Factors affecting image magnification in indirect ophthalmoscopy with Volk or similar lenses and a biomicroscope.

Purpose: To explore the factors affecting the linear magnification of the intermediate fundus image during indirect ophthalmoscopy with a slit-lamp biomicroscope.

Methods: A simple paraxial model, based on a 'reduced' eye and a 'thin' ophthalmoscopy lens, is used to develop equations showing the effects of the power and ametropia of the eye, and the equivalent power and position of the ophthalmoscopy lens on fundus magnification. Predicted magnifications are compared with practical results found in earlier published experimental studies, which used Volk ophthalmoscopy lenses in conjunction with physical model eyes with adjustable levels of axial ametropia.

Customised aberration-controlling corrections for keratoconic patients using contact lenses.

Technological advancements in the design of soft and scleral contact lenses have led to the development of customised, aberration-controlling corrections for patients with keratoconus. As the number of contact lens manufacturers producing wavefront-guided corrections continues to expand, clinical interest in this customisable technology is also increasing among both patients and practitioners. This review outlines key issues surrounding the measurement of ocular aberrations for patients with keratoconus, with a particular focus on the possible factors affecting the repeatability of Hartmann-Shack aberrometry measurements.

Optical quality and visual performance with customised soft contact lenses for keratoconus.

Purpose: This study investigated how aberration-controlling, customised soft contact lenses corrected higher-order ocular aberrations and visual performance in keratoconic patients compared to other forms of refractive correction (spectacles and rigid gas-permeable lenses).

Methods: Twenty-two patients (16 rigid gas-permeable contact lens wearers and six spectacle wearers) were fitted with standard toric soft lenses and customised lenses (designed to correct 3rd-order coma aberrations). In the rigid gas-permeable lens-wearing patients, ocular aberrations were measured without lenses, with the patient's habitual lenses and with the study lenses (Hartmann-Shack aberrometry).

Exploring the optimum step size for defocus curves.

Purpose: To evaluate the effect of reducing the number of visual acuity measurements made in a defocus curve on the quality of data quantified.

Setting: Midland Eye, Solihull, United Kingdom.

Design: Evaluation of a technique.

Optical quality for keratoconic eyes with conventional RGP lens and simulated, customised contact lens corrections: a comparison.

Purpose: To compare monochromatic aberrations of keratoconic eyes when uncorrected, corrected with spherically-powered RGP (rigid gas-permeable) contact lenses and corrected using simulations of customised soft contact lenses for different magnitudes of rotation (up to 15°) and translation (up to 1mm) from their ideal position.

Methods: The ocular aberrations of examples of mild, moderate and severe keratoconic eyes were measured when uncorrected and when wearing their habitual RGP lenses. Residual aberrations and point-spread functions of each eye were simulated using an ideal, customised soft contact lens (designed to neutralise higher-order aberrations, HOA) were calculated as a function of the angle of rotation of the lens from its ideal orientation, and its horizontal and vertical translation.

Changes in refraction, ocular aberrations, and corneal structure after suspending rigid gas-permeable contact lens wear in keratoconus.

Purpose: This study reports on changes in visual acuity, ocular higher-order aberrations, and refraction after suspending rigid gas-permeable lens wear for 1 week in 15 patients with moderate to severe keratoconus. Alterations in the anterior surface, central corneal powers and axes, and central corneal thickness were also explored.

Methods: Scheimpflug photography and Hartmann-Shack aberrometry were performed at 2 visits, 7 days apart, after the patients had removed their habitual contact lenses.

Visual performance and optical quality with soft lenses in keratoconus patients.

Purpose: To assess visual performance and ocular aberrations in keratoconic patients using toric soft contact lenses (SCL), rigid-gas-permeable (RGP) contact lenses and spectacle lens correction.

Methods: Twenty-two keratoconus patients (16 RGP lens wearers and six spectacle wearers) were fitted with toric SCL. Ocular aberrations were measured with and without the patient's habitual RGP lenses and with the SCL in place.

Repeatability of ocular aberration measurements in patients with keratoconus.

Purpose: To explore the repeatability of lower-order and higher-order ocular aberrations measured in patients with keratoconus.

Methods: The IRX-3 (Imagine Eyes, Paris, France) aberrometer was used to record lower-order and higher-order aberrations in 31 eyes of 31 patients with keratoconus. Four monocular measurements were taken consecutively for each patient.

Forward light scatter and contrast sensitivity in keratoconic patients.

Purpose: The aim of this study was to obtain intraocular forward light scatter (FLS) data in keratoconus patients and to explore possible relationships with contrast sensitivity.

Method: Intraocular straylight was assessed in the right eye of 10 visually-normal subjects (31±5 years) and 5 keratoconus patients (34±9 years) using the van den Berg straylight meter. Contrast sensitivity was also measured in both groups, with and without a glare source provided by the Brightness Acuity Tester (BAT), using a Pelli-Robson chart.

Corneal changes after suspending contact lens wear in early pellucid marginal corneal degeneration and moderate keratoconus.

Objectives: This case study reports on how refraction, visual acuity, and ocular higher-order aberrations changed after rigid gas-permeable (RGP) lens wear was suspended by a patient with early pellucid marginal corneal degeneration (PMD) and by a patient with moderate keratoconus. Alterations in central corneal power and axes, central corneal thickness, and corneal topography were also explored.

Methods: Ocular aberrations and Scheimpflug photography were measured at 2 visits, 7 days apart, after the patients had removed their contact lenses.

Pellucid corneal marginal degeneration: A review.

Pellucid marginal corneal degeneration (PMD) is a rare ectatic disorder which typically affects the inferior peripheral cornea in a crescentic fashion. The condition is most commonly found in males and usually appears between the 2nd and 5th decades of life affecting all ethnicities. The prevalence and aetiology of this disorder remain unknown.

A comparison between subjective refraction and aberrometry-derived refraction in keratoconus patients and control subjects.

Purpose: This study compares the differences in the magnitude of the subjective refraction and three aberrometry-derived refractions along with visual acuity achieved with these refractions in a group of keratoconic patients and age-matched normal subjects.

Materials And Methods: Subjective refraction and Hartmann-Shack aberrometry was performed on six keratoconus patients and 12 normal subjects. In addition, the logMAR visual acuity achieved using the subjective and aberrometry auto-refraction data were measured in the six keratoconic subjects.

Dynamics of ocular aberrations in keratoconus.

Background: The aim was to investigate the fluctuations in monochromatic ocular aberrations with accommodation and tear-film changes in moderate keratoconic eyes.

Methods: We measured the changes in ocular higher-order aberrations in 10 moderate keratoconic and 10 visually normal eyes to accommodative stimuli ranging from zero to 5.00 DS using a Hartmann-Shack aberrometer.

Visual acuity and ocular aberrations with different rigid gas permeable lens fittings in keratoconus.

Objectives: The aim of this case report is to investigate the effect of rigid gas permeable (RGP) lens fitting on visual acuity and ocular higher-order aberrations by systematically applying RGP lenses with different back optic zone radii (BOZR) to a keratoconic eye.

Methods: Eight Menicon-EX RGP lenses (Menicon Co., Nagoya, Japan), which ranged from a BOZR of 7.