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In Photosystem I, light-induced electron transfer can occur in either of two symmetry-related branches of cofactors, each of which is composed of a pair of chlorophylls (ec2A/ec3A or ec2B/ec3B) and a phylloquinone (PhQA or PhQB). The axial ligand to the central Mg2+ of the ec2A and ec2B chlorophylls is a water molecule that is also H-bonded to a nearby Asn residue. Here, we investigate the importance of this interaction for charge separation by converting each of the Asn residues to a Leu in the green alga, Chlamydomonas reinhardtii, and the cyanobacterium, Synechocystis sp. PCC6803, and studying the energy and electron transfer using time-resolved optical and EPR spectroscopy. Nanosecond transient absorbance measurements of the PhQ to FX electron transfer show that in both species, the PsaA-N604L mutation (near ec2B) results in a ~50% reduction in the amount of electron transfer in the B-branch, while the PsaB-N591L mutation (near ec2A) results in a ~70% reduction in the amount of electron transfer in the A-branch. A diminished quantum yield of P700+PhQ- is also observed in ultrafast optical experiments, but the lower yield does not appear to be a consequence of charge recombination in the nanosecond or microsecond timescales. The most significant finding is that the yield of electron transfer in the unaffected branch did not increase to compensate for the lower yield in the affected branch. Hence, each branch of the reaction center appears to operate independently of the other in carrying out light-induced charge separation.

Photosystem I (PSI) is a large pigment-protein complex that unites a reaction center (RC) at the core with ∼100 core antenna chlorophylls surrounding it. The RC is composed of two cofactor branches related by a pseudo-C2 symmetry axis. The ultimate electron donor, P700(a pair of chlorophylls), and the tertiary acceptor, FX(a Fe4S4cluster), are both located on this axis, while each of the two branches is made up of a pair of chlorophylls (ec2 and ec3) and a phylloquinone (PhQ). Based on the observed biphasic reduction of FX, it has been suggested that both branches in PSI are competent for electron transfer (ET), but the nature and rate of the initial electron transfer steps have not been established. We report an ultrafast transient absorption study ofChlamydomonas reinhardtiimutants in which specific amino acids donating H-bonds to the 131-keto oxygen of either ec3A(PsaA-Tyr696) or ec3B(PsaB-Tyr676) are converted to Phe, thus breaking the H-bond to a specific ec3 cofactor. We find that the rate of primary charge separation (CS) is lowered in both mutants, providing direct evidence that the primary ET event can be initiated independently in each branch. Furthermore, the data provide further support for the previously published model in which the initial CS event occurs within an ec2/ec3 pair, generating a primary ec2+ec3-radical pair, followed by rapid reduction by P700in the second ET step. A unique kinetic modeling approach allows estimation of the individual ET rates within the two cofactor branches.

Ischemia and reperfusion injuries present major challenges for both military and civilian medicine. Improved methods for assessing the effects and predicting outcome could guide treatment decisions. Specific issues related to ischemia and reperfusion injury can include complications arising from tourniquet use, such as microvascular leakage in the limb, loss of muscle strength and systemic failures leading to hypotension and cardiac failure. Better methods for assessing the viability of limbs/tissues during ischemia and reducing complications arising from reperfusion are critical to improving clinical outcomes for at-risk patients. The purpose of this research is to develop and assess possible prediction models of outcome for acute limb ischemia using a pre-clinical model. Our model relies only on non-invasive imaging data acquired from an animal study. Outcome is measured by pathology and functional scores. We explore color, texture, and temporal features derived from both color and thermal motion imagery acquired during ischemia and reperfusion. The imagery features form the explanatory variables in a model for predicting outcome. Comparing model performance to outcome prediction based on direct observation of blood chemistry, blood gas, urinalysis, and physiological measurements provides a reference standard. Initial results show excellent performance for the imagery-base model, compared to predictions based direct measurements. This paper will present the models and supporting analysis, followed by recommendations for future investigations.

Over 70% of military casualties resulting from the current conflicts sustain major extremity injuries. Of these the majority are caused by blasts from improvised explosive devices. The resulting injuries include traumatic amputations, open fractures, crush injuries, and acute vascular disruption. Critical tissue ischemia—the point at which ischemic tissues lose the capacity to recover—is therefore a major concern, as lack of blood flow to tissues rapidly leads to tissue deoxygenation and necrosis. If left undetected or unaddressed, a potentially salvageable limb may require more extensive debridement or, more commonly, amputation. Predicting wound outcome during the initial management of blast wounds remains a significant challenge, as wounds continue to “evolve” during the debridement process and our ability to assess wound viability remains subjectively based. Better means of identifying critical ischemia are needed. We developed a swine limb ischemia model in which two imaging modalities were combined to produce an objective and quantitative assessment of wound perfusion and tissue viability. By using 3 Charge-Coupled Device (3CCD) and Infrared (IR) cameras, both surface tissue oxygenation as well as overall limb perfusion could be depicted. We observed a change in mean 3CCD and IR values at peak ischemia and during reperfusion correlate well with clinically observed indicators for limb function and vitality. After correcting for baseline mean R-B values, the 3CCD values correlate with surface tissue oxygenation and the IR values with changes in perfusion. This study aims to not only increase fundamental understanding of the processes involved with limb ischemia and reperfusion, but also to develop tools to monitor overall limb perfusion and tissue oxygenation in a clinical setting. A rapid and objective diagnostic for extent of ischemic damage and overall limb viability could provide surgeons with a more accurate indication of tissue viability. This may help reducing the number of surgical interventions required, by aiding surgeons in identifying and demarcating areas of critical tissue ischemia, so that a more adequate debridement may be performed. This would have obvious benefits of reducing patient distress and decreasing both the overall recovery time and cost of rehabilitation.

Like all photosynthetic reaction centers (RCs), the core of Photosystem I (PS1) is composed of two related membrane polypeptides that sequester electron transfer (ET) cofactors into two pseudo-symmetrical branches, each consisting of two chlorophylls (Chls) and a quinone. An open question in the evolution of photosynthesis is howthis symmetrical structure has been modified in type 2 RCs, in which ET proceeds exclusively down one branch. We have recently shown that directionality can be altered by breaking H-bonds to the ec3 Chl (Li et al. 2006), as visualized by the amplitudes of ET from the two phylloquinones (PhQA and PhQB). Here are presented new results on the first of a series of mutants designed to alter the environment of the ec2A/ec3A Chl pair. PsaAAla684 is close to this pair, with the methyl group pointing at ec2A. We have changed this residue to Asp. Like PsaA-Y696F, the PsaA-A684D mutant exhibited an increase in the faster component of PhQ reoxidation, consistent with a redirection of electrons down the B branch.

The energy and electron transfer processes in photosystem I particles carrying mutations around the primary electron acceptors have been studied. Direct evidence is provided for early electron transfer processes to occur efficiently in both cofactor branches.

Objective To describe the distribution and risk factors for pterygium in the predominantly black population of the Barbados Eye Study, which was based on a random sample of Barbadian-born citizens between the ages of 40 and 84 years. Methods The standardized protocol included ophthalmic and other measurements, automated perimetry, lens gradings, fundus photography, and a detailed interview. A 10% systematic sample of participants and those meeting specific criteria also received a comprehensive ophthalmologic evaluation. Results The Barbados Eye Study included 4709 participants, of whom 2978 were referred for an ophthalmologic evaluation and 2781 (93%) completed the examination. Cases of pterygium were found among 23.4% of 2617 black, 23.7% of 97 mixed(black and white), and 10.2% of 59 white participants examined. In addition to African ancestry, logistic regression analyses indicated a positive association between pterygium and age (odds ratio [OR], 1.01; 95% confidence interval[CI], 1.00-1.02), fewer years of education (OR, 1.43; 95% CI, 1.01-2.03), and an outdoor job location (OR, 1.87; 95% CI, 1.52-2.29). Having a darker skin complexion (OR, 0.66; 95% CI, 0.52-0.83), always using sunglasses outdoors(OR, 0.18; 95% CI, 0.06-0.59), and the use of prescription glasses (OR, 0.75; 95% CI, 0.60-0.93) were protective factors. Conclusions Approximately one quarter of the black participants examined had pterygia, a frequency that was 2.5 to 3 times higher than among whites in the Barbados Eye Study and elsewhere. Pterygium was almost twice as frequent among persons who worked outdoors but was only one fifth as likely among those who always used sunglasses outdoors. Educational interventions to modify these potential exposures may assist in preventing pterygium.

To characterize the intraoperative procedures employed by cataract surgeons in the United States and the beliefs underlying the practices, a standardized questionnaire was sent to a systematic random sample of members of the American Academy of Ophthalmology in 1992. Of 667 surveyed ophthalmologists, 550 completed the questionnaire (response rate, 82.5%). Phacoemulsification was used for more than 75% of routine cataract surgery by 46% of respondents, whereas standard extracapsular surgery was used for more than 75% of routine cataract surgery by 41% of respondents. Preferential use of phacoemulsification was independently associated with more recent graduation from medical school and higher reported annual surgical volume. Continuous tear capsulotomy was employed by 52% of ophthalmologists. Preference for this technique was independently associated with both the use of phacoemulsification and higher annual surgical volume. Seventy-one percent of respondents used retrobulbar anesthesia, whereas 28% used peribulbar anesthesia. Use of peribulbar anesthesia was independently associated with both greater surgical volume and performance of surgery in an ambulatory surgical center. Beliefs regarding comparative safety and effectiveness were reported to influence surgeons' preferences strongly among all of the competing techniques studied. Those performing phacoemulsification, in comparison with those performing extracapsular cataract extraction, reported that the expectation of reduced astigmatism and shorter recovery time strongly influenced their choice of procedure. Variation in preferred intraoperative techniques is substantial for cataract surgery and the beliefs that underlie the preferences. Such variation highlights the need to determine which techniques maximize patient outcomes and are most cost-effective.

Objectives: To assess the frequency and content of postoperative operative examinations by ophthalmologists and optometrists for cataract surgery patients without operative complications and to assess the referral patterns of optometrists when complications are identified. Design: In 1992 we conducted a survey of randomly selected members of the American Academy of Ophthalmology and American Optometric Association. Responses were obtained from 538 (82%) of 655 eligible ophthalmologists and 130 (84%) of 154 eligible optometrists. Results: Eighty-eight percent of responding ophthalmologists reported that patients had 4 or more visits within 4 months after surgery, 97% of ophthalmologists performed the first postoperative examination on their cataract surgery patients, and 60% of ophthalmologists reported that no other eye professional saw their patients postoperatively. Forty-six percent of responding optometrists participated in postoperative care of cataract surgery patients, and usually performed their first postoperative examination 7 days after surgery; 78% of these optometrists reported that they saw patients 3 or more times after surgery. Postoperatively, 83% of ophthalmologists and 75% of optometrists usually performed at least 1 dilated fundus examination, 87% of ophthalmologists and 47% of optometrists performed 4 or more slit-lamp examinations, 74% of ophthalmologists and 42% of optometrists performed 4 or more tonometry tests, and 83% of both groups performed 2 or more refractions. More than 80% of responding optometrists involved in postoperative care of cataract surgery patients immediately refer a patient to an ophthalmologist if there is evidence of acute glaucoma or an unexplained decrease in vision in the eye that was operated on. For less urgent complications, most optometrists promptly make a referral to an ophthalmologist. Conclusions: In 1992, a small percentage of ophthalmologists and optometrists were performing fewer follow-up examinations and tests for cataract patients than recommended by the American Academy of Ophthalmology. Not all optometrists immediately refer to an ophthalmologist any acute complication that they identify postoperatively.

Objective: To assess variation in optometrists' use of ophthalmic tests in the evaluation of patients being considered for cataract surgery who have no history of other eye disease. Design/Participants: National survey of a systematic sample of practicing members of the American Optometric Association (St Louis, Mo), who had referred at least one patient to an ophthalmologist for consideration of cataract surgery in 1991. Results: Ninety-two of 130 eligible responding optometrists reported that they routinely performed preoperative testing on patients being considered for cataract surgery. Of these 92 optometrists, 91 (99%) frequently or always performed refraction, and 82 (89%) frequently or always performed a dilated fundus examination in their evaluation of patients being considered for cataract surgery who had no history of other eye disease. None of these 92 optometrists reported using B-scan ultrasonography or electroretinograms frequently or always, and few used A-scan ultrasonography or visual evoked responses frequently or always. A substantial percentage frequently or always used formal visual field testing (47%), formal color vision testing (40%), fundus photography (24%), potential acuity measurement (25%), glare testing (23%), contrast sensitivity testing (19%), and specular microscopy (14%), while 11% to 81% of optometrists never performed these tests on such patients. More recent graduation from optometry school was associated with a decreased frequency of use of potential acuity measurement and contrast sensitivity testing and with an increased use of dilated fundus examinations. Conclusion: There is a substantial variation in optometrists' self-reported use of a number of ophthalmic tests in the preoperative evaluation of patients being considered for cataract surgery who have no history of other eye disease.

Little information is available either for the clinical value of many ophthalmic tests performed preoperatively in the evaluation of patients for cataract surgery or for variation in ophthalmologists' use of such tests. To assess variation in ophthalmologists' use of ophthalmic tests, we conducted a national survey of American Academy of Ophthalmology members. Thirty-three percent, 17%, 37%, and 19% of the respondents reported that they "frequently" or "always" perform glare testing, contrast sensitivity testing, potential acuity measurement, and specular microscopy, respectively, in patients being considered for cataract surgery who have no history of eye disease other than cataract. In contrast, 27%, 54%, 24%, and 48% of respondents reported that they never perform each of these four tests in such patients. Two ophthalmologist characteristics--a surgical volume of greater than 200 cataract extractions per year and performance of surgery in an ambulatory surgical center or private office (as opposed to a hospital)--were independently associated with an increased probability of performing each of these four tests frequently or always. Ten percent or less of the respondents reported that they frequently or always perform electroretinography, visual evoked response testing, photography of fundus or anterior segment, B-scan ultrasonography, formal color vision testing, and formal visual field testing in such patients. Thus, there is considerable variation in ophthalmologists' use of glare testing, contrast sensitivity testing, potential acuity measurement, and specular microscopy. A small percentage of ophthalmologists may be overusing several other tests in the evaluation of patients being considered for cataract surgery.

Objective: To better define the effectiveness and risks of modern cataract surgery. Design: Meta-analysis (formal systematic identification, selection, review, and synthesis) of published literature. Patients: Patients described in 90 studies published between 1979 and 1991 that addressed visual acuity (n=17 390 eyes) or complications (n=68 316 eyes) following standard extracapsular cataract extraction with posterior chamber intraocular lens implantation, phacoemulsification with posterior chamber intraocular lens implantation, or intracapsular cataract extraction with flexible anterior chamber intraocular lens implantation. Main Outcome Measures: The proportion of eyes with postoperative Snellen visual acuity of 20/40 or better and the proportion of eyes with each of 18 complications. Results: The pooled percentage of eyes (weighted by sample size) with postoperative visual acuity of 20/40 or better was 95.5% (95% confidence interval [CI], 95.1% to 95.9%) among eyes without preexisting ocular comorbidity and 89.7% (95% CI, 89.3% to 90.2%) for all eyes. The pooled percentage of eyes experiencing complications (weighted by sample size and, when pertinent, by quality score of the individual studies but not adjusted for variation in duration of follow-up) ranged from 0.13% for endophthalmitis to 19.7% for posterior capsule opacification. Pooled proportions of eyes with other complications were as follows: bullous keratopathy, 0.3%; intraocular lens malposition/dislocation, 1.1%; clinically apparent cystoid macular edema, 1.5%; and retinal detachment, 0.7%. Pooled results for postoperative Snellen visual acuity and most complications were similar for surgery performed via phacoemulsification vs standard extracapsular cataract extraction, although comparisons of the outcomes between these procedures should be interpreted with caution. Conclusions: The published literature indicates that modern cataract surgery yields excellent visual acuity and, although not free of complications, is a very safe procedure regardless of the extraction technique used.

OBJECTIVE: To assess the rigor of research methods reported in studies of the safety or effectiveness of contemporary cataract surgery. DESIGN: Formal systematic identification of pertinent studies and critical appraisal of each study's research methods. SUBJECTS: From 6113 unique, potentially relevant citations that we identified, 90 original studies published between 1979 and 1991 that addressed visual acuity or complications following standard extracapsular cataract extraction with posterior chamber intraocular lens implantation, phacoemulsification with posterior chamber intraocular lens implantation, or intracapsular cataract extraction with flexible anterior chamber intraocular lens implantation. MAIN OUTCOME MEASURES: Strength of study design, performance, and reporting in 11 methodologic areas assessed with a standardized abstraction form by two reviewers masked to authors, their institutions, and the journal of publication. Results of reviews were tallied to produce an overall quality score (measure of rigor in research methods) for each study. RESULTS: The mean (+/- SD) quality score was 43.1 +/- 20.1 out of a maximum possible score of 100. Studies received intermediate scores on description of baseline ocular disease and low scores on descriptions of other characteristics of enrolled patients, standardization of outcome assessment and follow-up duration, and handling of patient attrition. Eighty-three studies (92%) lacked a comparison group. The rigor of research methods in studies varied by the journal of publication, did not improve over time, and was no greater for studies with larger vs smaller sample sizes. CONCLUSIONS: The rigor of research methods in studies of cataract surgery can be improved if more attention is paid to fundamental principles of study design, data analysis, and reporting.