Scleral Versus Corneal RGP Contact Lenses in Irregular Cornea Disorders
Condition: Irregular; Contour of Cornea; Keratoconus; Pellucid Marginal Corneal Degeneration; Injury of Cornea; Irregular Astigmatism
MeSH terms: Keratoconus; Astigmatism; Corneal Diseases
Study type: Interventional

Summary: 
      The most common causes for irregular cornea (IC) in hospital contact lens practice are
      Keratoconus (KC) and related cornea thinning disorders. These conditions cause mild to marked
      impairment of vision and cannot be effectively corrected by spectacles and soft contact
      lenses. The gold standard in the management of KC is Corneal Rigid Gas Permeable contact
      lenses (corneal lenses), which correct approximately 90% of the corneal irregularity.

      Compared with a normal cornea, the cornea in KC is irregular and this results in a compromise
      to the fit of rigid corneal lenses. Specifically, they bear on the cornea and this, together
      with the vulnerability of the cornea in KC, are implicated in corneal scarring, and disease
      progression as well as a significantly reduced vision related quality of life (QoL) in KC
      compared with corneal lens wearers who have no KC.

      In cases where the compromise fit of corneal lenses proves problematic, large diameter
      Scleral RGP contact lenses (scleral lenses) may be used as a problem solver. Unlike the
      smaller corneal lenses which bear on the cornea, the scleral lenses completely bridge over
      the cornea and bear on the sclera.

      The aim of this research is to investigate the performance of scleral lenses in KC
      participants who habitually wear corneal lenses.

      The research question: is there a measurable difference in the visual performance and visual
      quality of life in participants with Irregular cornea disorders like keratoconus and other
      related conditions, who habitually wear corneal lenses in comparison with scleral lenses.
    

Detailed description: 
      The cornea is the transparent, fixed focus lens at the front of the eye. The cornea's
      curvature should be regular for good vision. The most common causes of irregular cornea (IC)
      in hospital contact lens practice are Keratoconus (KC) and related cornea thinning disorders.
      These conditions cause mild to marked impairment of vision due to High Order optical
      Aberrations (HOA), which degrade the retinal image quality and cannot be effectively
      corrected by spectacles and soft contact lenses. The gold standard in the management of KC
      are Corneal Rigid Gas Permeable contact lenses (corneal lenses), which correct approximately
      90% of the corneal irregularity.

      The corneal lenses fit differently in patients with a normal cornea compared to KC where they
      bear on the cornea. This fitting characteristic and the vulnerability of the cornea in KC are
      implicated in corneal scarring and disease progression as well as a significantly reduced
      vision related quality of life (QoL) in KC compared with corneal lens wearers who have no KC.

      In cases where corneal lenses are not well tolerated, cause corneal insult, reduced visual
      performance or poor physical fitting characteristic, the large diameter Scleral RGP contact
      lenses (scleral lenses) may be used as a problem solver. Unlike the smaller corneal lenses
      which bear on the cornea, the scleral lenses completely bridge over the cornea and bear on
      the sclera.

      The aim of this research is to investigate the performance of scleral lenses in participants
      who habitually wear corneal lenses.

      Methodology The proposed quantitative experimental methodology is a randomised controlled
      trial (RCT) with cross over. The experimental intervention is a scleral RGP contact lens
      fitted from a fitting set and manufactured to exact specifications to optimise its physical
      fitting characteristics and optical performance. The control intervention is conventional
      design Corneal Rigid Gas Permeable contact lenses (corneal lenses). These lenses are
      considered the gold standard in the management of the visual disability caused by keratoconus
      and other IC disorders (Robertson, Cavanagh 2011).

      Main inclusion criteria; patients aged 18-69 with irregular cornea disorder like keratoconus
      who wear corneal lenses.

      Exclusion criteria: Patients who are satisfied and have good vision and comfort with soft
      contact lenses or spectacles.

      Procedure After the consent procedure all subjects will undergo a National Eye Institute
      Visual Function Quality NEI-VFQ assessment and baseline Best Corrected Visual Acuity (BCVA)
      and Contrast Sensitivity Function (CSF) will be recorded.

      Detailed fitting of an alternative type of corneal lenses and scleral lenses using a state of
      the art design of corneal and scleral RGP lens designs, which have been widely used in many
      clinics world-wide for some years. Appropriate clinical guidelines and best practice will be
      followed for the fitting and use of contact lenses. The lead applicant is a contact lens
      specialist who is highly experienced in fitting corneal and scleral RGP contact lenses.

      Once the fitting has been completed the final lenses will be checked on eye at collection and
      will be checked after three weeks post collection of the best fitting lens and for the final
      results of visual performance and quality of life after 8-12 weeks of daily lens wear.

      After this check up there will be a washout period of at least one month, during which the
      participants will wear their original corneal lenses before the wearing of the other
      intervention is started.

      The crossover to the other lens will be implemented after the washout period. During this
      phase checkups will be performed in an identical manner to the first phase.

      Lens designs and fitting The participants will initially be fitted with corneal lenses and
      scleral lenses to achieve an optimal fit. Horizontal and vertical displacement as well as
      angular scleral lens rotation would be measured to establish best lens parameters. The
      corneal lenses will be the Rose K™ design which is widely used all over the world and
      manufactured by Menicon David Thomas contact lens laboratory. The scleral lenses will be the
      Zenlens™, which is amenable to a wide variety of customised adjustments for fit optimisation,
      manufactured by UCO Lavec BV laboratory in the Netherlands.

      Randomisation The research coordinator, colleague optometrist Anthony Stanton will randomise
      and register the participants to treatment and control groups. The participants and the chief
      investigator will be masked to the type of lens supplied.

      Outcome measures Visual quality Two key measures of visual function, monocular best-corrected
      visual acuity (BCVA) and contrast sensitivity function (CSF) will be assessed at the
      beginning and the end of the lens wearing period and will constitute the outcome measures of
      this RCT. Both BCVA and CSF testing will use a commercially available instrument the CSV
      1000E, which standardises test conditions and has been used in several research studies.

      Quality of life The National Eye Institute-Visual Function Questionnaire (NEI-VFQ) (Mangione
      2000) is a vision-related quality of life instrument designed to assess patients' perception
      of visual function and quality of life. This instrument, which has been used by other
      researchers investigating keratoconus (Kymes et al., 2004, 2008), will be applied as a
      baseline in the beginning of the study and at the completion of the period of use of each
      intervention.

      Statistical and Data analysis A sample size calculation has been carried out that is based,
      conservatively, on a parallel trial design using data from previous research (Marsack, Parker
      et al. 2007, Nejabat, Khalili et al. 2012, Davis, Schechtman et al. 2006). The sample size
      calculation using the (Armitage and Berry, 1987) formula gives a required sample size of 15
      participants in each group. The plan is therefore to continue the study until at least 30
      have completed the study, 15 starting with scleral lenses and 15 with corneal lenses.

      Preliminary checks will be carried out to ensure that there are no carry-over effects from
      the first to the second treatment periods, as recommended in the literature (Haynes et al.,
      2006; Wellek & Blettner, 2012).

      We think it unlikely that there will be cross-over effects because the washout period should
      prevent this. However, in the unlikely event that there are significant washout effects or if
      a large proportion of participants drop out before the second treatment period then the study
      will be treated as a non-crossover RCT and the data from the first period will be analysed in
      the usual way as recommended by Haynes et al. (2006). Our conservative sample size
      calculation allows for this possibility.

      If there is a satisfactory outcome to the preliminary checks then the study will be analysed
      as a cross-over RCT (Haynes et al., 2006; Wellek & Blettner, 2012).

      Plan and timescale The length of participation in the study for each subject is anticipated
      not to exceed 5-7months during which time they are likely to be required to attend on 4-6
      occasions. Study total length is anticipated to be from early 2015 to late 2016. The RCT will
      be conducted at the Central Middlesex Hospital (CMH) Ophthalmology Department where the lead
      researcher is a senior contact lens specialist optometrist.
    

Intervention name(s): Scleral rigid gas permeable contact lenses (SRGPcl) (Zenlens™); Corneal Rigid gas Permeable contact lenses (CRGPcl) (Rose K2)
Intervention type(s): Device; Device
Intervention description(s): Custom manufactured scleral rigid gas permeable contact lenses. These lenses are designed to fit the eye with high level of precision. The aim is to bridge the cornea and fit in alignment with the sclera, thus avoiding any detrimental effects associated with the corneal rigid gas permeable lenses.; The Rose K2 lens is a widely used corneal gas permeable lens designed for keratoconus and other irregular cornea disorders
Other intervention name(s): Scleral lenses; Zenlens; Custom Scleral Contact Lenses; RGP Scleral Lenses; Rose K2 corneal gas permeable contact lenses
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: Randomised control trial with a 2x2 crossover
Masking: Single (Investigator)
Primary purpose: Treatment
Keywords: Corneal rigid gas permeable contact lenses; Scleral rigid gas permeable contact lenses; Custom Scleral contact lenses; Keratoconus; Irregular cornea; Pellucid marginal degeneration; Post keratoplasty irregular cornea; Post refractive surgery irregular cornea; Traumatic irregular cornea