Assessment of Macular Function during Vitrectomy: New Approach Using Intraoperative Focal Macular Electroretinograms.

PURPOSE: To describe a new technique to record focal macular electroretinograms (FMERGs) during vitrectomy to assess macular function. METHODS: Intraoperative FMERGs (iFMERGs) were recorded in ten patients (10 eyes) who undergo vitrectomy. iFMERGs were elicited by focal macular stimulation. The stimulus light was directed to the macular area through a 25 gauge (25G) glass fiber optic bundle. Background light was delivered through a dual chandelier-type light fiber probe. Focal macular responses elicited with combinations of stimulus and background luminances were analyzed. RESULTS: A stimulus luminance that was approximately 1.75 log units brighter than the background light was able to elicit focal macular responses that were not contaminated by stray light responses. Thus, a stimulus luminance of 160 cd/m2 delivered on a background of 3 cd/m2 elicited iFMEGs from only the stimulated area. This combination of stimulus and background luminances did not elicit a response when the stimulus was projected onto the optic nerve head. The iFMERGs elicited by a 10° stimulus with a duration of 100 ms and an interstimulus interval of 150 ms consisted of an a-, b-, and d-waves, the oscillatory potentials, and the photopic negative response (PhNR). CONCLUSIONS: Focal ERGs with all components can be recorded from the macula and other retinal areas during vitreous surgery. This new technique will allow surgeons to assess the function of focal areas of the retina intraoperatively.

Biomechanical assessment in models of glaucomatous optic neuropathy.

The biomechanical environment within the eye is of interest in both the regulation of intraocular pressure and the loss of retinal ganglion cell axons in glaucomatous optic neuropathy. Unfortunately, this environment is complex and difficult to determine. Here we provide a brief introduction to basic concepts of mechanics (stress, strain, constitutive relationships) as applied to the eye, and then describe a variety of experimental and computational approaches used to study ocular biomechanics. These include finite element modeling, direct experimental measurements of tissue displacements using optical and other techniques, direct experimental measurement of tissue microstructure, and combinations thereof. Thanks to notable technical and conceptual advances in all of these areas, we are slowly gaining a better understanding of how tissue biomechanical properties in both the anterior and posterior segments may influence the development of, and risk for, glaucomatous optic neuropathy. Although many challenging research questions remain unanswered, the potential of this body of work is exciting; projects underway include the coupling of clinical imaging with biomechanical modeling to create new diagnostic tools, development of IOP control strategies based on improved understanding the mechanobiology of the outflow tract, and attempts to develop novel biomechanically-based therapeutic strategies for preservation of vision in glaucoma.

Rats maintain an overhead binocular field at the expense of constant fusion.

Fusing left and right eye images into a single view is dependent on precise ocular alignment, which relies on coordinated eye movements. During movements of the head this alignment is maintained by numerous reflexes. Although rodents share with other mammals the key components of eye movement control, the coordination of eye movements in freely moving rodents is unknown. Here we show that movements of the two eyes in freely moving rats differ fundamentally from the precisely controlled eye movements used by other mammals to maintain continuous binocular fusion. The observed eye movements serve to keep the visual fields of the two eyes continuously overlapping above the animal during free movement, but not continuously aligned. Overhead visual stimuli presented to rats freely exploring an open arena evoke an immediate shelter-seeking behaviour, but are ineffective when presented beside the arena. We suggest that continuously overlapping visual fields overhead would be of evolutionary benefit for predator detection by minimizing blind spots.

Clinical assessment of optic nerve disorders.

Optic nerve disorders range from the manifestations of life-threatening intracranial or systemic disease, to minor congenital anomalies. Careful clinical assessment, which relies upon a thorough evaluation of symptoms as well as signs, is essential for effective and timely investigation and treatment. Examination methods and pitfalls to be avoided are discussed.

[Modern diagnostic methods for suspected glaucoma and glaucoma]. / Moderne diagnostische Verfahren bei Glaukomverdacht und Glaukom.

BACKGROUND: Diagnosis of early glaucomatous damage as well as the detection of glaucomatous change are still difficult tasks. During the last years numerous new diagnostic techniques have been investigated and some of them have been introduced to the market. METHODS: This paper reviews the different aims of diagnostic technologies in the field of glaucoma. Methods appearing suitable for a large-scale use by ophthalmologists will be judged according to their suitability to meet the goals of early diagnosis, objective diagnosis, progression analysis and screening. CONCLUSIONS: The new diagnostic techniques have not yet greatly influenced our diagnostic procedure. This is mainly due to the fact that, for the most difficult borderline cases of glaucoma, these methods are of limited value, or have not yet been sufficiently investigated. Nevertheless, the Heidelberg retina tomograph (HRT), the nerve fiber analyzer GDX, short wavelength perimetry (SWAP), and the frequency doubling test (FDT) may play a role in these cases. For follow-up, HRT and GDx have proven valuable, especially in early stages of the disease. The very short testing time of FDT together with good specificity qualifies this test for glaucoma screening.