Techniques, Tools, and Models in Vision Research

Abstract

ICG Leukocyte Angiography: Measuring Choroidal Flow

Takasu et al. (p. 2844) developed a new method which allows direct visualization of leukocytes in the choroid of pigmented animals, and measured the flow velocity of leukocytes in the retinal and choroidal circulation of pigmented rabbits and monkeys through autologous indocyanine green (ICG)-stained leukocytes. This method, called ICG leukocyte angiography, may be applicable to humans because of the minimal toxicity of ICG and holds a possibility of disclosing a role of leukocytes in the pathogenesis of various ocular diseases. 

Generic Ribozymes: Molecular Tools for Dominant Disease

Over 150 rhodopsin and peripherin mutations have been associated with autosomal dominant retinitis pigmentosa (adRP). While gene therapies for dominant diseases may be directed to specific mutations, the immense genetic heterogeneity associated with these disorders make such ‘tailor-made’ therapies impractical. The paper by O’Neill et al. (p. 2863) proposes a means of overcoming this significant hurdle using generic ribozyme-based approaches for combating mutational heterogeneity inherent in adRP. Kinetic profiles for monomeric and multimeric mutation-independent ribozymes targeting rhodopsin and peripherin RNAs indicate that these ribozymes are extremely efficient, and therefore may be of significant therapeutic value. The generic ribozymes described are the first therapeutically relevant ribozymes for combating adRP to be reported. 

Component Perimetry: A Fast Visual Field Test

Patients suffering from visual field defects usually do not subjectively perceive their scotomata in natural scenes. But when confronted with stimuli consisting of dynamic visual noise, most patients suffering from suprageniculate lesions subjectively experience their field defects. Bachmann and Fahle (p. 2870) presented stimuli whose elements varied over time regarding color, motion direction, line orientation, or else stereoscopic depth, in order to screen for defects in different submodalities of vision. Size of visual field defects obtained with these stimuli corresponds well to that found with automated perimetry, indicating that component perimetry is a subjective but relatively reliable method for fast screening of the visual field. 

Confocal Microscopy: Recording Corneal Thickness

Confocal microscopy appears to allow early detection of beginning neuropathy, since decreases in corneal subbasal nerve fiber bundle counts per confocal microscopic field precede impairment of corneal sensitivity measured by Cochet-Bonnet esthesiometry. Rosenberg et al. (p. 2915) show that, compared to control subjects, the corneal thickness is increased in diabetic patients without neuropathy, but does not further increase with the duration of the disease. The epithelium of diabetic patients with severe neuropathy is significantly thinner than that of diabetic patients without neuropathy. Apparently, a reduction in neurotrophic stimuli in severe neuropathy induces a thin epithelium which may lead to recurrent erosions. 

Confocal Microscopy Through Focusing: Better, Cheaper, Easier?

In vivo confocal microscopy through focusing (CMTF) provides a 3-D stack of high-resolution corneal images and allows objective measurements of corneal sublayer thickness and backscattering. However, current systems require time-consuming off-line image processing and analysis on unfamiliar platforms. In this study by Li et al. (p. 2945), software was developed to allow in vivo 2-D imaging, CMTF image acquisition, interactive 3-D reconstruction, and analysis of CMTF data to be performed on-line on a PC system. This is a low-cost, easy-to-use program which should help to expand the use of in vivo confocal microscopy for both ophthalmic research studies and clinical patient diagnoses. 

Ultrasonography vs. CSLO in Optic Disc Swelling

Comparisons between ultrasonographic and laser scanning tomographic measurements have been previously reported for optic disc cupping. Tamburrelli et al. (p. 2960) cross-sectionally evaluated the agreement between these methods for disc swelling in patients with idiopathic intracranial hypertension. Ultrasonographic and tomographic readings were correlated, despite a significant discrepancy that currently limits their interchangeability for clinical use. The present findings have implications that are relevant for the understanding of pathophysiology of papilledema. The different reference planes used for measurements obtained by the two methods might allow one to analyze the proportion of ophthalmoscopically apparent and non-apparent edema and their relation to functional damage. 

Wholemounts: Exposing Eye Morphology

McMenamin (p. 3043) provides a detailed methodological account of the optimal method for preparing whole- mounts of iris/ciliary body and choroid for immunohistochemical analysis. This method has proved invaluable for immunologists and immunopathologists for the demonstration of various lymphocyte and mononuclear phagocyte subtypes in many experimental ocular inflammation models. It has been of particular value in showing the great number of dendritic cells and resident tissue macrophages, observations that have not been possible with the limited sampling of conventional methods of histology. As with the well-established technique of retinal wholemounts, this method provides an opportunity to study neural and vascular components in these tissues as well. 

Confocal Microscopy: Visualizing Internal Circulation in the Lens

Measurements of lens membrane potential and chloride concentration have been used to predict the existence of a circulating flux of chloride ions in this tissue. Young et al. (p. 3049) provide visual evidence in favor of the existence of this flux. The study shows that blocking chloride channels in the lens induces two spatially distinct zones of fiber cell damage: a peripheral zone of fiber cell swelling and a deeper zone of extracellular space dilations. This pattern of tissue damage is consistent with blocking the outward flux of chloride ions in peripheral cells and the influx chloride into deeper fiber cells, as predicted by the lens internal circulation model. 

Reflected-Light Photography: Capturing Cases of PCO

Posterior capsule opacification (PCO) is the most frequent complication of cataract surgery. Photographic techniques to document PCO are useful in studies of PCO incidence and progression as they allow investigators to assess the presence and severity of PCO in a standardized fashion. A number of photographic techniques have been used for this purpose. Camparini et al. (p. 3074) have compared the relative merit of retroillumination images and of reflected-light slit lamp images obtained utilizing a large beam width in the assessment of PCO. The results show that reflected-light photographs can capture some cases of PCO that are missed by retroillumination images. This observation is relevant to clinical and epidemiological studies on PCO.