Contrast is the differential luminance between one object and another. Contrast sensitivity (CS) quantifies the ability to detect this difference: estimating contrast threshold provides information about the quality of vision and helps diagnose and monitor eye diseases. High contrast visual acuity assessment is traditionally performed in the eye care practice, whereas the estimate of the discrimination of low contrast targets, an important complementary task for the perception of details, is far less employed. An example is driving when the contrast between vehicles, obstacles, pedestrians, and the background is reduced by fog. Many conditions can selectively degrade CS, while visual acuity remains intact. In addition to spatial CS, “temporal” CS is defined as the ability to discriminate luminance differences in the temporal domain, i.e., to discriminate information that reaches the visual cortex as a function of time. Likewise, temporal sensitivity of the visual system can be investigated in terms of critical fusion frequency (CFF), an indicator of the integrity of the magnocellular system that is responsible for the perception of transient stimulations. As a matter of fact, temporal resolution can be abnormal in neuro-ophthalmological clinical conditions. This paper aims at considering CS and its application to the clinical practice.
Perception is the ability to see, hear, or become aware of external stimuli through the senses. Visual stimuli are electromagnetic waves that interact with the eye and elicit a sensation. Sensations, indeed, imply the detection, resolution, and recognition of objects and images, and their accuracy depends on the integrity of the visual system. In clinical practice, evaluating the integrity of the visual system relies greatly on the assessment of visual acuity, that is to say on the capacity to identify a signal. Visual acuity, indeed, is of utmost importance for diagnosing and monitoring ophthalmological diseases. Visual acuity is a function that detects the presence of a stimulation (a signal) and resolves its detail(s). This is the case of a symbol like “E”: the stimulus is detected, then it is resolved as three horizontal bars and a vertical bar. In fact, within the clinical setting visual acuity is usually measured with alphanumeric symbols and is a three-step process that involves not only detection and resolution, but, due to the semantic content of letters and numbers, their recognition. Along with subjective (psychophysical) procedures, objective methods that do not require the active participation of the observer have been proposed to estimate visual acuity in non-collaborating subjects, malingerers, or toddlers. This paper aims to explain the psychophysical rationale underlying the measurement of visual acuity and revise the most common procedures used for its assessment.
Background: To settle the fundamentals of a numerical procedure that relates retinal ganglion-cell density and threshold sensitivity in the visual field. The sensitivity of a generated retina and visual pathways to virtual stimuli are simulated, and the conditions required to reproduce glaucoma-type defects both in the optic-nerve head (ONH) and visual fields are explored.
Methods: A definition of selected structural elements of the optic pathways is a requisite to a translation of clinical knowledge to computer programs for visual field exploration. The program is able to generate a database of normalized visual fields. The relationship between the number of extant receptive fields and threshold sensitivity is plotted for background sensitivity and corresponding automated perimetry. A solution in two planes to the 3D distribution of axons in the ONH is proposed. Visual fields with induced damage in the optic disc are comparable in pattern and quantity to glaucomatous records.
Results: The two-level simulation of the ONH facilitates the analysis of optic-cup/retinal defects. We can generate the virtual optic pathways tailored to the age and morphology of the patient’s eye, and it is possible to reproduce glaucomatous damage by “reverse engineering” engineering. The virtual cortical model renders a quantitative relationship between visual defect and neural damage.
Conclusions: A two-level computing of the retina/optic nerve facilitates the analysis of neuroretinal defects and can be incorporated to automatic perimeters to facilitate visual field analysis.
Background: To compare objective electrophysiological contrast sensitivity function (CSF) in patients implanted with either multifocal intraocular lenses (MIOLs) or monofocal intraocular lenses (IOLs) by pattern reversal visual evoked potentials (prVEP) measurements.
Methods: Fourty-five cataract patients were randomly allocated to receive bilaterally: apodized diffractive-refractive Alcon Acrysof MIOL (A), full diffractive AMO Tecnis MIOL (B) or monofocal Alcon Acrysof IOL (C). Primary outcomes: 1-year differences in objective binocular CSF measured by prVEP with sinusoid grating stimuli of 6 decreasing contrast levels at 6 spatial frequencies. Secondary outcomes: psychophysical CSF measured with VCTS-6500, photopic uncorrected distance (UDVA), and mesopic and photopic uncorrected near and intermediate visual acuities (UNVA and UIVA respectively).
Results: Electrophysiological CSF curve had an inverted U-shaped morphology in all groups, with a biphasic pattern in Group B. Group A showed a lower CSF than group B at 4 and 8 cpd, and a lower value than group C at 8 cpd. Psychophysical CSF in group A exhibited a lower value at 12 cpd than group B. Mean photopic and mesopic UNVA and UIVA were worse in monofocal group compared to the multifocal groups. Mesopic UNVA and UIVA were better in group B.
Conclusions: Electrophysiological CSF behaves differently depending on the types of multifocal or monofocal IOLs. This may be related to the visual acuity under certain conditions or to IOL characteristics. This objective method might be a potential new tool to investigate on MIOL differences and on subjective device-related quality of vision.
Abstract: Contrast is the differential luminance between one object and another. Contrast sensitivity (CS) quantifies the ability to detect this difference: estimating contrast threshold provides information about the quality of vision and helps diagnose and monitor eye diseases. High contrast visual acuity assessment is traditionally performed in the eye care practice, whereas the estimate of the discrimination of low contrast targets, an important complementary task for the perception of details, is far less employed. An example is driving when the contrast between vehicles, obstacles, pedestrians, and the background is reduced by fog. Many conditions can selectively degrade CS, while visual acuity remains intact. In addition to spatial CS, “temporal” CS is defined as the ability to discriminate luminance differences in the temporal domain, i.e., to discriminate information that reaches the visual cortex as a function of time. Likewise, temporal sensitivity of the visual system can be investigated in terms of critical fusion frequency (CFF), an indicator of the integrity of the magnocellular system that is responsible for the perception of transient stimulations. As a matter of fact, temporal resolution can be abnormal in neuro-ophthalmological clinical conditions. This paper aims at considering CS and its application to the clinical practice.
Abstract: Advances in intraocular lens (IOL) design have rendered cataract surgery a refractive procedure. Newer IOL types include bifocal, trifocal and extended depth of focus (EDOF) IOLs. Their basic difference nestles in the number of focal points that each lens provides, which in turn leads to different visual outcomes. Familiarity of surgeons with the various characteristics of each lens is of utmost importance for accurate IOL selection to match each patient’s needs. In this review, we aim to compare the clinical outcomes after implantation of multifocal and EDOF IOLs in terms of distance, intermediate and near vision, contrast sensitivity, and reading performance. Finally, we discuss the defocus curve and the optical and photic phenomena associated with each type of IOL.
Abstract: Pediatric uveitis is an inflammatory ocular disease that can lead to sight-threatening complications. Pediatric patients have distinct challenges in the diagnosis and management of uveitis, secondary to difficulties in performing ophthalmic examinations in young children, delayed diagnosis due to lack of adherence with recommended screening schedules, medication side-effects, and increased burden of disease into adulthood. Measurement of outcomes in pediatric uveitis has traditionally relied upon the ophthalmic examination and general quality of life (QOL) measures. However, the ophthalmic examination does not take into account the impact of uveitis on a child’s QOL and general QOL measures do not adequately assess the specific effects of vision. Several vision-related quality of life (VR-QOL) instruments have been used to measure outcomes in both adults and children including: the National Eye Institute Visual Function Questionnaire (NEI VFQ-25), Vision-related Quality of Life of Children and Young People (VQoL_CYP), the Children’s Visual Function Questionnaire (CVFQ), and the Effect of Youngsters’ Eyesight on Quality of Life (EYE-Q). However, the NEI VFQ-25 is not a valid or applicable measure in children, and the VQoL_CYP and CVFQ are not uveitis specific and may not characterize disease specific burdens. The EYE-Q is the only uveitis-specific pediatric questionnaire that measures visual functioning and VR-QOL in 5–18 years old children and adolescents with uveitis. It has been shown to be a valid and reliable assessment tool in several cohorts of children with uveitis. A comprehensive assessment of the impact of uveitis on a child that includes a vision-specific measure, such as the EYE-Q, allows for better understanding of the true burden of uveitis in children. For this review, we describe traditional outcome measures in uveitis studies, general QOL measures and vision-specific measures in adults and in children.
