Biomedical subjects

S Wu

Publications and source records attributed to S Wu.

At least 397 records · Page 22Linked to original sources

PubMed1995

Intense nutritional support in inflammatory bowel disease.

The value of intense nutritional support in inflammatory bowel disease is still debated. Claims have been made that total enteral nutrition is as effective as total parental nutrition. In this review, the use of parenteral and enteral nutritional support as primary therapy in patients with inflammatory bowel disease has been critically evaluated. Most studies have been uncontrolled and nonrandomized with short-term follow-up. The literature does suggest, however, that intense nutritional support may have an adjunctive role to drug therapy in achieving remission in Crohn's disease, especially in corticosteroid-refractory patients. Nutritional support has a lesser role in chronic ulcerative colitis, except for assistance in pre- and postoperative management. The data do not support one variety of nutritional support over another, although enteral support should be used if possible, as it is less costly and potentially less complicated.

Food, Formulated↗

PubMed1995

Effect of levonorgestrel-releasing intrauterine device on hormonal profile and menstrual pattern after long-term use.

In the present study 14 women after 6 years' use of levonorgestrel-releasing IUD were investigated for the changes of LH, progesterone (P), estradiol (E2), prolactin (PRL) and serum binding globulin (SHBG) in relation to the levonorgestrel levels throughout a segment of 26-40 days with the aim of comparing the hormonal profiles with those during the first year of use of Lng-IUD. Ultrasound scanning was used to follow the development of follicles along with the RIA measurement of hormones. The results of serum LH, P and E2 showed ovulation in 11 cases with either normal menstrual cycles (5 cases), prolonged or irregular cycles (4 cases) or with amenorrhea for 2-3 years (2 cases). One case showed insufficiency of luteal function and 2 cases showed anovulation but with follicular hyperactivity. Higher percentages of ovulatory cycles (78.5%) were found after 6 years of use. No case of complete suppression of ovulation was found. Anovulatory cycles only constituted 14.3%. Clinically, the development of follicles followed by ultrasound scanning further confirmed the hormonal findings. The persistent enlargement of follicles coincided with high levels of E2. After 6 years of use, the serum levels of levonorgestrel were still maintained at mean levels of 314.26 pmol/L and 470.63 pmol/L in the ovulatory and anovulatory groups, respectively. It is concluded that over two-thirds of the cases have ovulatory cycles after long-term use of Lng-IUD; the contraceptive effect is mainly due to its local action on the endometrium, with much less effect on the ovarian function.

Adult↗

PubMed1995

A morphometric study on the endometrial activity of women before and after one year with LNG-IUD in situ.

The endometrium was studied by morphometry in 34 healthy women before and after one year's use of an IUD releasing levonorgestrel at a rate 20 micrograms/24 hr (LNG-IUD-20). The effect was compared with that of an IUD releasing 2 micrograms levonorgestrel/24 hr (LNG-IUD-2). The appearance of suppressed endometrial proliferative activity and increased inflammatory reaction was similar in the two experimental groups, suggesting that the morphological alterations were independent of the LNG dosage. The result of this study, combined with clinical data, suggests that LNG-IUD-20 could replace LNG-IUD-2 without any additional side effects. The efficacy of LNG-IUD-20 is also likely to last for a longer period than the LNG-IUD-2.

Adult↗

PubMed1995

Attenuation of esophageal shortening during peristalsis with hiatus hernia.

BACKGROUND & AIMS: Minimal quantitative information exists on esophageal shortening during peristalsis in the human esophagus. The aim of this study was to ascertain the effect of hiatus hernia on longitudinal muscle-mediated peristaltic esophageal shortening. METHODS: Seven volunteers and 11 patients with hiatal hernia had metal clips endoscopically affixed at the squamocolumnar junction and 3-5 cm proximal to it (n = 11). Location of the lower esophageal sphincter and axial clip movement were assessed using concurrent manometry and videofluoroscopy during barium swallows in a supine and upright posture with and without abdominal compression. RESULTS: Three subject groups were defined by the proximity of the squamocolumnar junction to the diaphragmatic hiatus: group 1, < or = 0 cm; group 2, between 0 and 2 cm; and group 3, > or = 2 cm. Peristaltic esophageal shortening was progressively diminished, re-elongation progressively prolonged, and the degree of contraction observed in the distal esophageal segment reduced with progressive degree of hiatus hernia. There was minimal mobility of the squamocolumnar junction relative to the hiatus with posture or abdominal compression. CONCLUSIONS: Longitudinal muscle contraction during peristalsis normally causes transient elevation of the squamocolumnar junction above the diaphragm. Esophageal shortening during primary peristalsis is reduced with increasing degree of hiatus hernia, suggesting that there is diminished opposition of longitudinal muscle contraction from the phrenoesophageal attachments.

Adult↗

PubMed1995

Effects of flicker adaptation and temporal gain control on the flicker ERG.

The flicker electroretinogram (ERG) to stimuli varying in temporal frequency and modulation depth was recorded to investigate retinal gain control. With increasing modulation of a sinusoidal flickering stimulus, the flicker ERG shows an amplitude compression and a phase retardation (of the fundamental component) at 16 Hz, an amplitude expansion and a phase advance around 40-48 Hz, and an approximately linear response at 72 Hz. With sum-of-two-sinusoids stimuli, the second stimulus enhances the fundamental response to a 40 or 48 Hz test stimulus at low modulations, and reduces the variation in phase with modulation. This interaction depends primarily on the amplitude of the response to the second stimulus, but not its frequency. With temporally alternating stimuli, a similar but smaller interaction effect is measured. The results suggest that there is an active nonlinear gain control mechanism in the outer retina and this gain control works by adjusting the phase delay of the retinal response. The phase control mechanism is set by the amplitude of the outer retinal response integrated over time.

Adaptation, Ocular↗

PubMed1995

Effectiveness of Norplant implants through seven years: a large-scale study in China.

The effectiveness of Norplant implants over a seven year period of continuous use was studied in a multicenter trial. Pregnancy rates were 0.4 per 100 in both year six and year seven. More than 3,600 women completed 6 years and more than 2,400 women completed 7 years. Pregnancy rates increased with weight (p < .05) and decreased with age, but in years 6 and 7 combined, the pregnancy rate neither reached nor exceeded 1 per 100 woman years in any 5 year age group or in any 10 kg weight group.

Adult↗

PubMed1995

Genetic control of mitosis, meiosis and cellular differentiation during mammalian spermatogenesis.

Gametogenesis in both the male and female mammal represents a specialized and highly regulated series of cell cycle events, involving both mitosis and meiosis as well as subsequent differentiation. Recent advances in our understanding of the genetic control of the eukaryotic cell cycle have underscored the evolutionarily-conserved nature of these regulatory processes. However, most of the data have been obtained from yeast model systems and mammalian cell lines. Furthermore, most of the observations focus on regulation of mitotic cell cycles. In the present paper: (i) aspects of gametogenesis in mammals that represent unique cell-cycle control points are highlighted; (ii) current knowledge on the regulation of the germ cell cycle, in the context of what is known in yeast and other model eukaryotic systems, is summarized; and (iii) strategies that can be used to identify additional cell cycle regulating genes are outlined.

Animals↗

PubMed1995

N-(4-hydroxyphenyl)retinamide (4-HPR)-mediated biological actions involve retinoid receptor-independent pathways in human breast carcinoma.

Retinoid response pathways involve retinoic acid receptors (RARs) and retinoid X receptors. N-(4-hydroxyphenyl) retinamide (4-HPR), a derivative of all-trans-retinoic acid (RA) is currently in clinical trials as a chemopreventive agent for breast cancer. The issue whether 4-HPR mediates its biological actions via classical retinoid receptor pathways remains to be investigated. In this study, we provide several lines of evidence that 4-HPR mediates its biological actions via a novel pathway(s) that does not involve the classical retinoid receptor pathways. For example, 4-HPR was more potent than RA as an antiproliferative agent and inhibited growth of otherwise RA-resistant human breast carcinoma cells. Exposure to 4-HPR resulted in the generation of DNA fragmentation with subsequent cell death in both RA-positive estrogen receptor (ER)-positive as well as RA-refractory ER-negative breast carcinoma cell lines. N-(4-Methoxyphenyl)retinamide (4-MPR), which is the major 4-HPR metabolite in circulation, was biologically inert in this system. 4-HPR and 4-MPR bound poorly to the RAR alpha, beta and gamma in vitro and only minimally activated the retinoic acid receptor element (RARE) and retinoid X receptor response elements (RXREs) in human breast carcinoma cells. Neither 4-HPR nor 4-MPR are metabolized to any of the known conventional retinoids. In addition, 4-HPR or 4-MPR transactivation of RAREs or RXREs transfected into MCF-7 and MDA-MB-231 cells was not noted at 48 h. Nevertheless 4-HPR-mediated cell death was observed at 48 h, further suggesting that neither 4-HPR nor 4-MPR are metabolized to retinoids which activate the RAREs or RXREs in breast carcinoma cells. Furthermore, unlike RA, which exhibited anti-AP1 activity, 4-HPR inhibition of growth did not involve anti-AP1 activity. These results suggest that 4-HPR acts by a unique pathway that is not mediated by retinoid receptors.

Anticarcinogenic Agents↗

PubMed1995

Immune responses to novel Escherichia coli and Salmonella typhimurium vectors that express colonization factor antigen I (CFA/I) of enterotoxigenic E. coli in the absence of the CFA/I positive regulator cfaR.

An asd-stabilized plasmid carrying enterotoxigenic Escherichia coli cfaABCE genes was constructed and called pJGX15C-asd+. Expression of colonization factor antigen I (CFA/I) by this plasmid occurs independently of the cfaABCE positive regulator cfaR in attenuated Salmonella delta aro delta asd strain H683 and nonpathogenic laboratory E. coli asd strain chi 6212. Oral immunization of mice with nonpathogenic E. coli chi 6212 (pJGX15C-asd+) does not elicit significant serum or mucosal responses against CFA/I. In contrast, oral immunization with a single dose of attenuated S. typhimurium H683(pJGX15C-asd+) elicits a 10(5)-fold increase in CFA/I-specific serum immunoglobulin G and significant elevation of CFA/I-specific immunoglobulin A-secreting B cells in the lamina propria, mesenteric lymph nodes, and spleen. Thus, only the Salmonella-CFA/I construct effectively delivered CFA/I to the inductive sites of the gut-associated and systemic lymphoid tissues.

Animals↗

PubMed1995

Detection of p24 antigen with and without immune complex dissociation for longitudinal monitoring of human immunodeficiency virus type 1 infection.

Sequential specimens obtained from 87 multicenter AIDS cohort study participants were tested by three p24 antigen tests. They included a polyclonal enzyme immunoassay (EIA), a monoclonal EIA, and a monoclonal EIA after immune complex dissociation (ICD) of specimens. Subjects were grouped into two categories defined by real-time testing with the polyclonal EIA: 39 had become positive for p24 antigen (antigen converters) during follow-up, and 48 had progressed to AIDS without detectable antigenemia. Twenty-four (61%) antigen converters were positive by ICD-monoclonal EIA about 1 year earlier than by monoclonal EIA. In contrast, only 12 (25%) patients who progressed to AIDS without detectable antigenemia became positive by ICD-p24 EIA before developing AIDS. Thus, the main benefit of ICD treatment may be to detect p24 antigenemia approximately 1 year before the regular assay rather than to identify additional antigenemic people. Quantitative plasma RNA levels were also determined in longitudinal samples from 20 antigen converters and 7 men who developed AIDS without antigenemia. Although mean human immunodeficiency virus type 1 RNA levels were higher in antigen-positive than in antigen-negative samples (P = 0.002), more than half (11 of 20) of the antigen converters had no measurable change in human immunodeficiency virus type 1 RNA associated with change to antigen positivity.

Acquired Immunodeficiency Syndrome↗

PubMed1995

A 10-amino-acid sequence in the N-terminal A/B domain of thyroid hormone receptor alpha is essential for transcriptional activation and interaction with the general transcription factor TFIIB.

The effects of the thyroid hormone (3,5,3'-triiodo-L-thyronine [T3]) on gene transcription are mediated by nuclear T3 receptors (T3Rs). alpha- and beta-isoform T3Rs (T3R alpha and -beta) are expressed from different genes and are members of a superfamily of ligand-dependent transcription factors that also includes the receptors for steroid hormones, vitamin D, and retinoids. Although T3 activates transcription by mediating a conformational change in the C-terminal approximately 220-amino-acid ligand-binding domain (LBD), the fundamental mechanisms of T3R-mediated transcriptional activation remain to be determined. We found that deletion of the 50-amino-acid N-terminal A/B domain of chicken T3R alpha (cT3R alpha) decreases T3-dependent stimulation of genes regulated by native thyroid hormone response elements about 10- to 20-fold. The requirement of the A/B region for transcriptional activation was mapped to amino acids 21 to 30, which contain a cluster of five basic amino acids. The A/B region of cT3R alpha is not required for T3 binding or for DNA binding of the receptor as a heterodimer with retinoid X receptor. In vitro binding studies indicate that the N-terminal region of cT3R alpha interacts efficiently with TFIIB and that this interaction requires amino acids 21 to 30 of the A/B region. In contrast, the LBD interacts poorly with TFIIB. The region of TFIIB primarily involved in the binding of cT3R alpha includes an amphipathic alpha helix contained within residues 178 to 201. Analysis using a fusion protein containing the DNA-binding domain of GAL4 and the entire A/B region of cT3R alpha suggests that this region does not contain an intrinsic activation domain. These and other studies indicate that cT3R alpha mediates at least some of its effects through TFIIB in vivo and that the N-terminal region of DNA-bound cT3R alpha acts to recruit and/or stabilize the binding of TFIIB to the transcription complex. T3 stimulation could then result from ligand-mediated changes in the LBD which may lead to the interaction of other factors with cT3R alpha, TFIIB, and/or other components involved in the initiation of transcription.

Amino Acid Sequence↗

PubMed1995

CT analysis of postoperative changes after thalamotomy for Parkinson's disease.

Stereotactic operations have long been used to relieve agitation and muscle rigidity in Parkinson disease. Because of its high-density resolution, CT is quite effective to portray the location, size, shape and density of the thermocoagulative focus. The foci were classified into different types according to their changes in different time periods. Correlation with pathological changes was discussed.

Adult↗

PubMed1995

Generation of pre-beta 1-HDL and conversion into alpha-HDL. Evidence for disturbed HDL conversion in Tangier disease.

HDL encompasses several apoA-I-containing particles that differ by size and show pre-beta- or alpha-mobility on agarose gel electrophoresis: pre-beta 1-LpA-I, pre-beta 2-LpA-I, pre-beta 3-LpA-I, alpha-LpA-I2, and alpha-LpA-I3. The quantitatively minor subclass pre-beta 1-LpA-I serves as an initial acceptor of cell-derived cholesterol. In this study, we generated a pre-beta 1-LpA-I-like particle in vitro by the incubation of biotinylated apoA-I with cholesterol-loaded macrophages. Both native pre-beta 1-LpA-I and in vitro-generated pre-beta 1-LpA-I were indistinguishable from lipid-free apoA-I by two-dimensional nondenaturing polyacrylamide gradient gel electrophoresis but exhibited a different size upon gel filtration. In vitro-generated biotin-pre-beta 1-LpA-I took up twofold to threefold more [3H]cholesterol from labeled fibroblasts during a 1-minute pulse incubation than lipid-free apoA-I. The in vitro conversion of biotin-pre-beta 1- LpA-I was investigated in the presence of plasmas of healthy probands and patients with Tangier disease, with apoA-I deficiency, and with lecithin-cholesterol acyltransferase (LCAT) deficiency. Incubation of biotin-pre-beta 1-LpA-I with plasmas either from normoalphalipoproteinemic probands or from a patient with apoA-I deficiency generated a biotinylated particle with the size and electrophoretic mobility of alpha-LpA-I2. This conversion was sensitive to heating at 56 degrees C but not to the removal of calcium. Inhibition of LCAT by dithiobisnitrobenzoic acid led to the formation of alpha-LpA-I3 instead of alpha-LpA-I2.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

Lipoproteins containing apolipoprotein A-IV but not apolipoprotein A-I take up and esterify cell-derived cholesterol in plasma.

Two-dimensional nondenaturing polyacrylamide gradient gel electrophoresis (2D-PAGGE) identifies distinct apoA-I-or apoE-containing subclasses of high-density lipoproteins (HDLs), each of which plays a different role in reverse cholesterol transport. In this study we used 2D-PAGGE to investigate the role of apoA-IV-containing lipoproteins in reverse cholesterol transport in native plasma. Incubation of 2D electrophoretograms with anti-apoA-IV antibodies identified up to three subclasses of particles. The smaller particle subclasses, LpA-IV-1 and LpA-IV-2, were found in every plasma sample. The largest particle subclass, LpA-IV-3, was observed in fewer than 10% of the plasmas analyzed. 2D-PAGGE of apoA-I-deficient plasma and apoA-I-depleted plasma and anti-apoA-I immunosubtracting 2D-PAGGE of normal plasma revealed that LpA-IV-1 and LpA-IV-2 do not contain apoA-I. The importance of LpA-IV-1 and LpA-IV-2 for uptake and esterification of cell-derived cholesterol was investigated using pulse-chase incubations of plasma with [3H]cholesterol-labeled fibroblasts followed by anti-apoA-I immunosubtracting 2D-PAGGE. During 1-minute pulse incubation with cells, [3H]cholesterol was taken up by gamma-LpE > LpA-IV-1 > pre-beta 1-LpA-I > LpA-IV-2 (">" denotes "more than"). During subsequent chase incubation without cells, proportionately less radioactivity disappeared from LpA-IV-1 and LpA-IV-2 than from pre-beta 1-LpA-I and gamma-LpE. During 5-minute pulse incubations, radioactive cholesteryl esters were formed in pre-beta 3-LpA-I > alpha-LpA-I > LpA-IV-1 > LpA-IV-2. The fractional estertification rate was highest in pre-beta 2-LpA-I and lowest in alpha-LpA-I.(ABSTRACT TRUNCATED AT 250 WORDS)

Apolipoprotein A-I↗

PubMed1995

Reverse cholesterol transport in plasma of patients with different forms of familial HDL deficiency.

HDLs encompass structurally heterogenous lipoproteins that fulfill specific functions in reverse cholesterol transport. Two-dimensional nondenaturing gradient gel electrophoresis (2D-PAGGE) of normoalphalipoproteinemic plasma and subsequent immunoblotting with anti-apoA-I-antibodies differentiates pre-beta 1-LpA-I, pre-beta 2-LpA-I, pre-beta 3-LpA-I, alpha-LpA-I2, and alpha-LpA-I3. Immunodetection with anti-apoE antibodies differentiates gamma-LpE and alpha-LpE. Pulse-chase incubations of plasma with [3H]unesterified cholesterol ([3H]UC)-labeled fibroblasts and subsequent 2D-PAGGE revealed that cell-derived [3H]UC is taken up by pre-beta 1-LpA-I and gamma-LpE. From these initial acceptors, [3H]UC is transferred to LDL via pre-beta 2-LpA-I-->pre-beta 3-LpA-I-->alpha-LpA-I. Some UC is esterified in pre-beta 3-LpA-I, and some is esterified in alpha-LpA-I after its retransfer from LDL. In this study we investigated the effect of various forms of familial HDL deficiency on reverse cholesterol transport. Plasma samples of patients with various forms of HDL deficiency are characterized by the lack of specific HDL subclasses. ApoE-containing HDLs, including gamma-LpE, are present in all kinds of HDL deficiency. However, all forms of LpA-I are absent in apoA-I-deficient plasma, pre-beta 3-LpA-I and alpha-LpA-I from the plasma of patients with Tangier disease (TD), and pre-beta 3-LpA-I and large alpha-LpA-I from the plasma of patients with lecithin:cholesterol acyltransferase (LCAT) deficiency and fish-eye disease (FED). After a 1-minute pulse with labeled fibroblasts, efflux of [3H]UC into HDL-deficient plasmas decreased, compared with normal plasma, by 49% (apoA-I deficiency), 36% (TD), 21% (LCAT deficiency), and 28% (FED). In apoA-I deficiency, only gamma-LpE takes up cell-derived [3H]UC. In the three other HDL-deficiency states, cell-derived [3H]UC is initially taken up by both pre-beta 1-LpA-I and gamma-LpE. The four HDL deficiencies are also characterized by differences in the esterification of cell-derived [3H]UC. No esterification occurs in LCAT-deficient plasma. In FED plasma, [3H]UC is esterified in LDL. In apoA-I deficiency and TD, however, [3H]UC is esterified in lipoproteins free of apoA-I and apoB. In the two latter cases, the transfer of [3H]cholesteryl ester to LDL is enhanced compared with normal plasma. The lack of specific HDL subclasses and the consequent changes in reverse cholesterol transport pathways differently affect net mass efflux of cholesterol from fibroblasts into HDL-deficient plasma.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1995

Cholesterol efflux, cholesterol esterification, and cholesteryl ester transfer by LpA-I and LpA-I/A-II in native plasma.

HDLs encompass structurally heterogeneous particles that fulfill specific functions in reverse cholesterol transport. Two-dimensional nondenaturing polyacrylamide gradient gel electrophoresis (2D-PAGGE) of normal plasma and subsequent immunoblotting with anti-apolipoprotein (apo) A-I antibodies differentiates an abundant particle with electrophoretic alpha-mobility and less abundant particles with electrophoretic pre-beta-mobility (pre beta 1-LpA-I, pre beta 2-LpA-I, pre beta 3-LpA-I). Immunodetection with anti-apoA-II antibodies identifies a single particle with alpha-mobility. To differentiate alpha-migrating HDL without apo A-II (alpha-LpA-I) from those with apoA-II (alpha-LpA-I/A-II), we combined 2D-PAGGE with immunoadsorption of apoA-II. Incubation of plasma with [3H]cholesterol-labeled fibroblasts in combination with immunosubtracting 2D-PAGGE allowed us to analyze the role of alpha-LpA-I and alpha-LpA-I/A-II in the uptake and esterification of cell-derived cholesterol in native plasma. Depending on the duration of incubations with cells, alpha-LpA-I took up two to four times more [3H]cholesterol than alpha-LpA-I/A-II. Irrespective of the duration of incubation, two to three times more [3H]cholesteryl esters accumulated in alpha-LpA-I than in alpha-LpA-I/A-II. Subsequent incubations in the presence of an inhibitor of lecithin:cholesterol acyltransferase led to preferential accumulation of [3H]cholesteryl esters in alpha-LpA-I/A-II. In conclusion, our data indicate that alpha-LpA-I is more effective than alpha-LpA-I/A-II in both uptake and esterification of cell-derived cholesterol. Moreover, alpha-LpA-I/A-II appears to accumulate cholesteryl esters, at least partially, from alpha-LpA-I.

Apolipoprotein A-I↗

PubMed1995

Effects of the apolipoprotein E polymorphism on uptake and transfer of cell-derived cholesterol in plasma.

The reverse cholesterol transport is initiated by the uptake of cholesterol into minor subfractions of high density lipoproteins (HDL) which contain either apolipoprotein (apo) A-I or apoE as their only apolipoproteins. From these initial acceptors, which are termed prebeta1-LpA-I and gamma-LpE, respectively, cell-derived cholesterol is transferred to LDL via the bulk of HDL termed alpha-LpA-I. In this study we analyzed the effect in plasma of the genetically determined apoE polymorphism on the formation of gamma-LpE, uptake and transfer of cell-derived cholesterol to LDL. Gamma-LpE was immunologically detectable in plasmas of individuals carrying at least one apoE3-allele but not in apoE3-free plasmas. During one minute incubation with [3H]cholesterol-labeled fibroblasts, gamma-LpE of plasmas from apoE3/3 subjects accumulated 7 and 13-fold more radioactivity than the respective fractions in plasmas from apoE2/2- and apoE4/4-subjects, respectively. Totally, 30% less [3H]cholesterol was released into plasmas of apoE2/2 and apoE4/4-individuals as compared with plasmas of apoE3/3-subjects. Moreover, plasmas of apoE3/3 individuals accumulated 50% and 65% more cell-derived [3H]cholesterol in alpha-LpA-I2 than plasmas of apoE4/4 and apoE2/2-subjects, respectively. These results indicate that the apoE-polymorphism is an important determinant of the uptake and transfer of cell-derived cholesterol in plasma.

Apolipoprotein A-I↗

PubMed1995

Direct measurement of human-cone-photoreceptor alignment.

We have developed an imaging reflectometer to measure cone-photoreceptor alignment. One makes measurements by bleaching the cone photopigment and imaging the distribution of light returning from the retina, which is illuminated from a small source imaged in the plane of the eye's pupil. If the source is near the optimal entry pupil position as determined psychophysically, the distribution of light returning from the retina is peaked, and the magnitude of the peak depends on the location of the source in the pupil of the eye. If the source is far from the optimal entry pupil position, then there is no measurable peak. The location of the peak varies across individuals and coincides with the reported location of best visibility of the measuring light and with previous psychophysical and reflectometric measurements of the Stiles-Crawford peak. The source of this directionality must arise either from the photoreceptors or from behind the photoreceptors because the peak is not present if measurements are made when the cone photopigments have high optical density.

Adult↗