Nonvisual ocular photoreception in the mammal

Rodents blind from outer retinal (rod and cone) degeneration still retain several light-dependent phenomena, including entrainment of the circadian clock and pupillary light responsiveness. This paradox is explained by the presence of intrinsically photosensitive retinal ganglion cells in the inner retina. These cells have unique properties, including a novel action spectrum, resistance to bleaching and adaptation under continuous light, and resistance to vitamin A depletion. Two candidate classes of photopigment have been proposed: melanopsin and cryptochromes. Physiologic analysis of circadian entrainment and pupillary light responsiveness in mice lacking these proteins leads to three conclusions: (1) outer and inner retinal photoreceptors provide partially redundant information to the inner retina, (2) melanopsin is required for inner retinal phototransduction in the absence of rod and cone signaling, and (3) cryptochromes contribute to the amplitude of inner retinal phototransduction but are not strictly required.

Bilateral tonic pupils: Holmes Adie syndrome or generalised neuropathy?

AIM

To compare the pupil signs in patients with bilateral pupillotonia caused by Holmes-Adie syndrome or generalised peripheral neuropathy.

METHODS

Infrared video pupillographic techniques were used to measure a number of pupil variables in patients with Holmes-Adie syndrome, generalised neuropathy (various aetiologies) and healthy age-matched control subjects.

RESULTS

Regardless of aetiology, the patients generally had pupil signs typical of pupillotonia (small dark diameters, large light diameters, tonic near responses, attenuated light responses with light-near dissociation, and sector palsy). However, significant differences were found in the prevalence and magnitude of several pupil variables in the two patient groups. In particular, sector palsy and anisocoria exceeding 1 mm (in the light) were seen much more commonly in Holmes-Adie patients than patients with generalised neuropathy. The presence of both these pupil signs can be used to distinguish between these diagnoses with a sensitivity of 58% and a specificity of 90%.

CONCLUSIONS

The tonic pupils of patients with Holmes-Adie syndrome are significantly different to those found in patients with generalised neuropathy; recognition of these differences may allow distinction between these diagnoses.

Dynamic analysis of dark-light changes of the anterior chamber angle with anterior segment OCT

PURPOSE

To describe the use of anterior segment optical coherence tomography (OCT) in studying the dynamic dark-light changes of the anterior chamber angle.

METHODS

Thirty-seven normal subjects with open angles on dark-room gonioscopy and 18 subjects with narrow angles were analyzed. The dynamic dark-light changes of the anterior-chamber angle were captured with real-time video recording. The angle opening distance (AOD500) and trabecular iris space area (TISA500) of the nasal angle and the pupil diameter in each of the representative serial images were measured. Linear regression analysis was performed to investigate the association between AOD500/TISA500 and pupil diameter. Demographic and biometry measurements associated with the AOD difference (AOD500((light)) - AOD500((dark))) and TISA difference (TISA500((light)) - TISA500((dark))) were analyzed with univariate and multivariate regression models.

RESULTS

The AOD500/TISA500 measured in the light in the open-angle and the narrow-angle groups were 694 +/- 330 microm/0.24 +/- 0.10 mm(2) and 265 +/- 78 microm/0.10 +/- 0.03 mm(2), respectively. These values were significantly greater than the AOD500/TISA500 measured in the dark (492 +/- 265 microm/0.16 +/- 0.08 mm(2) and 119 +/- 82 microm/0.05 +/- 0.04 mm(2), respectively, all with P < 0.001). The ranges of the AOD/TISA difference were 13 to 817 microm/0.011 to 0.154 mm(2), with an average of 180 microm/0.073 mm(2). Multivariate regression analysis identified a positive correlation between anterior chamber depth and the AOD/TISA difference. Fifty eyes showed significant correlations between AOD/TISA and pupil diameter, whereas one eye showed no association. Four eyes in the narrow angle group developed appositional angle closure in the dark.

CONCLUSIONS

The dynamic dark-light changes of the anterior chamber angle can be imaged and analyzed with anterior segment OCT. Although the angle width generally decreased linearly with increasing pupil diameter, the differences of the angle width measured in the dark and in the light varied substantially among individuals.

Recovery of vision and pupil responses in optic neuritis and multiple sclerosis

The recovery of visual performance and pupil responses were investigated in patients with demyelinating optic neuritis (ON) and multiple sclerosis (MS). The pupil constriction amplitude and the time delay (latency) of the pupil response were measured in 14 patients with a history of unilateral ON in response to either achromatic (luminance) or chromatic (isoluminant) stimulus modulation. Five of these subjects were diagnosed later with MS. In addition, we measured detection thresholds for achromatic stimuli using standard visual field perimetry and chromatic thresholds using a new colour assessment and diagnosis (CAD) test that isolates the use of colour signals. The results show that, despite significant improvements in visual function following the acute phase (as assessed using visual acuity and fields), significant pupil response deficits remain. The findings also demonstrate that accurate measurements of pupil responses and chromatic thresholds can reveal deficits that remain undetected with more conventional techniques. These preliminary findings suggest that the techniques described here can provide useful information about remitting and relapsing demyelinative phases, often observed during MS and ON.

Variations in the light-induced suppression of nocturnal melatonin with special reference to variations in the pupillary light reflex in humans

The purpose of the present study was to elucidate the existence of individual differences of pupil response to light stimulation, and to confirm the reproducibility of this phenomenon. Furthermore, the relationship between the individual differences in nocturnal melatonin suppression induced by lighting and the individual differences of pupillary light response (PLR) was examined. The pupil diameter and salivary melatonin content of 20 male students were measured at the same period of time (00:00-02:30 hr) on different days, accordingly. Illumination (530 nm) produced by a monochromatic light-emitting diode (LED) was employed as the light stimulation: pupil diameter was measured with 4 different levels of illuminance of 1, 3, 30 and 600 lux and melatonin levels were measured at 30 and 600 lux (respective controls were taken at 0 lux). Oral temperature, blood pressure and subjective index of sleepiness were taken in experiments where melatonin levels were measured. Changes of the pupil diameter in response to light were expressed as PLR and light-induced melatonin suppression was expressed as a control-adjusted melatonin suppression score (control-adjusted MSS), which was compared to the melatonin level measured at 0 lux. In the PLR, the coefficients of variation obtained at 30 lux or less were large (51.5, 45.0, 28.4 and 6.2% at 1, 3, 30 and 600 lux, respectively). Correlations of illuminance of any combination at 30 lux or less were statistically significant at less than 1% level (1 vs. 3 lux: r=0.68; 1 vs. 30 lux: r=0.64; 3 vs. 30 lux: r=0.73), which showed the reproducibility of individual differences. The control-adjusted MSS at 600 lux (-1.14+/-1.16) was significantly (p<0.05) lower than that registered at 30 lux (-0.22+/-2.12). PLR values measured at 30 and 600 lux were then correlated with control-adjusted MSS; neither indicated a significant linear relationship. However, the control-adjusted MSS showed around 0 under any of the illuminance conditions in subjects with high PLR. In control-adjusted MSS of low values (i.e., melatonin secretions were easily suppressed), subjects indicated typically low PLR. In subjects with low control-adjusted MSS (n=3), characteristic changes in the autonomic nervous system, such as body temperature and blood pressure, were noted in subjects exposed to low illuminance of 30 lux. The fact that the relationship between PLR and control-adjusted MSS portray a similar pattern even under different luminance conditions suggests that MSS may not be affected in those with high PLR at low illuminance, regardless of the illuminance condition.

Melanopsin-dependent persistence and photopotentiation of murine pupillary light responses

PURPOSE

To determine the relative contributions of inner and outer retinal photoreception to the pupillary light response.

METHODS

Wild-type, retinal degenerate (rd/rd), and melanopsin mutant (opn4(-/-)) mice were tested for pupillary light responsiveness by video pupillometry before, during, and after exposure to supersaturating light intensities. Similar lighting protocols were used to probe responses of intrinsically photosensitive retinal ganglion cells (ipRGCs) recorded with multielectrode arrays ex vivo.

RESULTS

Both outer retinal photoreceptors (rods and cones) and inner retinal photoreceptors (intrinsically photosensitive retinal ganglion cells [ipRGCs]) are sufficient to drive the pupillary light response in mice. After supersaturating light exposure, rather than bleaching or adapting, rd/rd mice showed paradoxical potentiation of responses to subsaturating light exposure. opn4(-/-) mice, in contrast, could not sustain pupillary constriction under continuous bright illumination, and showed desensitization after bright-light exposure. Both the intensity of light necessary to induce potentiation and the spectral sensitivity for sustained and potentiated responses differed from that necessary to trigger pupillary constriction, suggesting that photopotentiation is dependent on a pigment-state distinct from that triggering the pupillary light response itself. Multielectrode array recordings of ipRGCs from rd/rd retinas demonstrated persistent cell firing under continuous light exposure but did not show potentiation.

CONCLUSIONS

Unique photoreceptive properties of intrinsically photosensitive RGCs confer resistance to bleaching and/or adaptation under continuous bright illumination to the pupillary light response and suggest the presence of a photopigment with multiple absorption states.

Measurement of pupil reactivity using fast pupillometry

Analysis of human eye pupil reactivity is a very valuable diagnostic method used mainly for evaluation of the condition of the autonomic nervous system and the visual system. The paper presents an experimental pupillometer built in the Institute of Physics of the Wroclaw University of Technology. The apparatus makes it possible to record and analyze pupillary light reflex and spontaneous changes in the pupil diameter during a session in the dark. The detector system used in the pupillometer allows us to record the pupil diameter at a rate of 90 Hz with a linear accuracy of 0.008 mm. In this paper, the proposed detection method, the principle of operation and calibration of the apparatus and the possibilities of the measurement system are presented.

Origin of the Relative Afferent Pupillary Defect in Optic Tract Lesions

OBJECTIVE

To determine the percent decussation of pupil input fibers in humans and to explain the size and range of the log unit relative afferent pupillary defect (RAPD) in patients with optic tract lesions.

DESIGN

Experimental study.

PARTICIPANTS AND CONTROLS

Five patients with a unilateral optic tract lesion.

METHODS

The pupil response from light stimulation of the nasal hemifield, temporal hemifield, and full field of each eye of 5 patients with a unilateral optic tract lesion was recorded using computerized binocular infrared pupillography. Six stimulus light intensities, separated by 0.5-log unit steps, were used; 12 stimulus repetitions were given for each stimulus condition.

MAIN OUTCOME MEASURES

For each stimulus condition, the pupil response of each eye was characterized by plotting the mean pupil contraction amplitude as a function of stimulus light intensity. The percentage of decussating afferent pupillomotor input fibers was calculated from the ratio of the maximal pupil contractions elicited from each eye. The RAPD was determined pupillographically from full-field stimulation to each eye.

RESULTS

In all patients, the pupil response from the functioning temporal hemifield ipsilateral to the tract lesion was greater than that from the functioning contralateral nasal hemifield. This temporal-nasal asymmetry increased with increasing stimulus intensity and was similar in hemifield and full-field stimuli, eventually saturating at maximal light intensity. The log unit RAPD did not correlate with the estimated percentage of decussating pupil fibers, which ranged from 54% to 67%.

CONCLUSIONS

In patients with a unilateral optic tract lesion, the pupillary responses from full-field stimulation to each eye are the same as comparing the functioning temporal field with the functioning nasal field. The percentage of decussating fibers is reflected in the ratio of the maximal pupil contraction amplitudes resulting from stimulus input between the two eyes. The RAPD that occurs in this setting reflects the difference in light sensitivity between the intact temporal and nasal hemifields. Its magnitude does not correlate with the difference in the number of crossed and uncrossed axons, but its sidedness contralateral to the side of the optic tract lesion is consistent with the greater percentage of decussating pupillomotor input.

Pupil size and corneal laser surgery

PURPOSE OF REVIEW

The role of scotopic pupil size as a factor in predicting night vision complaints is controversial. This review summarizes reports in the literature, some that have found and some that have failed to find a correlation with scotopic pupil size and night vision complaints.

RECENT FINDINGS

Pupil-measuring devices are discussed along with informed consent issues and reports showing that wavefront aberrations increase with increasing pupil size. A new objective measuring device (Larson) showed a correlation with postoperative starbursts and pupil size and a decrease in starbursts with wavefront-guided treatments compared with conventional excimer laser treatments. Cortical adaptation allows many patients to adapt to their new night vision. Treatment options for those who remain symptomatic include drops to reduce pupil size and wavefront-guided retreatments.

SUMMARY

Reports in the literature are conflicting, and refractive surgeons would be wise to inform their patients that large scotopic pupil size is a potential risk factor for night vision complaints. By doing this they will follow the recommendations in recent patient information brochures of both VISX (Santa Clara, California) and Alcon (Orlando, Florida) and on the United States Food and Drug Administration web site.

[Dynamics of the pupillary light reflex in unilateral Horner's syndrome]

BACKGROUND

The aim of this study was to characterise the changes of the dynamic pupillary light reflex in patients with unilateral Horner's syndrome by appropriate pupillographic parameters.

METHODS

The dynamic changes of pupillary diameter in response to light flashes of 100 ms were recorded in darkness with two infrared video cameras in 15 patients.

RESULTS

Significant changes in the pupillary light reflex of the affected side were observed only during the phase of redilatation. The decelerated redilatation was defined by the following parameters: (1) time parameters (percentage of redilatation after 4 s and after 5 s, time to reach 67% and 75% of redilatation) and (2) amplitude-adjusted velocity parameters (relative velocity at 67% and at 75% of redilatation).

CONCLUSION

A slowed pupil redilatation in patients with Horner's syndrome can be detected also after short light flashes and is characterised by prolonged redilatation time parameters and reduced amplitude-adjusted redilatation velocity parameters.

Demonstration of Aqueous Streaming Through a Laser Iridotomy Window Against the Corneal Endothelium

OBJECTIVE

To determine the pathogenesis of the bullous keratopathy that is frequently observed in patients after argon laser iridotomy (ALI) by comparing the changes in aqueous flow after ALI with those that follow peripheral iridectomy in rabbit eyes.

METHODS

Silicone particles were injected into the anterior chamber of rabbit eyes as tracers to monitor aqueous flow. Particle tracking velocimetry with image analysis was used to determine the direction and speed of aqueous flow in 5 pigmented rabbits that underwent ALI and 5 that underwent peripheral iridectomy.

RESULTS

In the ALI group, silicone particles were found to stream through the iridotomy window against the corneal endothelium immediately after the pupil was constricted by a light stimulus. The mean +/- SD speed of the particles was 2.97 +/- 1.51 mm/s. In contrast, the mean +/- SD flow rate through the iridectomy window in the peripheral iridectomy group was significantly slower at 0.36 +/- 0.30 mm/s (P = .01).

CONCLUSION

Constriction of the pupil elicited marked aqueous streaming through the ALI window against the corneal endothelium. Clinical Relevance The mechanical stress to the corneal endothelium by the abnormal aqueous stream may be partially responsible for the corneal decompensation that follows ALI.

Measurement of the spatial shift of the pupil center

PURPOSE

To evaluate the effectiveness of the pupil center as an anatomic landmark for excimer laser treatments.

SETTING

Sekal-Microchirurgia-Rovigo Centre, Rovigo, Italy.

METHODS

Pupillometry with the Costruzione Strumenti Oftalmici S.R.L. (CSO) pupil-measuring module (incorporated in Eye Top videokeratoscope) was performed in 52 patients with a diagnosis of myopia and in 25 patients with a diagnosis of hyperopia. Measurements both in mesopic and photopic conditions consisted of pupil diameters, spatial shift of the pupil center, and the distance between the pupil center and keratoscopic axis.

RESULTS

The mean pupil diameter in photopic conditions of illumination in myopic eyes was 3.52 mm +/- 0.56 (SD), while in mesopic conditions it was 5.37 +/- 0.78 mm; in hyperopic eyes the mean photopic pupil diameter was 3.01 +/- 0.46 mm, while the mean mesopic diameter was 5.12 +/- 0.48 mm. The mean spatial shift of the pupil center in myopic eyes was 0.086 mm (maximum 0.269 mm), while in the hyperopic eyes it was 0.095 mm (maximum 0.283 mm). The mean distance between the pupil center and keratoscopic axis in myopic eyes was 0.226 +/- 0.13 mm (maximum 0.75 mm), while in hyperopic eyes it was 0.45 +/- 0.19 mm (maximum 0.8 mm).

CONCLUSIONS

The mean of the measured pupil sizes was greater in myopic eyes than in hyperopic eyes. The spatial shift of the pupil center, as the pupil dilates, was relatively small in all groups; therefore, the pupil center is a good anatomic landmark for both traditional refractive surgery and wavefront-guided treatments. The mean distance between the keratoscopic axis and pupil center was greater in the hyperopic group than in the myopic group. Therefore, centration of any laser treatment on the basis of the keratoscopic analysis should be done carefully, especially in hyperopic eyes and in cases in which the pupil center is meaningfully shifted from keratoscopic axis, even in photopic conditions of illumination.

Influence of pupillary diameter, ciliary muscle tone, and ambient light on nerve fiber layer measurements with scanning laser polarimetry

PURPOSE

To evaluate the influence of the pupillary diameter, ciliary muscle tone, and room light on nerve fiber layer measurements with the scanning laser polarimeter (GDx).

METHODS

One randomly selected eye of ten normal volunteers was examined with the GDx in a two-day protocol under eight testing conditions (pilocarpine 1%, phenylephrine 10%, tropicamide 1%, or no drops with room lights on or off). The twelve parameters, obtained by the GDx, were compared under the eight testing conditions, using two way ANOVA for repeated measurements and Tukey HSD post hoc test.

RESULTS

Ten of the twelve parameters were statistically significantly different (P < 0.05) when measured under the three medication or no medication conditions, controlling for the ambient light status. There were no significant differences when measured with the light on or off, controlling for use of drops.

CONCLUSIONS

Nerve fiber layer measurements with the GDx were influenced by drugs affecting pupillary diameter, but not by the status of room light or ciliary muscle tone.

Comparison of pupil responses to luminance and colour in severe optic neuritis

OBJECTIVE

The pupil response to light flux increments is abnormal in severe optic neuritis, but little is known about the effects of this condition on the pupil colour response. The aim of this study was to examine how optic neuritis affects pupil responses to light flux and colour modulation and the extent to which such pupil responses mirror the loss and recovery of vision.

METHODS

A new pupil examination technique that makes use of sinusoidal modulation of either luminance contrast or chromatic saturation was employed. This technique enables the automatic extraction of both pupil response amplitude and latency and achieves a high signal to noise ratio with fewer averages.

RESULTS

The study reveals a greater loss of pupil response amplitude and significantly longer latencies to chromatic modulation (i.e. approximately 80 ms). Stimulation of the unaffected eye in the optic neuritis group results in smaller response amplitudes when compared to the normal group for both light flux and colour modulation.

CONCLUSIONS

Pupil response components can be affected differently in optic neuritis. These findings suggest that the pupil colour response, in particular, may provide a useful, objective estimator to judge the extent of damage and recovery in diseases of the optic nerve.

Measurement of Refractive State and Deprivation Myopia in Two Strains of Mice

PURPOSE

The mouse eye has a bright retinal image (f/number <1) but low optical quality (visual acuity about 0.5 cpd) that may render emmetropization unnecessary. However, this species is potentially a powerful model to study eye growth and myopia because its genome can be readily manipulated and has been completely sequenced. We have investigated how precisely eyes of mice can be refracted and tested whether deprivation myopia can be induced by frosted diffusers.

METHODS

An automated eccentric infrared photorefractor was adapted to refract eyes of two mouse strains--C57BL/6 (B6) and DBA/2 (D2)--during Tropicamide cycloplegia without anesthesia. Axial lengths were measured in highly magnified video images of freshly excised eyes. Plastic hemispherical diffusers were applied between postnatal days and 29 and left attached for 7 or 14 days.

RESULTS

(1) Trial lenses ranging from +10 to -10 D produced high correlations between the brightness slope in the pupil and applied lens power (r = 0.81 and r = 0.87), demonstrating reliable refraction. Five repeated measures in 12 eyes showed an average standard deviation of 3.0 D, equivalent to an axial length change <10 microm (derived from schematic eye modeling). (2) Deprivation produced a significant shift toward myopia, relative to untreated eyes, but only after 14 days and only in B6 mice (p = 0.02 with or p = 0.00038 without one outlier; N = 9). In contrast, DBA/2J were unaffected by occlusion, perhaps due to mutations that target eye, lens, or anterior segment. (3) Both eyes of untreated animals often had axial lengths that differed markedly. Surprisingly, we detected no significant correlation between refractive error and axial length after treatment.

CONCLUSIONS

The infrared refraction technique is sufficiently sensitive to resolve equivalent changes in axial length of only +/- 10 microm in alert mice. Prolonged occlusion produces a significant myopic shift in B6 mice, but not in D2 mice. Even among isogenic B6 mice, the response is variable for reasons that presumably trace back to subtle developmental, environmental, and technical factors.

Measuring eye aberrations with Hartmann-Shack wave-front sensors: should the irradiance distribution across the eye pupil be taken into account?

A usual approximation in Hartmann-Shack aberrometry is that the centroid displacements are proportional to the spatial averages of the wave-front slopes at the sampling subapertures. However, these spatial averages are actually weighted by the local irradiance distribution across each microlens. The irradiance across the eye pupil is not uniform in usual reflectometric aberrometers, which is due to several factors including retinal scattering and cone waveguiding directionality. It is shown that neglecting this fact in usual least-squares reconstruction procedures gives rise to a biased estimation of the aberration coefficients. The magnitude of this bias depends on the actual irradiance distribution across the eye pupil, the mode being estimated, the detailed modal composition of the aberrated wave front, and the geometry of the wave-front sampling array. Order-of-magnitude calculations suggest that this bias may well be in the range 5%-10% for relatively smooth irradiance distributions. The systematic nature of this error makes it advisable to check for its presence and, if required, to compensate for it by an adequate choice of the least-squares reconstruction matrix.

Diode laser transscleral cyclophotocoagulation in the treatment of chronic angle-closure glaucoma: a preliminary study

PURPOSE

To evaluate the efficacy and safety of diode laser transscleral cyclophotocoagulation in the treatment of chronic angle-closure glaucoma.

PATIENTS AND METHODS

A prospective, non-comparative interventional pilot study was conducted. Fourteen eyes of 14 Chinese patients with chronic angle-closure glaucoma whose intraocular pressures were greater than 21 mm Hg on medications were treated with diode laser transscleral cyclophotocoagulation using the G-probe at the United Christian Hospital between February 2000 and May 2001. The inferior 270 degrees quadrant (from 2 to 11 o'clock for right eye and from 1 to 10 o'clock for left eye) was treated and the patients were followed up regularly. The initial laser energy was set at 2,000 mWatt with a duration of 2 seconds. The post-treatment anti-glaucoma medications were adjusted according to the intraocular pressure. If medications failed to lower the intraocular pressure to below 21 mm Hg, cyclophotocoagulation to the same inferior 270 degrees quadrant was repeated.

RESULTS

All patients completed a 12-month follow-up period. The total success rate defined as IOP < 21 mm Hg with or without medication(s) was 85.7% at 1 year of follow-up review. The mean +/- SD intraocular pressure decreased from pre-treatment level of 36.9 +/- 11.7 mm Hg to 18.9 +/- 6.5 mm Hg at 1 year after treatment. The difference was statistically significant (P < 0.001) (Paired t test). The mean +/- SD number of IOP-lowering eyedrops was significantly reduced from 1.9 +/- 0.7 before cyclophotocoagulation to 0.4 +/- 0.8 at 1 year after treatment (P = 0.0002) (Paired t test). Two eyes required repeat treatment. Seven eyes (50%) had atonic pupil following the laser treatment.

CONCLUSION

Diode laser transscleral cyclophotocoagulation is effective in lowering the intraocular pressure in chronic angle-closure glaucoma and its effect lasts for at least 1 year.

Spectral sensitivity of the pupillary system

BACKGROUND

The spectral sensitivity of the pupillary mechanism is reported to be greater in the blue part of the visible spectrum compared to the sensitivity of the visual system as defined by V(lambda) for a two-degree field. This means that blue light gives rise to smaller pupils compared to those that occur with light of other colours of the same luminance. This has been interpreted as indicating that there may be a rod input to pupil response even at photopic levels of illumination. An alternative explanation is that the smaller pupil size for blue light is an artefact arising from the use of the CIE V(lambda) function which is based on the spectral sensitivity of the eye to a two-degree field. In most investigations of pupil response, the adapting luminous field is much larger than two degrees.

METHOD

The size of the static pupil was measured using an entoptic method when the eye was adapted to a large 'Ganzfeld' field of wavelengths of 624, 580, 521, 467 and 429 nm and luminances ranging from mesopic to photopic.

RESULTS

The pupil is smaller for light of shorter wavelengths compared to that for light of longer wavelengths of the same luminance. This effect disappears at photopic luminances when luminance is calculated using the V(10 degrees ) (lambda) function instead of the V(2 degrees ) (lambda) function but is still evident at mesopic levels. When pupil size is plotted against equivalent luminance for a 10-degree field V(10 degrees ) (lambda, L(eq)) pupil size is independent of wavelength.

CONCLUSION

The apparent enhanced sensitivity of the pupil to blue light at photopic levels is an artefact arising from the inappropriate use of the V(2 degrees ) (lambda) for the measurement of luminance when the adapting field in pupil response measurements is a large field. Pupil size is a simple linear function of the log of equivalent luminance calculated for large fields for adapting luminances from photopic to mesopic and is independent of the wavelength of the adapting field for the whole range of adapting luminances.

Wavelength dependence of reflectometric cone photoreceptor directionality

We present evidence for the wavelength dependence of the directionality of light reflected from cone receptor cells (optical Stiles-Crawford effect): Blue light is more directional than red. According to the waveguide-scattering model of Marcos et al. [J. Opt. Soc. Am. A 15, 2012 (1998)], directionality is the sum of a waveguide component and a scattering component. The latter is proportional to 1 over wavelength squared, and it is related to the row-to-row spacing of the cone lattice. Our results allow a firm confirmation of Marcos et al.'s theory. For a 1.9-deg foveal area, group mean (n = 18) cone spacing was 3.42 microm, in good agreement with anatomical data. Group mean waveguide directionality was 0.077 mm(-2).