Afferent pupillary defect in macular degeneration

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.

Maintaining ocular safety with light exposure, focusing on devices for optogenetic stimulation

Optogenetics methods are rapidly being developed as therapeutic tools for treating neurological diseases, in particular, retinal degenerative diseases. A critical component of the development is testing the safety of the light stimulation used to activate the optogenetic proteins. While the stimulation needs to be sufficient to produce neural responses in the targeted retinal cell class, it also needs to be below photochemical and photothermal limits known to cause ocular damage. The maximal permissible exposure is determined by a variety of factors, including wavelength, exposure duration, visual angle, pupil size, pulse width, pulse pattern, and repetition frequency. In this paper, we develop utilities to systematically and efficiently assess the contributions of these parameters in relation to the limits, following directly from the 2014 American National Standards Institute (ANSI). We also provide an array of stimulus protocols that fall within the bounds of both safety and effectiveness. Additional verification of safety is provided with a case study in rats using one of these protocols.

Estimation of retinal ganglion cell loss in glaucomatous eyes with a relative afferent pupillary defect

PURPOSE

To estimate retinal ganglion cell (RGC) losses associated with a relative afferent pupillary defect (RAPD) in glaucoma.

METHODS

A cross-sectional study was conducted including both eyes of 103 participants from the Diagnostic Innovations in Glaucoma Study. A total of 77 subjects had glaucoma in at least one eye and 26 were healthy. Pupil responses were assessed using an automated pupillometer that records the magnitude of RAPD as an "RAPD score." Standard automated perimetry (SAP) and optical coherence tomography (OCT) also were performed. Retinal ganglion cell counts were estimated using empirical formulas that combine estimates from SAP and OCT. The estimated percentage RGC loss was calculated using the combined structure function index (CSFI).

RESULTS

There was good correlation between RAPD magnitude and intereye differences in estimated RGCs (R(2) = 0.492, P < 0.001), mean deviation (R(2) = 0.546, P < 0.001), retinal nerve fiber layer thickness (R(2) = 0.362, P < 0.001), and CSFI (R(2) = 0.484, P < 0.001). Therefore, a high RAPD score is likely to indicate large asymmetric RGC losses. The relationship between intereye difference in RGC counts and RAPD score was described best by the formula; RGC difference = 21,896 + 353,272 * RAPD score. No healthy subjects had an absolute RAPD score > 0.3, which was associated with asymmetry of 105,982 cells (or 12%).

CONCLUSIONS

Good correlation between the magnitude of RAPD and intereye differences in mean deviation and estimated RGC counts suggests pupillometry may be useful for quantifying asymmetric damage in glaucoma. (ClinicalTrials.gov number, NCT00221897.).

Symmetry of the pupillary light reflex and its relationship to retinal nerve fiber layer thickness and visual field defect

PURPOSE

To assess the relationship between the pupillary light reflex (PLR) and visual field (VF) mean deviation (MD) and retinal nerve fiber layer (RNFL) thickness.

METHODS

A total of 148 patients with glaucoma (mean age 67 ± 11, 49% female) and 71 controls (mean age 60 ± 10, 69% female) were included in this study. Using a pupillometer, we recorded and analyzed pupillary responses at varied stimulus patterns (full field, superonasal and inferonasal quadrant arcs). We compared the responses between the two eyes, compared responses to stimuli in the superonasal and inferonasal fields within each eye, and calculated the absolute PLR value of each individual eye. We assessed the relationship among PLR, MD, and RNFL thickness using the Pearson correlation coefficient. For analyses performed at the level of individual eyes, we used multilevel modeling to account for between-eye correlations within individuals.

RESULTS

For every 0.3 log unit difference in between-eye asymmetry of PLR, there was an average 2.6-dB difference in visual field MD (correlation coefficient R = 0.83, P < 0.001) and a 3.2-μm difference in RNFL thickness between the two eyes (R = 0.67, P < 0.001). Greater VF damage and thinner RNFL for each individual eye were associated with smaller response amplitude, slower velocity, and longer time to peak constriction and dilation after adjusting for age and sex (all P < 0.001). However, within-eye asymmetry of PLR between superonasal and inferonasal stimulation was not associated with corresponding within-eye differences in VF or RNFL.

CONCLUSIONS

As measured by this particular device, the PLR is strongly correlated with VF functional testing and measurements of RNFL thickness.

Electrophysiological assessment of optic nerve disease

The electrophysiological findings in optic nerve and primary ganglion cell dysfunction are reviewed. The value of the pattern reversal visual-evoked potential (VEP) in the diagnosis of optic nerve disease, and the pattern appearance VEP in the demonstration of the intracranial misrouting associated with albinism, are discussed. The pattern electroretinogram (PERG) is used in the direct assessment of ganglion cell function. The use of PERG or multifocal electroretinography (mfERG), to enable the distinction between VEP delay due to optic nerve disease and that due to macular dysfunction, is described.

Pupil assessment in optic nerve disorders

BACKGROUND

The normal pupillary constriction to light is an involuntary reflex that can be easily elicited and observed without specialized equipment or discomfort to the patient. Attenuation of this reflex in optic nerve disorders was first described 120 years ago. Since then, pupil examination has become a routine part of the assessment of optic nerve disease.

CLINICAL TECHNIQUES

The original cover/uncover test compares pupillomotor drive in the two eyes, but requires two working pupils and is relatively insensitive. The swinging flashlight test is now the standard clinical tool to detect pupillomotor asymmetry. It requires only one working pupil, is easily quantified, and has high sensitivity in experienced hands, but interpretation of the results needs care. Measurement of the pupil cycle time is the only clinical test that does not rely on comparison with the fellow eye, but it can only be measured in mild to moderate optic nerve dysfunction, is more time consuming, and less sensitive.

LABORATORY TECHNIQUES

Infrared video pupillography allows recordings to be made of the pupil responses to full-field or perimetric light stimulation under tightly controlled conditions with a high degree of accuracy. Frustratingly, there is a wide range in reflex gain in normal subjects limiting its usefulness unless comparison is made with the fellow eye or stimulation of unaffected adjacent areas of the visual field.

CORRELATION WITH OTHER TESTS

In general, pupillomotor deficit shows good correlation with visual field deficit. However, some diseases of the optic nerve are associated with relative sparing either of pupil function or visual function implying that pupil tests and psychophysical tests may assess function in different subpopulations of optic nerve fibres. Less is known of the relationship between pupil measurements and electrodiagnostic tests.

USES IN CLINICAL PRACTICE

Pupil assessment is invaluable when distinguishing functional from organic visual loss. Its usefulness in distinguishing between different causes of optic neuropathy and as a prognostic sign is gradually emerging.

Pattern electroretinography (PERG) and an integrated approach to visual pathway diagnosis

The pattern electroretinogram (PERG) provides an objective measure of central retinal function, and has become an important element of the author's clinical visual electrophysiological practice. The PERG contains two main components, a positivity at approximately 50ms (P50) and a larger negativity at approximately 95ms (N95). The P50 component is affected by macular dysfunction with concomitant reduction in N95. The PERG therefore complements the Ganzfeld ERG in the assessment of patients with retinal disease. In contrast, the ganglion cell origins of the N95 component allow electrophysiological evaluation of ganglion cell function both in primary disease and in dysfunction secondary to optic nerve disease, where selective loss of N95 can be observed. Both macular dysfunction and optic nerve disease can give abnormalities in the visual evoked cortical potential (VEP), and the PERG thus facilitates more meaningful VEP interpretation. This review addresses the origins and recording of the PERG, and then draws on extensive clinical data from patients with genetically determined retinal and macular dystrophies, other retinal diseases and a variety of optic nerve disorders, to present an integrated approach to diagnosis.

Maculopathies that resemble optic neuropathies

This chapter outlines some diseases in which diagnosis of retinal pathology can prove difficult and often mislead one to think of optic nerve disease. Clinicians should consider these entities when atypical features or unexplained visual loss occurs. A careful medical history, review of systems, and the appropriate use of ancillary studies (as outlined) can provide insights helpful in making the correct diagnosis.

The test light affects quantitation of the afferent pupillary defect

Nineteen patients with afferent pupillary defects (APDs) from a variety of lesions were examined using a brighter and dimmer test light. A denser neutral density filter was required to balance the afferent defect using the brighter test light in every case. For quantitation of an afferent defect to have meaning, the test light used must be specified. An indirect ophthalmoscope set to 6 V and held 1 foot from the eyes will allow easier detection of subtle relative APDs than it will if set to 3 V.

Pupillary defects in amblyopia

We examined the pupils of 55 amblyopic subjects to determine whether a pupillary defect could be detected in the amblyopic eye. We found relative afferent pupillary defects in 45 of the subjects; these defects were equal to or larger than 0.3 log unit (that is, easily visible) in 29 subjects. The pupillary defect was always in the amblyopic eye, but it could not be correlated with the severity or the cause of the amblyopia, with visual-evoked potential abnormalities, or with color vision defects.

Afferent pupillary defects in amblyopia

We detected mild afferent pupillary defects with the "swinging flashlight" test in 4 out of 45 amblyopic patients. Our study was designed to minimize the effect of observer bias and to control for the difficulty of testing the pupils in young children. We found afferent defects in both strabismic and anisometropic amblyopes. There was no apparent relationship between pupillary response and visual acuity: afferent defects were noted in association with better than 20/100 vision in three cases but were absent in a majority of patients with profound visual loss. Vision was improved by occlusion therapy in two amblyopes with pupillary abnormalities. We regard the occurrence of afferent pupillary defects as evidence for a physiological disturbance at the retinal level in at least some cases of amblyopia. Our findings suggest that the extent of retinal involvement in amblyopic eyes is independent of reduction in acuity, to which primary cortical abnormalities may contribute as well.