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Axonal degeneration and diminution of the axonal population in the optic nerve have been documented in aging and in various neuro-ophthalmic conditions. We applied morphometric techniques to the postmortem examination of optic nerves obtained from patients with acquired immunodeficiency syndrome. Twelve optic nerves (eight from patients with AIDS and four from age-matched control eyes) were stained with paraphenylenediamine and morphometrically analyzed with a computer-assisted image and measurement system. Degeneration was often severe and was scattered throughout all of the AIDS-affected optic nerves. In the AIDS-affected optic nerves, the mean axonal population was markedly lower than the mean obtained from normal optic nerves (880,000 vs 1,507,000). Despite the approximate 40% loss of axons, mean axonal diameters were not markedly different, suggesting that no particular class of axon was especially susceptible to AIDS-associated degeneration. The extent and pattern of axonal loss in optic nerves of patients with AIDS suggest that the changes may not only be secondary to damage at the retina, but may reflect an AIDS-associated primary optic neuropathy.

Patients with human immunodeficiency virus infection may have noninfectious and infectious retinopathies, as well as clinical symptoms consistent with optic nerve dysfunction. Noninfectious acquired immunodeficiency syndrome-related retinopathy is seen in most patients with AIDS. Morphologic studies have shown that the number of retrobulbar optic nerve fibers in patients with AIDS is decreased compared to the number of optic nerve fibers in normal control eyes. To determine whether these patients had a visual dysfunction consistent with damage to the macula and optic nerve, 78 subjects (156 eyes) were studied using color-vision and contrast-sensitivity testing. The Farnsworth-Munsell 100-Hue color-vision test was performed on all subjects and age-corrected color-vision scores for all groups were compared. A significant decrease in color discrimination was found in the patients with AIDS (P less than .001). Contrast-sensitivity testing disclosed a deficit of contrast threshold in patients with AIDS at four of five spatial frequencies and in patients with AIDS-related complex at three of the five spatial frequencies examined. This study demonstrated a functional visual deficit in eyes without retinitis consistent with dysfunction of the macula or optic nerve in patients with AIDS.

We describe three patients who experienced several types of visual problems while receiving interleukin 2 therapy for melanoma or lymphoma. Their symptoms included diplopia, binocular negative scotomata, scintillating scotomata, and palinopsia. All symptoms eventually resolved following discontinuation of therapy. It appears that focal neurologic deficits that affect the visual system may complicate interleukin 2 administration.

Transient blurring of near vision can be due to a variety of causes. We report the case of a 35-year-old man with a 10-year history of blurring of near vision that begins 30 to 45 seconds after he starts to eat and that lasts until 10 to 15 minutes after he stops eating. Magnetic resonance imaging and computed tomography of the brain and orbits did not reveal any abnormality, and stimulation of individual cranial nerves did not result in a loss of near vision. Retinoscopic refraction revealed the loss of 1.5 dioptres of accommodative power in each eye one minute after he began to eat. To the best of our knowledge such blurring of vision at near, immediately after initiating a meal, has not been previously reported. The neuroanatomy of the accommodation and of the gustatory pathways are discussed, as they may relate to this patient's visual complaint.

We examined three patients with optic disc edema and peripapillary hemorrhages. Each was found by standard echography to have calcified nodules within the retrobulbar portion of the optic nerves. These nodules were located approximately 2 mm posterior to the lamina cribrosa. Each patient had unilateral congestion of the optic nerve head with dilated, tortuous retinal veins that appeared much like a partial central retinal vein occlusion; one patient subsequently developed optic atrophy. The central location of the calcifications within the anterior aspect of the optic nerves suggests that each nodule may have been situated within the central retinal vein or artery. Calcifications within the retrolaminar space may be associated with some etiologies of unilateral congestion of the optic nerve head.

The Amsler grid is a suprathreshold target used to assess the central 10 degrees of the visual field; thus, it may fail to detect relative central scotomas. Low luminance conditions can be created by viewing the white grid on a black background through two cross-polarizing filters that vary light transmission and change the procedure to a threshold Amsler grid (TAG) test, thereby increasing its sensitivity. A total of 26 patients with diabetic retinopathy were tested by standard Amsler grid, TAG, and tangent screen. Four scotomas were detected by Amsler grid testing; each of these scotomas expanded in size on retesting with the TAG. TAG testing revealed 22 scotomas more than five times the number seen with conventional Amsler grid testing; tangent-screen examination confirmed 9 of these defects. In many cases, fundus photography and fluorescein angiography revealed pathology that correlated with the scotomas detected only by TAG testing. It thus appears that the TAG test is a rapid, high-yield, and sensitive means of assessing the central visual field in patients with diabetic retinopathy.

Complications reported after epikeratophakia for high myopia include under- and overcorrection, glare, irregular astigmatism, delayed reepithelialization, and decrease in best-corrected visual acuity. Overcorrection may also result in anisometropia. This report describes a patient who presented with constant diplopia and esotropia--an unusual manifestation of overcorrection after myopic epikeratophakia. The findings in this patient are those of an acquired accommodative esotropia.

Primary malignant melanoma of the central nervous system (CNS) is exceedingly rare. The earliest description by Virchow in 1859 has been followed by approximately 50 autopsy-proven cases reported in the literature. These tumors are considered to arise from leptomeningeal melanocytes whose embryonic origin is neural crest tissue. Given the rarity of primary CNS melanoma, the diagnosis requires a thorough search to exclude a dermatologic, ocular, or visceral site of tumor origin. We report an unusual case of primary CNS melanoma in a patient with painful, progressive cranial polyneuropathy that eluded antemortem diagnosis despite extensive clinical, radiographical, and laboratory investigations.

Many optic neuropathies and subtle maculopathies may have similar clinical presentations. This represents a challenge to the ophthalmologist to distinguish between the two on clinical grounds. These patients may not have obvious signs and their symptoms may be ambiguous. For example, a young man presenting with optic neuritis may have similar complaints to one suffering from central serous retinopathy. Several general principles can be used to distinguish between optic neuropathies and maculopathies. Additionally, specific psychophysical tests can be of help. The most important aspect of the history is in establishing the tempo of onset, duration and resolution of the symptoms. Optic nerve lesions often produce symptoms described as dimness or grayness, whereas macular lesions usually reduce visual acuity and produce metamorphopsia. The clinical examination requires comparing optic nerve function studies (afferent pupillary defects, color vision and brightness sense) to visual acuity. Additionally, assessing the central visual field especially through Amsler grid testing or threshold Amsler grid testing is very useful. Certain psychophysical tests can be performed in the office. Threshold amsler grid testing, photostress testing, contrast sensitivity, and the Pulfrich phenomena can all be put to advantage in distinguishing between optic neuropathies and maculopathies.

Optic nerves from ten patients with Alzheimer's disease were histologically examined and compared with those from age-matched controls. Specific and nonspecific measures of degeneration were noted in eight of ten Alzheimer's disease optic nerves; no degeneration was noted in any of the controls. Results of histologic examination of the retinas of one eye of three Alzheimer's disease patients also showed degeneration of retinal ganglion cells and their axons in the nerve fiber layer. Morphometric analysis suggested that in many cases of Alzheimer's disease, the optic nerve showed predominant loss of the largest class of retinal ganglion cells (M-cells) that contribute large caliber fibers to the optic nerve. The M-cell system is known to mediate specific visual functions, and selective involvement of the M-cell population leads to clinically measurable neuro-ophthalmic and psychophysical impairments in many Alzheimer's disease patients.

Three cases of intracranial meningiomas occurring in young pregnant women are presented. The typical growth pattern of these tumors is slow, producing insidious and chronic visual disturbances. In contrast, during pregnancy meningiomas may follow a rapidly progressive course, producing dramatic and relatively acute visual loss. This accelerated growth pattern is probably mediated by hormone receptors in these tumors. Nausea, vomiting, and other symptoms caused by the tumor may be attributed to pregnancy, delaying the diagnosis. Symptoms may abate spontaneously after delivery only to recur with greater rapidity and severity during subsequent pregnancies. Hormone-responsive intracranial meningiomas must be considered in the differential diagnosis of visual disturbances during pregnancy. Close cooperation between the ophthalmologist, neurosurgeon, obstetrician, and neonatologist is essential for an optimal outcome. Although surgical excision remains the treatment of choice, hormonal therapy may be valuable in treating unresectable or partially resectable meningiomas.

Patients with Alzheimer's disease, or more often their families, frequently complain of problems with vision. Nonetheless, clinicians have tended to attribute these symptoms to impaired cognitive functions. Alzheimer patients have been ascribed to disease in the cerebral cortex. However, we have demonstrated that patients with Alzheimer's disease also have a primary optic neuropathy. Degeneration is noted in the retinal ganglion cell layer of the retina and among axons of the optic nerve. In particular, there appears to be a predilection in early Alzheimer's disease for injury to the largest retinal ganglion cell axons. Clinical assessments of patients with Alzheimer's disease demonstrated that patients with only mild dementia have excellent visual acuity. However, they demonstrate deficits in eye movements, visual evoked responses, and contrast sensitivity functions. Patients with more severe Alzheimer's disease are hard to evaluate but they demonstrate severe impairments of vision of many types including visual acuity. The differential involvement of various types of retinal ganglion cells and of different visual functions in early Alzheimer's disease further emphasizes the nature of parallel processing in human vision.

We describe a simple device used to compare the sense of brightness in the two eyes. An investigation of brightness-sense with this device in normal persons and patients with optic nerve disease, maculopathies, cataract, and factitious visual impairment shows that brightness testing can provide useful information supplementary and complementary to conventional clinical and laboratory investigations. Impairment of brightness-sense was a consistent finding among patients with optic neuropathies and, in some cases, brightness testing appeared to be more sensitive than other techniques in establishing the presence of disease. Brightness-sense was also used to monitor the course of the patient's illness. Abnormalities were also found among some patients with unilateral maculopathies, but significant intereye differences in brightness-sense were not encountered among normal persons or patients with cataracts. Patients with factitious visual loss gave variable responses, and the nature of their disorder could be identified by the inconsistency of their responses.

The pathogenesis of the transient obscurations of vision that occur with papilledema is a subject of speculation and debate. We present four examples of transient obscurations of vision that were clinically indistinguishable from those of papilledema; they occurred in patients with elevated optic discs from causes not related to increased intracranial pressure. The underlying mechanism for visual obscurations in all of these patients appear to be transient ischemia of the optic nerve head consequent to increased tissue pressure. Axonal swelling, intraneural masses, and increased influx of interstitial fluid may all contribute to increases in tissue pressure in the optic nerve head. The consequent reduction in perfusion pressure renders the small, low-pressure vessels that supply the optic nerve head vulnerable to compromise. Brief fluctuations in intracranial or systemic blood pressure may then result in transient loss of function in the eyes. We postulate that such mechanisms may apply in all cases of optic disc elevation, including papilledema.

Funduscopic examination of two young adults complaining of blurred vision revealed small symmetrical macular lesions suggestive of solar retinopathy. Although both patients had recently looked at the sun for less than one minute, it is common to look at the sun for longer periods (ie, sunsets) without incurring visual symptoms of retinal lesions. Our biophysical analysis revealed the important parameters of solar retinopathy and the minimum exposure to the sun that would produce such lesions. Under ideal optical conditions, solar retinopathy can occur following extremely short observations of the sun.

A patient had aberrant regeneration of the inferior branch of the third nerve following penetrating orbital trauma. Examination of the right eye showed no light perception and a pupil that was nonreactive to accommodation, direct, and consensual light stimuli. However, on downgaze, there was marked constriction of the pupil in the blind eye. The phenomenon of oculomotor misdirection is discussed with respect to aberrant regeneration, ephaptic transmission, chromatolysis-induced nuclear reorganization, and recent neurophysiologic studies. Our case provides strong support for the concept of peripheral aberrant regeneration as the mechanism underlying some instances of oculomotor misdirection after third-nerve palsy.

An elderly woman was admitted to the hospital with a presumptive diagnosis of optic neuritis following abrupt loss of vision in her left eye. Noninvasive studies were unrevealing, and she was put on a course of prednisone. Further visual loss 2 weeks later prompted a second course of prednisone therapy. Six years later the patient died from cardiac arrest. The autopsy revealed an aneurysm arising from the origin of the left ophthalmic artery. Selected brain specimens were histologically examined by application of a newly developed staining technique capable of identifying degenerated axons in human brain tissue even after long survival periods. We traced degeneration from the site of compression at the left optic nerve to five primary visual nuclei. Furthermore, transsynaptic cellular changes were observed in the lateral geniculate nucleus.

We studied two cases of bilateral visual loss secondary to an optic neuropathy in patients with cryptococcal meningitis. In both cases a history of visual loss after the onset of an episode of cryptococcal meningitis was elicited. Visual fields were consistent with optic nerve disease. The patients' visual loss appeared to be the result of perineuritic adhesive arachnoiditis. Although no surgical interventions were carried out in our patients, medical or surgical intervention may be useful to prevent or relieve constrictive arachnoiditis and preserve vision in selected patients.

Altitudinal visual field defects were discovered in four young women on routine eye or general physical examinations. This led to extensive investigations because three of them were falsely presumed to have acquired disorders of the central nervous system. In each case the defect appeared to result from congenital hypoplasia of the optic nerve associated with maternal diabetes mellitus. Congenital optic nerve hypoplasia should be included in the differential diagnosis of visual field defects even when they are discovered in adults. Hypoplasia consequent to maternal diabetes mellitus is apt to be associated with excellent visual acuity and is usually an isolated defect. The female offspring of diabetic mothers may be at greater risk than the male offspring for the development of this anomaly.

It is a widely held belief that the products of axonal degeneration in the CNS are transitory and are caused by metabolic and phagocytic processes. However, recent light microscopic examinations of human and primate brains using the paraphenylene diamine staining method (PPD), which stains degenerating axons, have confirmed that the products of degeneration persist for years in visual pathways. The routine utilization of the PPD method for delineating human visual pathways requires further confirmation of axonal degeneration. Optic nerves, optic tracts, and lateral geniculate nuclei were collected from human brains that had clinical documentation of optic nerve damage prior to death. Optic nerves, optic tracts, and lateral geniculate nuclei taken from the brains of cynomolgus monkeys that had undergone enucleation 3 months to 1 year prior to sacrifice were also examined. All tissue was processed for electron microscopy; ultrathin sections were cut for electron microscopy, and consecutive sections were cut for light microscopy. In all cases, the homology of the degenerated processes was confirmed between the light microscopic (PPD) and the electron microscopic sections. Such ultrastructural examination demonstrates that the products of axonal degeneration remain in the primate visual system longer than previously supposed.

Partial or complete occlusion of the internal carotid artery is a familiar consequence of severe atherosclerosis seen in the elderly. Complete obstruction of both internal carotids is rare, particularly in the young or middle-aged. The rapid onset of bilateral internal carotid occlusion would be expected to produce devastating neurological sequelae and probably not be compatible with survival. We present a case of a young man with complete obstruction of both internal carotid arteries whose presenting symptoms were those of a visual field cut. The history suggests that the carotid occlusion occurred as a result of blunt trauma. The patient had no known predisposition to vascular abnormalities (no history of hypertension, hyperlipidemia, signs of systematic arteriosclerosis or vasculitis, and an unremarkable family history for vascular abnormalities). Computerized tomography revealed an infarct in his right parietal lobe. Angiography demonstrated complete occlusion of both internal carotid arteries and the right posterior communicating artery and failed to disclose the development of extensive collatorals, adding further evidence to the acuteness of the occlusion. The patient was followed by noninvasive studies and in the subsequent year showed marked neurological and ophthalmological improvement.

Morphologic investigations of the human visual pathways have been limited by the infeasibility of modern neuroanatomical approaches. Although contemporary methods for tracing axon pathways (such as tracer injections and electrophysiology) have elucidated the visual system in experimental animals, these techniques cannot be similarly applied in humans. Thus, the present view of the neuroanatomy of the human visual system is based largely on experimental animal studies, classical simple observations of gross human brains, and clinical inference. We demonstrate use of the stain, paraphenylenediamine (PPD), in conjunction with standard methods of tissue preparation for transmission electron microscopy. Osmium precipitates on degenerating neural processes, resulting in a dark profile when examined by electron microscopy. PPD chelates the osmium in osmium tetroxide-fixed tissue, and thus becomes a light-opaque marker of degenerating processes. This technique allows the identification and tracing of degenerating or degenerated axons. Postmortem studies of six patients, four with documented optic nerve lesions, are presented. The degenerated retinal ganglion nerve fibers are followed with PPD and confirmed with electron microscopy. Previously proposed, primary visual projections are confirmed and new retinofugal pathways are demonstrated in the human brain.

The feline RN contains neurons which fall into three size categories: giant (40--80 micrometer), medium (25--35 micrometer) and small (6--20 micrometer). These three populations of rubral neurons are distinguishable on the basis of a number of ultrastructural criteria and form classes not dissimilar from the traditional three divisions of cell types. Each of the three populations of rubral neurons can be further divided into three subgroups on the basis of a large number of configurational criteria discernible by the Golgi-Cox method. Each of these nine cell types are clearly separate, distinguishable by at least three criteria, and are found in different regions of the RN. It is shown that in the 5-day prenatal kitten, rubral neurons are already organized into the aforementioned three size categories. At this age most of the subpopulations are also distinguishable by the Golgi-Cox method. However, the giant rubral neurons (about 30 micrometer) and the medium sized cells (about 20 micrometer) are much smaller than in the adult cat. The dendrites elaborate many fine processes which emerge from multiple varicosities. The neuropil differs strikingly from that of the adult in that the vast majority of axons are small and unmyelinated. A number of changes in the RN are apparent as the kitten matures. The larger rubral cells undergo configurational changes before the smaller neurons, yet the giant cells continue to grow for a longer period of time. In the perinatal period, the extent of arborization of the dendritic trees diminishes, the number of spines decreases, and the long dendritic spines shorten. Somatic spines first appear in the giant cells at about one week after birth. In prenatal kittens, large cells frequently elaborate a tuft of fine branching processes in one region of the soma. These tufts later diminish in size and disappear by one week postnatal. Recent investigations (Pompeiano, '59; Condé, '66; King et al., '73' Sadun, '75) indicate that the RN of the cat is highly organized and very heterogenous. Afferent terminals are restricted to certain regions of certain cell types which are themselves specifically located within the RN. This specificity is apparent in perinatal kittens, despite the manifest immature appearance of the RN.

Transneuronal degeneration of retinal ganglion cells was directly demonstrated in a patient who had unilateral removal of the striate cortex forty years prior to necropsy. For comparison, another case is presented showing anterograde transneuronal atrophy forty years after enucleation of one eye.

We examined five patients with Alzheimer's disease who complained of poor vision. Two patients had mild Alzheimer's disease; they complained of problems with reading and of "bumping into things," yet both had normal visual acuities. One patient with moderate Alzheimer's disease had abnormal eye movements, visual-evoked potentials, and contrast sensitivity. The other two patients had severe Alzheimer's disease. Despite difficulties in performing the examination, we were able to see moderate impairments in visual acuity and visual fields, as well as marked dyschromatopsia, severe deficits in contrast sensitivity, and markedly abnormal eye movements and visual-evoked potentials.

It has been proposed that, in animals, a retinohypothalamic pathway exists which mediates the synchronization of the diurnal light-dark cycle with the central neural components regulating endogenous rhythms. There have been numerous anatomic, physiologic and behavioral investigations to substantiate this proposed connection in experimental animals. Morphologic investigation of a retinohypothalamic tract in man has awaited the development of a technique capable of axonal tracing in the human brain. The paraphenylenediamine method was applied to 7 post-mortem human brains. Degenerated axons were found in the suprachiasmatic nuclei of the hypothalamus in each of the 4 patients who had incurred prior optic nerve damage. The retinosuprachiasmatic pathway may be the anatomical substrate for the integration of retinal light information with endogenous rhythms in man.

We compared the tear pH values of 44 normal, healthy volunteers, 20 patients with ocular disorders other than rosacea, seven patients with untreated, active ocular rosacea, and five patients with tetracycline-treated ocular rosacea. The group with untreated, active ocular rosacea had significantly more alkaline tear pH values than the other groups tested. In patients with tetracycline-treated ocular rosacea, tear pH values were not significantly different from those of normal subjects.

Ethambutol is frequently used in the treatment of tuberculosis, and, although optic neuropathies have been reported with the use of ethambutol, this adverse side effect has been considered to be rare and generally reversible with discontinuation of the medication. However, we recently saw two patients with renal tuberculosis treated with ethambutol in whom visual loss from toxic optic neuropathies was severe and irreversible despite careful ophthalmological monitoring and prompt discontinuation of the agent at the first sign of impaired visual function. While ethambutol treatment is most commonly instituted for pulmonary tuberculosis, it is interesting to note that both of these patients had renal tuberculosis. Since ethambutol is actively excreted via the renal system, compromise of renal function such as due to renal tuberculosis may lead to serum concentration elevations of ethambutol sufficient to produce optic neuropathy.

Alzheimer's disease is a dementing disorder of unknown cause in which there is degeneration of neuronal subpopulations in the central nervous system. In postmortem studies, we found widespread axonal degeneration in the optic nerves of 8 of 10 patients with Alzheimer's disease. The retinas of four of the patients were also examined histologically, and three had a reduction in the number of ganglion cells and in the thickness of the nerve-fiber layer. There was no retinal neurofibrillary degeneration or amyloid angiopathy, which are typically seen in the brains of patients with Alzheimer's disease. The changes we observed in the patients with Alzheimer's disease were clearly distinguishable from the findings in 10 age-matched controls and represent a sensory-system degeneration that occurs in Alzheimer's disease. Study of the retina in patients with this disease may be helpful diagnostically, and isolation of the affected ganglion cells may facilitate molecular analysis of the disorder.

A young, healthy woman underwent craniotomy for the resection of a corpus callosum arteriovenous malformation. She was slow to awaken from anesthesia and was later noted to have a total external ophthalmoplegia. Her mental status quickly improved but the total ophthalmoplegia showed only minimal improvement for 2 weeks. After ruling out possible cerebrovascular and anesthetic complications, we concluded that the oculomotor impairment was due to postoperative toxic levels of Dilantin. Toxic Dilantin levels are known to rarely produce total ophthalmoplegia. In previously reported cases, this has always resolved with normalization of the serum Dilantin levels. This case represents the first report of Dilantin-induced ophthalmoplegia that took at least 3 months to resolve; it provides a detailed documentation of the course of ocular findings.

Camillo Golgi is well-known for his development of a staining technique that permitted profound contributions in histology. He is also well-known as the champion of a theory describing the organization of the nervous system as a reticular network. He shared the 1906 Nobel prize with Ramon y Cajal, who professed an antagonistic neuron theory which ultimately proved correct. We recently came across an original reprint of Golgi's work from an obscure reference. It deals with an important variation in the famous Golgi stain. In translating this original work into English, we present a piece of history, a comparison of Golgi's staining techniques, and a glimpse into Golgi's peculiar style and personality.

We examined ten patients from a consecutive series of 73 patients with either isolated cytomegalovirus papillitis or limited cytomegalovirus retinitis contiguous with the optic disk. Patients with peripheral retinitis and other areas of retinitis were excluded. All patients were treated with ganciclovir. Two distinct types of cytomegalovirus infection of the peripapillary area were identified. Type I was characterized by spread of limited retinitis to the optic disk margin, good central visual acuity, and permanent arcuate and altitudinal visual field defects that enlarged and became more complete as the retinitis progressed toward the disk. Type II appeared to be a true cytomegalovirus infection of the optic nerve characterized by primary, isolated papillitis with peripapillary retinitis, an early afferent pupillary defect, and good initial visual acuity, which rapidly deteriorated despite prompt antiviral therapy. Peripapillary cytomegalovirus retinitis appears to be an important and underreported cause of visual morbidity in patients with AIDS.

There is growing evidence for parallel processing of visual information. Visual information, spatially or temporally distinct, is transmitted to various regions of the brain. This paper presents clinical and anatomical evidence for parallel processing in the human visual system. The neuro-ophthalmologist often has psychophysical evidence for the separation of visual functions. Our own investigations have demonstrated that brightness sense and other visual functions may be impaired out of proportion to visual acuity in diseases of the optic nerve. Classes of retinal ganglion cells have been morphologically and physiologically described in several experimental animals. No such classification of retinal ganglion cell types has been made in man. However, psychophysical and retinal electrophysiological human studies suggest the segregation of human retinal ganglion cells into classes which subserve different functions. A new staining method (PPD) has made it possible to directly study the visual pathways in man. With this method, we have documented several previously undescribed human visual pathways to different brain visual nuclei: the lateral geniculate nucleus, the pretectum, the superior colliculus, the pulvinar, and three nuclei of the hypothalamus (SCN, PVN, SON). We have also developed a method which permits the accurate and rapid measurement of human retinal ganglion cell axon diameters through the optic nerve and through the fascicles of optic fibers entering several of these recently described visual nuclei. There is evidence for three size classes of axons which differentially distribute to the visual nuclei. These studies emphasize the need for overcoming the constraints of thinking that vision is the same as seeing.(ABSTRACT TRUNCATED AT 250 WORDS)

A pair of identical twins, whose features met Cogan's classic description of congenital ocular motor apraxia, were examined. Each had an absence of willed horizontal saccades and demonstrated classic head thrusting. Magnetic resonance imaging revealed hypoplasia of the corpus callosum. Fourth ventricle enlargement and generalized cerebral hypoplasia were also present but were more pronounced in the sibling with the more delayed motor development. The significance of these findings is discussed in light of our understanding of the control mechanism of volitional eye movements.

This study documents the light-microscopic and ultrastructural characteristics of ganglion cell degeneration in the retinas of patients with Alzheimer's disease (AD). The results show degeneration in the retinal ganglion cells (RGCs) characterized by a vacuolated, 'frothy' appearance of the cytoplasm. The degeneration is unique in AD because of the absence of neurofibrillary tangles within the RGCs, or of neuritic plaques or amyloid angiopathy in the retinas or optic nerves of any of the cases examined. These results suggest that neuronal degeneration in the ganglion cell layer (GCL) should be added to the constellation of neuropathologic changes found in patients with Alzheimer's disease.

The accessory optic system (AOS) has been extensively studied among vertebrates, including primates. It has never clearly been identified in man, and it has not been considered functionally important by clinicians. Because of a lack of a suitable neuroanatomical tract-tracing technique, anatomical demonstration of a retinofugal pathway to the human AOS had previously not been feasible. A modified osmium impregnation method has been shown to permit the tracing of degenerated fibers in man even after long survival periods. This technique employs p-phenylene diamine (PPD) as a marker of myelin and products of axonal degeneration. We applied the PPD method in the examination of one monkey brain (Cynomolgus) and two human autopsy brains with previous visual system lesions. The lateral, dorsal, and medial terminal accessory optic nuclei and the interstitial nucleus of the superior fasciculus, posterior fibers (LTN, DTN, MTN, and inSEp) in the monkey and the LTN, the DTN, and the inSEp in the human all showed degenerated axons and preterminal axonal profiles indicative of direct retinal input. The ventral midbrain tegmentum including the MTN area was not available for study in either of the human brains. The accessory optic projections in both the monkey and human brains proved to be bilateral but primarily crossed. The human visual system thus shares similarities with the simian, in the location and number of the AOS fiber bundles and terminal nuclei and in the organization of the retinofugal projections to these nuclei.