 |
|
Ocular Topography and Soft Contact Lens Fit
 The problem of contact lens dropout continues to affect the contact lens industry, with discomfort cited as the primary reason for discontinuation among lens wearers. The underlying causes of contact lens discomfort are many and varied, as indicated in a recent TFOS report (see item below) summarizing the problem. In the report, discomfort was attributed to factors related to the 'lens' (including lens material, design, fit and the lens care system/packaging used) and the 'environment' (including inherent or modifiable patient factors as well as ocular and/or external environmental factors). It stands to reason that a poorly fitting lens will adversely affect comfort; however, of the factors relating to lens fit, relatively little work has been published regarding ocular topography and soft contact lens fit. Recent advances in imaging technology and improved modelling have allowed us to more accurately predict the behavior of soft contact lenses on eye, with the aim of improving comfort for lens wearers. Soft contact lens fit could be related to the shape of the ocular surface (central corneal and peripheral ocular profile) and could predict up to 24% of the variance in certain lens fit parameters. More recently, a mathematical model to better understand the factors governing soft lens fit has been proposed that is based on the work of Kikkawa, in which the peripheral portion of soft lenses act like a series of concentric elastic rubber bands that progressively stretch to accommodate changes in the peripheral ocular curvature; the mathematical model employed a novel ellipto-conical corneal model to calculate lens edge strain as a predictor of lens tightness on eye. This approach seems very promising. To read more about this topic, click the link below.
Lee Hall BSc (Hons) PhD FBCLA
Investigator at Visioncare Research and Visiting Research Fellow at Aston University (UK)
|
 
Discomfort and Dryness with Contact Lens Wear
The Link between Ocular Surface Health and Soft Lens Wear Success
Also in Contact Lens Spectrum, Desmond Fonn looks at dryness and discomfort in soft lens wear. The premise or belief is that any pre-existing condition of the ocular surface, including tear film abnormalities, can influence how well patients are able to wear contact lenses and/or may predispose lens wearers to some level of discomfort while wearing lenses. 'Contact lens dryness' is sometimes used by patients as a symptom of contact lens wear, he writes, but that is actually a misnomer because it is unlikely that the contact lens actually becomes dry. Rather, it is the eye that feels dry, Fonn states. If the etiology of contact lens-related discomfort could be uncovered and remedied, it would appear reasonable to estimate that the number of contact lens wearers could be 40% to 50% greater than it currently is, according to Fonn. The most revealing - and disappointing - result of the Tear Film and Ocular Surface Society (TFOS) workshop is that very little is known about the etiology of CLD, although the TFOS Contact Lens Interactions with the Ocular Surface and Adnexa subcommittee concluded that LWE and meibomian gland dysfunction had the strongest association with contact lens-related discomfort. Fonn concludes his review by saying: 'Placing a contact lens on the ocular surface initiates multiple interactions with the eye that will ultimately determine the success or failure of lens wear. For patients to enjoy a lifetime of successful contact lens wear requires vigilant ongoing care by practitioners, ensuring patient compliance and that they always use the most suitable lenses and lens care products as recommended by their eyecare practitioner.' Ian Cameron and James Wolffsohn at the BCLA's 2015 clinical conference in Liverpool (UK) recently also looked at the TFOS International Workshop on Contact Lens Discomfort and concluded that there was no firm evidence for one specific management strategy. Also in their opinion, it may be the eye care practitioner that has the key to success - taking all variables into account. Cameron, an eye care practitioner from the UK, suggested that the various TFOS committees had spent a whole year "climbing a mountain and found us [eye care practitioners] at the top." Fonn, Contact Lens Spectrum - May 2015 |
The Modern Role of Soft Lenses for the Irregular Cornea
Customized Lens Powers, Thickness, Peripheral Systems, Diameter and Toricity
Mary Jo Stiegemeier in Contact Lens Spectrum looks at managing irregular corneas with soft lenses. Today, there are a number of ways to utilize soft lenses in the care of irregular cornea patients, she writes. In the past, we have used higher-modulus soft lenses to mask irregular astigmatism in the early stages of keratoconus, and we have used soft lenses as a base lens in piggyback lens systems, which still continues to work very well for managing keratoconus.
However, these options may not be enough as a patient progresses in the disease process. In recent years, new soft lens designs have become available that can help extend patients' wear time, improve comfort and physiology, and change that contact lens continuum. Today, advances in both specialty soft contact lenses and in our knowledge of the corneal, limbal, and scleral contour make this possible, as specialty lens laboratories can customize soft lens powers, thickness, peripheral systems, diameter and toricities to help improve patients' vision, comfort and wearability. A number of case reports are presented.
Stiegemeier, Contact Lens Spectrum - May 2015
|
Subjective versus Objective Soft Lens Evaluation On-Eye
Future technology may optimize soft lens evaluation on-eye
Lurdes Belda-Salmerón, Tom Drew, Lee Hall and James Wolffsohn looked at the usefulness of subjective soft lens evaluation. Soft lens centration, horizontal lag, post-blink movement in up-gaze and push-up recovery speed were assessed subjectively (by four observers) and objectively from slit-lamp biomicroscopy captured images and video. They found that experienced observers were variable in their estimations, that subjective estimates used less range than objective measures, that subjective estimates had lower precision and that subjective estimates generally had poorer repeatability than objective measures. The investigators concluded based on this that objective image analysis allows an accurate, reliable and repeatable assessment of soft contact lens fit characteristics, being a useful tool for research and optimization of lens fit in clinical practice. Eye care practitioners should be aware of this, and future technology may aid in objective assessment to improve soft lens evaluation on-eye.
|
European Academy of Optics and Optometry
Refractive Surgery Outcome, Pre-lens Tear Film Stability, Lens Edge Shape
A number of posters presented at the EAOO meeting in Budapest in May referred to soft lens fitting. McKernan O'Dwyer and Manion investigated the influence of previous soft contact lens wear on outcomes of corneal refractive surgery. There was a trend toward equal or even superior refractive surgery outcomes for efficacy, predictability and safety in the two weeks lens cessation group compared to the non-lens wearing group. These findings were reiterated in the 24 hours lens cessation group, with a trend toward superior refractive surgery outcomes for efficacy, predictability and safety compared to the non-lens wearing group following LASEK/PRK.
Müller, Marx and Sickenberger looked at subjective comparison of pre-lens tear film stability with video topography in daily disposable contact lenses. They observed three different lenses and found that the used method is suitable to evaluate in-vivo pre-lens tear film stability. From the results, they concluded that lens materials that release wetting agents and biocompatible materials can have a positive impact on the patient's lens wearing experience after 12 hours of wear.
Analysis of edge profile and lens design of daily contact lenses using optical coherence tomography (OCT) was the topic of a study by Roth and Rapp. They used modern OCT and high-resolution imaging to investigate edge profile and lens design of contact lenses on the eye. Four different daily wear contact lenses from four different manufacturers were included in the study and observed in-vivo on 36 eyes of 18 human subjects. Using this technique, they could identify different edge shapes (one-sided edge profiles, two-sided edge profiles, round apex, etc.).
EAOO meeting Budapest (HU), May 2015
|
ARVO 2015 Coverage
Photophobia Lenses, Drug Delivery, Toric Soft Lenses
A range of soft (specialty) lens topics were presented at the Association for Research in Vision & Ophthalmology (ARVO) meeting this spring. Greenspan (poster # 3081) described the use of prosthetic tinted lenses in photophobia. After a concussion, lights seem brighter and more painful in some patients. This can affect work, daily activities and quality of life in general. Sunglasses may not be very convenient indoors - but tinted soft lenses can block bright lights and provide comfort for the patient the study found.
Drug delivery with contact lenses has the potential to revolutionize how we treat ocular diseases, but our understanding of drug delivery on the eye has been hindered by the lack of an appropriate eye model. Previous studies reported a rapid drug release and plateau phenomenon that results from using a large volume vial as the release system. But Phan et al (poster # 3085) developed a new eye model that simulates the tear volume and tear flow similar to an on-eye situation. They found with this new model, with low volume physiological tear flow, that commercial lenses can maintain a sustained drug release profile for up to 24 hrs. The results suggest that contact lenses are promising devices for ocular drug delivery.
Conventional methods in contact lens practice using a slit lamp to evaluate toric contact lens' orientation and rotational stability are subjective, time-consuming, and not always precise. A novel video processing-based algorithm was developed by Aghazadeh et al (poster # 3091) to automatically track the standard orientation mark on contact lenses and provide an objective method to evaluate their rotational stability. The method provided means to better evaluate toric contact lens rotational stability compared to subjectively, can help better understand lens dynamics on eye with various toric lens ballast designs, and can help better understand lens rotation between blinks / during blinks and with lens superior-inferior movement.
Another novel technique is the use of toric soft lenses in vitreous surgery. Ohzeki et al studied the visibility of the fundus in a model eye inserted with a toric intraocular lens (IOL). Based on the results of the experiment, they concluded that toric contact lenses for vitreous surgery appear to be useful for improving the visibility during vitreous surgery in eyes implanted with toric IOLs.
ARVO meeting Denver (USA), May 2015
|
|
Custom Multifocal Lens Update 2015 Webinar
GPLI live webinar available online
Regarding presbyopic lens correction, 'no one lens or one lens design is going to work for everybody. And we probably should be happy about that' states Doug Benoit in a live webinar (April 2015) on the Custom Contact Lens Education platform GPLI, formerly known as the RGP Lens Institute. According to Benoit, this gives the specialty lens practitioner the opportunity to excel and make a difference for patients. Considering, and offering, a range of options is the solution to the problem. Apart from new materials, he emphasizes the role that new technology such as corneal topographers and wavefront aberrometers can play in optimizing presbyopic lens correction. The availability of a variety of designs has resulted in an increase in the success rate, according to Benoit. |
 |
This Newletter is Kindly supported by: 
|
| |
|
|
|
|
