None listed
Conditions
Brief summary
Following removal of a cataract, an intraocular lens (IOL) is implanted during surgery to enable refractive correction of the eye to maximise vision following surgery. Selecting the correct model and refractive power of the IOL is critical to achieve the appropriate refractive target. A sub-optimally selected IOL will typically result in post-operative residual refractive error, and decreased unaided vision that may be associated with falls and decreased quality of life in many cases. Refractive error is caused by the combined effect of the cornea and the lens and can be divided into lower order aberrations (LOA) and higher order aberrations (HOA). To select an appropriate model IOL to minimise total spherical aberration and accurate assessment of corneal aberration is required prior to surgery. The first part of this study will compare four clinical aberrometers that use different optical principals to assess HOA in the eye. Ocular accommodation is the process by which the crystalline lens adjusts the focus of the eye through conformational changes. A new strategy to accurately assess corneal curvature changes will be developed using 3D printed modifications to existing clinical tomographers and aberromters to allow corneal curvature assessment at near and distance fixation. Using this strategy even small changes in the corneal periphery should be quantifiable to definitively establish of the role of the cornea in accommodation. This is the second part of the project. Cataract surgery typically involves small incisions placed in the peripheral cornea to extract the cataract using phacoemulsification, and to enable implantation of an intraocular lens following cataract removal. The size of the corneal incisions depends on the IOL that is selected and the lens cartridge that is required for insertion. The final part of this study will aim to characterise the relative contribution of wound architecture and corneal biomechanics on surgically induced astigmatism.
Interventions
All the investigations involved in this study are non-invasive and non-contact procedures that are routinely used in clinical ophthalmology.
The first part of the study comparative diagnostic trial to compare clinical aberrometers. Participants will be examined on 4 different types of aberrometers (as described below) at a single half an hour long visit This part will commence in the first instance, approximately a month before the first cataract patient is assessed.
The second is non random
All the investigations involved in this study are non-invasive and non-contact procedures that are routinely used in clinical ophthalmology. The first part of the study comparative diagnostic trial to compare clinical aberrometers. Participants will be examined on 4 different types of aberrometers (as described below) at a single half an hour long visit This part will commence in the first instance, approximately a month before the first cataract patient is assessed. The second is non randomized observational trial to examine changes in corneal curvature associated with ocular accommodation assessed with corneal tomography and aberrometry and the relative influence of corneal biomechanics. Healthy participants will undergo corneal tomography and aberrometry, (Galilei 2 and Orbscan) and corneal biomehanics (Corvis-ST), as described below. The assessments will only take up to half an hour at a single visit. The second part will run concurrently with the third part of the study. The final and arguably the most important part, is observational cohort study to characterise the relationship between corneal incision architecture and corneal biomechanics on two different incision sizes of surgically induced astigmatism following cataract surgery, using clinical aberrometry, corneal accommodation using tomography and corneal biomechanics. In this part, all the patients will be assessed at least a few hours once before the surgery, and 3 times after the surgery, which is standard of care for patients after cataract surgery. Assessments only take about 30 additional minutes more than their regular follow-up visit. Visual acuity: Vision will be assessed using a letter chart. This is done as a standard of care for all the patients undergoing cataract surgery. Slit-lamp biomicroscopy: Standard eye examination will be performed using a special microscope called a slit-lamp, which is used in every eye clinic room. Aberrometry and tomography: The curvature of the front part of eye will be measured using special instruments known as the Orbscan II, Zywave, OPDIII, iDesign and Galilei 2 (only Galilei 2 for the third part). The instruments are used to assess the shape, refractive properties and thickness of cornea. Biomechanical properties of cornea: The biomechanics (rigidity and flexibility) of the front part of your eye will be measured with a special instrument called Corvis-ST. This instrument also uses a gentle air puff for measurement. It does not cause any discomfort or pain to the eyes. Optical Coherence Tomography: The instrument produces high resolution images the front of the eye with a special laser camera called anterior segment - Optical Coherence Tomographer (AS-OCT). Specular microscopy: This technique is used to evaluate the health of corneal endothelium. The endothelial cell density will be quantified after obtaining clinical images.
Sponsors
The University of Auckland
Eligibility
Sex/Gender
All
Age
18 Years to No maximum
Healthy volunteers
Yes
Inclusion criteria
Part 1 and 2: Ametropia <1D (defocus or astigmatism). Participants can be healthy volunteers. Part 3: Patients scheduled for routine cataract surgery.
Exclusion criteria
Part 1: Ametropia >1D (defocus or astigmatism) Part 1, 2 and 3: Pre-existing ocular pathology or previous ocular surgery, Contact lens use, Strabismus, Previous ocular trauma
Outcome results
None listed