Microholes of the fovea centralis

Foveal microholes are a possible cause of unilateral or bilateral small central visual defects in the absence of other macular pathology. In 18 eyes of 17 patients we noted the following features: small, dark-reddish holes in the centre of the fovea ranging from 50 to 150 micron in size; normal adjacent retinal pigment epithelium and neuroepithelium; unilateral in most cases; males and females are equally affected; mean age 40 years; insidious onset; no history of direct eye trauma or sungazing; non-progressive; relatively favourable visual outcome; no relationship with regular macular holes; aetiology unknown. These distinctive features justify reporting these patients as an important separate group.     

Drusen of the optic nerve head.

Fifty-two eyes with drusen of the optic nerve head from the autopsy and surgical files of the Eye Pathology Laboratory of the Wilmer Institute from January 1967 through December 1975 were reviewed, and histochemical and electron microscopic studies performed. Histopathologic associations with the drusen included 19 eyes with associated optic nerve atrophy, 16 eyes with peripapillary crowding, one case involving prominent dilated vessels pushed aside by the drusen, and one eye with central retinal vein occlusion. Drusen appear to be composed predominantly of a mucoprotein matrix with significant quantities of acid mucopolysaccharides along with small quantities of ribonucleic acid and, occasionally, iron. The literature is reviewed and various correlations and pathogenetic theories are discussed.     

Pseudoduplication of the optic nerve head.

BACKGROUND: Pseudo-doubling of the optic nerve head is a spectacular clinical entity, in which a lesion resembling an optic disk appears adjacent to the true optic disk. CASE REPORT: A case of unilateral pseudo-doubling of the optic disk with bilateral optic nerve pits is presented. CONCLUSIONS: The lesion is congenital, and represents a chorioretinal coloboma with optic disk involvement. Pseudo-doubling can be differentiated from true doubling of the optic nerve by the imaging techniques of ultrasonography, computerized tomography, and magnetic resonance imaging.     

The normal optic nerve head.

BACKGROUND: The normal optic nerve head varies from one person to another, and there is often intraindividual variation as well. Factors such as race and age play an important role in distinguishing what may be considered normal variations in optic nerve head appearance. METHODS: A literature search and review of the latest studies on the optic nerve head was conducted. RESULTS: Results of recent studies showed that variations in the average cup-to-disc ratio exist for different races, and with age there is a gradual loss of nerve fibers leading to an overall increase in the cup-to-disc ratio. There is also evidence that congenitally larger optic nerves have larger cup-to-disc ratios and more nerve fibers. Smaller optic nerves, in contrast, have smaller cup-to-disc ratios and fewer nerve fibers. These findings are presented along with sample photographs depicting the normal variations in optic nerve head appearance. CONCLUSION: Over the past 30 years, technology has allowed for changing views about what may be considered normal in reference to the optic nerve head. This information is valuable to the eye care practitioner in helping to make appropriate patient care management decisions.     

Microvasculature of the rat optic nerve head.

PURPOSE: To describe the arterial blood supply, capillary bed, and venous drainage of the rat optic nerve head. METHODS: Ocular microvascular castings from 6 Wistar rats were prepared by injection of epoxy resin through the common carotid arteries. After polymerization, tissues were digested with 6 M KOH, and the castings washed, dried, and coated for scanning electron microscopy. RESULTS: Immediately posterior to the globe, the ophthalmic artery trifurcates into the central retinal artery and two posterior ciliary arteries. The central retinal artery directly provides capillaries to the nerve fiber layer and only contributes to capillary beds in the neck of the nerve head. The remainder is supplied by branches of the posterior ciliary arteries that are analogous to the primate circle of Zinn-Haller. Arterioles arising from these branches supply the capillaries of the transitional, or laminar, region of the optic nerve head. These capillaries are continuous with those of the neck and retrobulbar optic nerve head. All optic nerve head capillaries drain into the central retinal vein and veins of the optic nerve sheath. A flat choroidal sinus communicates with the central retinal vein, the choriocapillaris, and with large veins of the optic nerve sheath. CONCLUSIONS: The microvasculature of the rat optic nerve head bears several similarities to that of the primate, with a centripetal blood supply from posterior ciliary arteries and drainage into the central retinal and optic nerve sheath veins. Association of nerve sheath veins with the choroid represents an important difference from the primate.     

Sarcoidosis with neovascularization of the optic nerve head

A 25-year-old man with systemic sarcoidosis had neovascularization of the optic nerve heads and associated bilateral vitreous hemorrhages. Oral administration of prednisone produced a prompt resolution of these unusual neovascular fronds and cleared the vitreous hemorrhages.     

Biomechanics of the optic nerve head

Biomechanical factors acting at the level of the lamina cribrosa (LC) are postulated to play a role in retinal ganglion cell dysfunction and loss in glaucoma. In support of this postulate, we now know that a number of cell types (including lamina cribrosa cells) are mechanosensitive. Here we briefly review data indicating cellular stretching, rate of stretching and substrate stiffness may be important mechanosensitivity factors in glaucoma. We then describe how experiments and finite element modeling can be used to quantify the biomechanical environment within the LC, and how this environment depends on IOP. Generic and individual-specific models both suggest that peripapillary scleral properties have a strong influence on LC biomechanics, which can be explained by the observation that scleral deformation drives much of the IOP-dependent straining of the LC. Elegant reconstructions of the LC in monkey eyes have shown that local strains experienced by LC cells depend strongly on laminar beam microarchitecture, which can lead to large local strain elevations. Further modeling, suitably informed by experiments, is needed to better understand lamina cribrosa biomechanics and how they may be involved in glaucomatous optic neuropathy.     

Tumors of the optic nerve head

A variety of primary and secondary tumors can involve the optic nerve head. Examples of primary optic disc tumors include capillary, cavernous and racemose hemangiomas, astrocytomas, and melanocytomas. Secondary optic disc tumors include metastatic carcinoma, leukemia, and those which invade the nerve head from adjacent structures (choroidal melanoma, retinoblastoma, and meningioma). These tumors may produce a variety of clinical features and are discussed in this review. Included also are histopathologic correlations and guidelines for management of the individual entities.     

The relative numbers of long-wavelength-sensitive to middle-wavelength-sensitive cones in the human fovea centralis

The determination of the relative numbers of different cone types in the human retina is fundamental to our understanding of visual sensitivity and color vision; yet direct measurement which provide this basic information have not previously been made for all cone types. Here we present a model which links the detection of a test light of small dimension to the number of cones contributing to detection of the light. We selectively isolated either the long-wavelength-sensitive (L) or the middle-wavelength-sensitive (M) cones, by choosing combinations of wavelengths of adapting backgrounds and tests to favor detection by the cone class of interest. Our model was applied to the detection functions measured for six color normal observers to obtain estimates of the relative numbers of L to M cones. Our estimates ranged between 1.46 and 2.36 for our observers with a mean value near two L cones for every M cone in human fovea centralis.     

Acute presumed histoplasmosis of the optic nerve head.

A 38-year-old man from the Ohio Valley area presented to the Ophthalmology Cinic at a west coast hospital (USA) because of sudden loss of the right inferior temporal visual field after severe right frontal headache of several hours' duration. During the following months, diffuse peripapillary atrophy and peripheral punched-out lesions developed. When he had been seen initially, the fundus of the left eye had also revealed extensive, diffuse, peripapillary atrophy and scarring. All laboratory tests were normal except a histoplasmin intradermal skin test. The clinical appearance of both eyes 8 months after the acute episode in the right eye supports the diagnosis of presumed ocular histoplasmosis.     

Blood circulation of the optic nerve with respect to the development of glaucomatous papilla excavation

Recent research findings in microvascular anatomy enable the authors to make as new suggestion regarding the arrangement of the intraorbital vasculature of the optic nerve. In anatomical specimens three separate zones can be identified, sharply delimited and each with its own source of blood supply. After briefly describing the vasculature of the distal segment (neck) of the optic nerve the authors report several new theories concerning the pathogenesis of glaucomatous cupping of the optic disk.     

Afferent pupillary defect associated with optic nerve head drusen.

BACKGROUND: Optic nerve head drusen (ONHD) are a relatively uncommon finding with an estimated prevalence of anywhere from 0.3% to 2%. Reports of relative afferent pupillary defects (RAPDs) associated with ONHD are scarce. CASE REPORT: A patient with an RAPD was found to have ONHD as the only apparent etiology of the RAPD. The various diagnostic tests relevant to the case, the differential diagnosis, and the pathological features of ONHD are discussed. CONCLUSIONS: It is important for the clinician to consider an RAPD as a possible pathological feature of ONHD--especially with an asymmetric presentation.     

Infarction of the optic nerve head in children with accelerated hypertension.

Four cases of anterior ischaemic optic neuropathy occurred in children with accelerated hypertension. The cause may have been a sudden relative fall in arterial pressure which reduced the perfusion of the optic disc, whose circulation was compromised by long-standing hypertensive vascular disease.     

Extraocular muscle insertions relative to the fovea and optic nerve: humans and rhesus macaque

PURPOSE: To identify extraocular anatomic relationships of muscle insertions relative to the fovea and the optic nerve. METHODS: Thirty-eight human eye bank eyes and 10 rhesus macaque (Macaca mulatta) eyes were measured. Ten human volunteers were used to determine the horizontal rectus muscle-to-globe apposition in primary, left, and right gaze. RESULTS: External globe measurements (human/rhesus; mm +/- SD) from the temporal border of the optic nerve (ON) to the center of the fovea (F) were 3.7 +/- 0.6 and 2.6 +/- 0.2; F to the posterior border of the inferior oblique (IO) insertion, 2.5 +/- 0.8 and 0.5 +/- 0.4; ON to the posterior border of the IO, 5.6 +/- 0.9 and 2.8 +/- 0.3; horizontal axial plane (H) of the eye, defined by the long posterior ciliary artery, to the IO, 2.0 +/- 0.8 and 0.5 +/- 0.4; and H to F, 1.0 +/- 0.6 and 0.4 +/- 0.3, respectively. The IO insertion formed an arc, inferior to H, with an anterior-to-posterior cord insertion width of 9.2 +/- 0.7 and 7.7 +/- 0.3. The IO angle of insertion (theta) was 30 degrees in 84% (32/38) and 0 degrees in 16% (6/38) of human eyes and 25 to 30 degrees in all rhesus. In 20 human volunteers, from the ON to the apex of lateral rectus globe apposition was 13.9 +/- 1.1 in primary, 17.2 +/- 1.9 in lateral, and 9.3 +/- 1.7 in medial gaze. CONCLUSIONS: The fovea is located mostly superior and slightly posterior to the posterior border of the IO insertion. Topographic relationships of the extraocular muscles relative to the fovea are essential for the design of extraocular drug delivery systems.     

Computer-assisted optic nerve head assessment

An IBM-compatible microcomputer-based system has been developed for the assessment of pallor area size, shape and degree of pallor in the optic nerve head. The system allows the instantaneous capture of optic nerve head images, and software analysis of these images produces measurements of the pallor area in about 2 min. The various methods of image analysis are presented. These are enhancement, thresholding, and digital filtering for edge detection. The results of their application to the images of the optic nerve head are shown. The results of the system's analysis on a particular optic nerve head are also shown. The potential uses and difficulties of such a system are discussed.     

Monocular fixation with the optic nerve head: a case report.

PURPOSE: To document and discuss the case of a patient with left esotropia (ET) who uses the left optic nerve head (ONH) for monocular 'fixation'. CASE REPORT: The patient was an 80-year-old male with left ET from early childhood. Retinal tracking monocular fixation measurements with a Nidek MP-1 revealed stable fixation within the left ONH area. In an attempt to challenge the initial observation, further assessments of fixation were performed with a smaller target size and requiring various gaze positions. MP-1 fixation data showed remarkably stable monocular fixation (+/-1 degrees over 30 s) mostly within the left ONH for all the target sizes and positions of gaze tested. Additional clinical binocular evaluations showed concomitant left ET approximately 28 Delta, no movement with cover test regardless of fixation target and no significant monocular motility restrictions. Visuoscopy also revealed fixation at the left ONH. There was a strong family history of ET, but none of the other affected descendants tested (n = 3) demonstrated the same behaviour. CONCLUSIONS: This is the first report documenting an abnormally developed monocular ocular motor system, with principal visual direction and zero retinomotor value shifted from the fovea to the ONH. We do not believe that there is any direct visual input from the ONH. The patient may use visual information obtained by glancing with peri-papillary areas to determine the target position (although this was largely ruled out), or obtain position information from the average luminance produced by scattered light around the ONH margin. The abnormal oculocentric direction might then be combined with extraretinal information (efferent copy or extraocular muscle proprioception) of the eye location in the orbit to stabilize the fixation. This patient does not have the blind spot syndrome (Swan, 1948). We propose the use of a retinal perimeter for documentation of eccentric fixation in strabismus.     

Gap junctions between optic nerve head astrocytes.

Astrocytes of the primate and human optic nerve head are joined to each other by the gap junction type of intercellular membrane specialization. Although the precise function of these contacts is not fully determined, they may serve such diverse roles as adhesive bonding and intercellular electrical and chemical coupling.