Effect of Peripheral Defocus on Axial Growth in Hyperopes
Condition: Hyperopia; Amblyopia; Anisohyperopia
MeSH terms: Amblyopia; Hyperopia
Study type: Interventional

Summary: 
      Hyperopia, also known as farsightedness, is a common type of refractive error where distant
      objects may be seen more clearly than objects that are near.

      Hyperopia is a known risk factor for amblyopia, (lazy eye), which may occur as a result of a
      squint (turn), or due to different levels of hyperopia between each eye (anisohyperopia).

      Hyperopia and anisohyperopia often persist into adulthood resulting in impairment to
      binocular vision. Current management involves prescribing spectacles or contact lenses to
      correct the hyperopia in each eye, usually as a lifelong intervention.

      In recent years there has been a great deal of interest in delaying progression of myopia
      (short-sightedness) by slowing down the growth of the eye using a particular type of contact
      lens termed a centre-distance multifocal design. There have been some encouraging results in
      this area to date.

      The proposed study here would explore the use of centre-near multifocal design contact lenses
      to encourage growth of the eye, thereby reducing hyperopia. There are three elements to the
      programme of research:

        1. The natural progression of axial growth and refractive error will be measured in
           hyperopic and anisohyperopic subjects aged between 5 and 19. In other words, the natural
           growth of the eye will be followed without any intervention

        2. As a paired eye control study anisohyperopes aged between 8 and 15 will be fitted with a
           centre-near multifocal design contact lens in their more hyperopic eye and a single
           vision contact lens in the fellow eye, if required. The progression of axial growth and
           refractive error will be measured and compared in each eye

        3. Subjects' aged between 8 and 15 with similar levels of hyperopia in each eye will be
           fitted with centre-near multifocal design contact lenses in each eye. The progression of
           axial growth and refractive error will be measured and compared to subjects in the
           natural progression study
    

Detailed description: 
      Currently, hyperopia receives much less research attention than myopia even though the impact
      of moderate to high levels of hyperopia especially in one eye (anisohyperopia) can lead to
      amblyopia if not corrected fully at a young age. Hyperopia occurs as a consequence of
      insufficient ocular growth and a failure to emmetropise (reach the expected normal level) in
      childhood with the majority of hyperopic refractive errors resulting from an eye that is too
      short for its refractive power. In anisohyperopia it is unclear why one eye may remain
      hyperopic while the fellow eye grows towards an emmetropic state. Studies on animals have
      suggested that manipulating peripheral defocus through optical means while simultaneously
      providing correct axial focus can either discourage or encourage axial growth to effectively
      treat myopia or hyperopia respectively. Recent research has established that progression of
      myopia and axial growth can be significantly reduced in children and adolescents through the
      use of bifocal or multifocal contact lenses.

      The optometrist has a central role in the clinical management of refractive error in children
      and in the application of future modalities that may modify the development of ametropia. The
      following proposal, therefore, presents a programme of work that is both relevant to the
      optometrist and novel in hyperopia research. By combining assessment of ocular biometry,
      monitoring of normal growth rates, an intervention study using bifocal contact lenses in
      children will be the first to provide new data on whether human eyes can be stimulated to
      grow in response to a specific type of defocus. Consequently the research will offer a new
      perspective on the management of hyperopia and anisohyperopia. The findings will offer a
      potential new approach towards amblyopia treatment in children and insight into a strategy
      for optimal correction to encourage axial growth in hyperopia.

      There will be three elements to the proposed programme of research:

        -  Refractive error and axial growth will be followed over a three year period in hyperopic
           and anisohyperopic subjects aged between 5 and 19 years old to gain understanding of
           natural progression of these parameters in the specified cohort

        -  Simultaneous vision bifocal/mulitfocal soft contact lenses will be used to encourage
           axial growth in hyperopic children and adolescents with axial hyperopia in an effort to
           reduce hyperopia. The bifocal centre near design contact lenses will be prescribed to
           provide for clear central vision at both distance and near thus exposing the retina to
           peripheral hyperopic defocus from the distance zone

        -  This concept will also be applied to anisometropes as they represent a unique example of
           ocular development, where the two eyes of an individual, with an identical genetic
           background and seemingly subject to identical environmental influences, can grow
           asymmetrically to produce significantly different refractive errors. This correction and
           manipulation strategy has the potential to be applied to the more hyperopic eye to
           encourage eye growth and reduction of hyperopia with associated benefits of improved
           binocular vision and stereopsis.

      For the natural progression study healthy hyperopic children and adolescents aged between 5
      and 19 years of age will be recruited via the researcher's optometry practices and Aston
      University optometry clinic. The growth and visual characteristics of the eyes will be
      followed over time without any intervention by the research team. Following consent, at the
      initial visit, all participants will undergo a number of visual assessments including
      measurement of the axial length of the eye, focusing ability over a range of distances, eye
      muscle balance, vision at a range of different contrasts, pupil size and quality of
      stereovision and objective assessment of the crystalline lens parameters. Measures of the
      participant's spectacle prescription by objective and subjective means will also be
      undertaken following the instillation of eye drops to relax the muscles of the eye and to
      dilate the pupils. The eye drops will take around 40 minutes to work with the pupils
      returning to normal size after approximately 24 hours. The majority of these assessments are
      similar to those undertaken during a routine eye examination. The height of the subjects will
      also be taken at baseline and at six monthly intervals throughout the study. Parents and
      children will also be asked to complete a background questionnaire at this visit. The first
      visit is expected to last around 90 minutes. Participants will be reviewed every six months
      over a period of three years where the measures taken at baseline will be repeated.
      Instillation of eye drops to dilate the pupils and relax the eye muscles will be used on
      alternate visits.

      For the intervention study, at the initial visit all participants will undergo a number of
      visual assessments including measurement of the shape and length of the eye, focusing ability
      over a range of distances, eye muscle balance, vision at a range of different contrasts,
      pupil size and quality of stereovision. Measures of the participant's spectacle prescription
      by objective and subjective means will also be undertaken following the instillation of eye
      drops to relax the muscles of the eye and to dilate the pupils. Subjects in the intervention
      groups will be reassessed after a period of six months to establish a measure of natural eye
      growth prior to being fitted with contact lenses. Parents and children will also be asked to
      complete a background questionnaire at this visit. The first visit is expected to last around
      90 minutes.

      The second visit for the intervention group will be to assess the individual's suitability
      for contact lens wear using a microscope. The participant and parent will be instructed on
      how to insert, remove and care for their contact lenses. The fitting of the contact lenses
      and level of vision will be assessed. For the anisohyperopes, the more hyperopic eye will be
      fitted with a commercially available soft multifocal contact lens and the less hyperopic eye
      will be fitted with a soft single vision contact lens. Subjects with similar levels of
      hyperopia in each eye will be fitted with commercially available soft multifocal contact
      lenses in both eyes. The participant will then be issued with a supply of contact lenses
      along with commercially produced instruction guides on caring for their contact lenses. The
      second visit is expected to last around 90 minutes.

      The child may need to attend for unscheduled visits if any problems arise during the early
      stages of contact lens wear. Otherwise they will be reviewed at one to two weeks after the
      dispensing visit and also one month later for routine contact lens aftercare appointments.

      Participants in the intervention groups will be reviewed at 6, 12, 18 and 24 months after the
      dispensing visit. During these visits the majority of measurements undertaken during the
      initial assessment will be repeated along with routine contact lens aftercare. Eye drops to
      relax the eye muscles and dilate the pupils will be instilled at the 12 and 24 month visits.
      For the anisohyperopic subjects, if the level of hyperopia in the more hyperopic eye reduces
      to a level that matches the less hyperopic eye then the intervention will be stopped. For the
      non-anisohyperopic subjects, the intervention will be stopped when the refractive error has
      reached a mean spherical error of +0.50D. At the end of an intervention period of 24 months
      the participants will be assessed after a period of 6 months to assess the growth of their
      eyes post-intervention.
    

Intervention name(s): Multifocal contact lenses; Single vision contact lenses
Intervention type(s): Device; Device
Allocation: Non-Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: hyperopes; axial length; peripheral defocus