Origin of the Relative Afferent Pupillary Defect in Optic Tract Lesions

Disorders of the Pupil

OBJECTIVE

This article reviews the underlying disorders causing pathologic anisocoria or abnormal pupils to help clinicians efficiently pursue appropriate investigations.

LATEST DEVELOPMENTS

The pupils reflect the activity of several central nuclei, peripheral ganglia, and nerves that control two muscles of the iris: the radial dilator and the circular sphincter. Acquired asymmetry of pupil size and abnormal pupillary movement signal damage within the neural (parasympathetic or sympathetic) pathways to the eye or damage to the muscles that move the pupil. Studies have further defined which topical agents are useful in diagnosing pupil disorders.

ESSENTIAL POINTS

Pupillary shape, size, and movement are readily observable. Knowledge of the relatively simple pupil anatomy and innervation can guide clinical examination to determine the pathophysiologic mechanism underlying a pupil abnormality.

Nerve fibre organisation in the human optic nerve and chiasm: what do we really know?

A recent anatomical study of the human optic chiasm cast doubt on the widespread assumption that nerve fibres travelling in the human optic nerve and chiasm are arranged retinotopically. Accordingly, a scoping literature review was performed to determine what is known about the nerve fibre arrangement in these structures. Meta-analysis suggested that the average number of fibres in each optic nerve was 1.023 million with an inter-individual range of approximately 50% of the mean. Loss of nerve fibres with age (approximately 3,400 fibres/year) could not account for this variability. The review suggested that there might be a retinotopic arrangement of nerve fibres in the orbital portion of the optic nerve but that this arrangement is most likely to be lost posteriorly with a more random distribution of nerve fibres at the chiasm. Limited studies have looked at nerve fibre arrangement in the chiasm. In summary, the chiasm is more 'H-shaped' than 'X-shaped': nerve fibre crossings occur paracentrally with nerves in the centre of the chiasm travelling coronally and in parallel. There is interaction between crossed and uncrossed fibres which are widely distributed. The review supports the non-existence of Wilbrand's knee. Considerable further work is required to provide more precise anatomical information, but this review suggests that the assumed preservation of retinotopy in the human optic nerve and chiasm is probably not correct.

Quantification of relative afferent pupillary defect by an automated pupillometer and its relationship with visual acuity and dimensions of macular lesions in age-related macular degeneration

Purpose

The occurrence of relative afferent pupillary defect (RAPD) secondary to optic nerve diseases and widespread retinal disorders is well established. However, only very few reports of RAPD in macular disorders exist in the literature. In this study, we used automated pupillometer to evaluate RAPD in eyes with macular lesions.

Methods

It was a prospective cross-sectional study. A total of 82 patients with choroidal neovascular membrane (CNVM) - 65 unilateral and 17 bilateral macular lesions - were enrolled. RAPD was assessed with an automated pupillometer and macular lesions evaluated with optical coherence tomography (OCT). The length of the ellipsoid zone disruption was measured as the longest length of lesion on the horizontal raster scans and the area of macular lesion was measured manually, mapping the affected area of ellipsoid zone on the enface images.

Results

: RAPD scores showed good correlation with the intereye difference in length of maximum ellipsoid zone disruption (r-value = 0.84, P value <0.001) and macular lesion area as measured on OCT in all unilateral cases (r-value = 0.84, P value <0.001). Best-corrected visual acuity was also found to have a significant correlation with lesion size on the OCT as well as the length of ellipsoid zone disruption in unilateral cases.

Conclusion

: RAPD evaluated with an automated binocular pupillometer is a noninvasive and objective method to assess macular lesions in CNVMs; it shows good correlation with structural lesion dimensions on OCT in unilateral cases. Further longitudinal studies are needed to assess the significance of these findings in disease progression as well as correlation with lesion response to treatment.

Localizing Thalamomesencephalic Afferent and Efferent Pupillary Defects

ABSTRACT

A 42-year-old Algerian man presented for binocular oblique diplopia, hypersomnolence with drop attacks, bilateral hearing loss, and thoracic pain. He had a right thalamomesencephalic hemorrhage due to an underlying cavernous malformation treated with subtotal surgical resection. On neuro-ophthalmic examination, the patient had a left relative afferent pupillary defect and a right oculosympathetic efferent pupillary defect (i.e., Horner syndrome) in addition to other thalamomesencephalic eye and neurologic signs (right fourth nerve palsy, hearing loss, hemiparesis, and thalamic pain). Clinicians should recognize the localizing value of this unique constellation of mesencephalic afferent and efferent pupillary defects.

Chiasmal and Postchiasmal Disease

PURPOSE OF REVIEW

This article reviews the anatomy, symptoms, examination findings, and causes of diseases affecting the optic chiasm, optic tracts, optic radiations, and occipital lobes.

RECENT FINDINGS

Modern ophthalmic imaging can be used to monitor the effects of diseases of the optic chiasm and tract on the retinal ganglion cells. It can also be used to visualize transsynaptic degeneration of the anterior visual pathway in the setting of acquired retrogeniculate lesions. Visual prostheses that directly stimulate the occipital lobe are a potential strategy for rehabilitation that is in active clinical trials.

SUMMARY

Detecting and characterizing visual deficits due to optic chiasm and retrochiasmal disease are important for the diagnosis, localization, and monitoring of neurologic disease; identifying patient disability; and guiding rehabilitation.

Quantification of RAPD by an automated pupillometer in asymmetric glaucoma and its correlation with manual pupillary assessment

Purpose:

The relative afferent pupillary defect (RAPD) is an important sign of asymmetrical retinal ganglion cell damage. The purpose of this study was to quantify RAPD by a pupillometer (RAPiDo, Neuroptics) and assess its correlation with asymmetric glaucoma and manual pupillary assessment.

Methods:

A total of 173 subjects were enrolled in the study and categorized into glaucoma, n = 130, and control, n = 43. Subjects were all recruited in the Glaucoma Clinic of the Aravind Eye Hospital in Madurai during their follow-up. They were 18 years and older, with best corrected visual acuity of 6/36 or better. Exclusion criteria included all retinal pathologies, optic atrophies, ocular injuries, severe uveitis, cloudy corneas, dense cataracts, or use of mydriatics or miotic drugs. RAPD was assessed in all subjects using an automated pupillometer and the results were compared with the swinging flash light test conducted on the same subjects by an experienced ophthalmologist. We looked at the correlation between RAPD and the intereye difference in cup-to-disc ratio (CDR), mean deviation (MD) of visual field testing, and retinal nerve fiber layer (RNFL) thickness. Sensitivity and specificity were assessed by area under the receiver operator characteristic (AUROC) analysis.

Results:

Glaucoma patients had significant RAPD (0.55 ± 0.05 log units) when compared with the controls (0.25 ± 0.05 log units), P < 0.001. Significant intereye differences in CDR, MD, and RNFL between glaucoma and control (P < 0.001) were seen. There was a good correlation between the magnitude and sign of RAPD and these intereye differences in CDR (r = 0.52, P < 0.001), MD (r = 0.44, P < 0.001) and RNFL thickness (r = 0.59, P < 0.001). When compared with the experienced ophthalmologist, AUROC was 0.94, with 89% sensitivity and 91.7% specificity.

Conclusion:

The good correlation between the magnitude of RAPD, as measured by the automated pupillometer, and intereye differences in MD, CDR, and RNFL thickness in glaucomatous, and the good sensitivity and specificity when compared with the experienced ophthalmologist, suggest that pupillometry may be useful as a screening tool to assess asymmetric glaucoma.

Utility of optical coherence tomography in the evaluation of sellar and parasellar mass lesions

PURPOSE OF REVIEW

Anterior visual pathway compression is a common feature of sellar region masses. We review the visual pathway neuroanatomy pertaining to sellar and parasellar lesions and describe recent advances in optical coherence tomography (OCT) imaging that have provided a novel quantitative perspective in the evaluation and management of such patients.

RECENT FINDINGS

Ultrastructural measurements of optic nerve integrity using OCT, namely peripapillary retinal nerve fiber layer (pRNFL) and the ganglion cell and inner plexiform layer (GCIPL) thicknesses, have been shown to correlate with visual acuity and visual field deficits on perimetry in patients with compressive sellar region masses. In some cases, OCT can visualize early signs of anterior visual pathway involvement in the absence of clinically evident visual field loss or optic disc pallor. OCT is particularly useful when assessing patients who demonstrate less reliable visual field testing. Furthermore, there is growing awareness that pRNFL and GCIPL thinning preoperatively correlate with worse visual recovery following chiasmal decompression, highlighting the prognostic utility of OCT in this patient population.

SUMMARY

OCT provides a complimentary, yet critical, role in quantitatively assessing ultrastructural retinal injury in patients with sellar and parasellar lesions compressing the anterior visual pathway and should be incorporated into routine evaluation.

The value of visual field testing in the era of advanced imaging: clinical and psychophysical perspectives

White‐on‐white standard automated perimetry (SAP) is widely used in clinical and research settings for assessment of contrast sensitivity using incremental light stimuli across the visual field. It is one of the main functional measures of the effect of disease upon the visual system. SAP has evolved over the last 40 years to become an indispensable tool for comprehensive assessment of visual function. In modern clinical practice, a range of objective measurements of ocular structure, such as optical coherence tomography, have also become invaluable additions to the arsenal of the ophthalmic examination. Although structure‐function correlation is a highly desirable determinant of an unambiguous clinical picture for a patient, in practice, clinicians are often faced with discordance of structural and functional results, which presents them with a challenge. The construction principles behind the development of SAP are used to discuss the interpretation of visual fields, as well as the problem of structure‐function discordance. Through illustrative clinical examples, we provide useful insights to assist clinicians in combining a range of clinical results obtained from SAP and from advanced imaging techniques into a coherent picture that can help direct clinical management.

Analysis of retinal nerve fibre layer, visual evoked potentials and relative afferent pupillary defect in multiple sclerosis patients

OBJECTIVE

The aim of this study was to analyse retinal nerve fibre layer (RNFL), pattern-reversal visual evoked potentials (pVEPs) and relative afferent pupillary defect (RAPD) changes in multiple sclerosis (MS) patients with the consideration of past optic neuritis (ON).

METHODS

Ophthalmological, neurological, OCT, RNFL and pVEP studies were conducted in 59 MS patients. RAPD tests were performed in 47 of them. Control group consisted of 28 healthy volunteers.

RESULTS

Abnormal RNFL was found in 59% of cases of eyes with ON and 28% of eyes without ON. In eyes with ON, significantly lower RNFL values were indicated in the temporal and lower quadrants. Elongation of pVEP latency was found in 83% of eyes with ON and 60% of eyes without ON. The average value of pVEP latency was larger and the amplitude was lower in the subgroup of eyes with RNFL at the borderline or below the norm. RAPD was observed only in eyes with ON and with RNFL thinning. No association was found between the RAPD and pVEP parameters.

CONCLUSIONS

VEPs were more frequently abnormal than RNFL in MS patients. RNFL damage in eyes without ON may indicate neurodegenerations in CNS of MS patients; it can also be the consequence of subclinical ON.

SIGNIFICANCE

An analysis of RNFL and VEP can be useful for evaluating the optic nerve in MS patients.

Differential monocular vs. binocular pupil responses from melanopsin-based photoreception in patients with anterior ischemic optic neuropathy

We examined the effect of anterior ischemic optic neuropathy (AION) on the activity of intrinsically photosensitive retinal ganglion cells (ipRGCs) using the pupil as proxy. Eighteen patients with AION (10 unilateral, 8 bilateral) and 29 age-matched control subjects underwent chromatic pupillometry. Red and blue light stimuli increasing in 0.5 log steps were presented to each eye independently under conditions of dark and light adaptation. The recorded pupil contraction was plotted against stimulus intensity to generate scotopic and photopic response curves for assessment of synaptically-mediated ipRGC activity. Bright blue light stimuli presented monocularly and binocularly were used for melanopsin activation. The post-stimulus pupil size (PSPS) at the 6th second following stimulus offset was the marker of intrinsic ipRGC activity. Finally, questionnaires were administered to assess the influence of ipRGCs on sleep. The pupil response and PSPS to all monocularly-presented light stimuli were impaired in AION eyes, indicating ipRGC dysfunction. To binocular light stimulation, the PSPS of AION patients was similar to that of controls. There was no difference in the sleep habits of the two groups. Thus after ischemic injury to one or both optic nerves, the summated intrinsic ipRGC activity is preserved when both eyes receive adequate light exposure.

Homonymous hemianopia: challenges and solutions

Stroke is the most common cause of homonymous hemianopia (HH) in adults, followed by trauma and tumors. Associated signs and symptoms, as well as visual field characteristics such as location and congruity, can help determine the location of the causative brain lesion. HH can have a significant effect on quality of life, including problems with driving, reading, or navigation. This can result in decreased independence, inability to enjoy leisure activities, and injuries. Understanding these restrictions, as well as the management options, can aid in making the best use of remaining vision. Treatment options include prismatic correction to expand the remaining visual field, compensatory training to improve visual search abilities, and vision restoration therapy to improve the vision itself. Spontaneous recovery can occur within the first months. However, because spontaneous recovery does not always occur, methods of reducing visual disability play an important role in the rehabilitation of patients with HH.

Band atrophy of the optic nerve: A report on different anatomical locations in three patients

Lesions of the optic tract are accompanied by various signs that help to distinguish them from hemianopias located posterior to the lateral geniculate body. Band optic nerve atrophy is one of these signs and typically occurs contralateral to the optic tract lesion. We report on three patients with band atrophy in the fundus of the eye. These three patients present examples of how three lesions with different anatomic locations can cause band atrophy of the optic disk in similar ways. In these cases, the presence of relative afferent pupillary defect (RAPD) and band atrophy becomes important in identifying the injury to the optic tract, because when the hemianopia is complete visual fields do not allow distinguishing optic tract lesions from occipital lesions. The RAPD occurs in the eye in which the visual field defect is greater. In this paper we review the different theories about the explanation for RAPD in patients with optic tract lesions. It does not seem as simple as the anatomical differences between the number of fibers that decussate in particular cases, rather, it is associated with the difference between the sensitivity levels of the two functioning hemiretinas.

Objective characterization of the relative afferent pupillary defect in MS

OBJECTIVE

To develop an objective and precise neurophysiologic method from which to identify and characterize the presence and magnitude of relative afferent pupillary defects (RAPD) in patients with MS.

METHODS

Binocular infrared pupillometry was performed in 40 control subjects and 32 MS patients with RAPDs, using two precisely defined sequences of alternating light flashes (right-left and left-right). We analyzed three distinct pupillary metrics in response to light stimulation. These included percent diameter change (DC), constriction curve area (CCA), which measures change in diameter over time, and the phase-plane curve area (PCA) which measures change in diameter with change in velocity. Direct and consensual response ratios (for each eye) were computed and analyzed for each metric in response to both the first flash (i.e. first phase) and second flash (i.e. second phase) of the 'swinging flashlight' test.

RESULTS

Second flash pupillary response metric asymmetry ratios yielded the highest discriminatory power for RAPD detection. Receiver operating characteristic areas under the curve for each of the pupillary metric response asymmetry ratios were as follows: diameter change: 0.97; constriction curve area: 0.96; phase-plane curve area: 0.95 (p<0.0001 for all comparisons compared to normal subjects). The sum of these three squared ratios (SSR) yielded a combined metric with the greatest discriminatory power (receiver operator characteristic area under the curve=0.99).

CONCLUSIONS

Second flash (i.e. the second phase of the swinging light test) pupillary metric response asymmetry ratios are highly sensitive and specific for the confirmation and characterization of an RAPD in patients with MS. This objective neurophysiologic method may be useful for studying the relationship between a stereotyped reflex, and nervous system architecture, with potential ramifications for detecting and monitoring neuroprotective and restorative effects of novel agents in MS treatment trials.

Pupillometric analysis for assessment of gene therapy in Leber Congenital Amaurosis patients

BACKGROUND

Objective techniques to assess the amelioration of vision in patients with impaired visual function are needed to standardize efficacy assessment in gene therapy trials for ocular diseases. Pupillometry has been investigated in several diseases in order to provide objective information about the visual reflex pathway and has been adopted to quantify visual impairment in patients with Leber Congenital Amaurosis (LCA). In this paper, we describe detailed methods of pupillometric analysis and a case study on three Italian patients affected by Leber Congenital Amaurosis (LCA) involved in a gene therapy clinical trial at two follow-up time-points: 1 year and 3 years after therapy administration.

METHODS

Pupillary light reflexes (PLR) were measured in patients who had received a unilateral subretinal injection in a clinical gene therapy trial. Pupil images were recorded simultaneously in both eyes with a commercial pupillometer and related software. A program was generated with MATLAB software in order to enable enhanced pupil detection with revision of the acquired images (correcting aberrations due to the inability of these severely visually impaired patients to fixate), and computation of the pupillometric parameters for each stimulus. Pupil detection was performed through Hough Transform and a non-parametric paired statistical test was adopted for comparison.

RESULTS

The developed program provided correct pupil detection also for frames in which the pupil is not totally visible. Moreover, it provided an automatic computation of the pupillometric parameters for each stimulus and enabled semi-automatic revision of computerized detection, eliminating the need for the user to manually check frame by frame. With reference to the case study, the amplitude of pupillary constriction and the constriction velocity were increased in the right (treated eye) compared to the left (untreated) eye at both follow-up time-points, showing stability of the improved PLR in the treated eye.

CONCLUSIONS

Our method streamlined the pupillometric analyses and allowed rapid statistical analysis of a range of parameters associated with PLR. The results confirm that pupillometry is a useful objective measure for the assessment of therapeutic effect of gene therapy in patients with LCA.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00516477.

Toward a clinical protocol for assessing rod, cone, and melanopsin contributions to the human pupil response

PURPOSE. To better understand the relative contributions of rod, cone, and melanopsin to the human pupillary light reflex (PLR) and to determine the optimal conditions for assessing the health of the rod, cone, and melanopsin pathways with a relatively brief clinical protocol. METHODS. PLR was measured with an eye tracker, and stimuli were controlled with a Ganzfeld system. In experiment 1, 2.5 log cd/m(2) red (640 ± 10 nm) and blue (467 ± 17 nm) stimuli of various durations were presented after dark adaptation. In experiments 2 and 3, 1-second red and blue stimuli were presented at different intensity levels in the dark (experiment 2) or on a 0.78 log cd/m(2) blue background (experiment 3). Based on the results of experiments 1 to 3, a clinical protocol was designed and tested on healthy control subjects and patients with retinitis pigmentosa and Leber's congenital amaurosis. RESULTS. The duration for producing the optimal melanopsin-driven sustained pupil response after termination of an intense blue stimulus was 1 second. PLR rod- and melanopsin-driven components are best studied with low- and high-intensity flashes, respectively, presented in the dark (experiment 2). A blue background suppressed rod and melanopsin responses, making it easy to assess the cone contribution with a red flash (experiment 3). With the clinical protocol, robust melanopsin responses could be seen in patients with few or no contributions from the rods and cones. CONCLUSIONS. It is possible to assess the rod, cone, and melanopsin contributions to the PLR with blue flashes at two or three intensity levels in the dark and one red flash on a blue background.

Disorders of the pupil

Pupil size is determined by the interaction of the parasympathetic and the sympathetic nervous system. The parasympathetic system conducts the light reaction with its major center in the dorsal midbrain. The sympathetic nervous system acts either directly on the dilator muscle (peripherally) or centrally by inhibiting the Edinger-Westphal nucleus. Psychosensory reactions are transmitted via the sympathetic system. The afferent input of the light reflex system in humans is characteristically wired, allowing a detailed analysis of a lesion of the afferent input. Even in humans a subgroup of ganglion cells containing melansopsin plays an important role as a light sensor for the pupillary system. To diagnose normal pupillary function, pupils need to be isocoric and react bilaterally equally to light. Anisocoria indicates a problem of the efferent pupillary pathway. Pupillary disorders may involve the afferent pathways (relative afferent pupillary defect) or the efferent pathways. Physiological anisocoria is a harmless condition that has to be distinguished from Horner's syndrome. In this case pharmacological testing with cocaine eye-drops is helpful. Disorders of the parasympathetic system will impair the light response. They include dorsal midbrain syndrome, third-nerve palsy, and tonic pupil. Tonic pupils are mainly idiopathic and do not need imaging. Disorders of the iris, including application of cholinergic agents, need also to be considered in impaired pupillary light reaction.

Pupil perimetry demonstrates hemifield pupillary hypokinesia in a patient with a pretectal lesion causing a relative afferent pupil defect but no visual field loss

BACKGROUND

Lesions affecting the pretectum or the brachium of the superior colliculus (brachium) and sparing the optic tract cause a contralateral relative afferent pupil defect (RAPD) but no visual field loss. It has been assumed that the pupillomotor pathways within the brachium are a continuation of the pupillomotor pathways traveling in the optic tract. To investigate this assumption, we looked for hemihypokinesia by means of pupil perimetry.

METHODS

Pupillary hemifield stimulation was performed in a 65-year-old woman with normal visual fields and an isolated left RAPD due to a cerebral hemorrhage affecting the right dorsal midbrain. The pupil responses from light stimulation of the nasal inferior, nasal superior, and temporal inferior and temporal superior quadrants of both eyes were recorded using computerized binocular infrared pupillography. Each stimulus was presented 5 times and the mean amplitude of the pupil response was calculated for each stimulus location.

RESULTS

Pupil perimetry demonstrated a marked hemihypokinesia (reduced light reaction) in the hemifield contralateral to the site of the lesion.

CONCLUSIONS

Our experiment suggests that the brachium is indeed a continuation of the afferent pupillary fibers traveling in the optic tract.

Intrinsically photosensitive retinal ganglion cells

The recent discovery of melanopsin-expressing retinal ganglion cells that mediate the pupil light reflex has provided new insights into how the pupil responds to different properties of light. These ganglion cells are unique in their ability to transduce light into electrical energy. There are parallels between the electrophysiologic behavior of these cells in primates and the clinical pupil response to chromatic stimuli. Under photopic conditions, a red light stimulus produces a pupil constriction mediated predominantly by cone input via trans-synaptic activation of melanopsin-expressing retinal ganglion cells, whereas a blue light stimulus at high intensity produces a steady-state pupil constriction mediated primarily by direct intrinsic photoactivation of the melanopsin-expressing ganglion cells. Preliminary data in humans suggest that under photopic conditions, cones primarily drive the transient phase of the pupil light reflex, whereas intrinsic activation of the melanopsin-expressing ganglion cells contributes heavily to sustained pupil constriction. The use of chromatic light stimuli to elicit transient and sustained pupil light reflexes may become a clinical pupil test that allows differentiation between disorders affecting photoreceptors and those affecting retinal ganglion cells.