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In temperate climates, annual bedding plant crops are typically produced in heated greenhouses from late winter through early summer. Temperature, photoperiod, light intensity, and transplant date are commonly manipulated during commercial production so that plants are in flower for predetermined market dates. We used nine flowering models that predict the effect of mean daily temperature on time from transplant until first flowering, which can be used to identify the combinations of transplant dates and growing temperatures necessary for flowering to occur on chosen market dates. The computer program Virtual Grower was also used to estimate greenhouse heating costs based on user-defined inputs such as building material, construction style, temperature set point, heating system, and typical weather at the selected locations. Using the flowering models and Virtual Grower, the temperatures and transplant dates that consumed the least amount of energy for heating, on a per-crop basis, were estimated for two market dates and three U.S. locations. For flowering on March 15, the estimated energy consumption for heating per crop decreased in Michigan as the greenhouse setpoint increased from 15 to 24°C for all species. In contrast, the temperature that elicited the lowest heating cost per crop in North Carolina for a March 15 finish date varied among species. This kind of analysis allows the determination of the most energy-efficient production schedule for greenhouse- and crop-specific situations.

Greenhouses are used in many climates for season extension or year-round production and can be expensive to heat. Greenhouse users and growers are often faced with management decisions that rely on an understanding of how temperature settings, heating systems, fuel types, and construction decisions influence overall heating costs. There are no easy-to-use programs to calculate heating costs associated with these factors over full cropping seasons. A computer program called Virtual Grower was created that helps calculate heating costs at many U.S. sites. The program uses a weather database of typical hourly temperature, light, and wind information of 230 sites from the National Renewable Energy Laboratory in the calculations. A user can define unique design characteristics such as building material and construction style. The user also defines the type of heating system and heating schedule, and then the program will predict heating costs based on typical weather at the selected location. Shorter-term predictions with weather forecasts of 2 days or less can be made with the software if there is an internet connection through integration with local weather forecasts. Virtual Grower can serve as a platform from which many other features can be added, such as plant growth and scheduling. Continued development will improve the software and allow users to perform baseline analysis of their heating costs, identify areas in their production to improve efficiency, and take some of the guesswork out of energy analysis in unique greenhouses.

Potato yields in Northern Maine have remained fairly constant for the last 70 years. Many long-term projects have sought to identify the limitations to potato yield, but identifying limiting factors is difficult without first identifying the upper limits of potato production. A simple, light-driven mechanistic model is validated with specific case studies, and then, potential yield limitations to potato production in this region are identified based on analysis of the model. It was found that meteorologically-limited productivity peaks at about 55 Mg ha−1, which is about 80% higher than historical averages. Most yield increases in those specific case studies examined were due to enhancement of radiation capture, which was achievable either by improved water management or disease suppression. Strategies for sustained yield improvements should continue to improve on radiation capture, either by increasing the peak radiation capture potential, prolonging the radiation capture duration, or by shifting radiation capture to coincide with available light. This model is useful to set realistic productivity goals for this region, can be easily adapted to other regions, and indicates strategies for potato yield improvement.

Purpose: To evaluate the refractive results of 193-nm excimer laser photorefractive keratectomy (PRK) performed on 48 highly myopic eyes in a multicenter study. Methods: A Visx 2015 or 2000 argon-fluoride excimer laser and a single-zone ablation technique were used. Postoperatively, eyes were treated with topical fluoromethalone for up to 5 months. Most eyes were treated with a 6.0- to 6.2-mm beam diameter after undercorrections and increased regression were noted with a 5.5 mm beam in earlier studies. Forty-eight eyes were treated for myopia, which was between −8.0 and −15.25 diopters (D) (spherical equivalent). The mean preoperative refraction was −11.2 D. Retreatment was performed after 6 to 16 months on 11 eyes for undercorrection. All eyes not retreated were followed for at least 12 months. Results: At 6 months, follow-up was available on 47 eyes. Of these eyes, 40% and 64% achieved corrections within 1 and 2 D of attempted correction, respectively. At 1 year, 60% of eyes attained 20/40 visual acuity or better uncorrected. Eleven patients (23%) were retreated between 6 to 16 months for undercorrection and/or regression. After retreatment, 47% and 81% of eyes achieved corrections within 1 and 2 D of attempted correction, respectively. At 1 year, 15% of eyes lost two lines of best-corrected visual acuity, and no eyes lost more than two lines. There was slightly more corneal haze seen in this group compared with the haze seen in patients undergoing PRK for low and moderate myopia. Conclusions: These data show that excimer PRK can correct high amounts of myopia with reasonable stability after 6 months. Excimer PRK is an effective surgical treatment of severe myopia, but long-term follow-up is still needed to assess the stability of its effect.

BACKGROUND: Following excimer laser photorefractive keratectomy, patients experience significant ocular pain until corneal reepithelialization. Despite the use of cold compresses, bandage soft contact lenses, cycloplegics, narcotics, and topical corticosteroids, the pain has not been adequately controlled in many patients. METHODS: A randomized, double-masked, parallel-group study of diclofenac sodium 0.1% ophthalmic solution and its placebo vehicle was evaluated. Patients undergoing excimer myopic photorefractive keratectomy on their second eye were admitted overnight. Postoperative procedures included two drops of diclofenac or placebo immediately after surgery and then qid until reepithelialization, topical tobramycin (qid), 0.1% fluorometholone (q2h), cycloplegics, and a disposable soft contact lens. Thirty-two patients (diclofenac= 16, placebo= 16) were evaluated from + 30 minutes to +96 hours by several types of questionnaires. RESULTS: Most patients who received placebo experienced pain, starting within 1 hour, peaking at 4 to 6 hours and lasting 36 to 48 hours. The diclofenac-treated patients rarely experienced the early peak in pain, had less pain overall until 72 hours postoperatively, and experienced significantly less photophobia and burning/stinging. Significantly fewer patients on diclofenac required oral narcotics. Three patients (diclofenac =2, placebo= 1) developed corneal infiltrates, the etiology of which is not known. In a separate study we conducted, there was no difference in epithelial healing times between the diclofenac-treated eyes and those not receiving the drug. CONCLUSIONS: Diclofenac appears to significantly reduce the ocular pain following excimer photorefractive keratectomy. (Refract Corneal Surg. 1993;9:425-436.) RÉSUMÉ INTRODUCTION: Les patients éprouvent une douleur oculaire significative après la kératectomie photorefractive au laser excimer jusqu'à la ré-epithélialisation cornéenne. Malgré l'emploi de compresses froides, le port de lentilles de contact, la cycloplégle, l'utilisation de narcotiques, et de corticoïdes, la douleur ne fut pas contrôlée chez un grand nombre de patients.

The purpose of this study was to compare the survival of epikeratophakia tissue lenses prepared with cryolathing and lyophilization (frozen lenses) and without (fresh lenses) in donorsensitized recipients with vascularized corneas. Fresh lenses placed in vascularized corneas of immune recipients were subjected to immune attack. Frozen lenses placed in vascularized corneas of immunized recipients did not elicit an immune reaction. Neither fresh nor frozen lenses elicited immune reactions in nonvascularized corneas of immune recipients or in nonvascularized, nonimmune recipients. These results indicate that although the fresh lenses are more antigenic than the lenses in which the cells have been killed by freezing and lyophilization, the fresh lenses prepared using the BKS-1000 technique containing living stromal keratocytes are not likely to stimulate allograft immune reactions in unsensitized patients with avascular graft sites. (Refract Corneal Surg 1991;7:141-145.)

Whole plant carbon exchange rate (CER) measurements provide an integral assessment of how an entire plant responds to biotic and abiotic factors. CER determination is based on measurements of CO2 uptake and release that can be determined using various types of systems including Closed, Semi-closed, and Open systems. This review focused on important design and operational considerations of Open CER measurement systems. Primary mechanical and biological factors that may influence measurement accuracy including chamber leakage, CO2 differential between air inlet and outlet of a chamber, chamber air humidity, canopy air speed, acidity of growth media, and irrigation water to name a few. Proper design and operation of a whole canopy photosynthesis system are necessary to assure accuracy of the CER measurements that may be used to assess both short-term responses and long-term yield of a plant as a result of given stimuli.

Objective To assess the safety and effectiveness of the Autonomous Technologies Corporation LADARVision excimer laser system for photorefractive keratectomy correction of myopia and astigmatism. Design A multicenter, prospective, noncomparative case series. Participants The cohort consisted of 467 eyes corrected for spherical myopia and 211 eyes corrected for myopia with astigmatism. Intervention Treatments were performed at six sites in the United States using a 6-mm ablation zone for spherical myopes and a 5.5-mm zone with a 1.0-mm blend for astigmats. Main outcome measures Visual acuity, subjective refraction, corneal haze, intraocular pressure, complications, adverse reactions, patient satisfaction, and corneal endothelial changes. Results Twelve-month follow-up was available on 414 spherical eyes and 175 astigmatic eyes. The results for spherical eyes with correction between −1 and −5.99 diopters (D) were: uncorrected visual acuity (UCVA) of 20/40 or better achieved by 98.1%, 20/20 or better by 72%, 1.8% lost 2 lines and 0.3% lost greater than 2 lines of best spectacle-corrected visual acuity (BSCVA); 76.4% were within 0.50 D of the target correction and 94.4% were within 1.00 D. The results for myopia with astigmatism with spherical equivalent correction between −1 and −5.99 D were: UCVA of 20/40 or better in 97.4%, 20/20 or better in 61.7%, 2.5% lost 2 lines and no eyes lost greater than 2 lines BSCVA; 73.9% were within 0.50 D of the target correction and 95% were within 1.00 D. For spherical myopes combined with myopic astigmats corrected for 6 to 10 D, results were: UCVA of 20/40 or better in 93.4%, 20/20 or better in 61.2%, 2.3% lost 2 lines and no eyes lost greater than 2 lines of BSCVA; 67.2% were within 0.50 D of the desired correction and 87.8% were within 1.00 D. Refractive stability was achieved between 3 and 6 months for the spherical and astigmatic groups. No eyes had corneal haze graded as moderate or greater, and there was no significant decrease in endothelial cell density. Conclusions Patients treated for 1 to 10 D of spherical equivalent myopia, with or without astigmatism, showed early refractive stability, excellent UCVA, no significant loss of BSCVA, no loss of endothelial cell density, and very low levels of corneal haze to 12 months after surgery.

Photorefractive keratectomy for the correction of myopia was performed in 32 eyes of 16 green monkeys. The corneas healed satisfactorily, with normal formation of basal lamina and hemidesmosomal attachments visible in 14-week histologic specimens. No recurrent erosions were observed clinically. After a transient period of faint haze, all corneas were clear at 17 weeks and remained clear through the 1-year follow-up. In terms of accuracy, all corneas demonstrated a significant flattening compared with preoperative values, but no significant difference was seen between the groups with different intended corrections (1.5 and 3 diopters). The changes in corneal shape stabilized by 17 weeks, as measured by keratometry. The clinical results suggest that mechanical removal of the epithelium is preferable to laser ablation of the epithelium. Overall, the results demonstrate that excimer laser ablation of the corneal stroma can produce a stable diptric change in the primate cornea with good healing and long-term corneal clarity.

Excimer photorefractive keratectomy was performed at three centers on 16 highly myopic eyes (8 diopters [D] or more) and followed up for 6 months. Ablation depths ranged from 137 to 230 microns. The preoperative spherical equivalent of myopia ranged from -8.62 D to -14.50 D (mean +/- SD, -11.57 +/- 1.62 D). Six months after surgery, the mean refraction (spherical equivalent) was -0.90 +/- 2.13 D. Eleven of 16 eyes achieved refractions within 2 D of that attempted. All eight patients at one site were treated with a maximum-beam diameter of 6.0 mm and were corrected to within 2 D of that attempted, and all were 20/40 or better uncorrected. Three of eight eyes at the other two sites were treated with a 5.5- or 5.6-mm maximum-beam diameter, which achieved corrections within 2 D of that attempted. The epithelium healed within 3 to 4 days, and there were no erosions. Mild subepithelial reticular haze, similar to that seen with excimer photorefractive keratectomy for lower myopia, was seen in all patients, with two patients experiencing more significant corneal haze. This peaked at 3 to 6 weeks and then gradually diminished. All but two patients had a return of their best corrected preoperative visual acuity to within one Snellen line at 6 months. This preliminary study shows excimer photorefractive keratectomy to be a promising surgical treatment for patients with higher myopia.

Photorefractive keratectomy was performed at three centers using the 193-nm excimer laser on 31 sighted myopic eyes. Preoperative refractive errors (spherical equivalent) ranged from -12.00 to -4.00 diopters (D) (mean, -6.49 +/- 1.75 D). Peribulbar anesthesia, a 5.2- to 6.0-mm beam diameter, and topical corticosteroids were used for up to 6 months after surgery. The epithelium healed within 3 to 4 days, and all patients returned to their best corrected visual acuity within 1 line of their preoperative acuity. There was minimal subepithelial reticular haze, peaking at 3 weeks and diminishing over the next 3 to 4 months, which was not felt to be visually significant. At 6 months, the average residual refractive error was -1.85 +/- 2.5 D. Sixty-eight percent of eyes were corrected within 2 D and 55% within 1 D of attempted correction. There was no significant change in astigmatism, contrast sensitivity, corneal sensation, or endothelial cell counts. This preliminary work shows that photorefractive keratectomy has promise in the reduction of moderate myopia.

• Phototherapeutic keratectomy using a 193-nm excimer laser was performed at four centers on 33 sighted patients with corneal opacity and/or irregular astigmatism. Pathologic conditions included anterior stromal and superficial scarring from postinfectious and posttraumatic causes, including inactive herpes simplex virus, anterior corneal dystrophies, recurrent erosions, granular dystrophy, and band keratopathy. Most patients received peribulbar anesthesia and underwent removal of the epithelium prior to laser ablation. A majority of patients had a reduction in the amount of corneal scarring and approximately half had improved visual acuity. No intraocular reaction or changes in endothelial counts were seen, and some patients avoided the need for penetrating keratoplasty. Reepithelialization usually occurred within 4 or 5 days and we noted no significant scarring secondary to use of the laser. It was difficult to eliminate preexisting irregular astigmatism despite the use of surface modulators, such as methylcellulose. A hyperopic shift secondary to corneal flattening was encountered in approximately 50% of the patients. A combination of myopic ablation, followed immediately by a secondary hyperopic steepening, may minimize this refractive change. The 193-nm excimer laser is an effective new tool in the treatment of selected patients with superficial corneal opacity from a variety of conditions.

Prior to undertaking a study in sighted human eyes, we performed photorefractive keratectomy with the 193-nm excimer laser for the correction of myopia in nine legally blind eyes to evaluate safety, efficacy, predictability, and stability. In most cases, reepithelialization was complete by 5 days after surgery; no recurrent erosions were seen. By the end of the 6-month study, all of the corneas had a 0 or 1+ clarity score, on a scale of 0 (clear) to 5+ (opaque). Keratometry and pachometry demonstrated stable flattening of the corneas. One month after surgery, changes in refraction evaluated by retinoscopy showed fair predictability, with no significant increase in refractive or keratometric astigmatism, followed by some regression of effect by the end of the study, possibly caused by anatomical remodeling. The amount of regression appeared to be directly related to the amount of correction intended, suggesting that this effect would not be clinically important in the treatment of mild to moderate myopia.

We evaluated the effect of a collagen shield on epithelial healing in keratectomy wounds in rabbit eyes. Superficial keratectomies 6 mm in diameter were created in 12 eyes of six rabbits. Six eyes received collagen shields every eight hours; six eyes received no treatment (control group). Epithelial healing was significantly faster (P less than .01) in corneas treated with collagen shields (47.8 +/- 1.1 microns/hr) compared to untreated control corneas (40.8 +/- 1.6 microns/hr). Regression analysis gave a projected time for closure of treated corneas of 73.96 hours, compared to 83.41 hours for untreated corneas. Scanning electron microscopy of collagen shields after eight hours of wear showed a large number of polymorphonuclear leukocytes entrapped in the collagen matrix. Light microscopy of healed corneas showed that the appearance of the regenerated epithelium in treated and untreated corneas was similar. These results demonstrate that collagen shields speed reepithelialization of keratectomy wounds in the rabbit cornea.

• Seven patients underwent penetrating keratoplasty after epikeratophakia for keratoconus. All seven patients achieved clear grafts and 20/40 or better best corrected visual acuity after penetrating keratoplasty. Three of the seven patients had one or more episodes of rejection after penetrating keratoplasty; all were treated successfully. No grafts were lost. The results in terms of graft clarity and visual acuity are comparable with those in patients undergoing penetrating keratoplasty for keratoconus with no previous ocular surgery. Whether the relatively high rate of rejection episodes (three [43%]) seen in this small number of patients indicates some relationship between previous epikeratophakia and subsequent rejection after penetrating keratoplasty remains to be seen.

In the Nationwide Study of Epikeratophakia, 22 eyes underwent penetrating keratoplasty (PKP) after epikeratophakia for keratoconus. Reasons for PKP included visual acuity unsatisfactory to the patients (6 eyes), recipient corneal scarring (4 eyes), recipient Descemet's folds (3 eyes), scarring in the tissue lens (2 eyes), vascularization of the tissue lens (2 eyes), astigmatism (2 eyes), failure of the tissue lens to reepithelialize (1 eye), corneal ulcer (1 eye), and scarring of the donor and recipient cornea (1 eye). After PKP, all patients had clear grafts and 20/40 or better visual acuity. Average follow-up was 17 months. Three of the 22 patients (13.6%) had graft reaction episodes, all of which were treated successfully, resulting in clear grafts. The authors conclude that previous epikeratophakia does not adversely affect the outcome of subsequent PKP for keratoconus.

To the Editor. —The use of the excimer laser to ablate corneal tissue for the correction of optical errors, such as myopia, hyperopia, and astigmatism, was first suggested by Stephen Trokel, MD, of the Edward S. Harkness Eye Institute, Columbia University, New York, NY. We report a case of a patient who received excimer laser ablation that was designed to flatten the cornea in a putatively blind eye. This was performed as part of the early human safety and efficacy "blind eye" trials under the aegis of the Investigational Device Exemption granted by the Food and Drug Administration to Dr Trokel. Within 7 weeks of laser ablation, the patient, who had apparently been suffering from functional rather than physiologic blindness, had a visual acuity of 20/25 and then 20/20 without correction. After 6 months of follow-up, the cornea remained clear and the visual acuity appeared to be stable. This is