Research Update

Research Update Issue 7

July 2017  

Welcome to our monthly research update
Welcome to Research Update, a new resource available to IACLE and BCLA members to support your teaching and practice. Each month we will send you a summary of some of the interesting findings appearing in peer-reviewed journals that month. Our aim is to help you keep up to date with the latest contact lens and anterior eye research, and to locate articles when you want to know more about a particular topic.
More information on Research Update and how to use it in your contact lens teaching here. Access archived issues via Member Login under Research.
Issue 7 – July 2017
One group of ametropes is arguably less well understood than others: those with astigmatism. In this issue, we look at how different types of astigmatism influence visual acuity and also the possibility of estimating total corneal astigmatism from anterior corneal data.

An Australian research group investigates changes in corneal sensitivity and nerve morphology in orthokeratology. Two reviews look at the effects of refractive interventions on the cornea. A study from China examines changes in tear film and blink pattern after corneal refractive surgery. We also seek an answer to the often-asked practical question: ‘What is the ideal contact lens cessation time prior to corneal refractive surgery?’ And finally, we report a study that explores the impact of increasing myopia on central corneal nerve density.


The IACLE Education Team
COMING SOON: our review of the new TFOS DEWS II Report, now available via The Ocular Surface here and on the TFOS website here
Journals reviewed in this issue  

  Journal of Optometry 10:3
  Cornea 36:7
  Eye & Contact Lens 43:4
  Contact Lens & Anterior Eye Articles in Press
  Ophthalmic & Physiological Optics 37:4

Influence of type of astigmatism on VA
To investigate change in visual acuity (VA) produced by different types of astigmatism (power and orientation of principal meridians) on normal, accommodating eyes, Remón et al used the lens-induced method to simulate astigmatic blur conditions on healthy emmetropic eyes. VA correlated with blur strength in a different way for each type of astigmatism, depending on accommodative demand. VA is better when one of the focal lines lies on the retina irrespective of the axis orientation, while accommodation favors this situation.

Journal of Optometry 2017;10:3 141-148. Click here for full text


Estimating corneal astigmatism from anterior corneal data
Næser et al reviewed the records of 951 patients examined with Pentacam high-resolution Scheimpflug camera to determine keratometric astigmatism (KA), posterior corneal astigmatism (PCA), and total corneal astigmatism (TCA), and to establish a model for estimating TCA from anterior corneal data. They found a strong linear correlation (r2 = 0.90) between KA and TCA meridional powers. TCA could be accurately estimated from anterior corneal data with a new formula. Applications include toric intraocular lens calculation.

Cornea 2017;36:7 828-833. Click here for abstract


Corneal sensitivity and nerve density in Ortho-K
This cross-sectional study by Lum et al looked at changes in corneal sensitivity and nerve morphology in orthokeratology (OK) contact lens wear. Corneal sensitivity, nerve morphology and nerve fiber density (NFD) of 54 subjects grouped in three categories (no lens wear, soft lens wear and OK wear) were measured. There was a significant difference in corneal sensitivity between the three groups. Long-term OK lens wear was associated with a decrease in central corneal sensitivity and NFD. Corneal nerves play an important role in the blink reflex and tear production.

Eye & Contact Lens 2017;43:4 218-224. Click here for abstract


Tear film instability after corneal refractive surgery…
In this study Chen et al investigated associations between changes in tear film instability and the lipid layer thickness (LLT) and blink pattern after corneal refractive surgery (CRS). The LLT and blink pattern of 40 patients were evaluated, one week before and 30 days after CRS. The authors conclude that the LLT and blink pattern are involved in maintaining tear film stability after CRS. Artificial tears containing lipids, and well directed blink training, might be beneficial to maintain tear film stability after CRS.

Cornea 2017;36:7 810-815. Click here for abstract


…and effects of soft CL wear prior to surgery
To examine the influence of previous soft contact lens (SCL) wear on corneal refractive surgery (CRS) outcomes, Lloyd-McKernan et al reviewed patient records for two groups of LASIK and LASIK/PRK patients: those who ceased SCL wear for two weeks or for 24h prior to CRS. CRS outcomes (efficacy, predictability, VA and refractive error) were compared pre-operatively and one and six months post-operatively. Previous SCL wear had no negative impact on visual outcomes compared with a non-CL control group, regardless of previous SCL cessation time. Longer cessation times may be advisable for hyperopic SCL wearers.

Cont Lens Anterior Eye 2017; Click here for full text


Corneal nerve density in myopia
Harrison et al explored the impact of increasing myopia on central corneal nerve density by comparing sub basal nerve plexus density measured by confocal microscopy. Corneal nerves of 70 healthy adult subjects aged 21-50 years were imaged over the central cornea with a Nidek CS4 confocal microscope. Nerves were evaluated using the NeuronJ program for density calculation. Corneal nerve density in the sub-basal plexus decreased with increasing myopia, a noteworthy finding for corneal surgery and contact lens wear.

Ophthalmic Physiol Opt 2017;37:4 297-304 Click here for abstract

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