Spectrum writes about 'Advancing Soft Multifocal Contact Lens Design.' Today's soft multifocal options include aspheric, concentric, multi-zone, alternating zone, and segmented designs, and there are daily disposable and high-Dk frequent replacement options. But custom designs offer even more versatility, he states. Specialty labs can make lenses with virtually any curvature, diameter, and power. Each lab may have more than one design available. They can make lenses with center-distance or center-near zones. A few custom labs have the ability to adjust the diameter of the center power zone. This gives a practitioner the ability to customize the power zones to different pupil sizes, and it also provides more flexibility in fine-tuning vision at distance and near based on a patient's visual response according to the author.
|
IN THE LITERATURE
Presbyopia II
Aberrations, Future, Generation X
Many patients abandon contact lenses at the onset of presbyopia due to reduced quality of vision, Pete Kollbaum and Arthur Bradley write in Review of Cornea & Contact Lenses. 'The decrease in perceived quality of vision reported by patients with simultaneous image multifocal lenses is most likely a direct result of the unavoidable presence of a defocused image in the combined multifocal image,' they state. When a standard soft lens is placed on their eye, aberrations are induced. A center-near soft multifocal lens induces some negative spherical aberration, for instance. Also, aberrations are induced when a lens decenters on their eye - often inferiorly and/or temporally. This needs to be corrected for, but to do so it is imperative to know the baseline situation of the aberrations of the eye. These arguments imply that multifocal corrections can be improved by measuring/knowing the aberration structure of our patients' eyes and the contact lenses we aim to use. Glenda Secor in the same special looks at the practice management side of dealing with presbyopia in contact lens wearers: 'Change is Good: Encouraging the Switch to Multifocals' is the title of the online article. She specifically mentions Generation X: The newest generation of presbyopes, those of us born between the early 1960s and early 1980s. Their needs and expectations are unique to their generation and life experiences. They have always known technology as a tool to enhance their lives, and their self-reliance and independence sometimes makes change even more difficult, she writes. According to the author, flexibility and creativity with mature presbyopes is key to their success. For more: see the 'Perspectives on Presbyopia' special via the link below.
Review of Cornea & Contact Lenses - Nov 2014
|
IN PRACTICE
High or Low SAG? Soft Lens Fitting or Soft Lens Selection
The sagittal value (SAG) of lenses is important in soft lens fitting, according to Jaime Ibanez from Colombia. In fact, he asks, 'Do you fit or do you select soft contact lenses?' Several images on the blog on his website show high and low sagittal heights of eyes, with ill-fitting soft lenses on eye. Some images depict a very steep irregular corneo-scleral shape with a low-sagittal value lens, which caused the formation of folds as the lens landed flat onto an ocular surface with a high sagittal depth. After modifying lens parameters such as base curve radius, peripheral curve radius and diameter, the sagittal value of the lens increased to match the shape of the corneo-scleral profile. The result was a well-centered lens that aligned its optical center with the visual axis and a tangential resting area onto the conjunctiva. According to Ibanez, manufacturers should provide the SAG value and the eccentricity of their contact lenses and contribute to scientifically fit contact lenses instead of those fit by trial and error and guessing. And we should stop selecting lenses based on the incorrect association between the base curve and the keratometry readings, he states.
SRPCIRCLE blog Jaime Ibanez
|
|
|
|
|
|
This Newletter is Kindly
supported by:
|
|
