Exploring the Psychophysics of Keratoconus Using the Moorfields Acuity Chart

Study Overview
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Brief Summary
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The measurement of visual acuity is made using black letters of varying size superimposed on a uniform white background. The objective is to determine the smallest letter, or optotype, that can be correctly identified. One limitation of current tests is the variability of measurements, this making it difficult for clinicians to determine if changes in visual acuity are related to ocular disease. This variability has been attributed to the design of current optotypes, in particular their differing legibilities. Our group has recently demonstrated that a new type of letter chart (Moorfields Acuity Chart), containing letters with a black core and a white border presented on a grey background, reduces the variability of visual acuity measurements. In this study the investigators wish to determine if changes in vision owing to keratoconus, a disease that causes the cornea to adopt an irregular shape, may be detected more easily using the Moorfields Acuity Chart compared with conventional letter charts.

Official Title
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Exploring the Psychophysics of Keratoconus Using the Moorfields Acuity Chart

Conditions
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Keratoconic Subjects

Intervention / Treatment
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* Device: Moorfields Acuity Chart


Participation Criteria
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Eligibility Criteria
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Keratoconic subjects (50): Age 18-40 years. The presence of keratoconus in at least one eye. The absence of significant media opacities (e.g. cataract, corneal scarring). The absence of any other ocular pathology (e.g. glaucoma, diabetic retinopathy, uveitis). The absence of amblyopia in the test eye. No previous ocular surgery (e.g. corneal crosslinking, cataract surgery, etc.) Best corrected visual acuity better than or equal to 6/60 (1.0 logMAR). Pupil diameter ≥3 mm and ≤7 mm in normal room illumination. Healthy subjects (30): Age 18-35 years. The absence of clinically significant keratoconus. The absence of significant media opacities. (e.g. cataract, corneal scarring). The absence of any other ocular pathology (e.g. glaucoma, diabetic retinopathy, uveitis). The absence of amblyopia in the test eye. No previous ocular surgery (e.g. corneal crosslinking, cataract surgery, etc.) Best corrected visual acuity better than or equal to 6/9 (0.1 logMAR). Pupil diameter ≥3 mm and ≤7 mm in normal room illumination.

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 35 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Non-Randomized
Intervention Model: Single Group Assignment
Interventional Model Description: This in a basic science exploratory study to examine the effect of keratoconus on visual acuity as measured using pseudo-high-pass filtered optotypes. The MAC will be compared with the standard charts currently used to monitor visual acuity (logMAR chart) and contrast sensitivity (Pelli-Robson). Researcher effects and researcher bias will be controlled by setting a written protocol for all testing procedures. Each procedure will be standardised and random checks will be made by the chief investigator on all anonymous record sheets. Neither the chief investigator nor the co-researchers will act as participants for this study.
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Keratoconic subjects<br>Short clinical interview (Questions pertaining to ocular and systemic health, medications, family history and date of birth). (approx. 2 minutes) Visual acuity measurement using EDTRS chart at 4 m (approx. 4 minutes) Refraction: retinoscopy and subjective, at 4m (approx. 10 minutes) Anterior eye examination (approx. 4 minutes) Fundus examination using binocular indirect ophthalmoscopy or a standard ophthalmoscope - to screen for eye disease that is likely to affect visual ability in this study. (approx. 5 minutes) Corneal topography measurement with an Oculus Pentacam (Oculus Gmbh., Germany). (approx. 5 minutes) Two measurements of visual acuity will be made: Standard ETDRS logMAR acuity measurement (5 minutes) Vanishing Optotype logMAR acuity measurement (5 minutes) | Device: Moorfields Acuity Chart<br> <br> |
| Experimental: Healthy subjects<br>Short clinical interview (Questions pertaining to ocular and systemic health, medications, family history and date of birth). (approx. 2 minutes) Visual acuity measurement using EDTRS chart at 4 m (approx. 4 minutes) Refraction: retinoscopy and subjective, at 4m (approx. 10 minutes) Anterior eye examination (approx. 4 minutes) Fundus examination using binocular indirect ophthalmoscopy or a standard ophthalmoscope - to screen for eye disease that is likely to affect visual ability in this study. (approx. 5 minutes) Corneal topography measurement with an Oculus Pentacam (Oculus Gmbh., Germany). (approx. 5 minutes) Two measurements of visual acuity will be made: Standard ETDRS logMAR acuity measurement (5 minutes) Vanishing Optotype logMAR acuity measurement (5 minutes) | Device: Moorfields Acuity Chart<br> <br> |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| The relative difference in visual acuity measurement between subjects with and without keratoconus when examined with different types of visual acuity chart. |  | 9 months | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| The relationship (if any) between optical imperfections (high order aberrations) and measurements of visual acuity when measured using different test chart designs. |  | 9 months |