BCLA CLEAR presbyopia: Mechanism and optics.

With over a billion adults worldwide currently affected, presbyopia remains a ubiquitous, global problem. Despite over a century of study, the precise mechanism of ocular accommodation and presbyopia progression remains a topic of debate. Accordingly, this narrative review outlines the lenticular and extralenticular components of accommodation together with the impact of age on the accommodative apparatus, neural control of accommodation, models of accommodation, the impact of presbyopia on retinal image quality, and both historic and contemporary theories of presbyopia.

Translation and validation of the contact lens dry eye questionnaire 8 (CLDEQ-8) in Canadian French.

PURPOSE: To present the process that led to the creation of the French Canadian translated version of the Contact Lens Dry Eye Questionnaire-8 (which allows for an assessment of symptoms while wearing soft contact lenses) as well as the validation data of the f-CLDEQ-8. METHODS: The CLDEQ-8 went through the process of reverse translation, which was then reviewed and improved by an experts' committee to create a first version of the French questionnaire. Cognitive interviews were conducted to pretest the tool and ensure content validity. After a review of the pretest, the f-CLDEQ-8 was created. A web-based version of this questionnaire was sent to contact lens wearers (CLW) recruited out of a clinical setting for completion at two different endpoints interspaced by 7 days. Internal consistency and test-reliability were calculated using Cronbach's alpha and Intra-class Correlation coefficient (ICC), respectively. Convergent validity between the f-CLDEQ-8 score and overall opinion of the contact lenses was evaluated with a correlation. RESULTS: 9 CLW with different socio-economic statuses and education levels went through a cognitive interview with the back-translated version of the f-CLDEQ-8 to improve the questionnaire wording and enhance its comprehension. 63 CLW (34.2 ± 10.1 years old and 2/3 of them women) completed the f-CLDEQ-8 twice. An average Cronbach alpha of 0.928 was found and an ICC of 0.944 (CI at 95 % 0.905;0.966). A moderately strong correlation of -0.714 (CI at 95 % -0.817;-0.566) was found between the overall opinion of the contact lenses and the total score to the f-CLDEQ-8. CONCLUSION: The French language version (f-CLDEQ-8) generated from the original CLDEQ -8 was shown to be easy to use, reliable and culturally adapted to French spoken in Canada.

CLEAR - Orthokeratology.

Orthokeratology (ortho-k) is the process of deliberately reshaping the anterior cornea by utilising specialty contact lenses to temporarily and reversibly reduce refractive error after lens removal. Modern ortho-k utilises reverse geometry lens designs, made with highly oxygen permeable rigid materials, worn overnight to reshape the anterior cornea and provide temporary correction of refractive error. More recently, ortho-k has been extensively used to slow the progression of myopia in children. This report reviews the practice of ortho-k, including its history, mechanisms of refractive and ocular changes, current use in the correction of myopia, astigmatism, hyperopia, and presbyopia, and standard of care. Suitable candidates for ortho-k are described, along with the fitting process, factors impacting success, and the potential options for using newer lens designs. Ocular changes associated with ortho-k, such as alterations in corneal thickness, development of microcysts, pigmented arcs, and fibrillary lines are reviewed. The safety of ortho-k is extensively reviewed, along with an overview of non-compliant behaviours and appropriate disinfection regimens. Finally, the role of ortho-k in myopia management for children is discussed in terms of efficacy, safety, and potential mechanisms of myopia control, including the impact of factors such as initial fitting age, baseline refractive error, the role of peripheral defocus, higher order aberrations, pupil size, and treatment zone size.

Analysis of Two Orthokeratology Lens Designs and Comparison of Their Optical Effects on the Cornea.

PURPOSE: This study aims to analyze two commercial orthokeratology lens designs and compare their optical effects at the corneal level. METHODS: This is a retrospective study on subjects seeking an orthokeratology fitting for myopia management at the Université de Montréal clinic between January 2013 and August 2015. Group A included the first 64 subjects fitted with a 4-curve lens design (Paragon CRT; Paragon) who met the inclusion criteria, whereas group B included the same number of subjects fitted with a 5-curve lens design (Dreamlens; Polymer Technology, Rochester, NY). Topographic tangential maps were collected at baseline and 3 months after fitting. The differential map was generated for each patient and analyzed, which involved determining the radius of the central distance zone (CDZ) and the power and width of the high convex zone (HCZ). Results were compared between the two groups, taking baseline refraction into account. Finally, a correlation was estimated between topographic data and corneal parameters (flat and steep K, the corneal eccentricity of each principal meridian). RESULTS: The CDZ for group A is significantly larger than the one generated for group B both horizontally (t(126)=12.12, P<0.01) and vertically (t(126)=15.690, P<0.01). However, there was no significant difference regarding the HCZ power generated. The only correlations found were a strong positive association between CDZ radius and HCZ power generated by lens A nasally (r=0.450; P=0.000) and temporally (r=0.558; P=0.000), and a weaker association between the baseline refractive error, along with the nasal (r=0.237; P=0.033) and temporal (r=0.288; P=0.028) HCZ power for lens B. CONCLUSION: The four- and five-curve orthokeratology lens designs generate significantly different optical modifications on the cornea. This can affect reports on orthokeratology efficacy for myopia management as well as the lens selection when used for myopia correction.

The use of high modulus silicone hydrogel (SiHy) lens in the management of epithelial defects.

Corneal dystrophies are relatively rare bilateral anomalies. Meesman dystrophy is typically asymptomatic with little effect on visual performance. This case highlights the use of a high modulus silicone hydrogel (SiHy) lens in the management of an atypical presentation of Meesman's dystrophy with associated visual impairment due to epithelial defects. The selection of a SiHy material provided increased oxygenation to re-establish corneal integrity. However, selecting the appropriate modulus was an additional factor to consider in this case since it had a direct effect on the visual outcome. The higher modulus SiHy lenses provided a better visual success for this patient than one with a lower modulus. Modulus consideration may prove to be an additional factor in the lens choice of SiHy in the management of epithelial defects.

Plasma density inside a femtosecond laser filament in air: strong dependence on external focusing.

Our experiment shows that external focusing strongly influences the plasma density and the diameter of femtosecond Ti-sapphire laser filaments generated in air. The control of plasma filament parameters is suitable for many applications such as remote spectroscopy, laser induced electrical discharge, and femtosecond laser material interactions. The measurements of the filament showed the plasma density increases from 10(15)cm(-3) to 2 x 10(18)cm(-3) when the focal length decreases from 380 cm to 10 cm while the diameter of the plasma column varies from 30 microm to 90 microm. The experimental results are in good qualitative agreement with the results of numerical simulations.