Phospholipid analyses of rabbit ocular surface tissues.

The tissues of the integument covering the ocular surface comprise a mucus membrane functioning as a protective physical barrier and has the ability to mount a defensive inflammatory response. Since lipid metabolism has a role in both of these functions, we studied normal membrane phospholipids (PL) of the cornea and bulbar conjunctiva to (1) determine baseline PL profiles of these tissues, (2) compare and contrast these individual PL metabolite profiles as well as groups of metabolites, and (3) describe pathway-specific metabolic interrelations among these tissues. Corneal and conjunctival tissue samples were isolated from rabbit eyes (n = 30) and extracted with chloroform-methanol using a modified Folch procedure. 31P nuclear magnetic resonance spectroscopy was used to qualitatively and quantitatively measure tissue PL profiles. The cornea and conjunctiva, respectively, have the following PL composition (mole % of total detected phospholipid): phosphatidylglycerol (PG) -, 0.4; lysophosphatidylethanolamine 1.2, -; phosphatidic acid -, 0.4; diPG (cardiolipin) 2.1, 3.5; unknown PL at the chemical shift of 0.13 δ 1.5, 0.9; ethanolamine plasmalogen 11.2, 13.0; phosphatidylethanolamine 11.5, 12.8; phosphatidylserine 8.9, 10.1; sphingomyelin 10.2, 10.7; lysophosphatidylcholine 0.9, 1.4; phosphatidylinositol 5.3, 5.3; phosphatidylcholine (PC) plasmalogen or alkylacylPC 2.2, 1.9; PC 45.1, 40.0. In addition, 28 PL metabolic indices were calculated from these data, which permitted pathway-specific lipid analyses. This study (1) establishes PL profiles of the two ocular tissues of the integument that cover the surface of the eye, (2) compares and contrasts indices comprised of ratios and combinations of PL, and (3) describes pathway-specific metabolic interrelations among these tissues to serve as baselines for studies involving the distribution of tissue phospholipids.

Adenosine Triphosphate (ATP) and Protein Aggregation in Age-Related Vision-Threatening Ocular Diseases.

Protein aggregation is the etiopathogenesis of the three most profound vision-threatening eye diseases: age-related cataract, presbyopia, and age-related macular degeneration. This perspective organizes known information on ATP and protein aggregation with a fundamental unrecognized function of ATP. With recognition that maintenance of protein solubility is related to the high intracellular concentration of ATP in cells, tissues, and organs, we hypothesize that (1) ATP serves a critical molecular function for organismal homeostasis of proteins and (2) the hydrotropic feature of ATP prevents pathological protein aggregation while assisting in the maintenance of protein solubility and cellular, tissue, and organismal function. As such, the metabolite ATP plays an extraordinarily important role in the prevention of protein aggregation in the leading causes of vision loss or blindness worldwide.

Association of Dry Eye Symptoms and Signs in Patients with Dry Eye Disease.

PURPOSE: To determine the correlations among symptoms and signs of dry eye disease (DED) in the Dry Eye Assessment and Management (DREAM) study. METHODS: A total of 535 patients with moderate-to-severe DED were assessed for symptoms using the Ocular Surface Disease Index (OSDI) and four DED signs in both eyes (conjunctival lissamine green staining, corneal fluorescein staining, Schirmer's testing, and tear break-up time (TBUT)) following standardized protocols at baseline and follow-up visits (months 3, 6, and 12). Spearman correlation coefficients (rho) were calculated for correlations among symptoms and signs of DED at baseline and among changes in symptoms and signs from baseline at 12 months. The confidence intervals and p-values for correlation coefficients were calculated using a cluster bootstrapping to account for inter-eye correlation. RESULTS: At baseline, OSDI total score was not correlated with signs; however, OSDI subscale score of ocular symptoms was weakly correlated with corneal staining score (rho = 0.14, p = .002) and Schirmer test score (rho = 0.11, p = .01). There were statistically significant correlations among the four signs (p < .001), with absolute correlation coefficient ranging from 0.14 (conjunctival staining score vs. TBUT) to 0.33 (conjunctival staining score vs. cornea staining score). The correlations among changes in symptoms and signs were weaker, with the highest correlation between change in conjunctival staining and corneal staining (rho = 0.21, p < .001). CONCLUSIONS: Consistent with previous studies, among DREAM participants with moderate-to-severe DED at baseline, correlations of DED symptoms with signs were low and correlations among four objective signs were low to moderate. The correlations among changes in symptoms and signs were even weaker.

Association of Tear Osmolarity With Signs and Symptoms of Dry Eye Disease in the Dry Eye Assessment and Management (DREAM) Study.

Purpose: To determine the relationships of (1) tear osmolarity (TO) levels with the severity of signs and symptoms of dry eye disease (DED) and (2) changes in TO with changes in signs and symptoms. Methods: Patients (N = 405) with moderate to severe DED in the Dry Eye Assessment and Management (DREAM) Study were evaluated at baseline and at six and 12 months. Associations of TO with signs and symptoms were evaluated using Pearson correlation coefficient (r) and regression models. Results: The mean (standard deviation [SD]) TO was 303 (16) mOsm/L at baseline and 303 (18) mOsm/L at both six and 12 months. TO was higher in older patients (306 mOsm/L for ≥70 years vs. 300 mOsm/L for <50 years; P = 0.01) and those with Sjögren's disease (311 vs. 302 mOsm/L; P < 0.0001). TO did not differ between patients randomized to placebo and omega-3 fatty acid supplementation. TO was weakly correlated with conjunctival (r = 0.18; P < 0.001) and corneal staining scores (r = 0.17; P < 0.001), tear film break-up time (r = 0.06; P = 0.03), and Schirmer test score (r = -0.07; P = 0.02) but not with Ocular Surface Disease Index scores (r = 0.03; P = 0.40). Changes in signs and were not significantly correlated with change in TO at six or 12 months. Conclusions: Within DREAM, TO was weakly correlated with DED signs, explaining <5% variability in signs. Changes in tear osmolarity were not associated with changes in signs and symptoms of DED, indicating that the association may not be causal.

Cutaneous Permeation of a Percutaneously Applied Glucocorticoid Using Plant-Based Anionic Phospholipids in Hydrogenated Vegetable Oil: A Preliminary Study.

Purpose: It is important that, when corticosteroids are used therapeutically, concentrations be reduced as much as possible to mitigate potential adverse events and side effects. This preliminary study compares the permeation for the delivery of a corticosteroid in a 1% hydrocortisone-supplemented topical cream containing anionic polar phospholipids (APP) in hydrogenated vegetable oil (triglyceride) versus a market-leading 1% hydrocortisone in a mineral hydrocarbon-based skin cream. Methods: Using the Franz diffusion cell method with cadaveric skin, the permeation of a 1% hydrocortisone-supplemented cream containing APP (test preparation) was compared with a commercially available 1% hydrocortisone cream (control preparation). The principal APP in the test preparation were phosphatidylinositol, phosphatidylserine and phosphatidylglycerol. Permeation was determined at 4 and 8 h time intervals. Results: The permeation values for the 1% hydrocortisone supplemental APP cream (test preparation) were comparatively very high 1180 ng/cm2 at 4 h and 2173 ng/cm2 at 8 h, in contrast to the 1% hydrocortisone cream (control preparation) values of 13 ng/cm2 at 4 h and 98 ng/cm2 at 8 h. Permeation of skin cream increased significantly from 0 to 4 and 8 h, when comparing the APP test preparation with the control preparation (p < 0.001). This translates, respectively, into the 90-fold greater and a 20-fold greater penetration of the test preparation APP cream over the 1% hydrocortisone cream at 4 h and 8 h time points. Conclusions: This preliminary study demonstrates the enhanced permeation of 1% hydrocortisone when applied topically to the skin in an APP skin cream vehicle. This enhanced permeation suggests the potential use of APP technology to deliver therapeutically effective hydrocortisone treatment to the skin at markedly reduced concentrations of steroid. As such, APP technology may offer an improved approach to the treatment of dermatoses associated with inflammatory diseases and conditions requiring prolonged topical corticosteroid therapy.

Phosphatic metabolism in dark- and light-adapted rat retinas.

This study defines retinal phosphatic metabolites and their adjustment to illumination in rat retinas under conditions that preserve retinal function. Metabolic data are measured using high-performance liquid chromatography (HPLC) and 31P nuclear magnetic resonance (31P NMR) spectroscopy after 10 min of light exposure in vivo compared with retinas from dark-adapted rats. Multiple high-energy and low-energy phosphatic metabolites of intermediary metabolism were quantified. The concentration of the high-energy phosphate adenosine triphosphate (ATP) remained unchanged from dark- to light-adaptation. Under the same conditions the concentrations of the high-energy phosphates guanosine triphosphate (GTP) and creatine phosphate increased, whereas the inorganic phosphate decreased. Comparing dark-adapted controls with retinas light-adapted either in vitro or in vivo, the evidence is consistent with a light-dependent increase in GTP and a decrease in cyclic guanosine monophosphate. Although cyclic adenosine monophosphate (cAMP) levels were lower in retinas light-adapted in vivo than in the dark-adapted controls, this did not seem to be an effect of light, as cAMP levels decreased similarly after 10 min incubation in dark or light in parallel with recovery of ATP/adenosine diphosphate ratios. This study: (1) reports on retinal metabolic changes with adjustment in illumination, (2) provides baseline measurements of retinal phosphatic metabolites in whole retinas, and (3) reports on the validity of chromatographic and spectroscopic methods used for studying retinal metabolism establishing a high correlation among measurements made using HPLC and 31P NMR.

Implications of a Diabetic Foot Xerosis Treatment With an Emulsion Containing the Plant-Based Anionic Phospholipids.

PURPOSE: This study compares and contrasts a skin cream containing plant-based anionic polar phospholipid (APP) technology with a mineral oil hydrocarbon (petrolatum)-based (MHB) skin cream technology in the treatment of skin xerosis (dryness) in diabetic feet. Skin cream with APP technology promotes phospholipid absorption, reparation of intercellular lamellae, and organization of water promoting hydration; whereas skin cream with mineral hydrocarbon-based (MHB) technology principally covers skin, preventing dehydration. METHODS: Subjects (n = 54) with diagnoses of diabetes mellitus and foot skin dryness were studied using a multicenter, double-blind, masked-study design. An emulsion cream containing 0.05% APP in triglycerides (APP preparation) was compared to MHB skin cream, Eucerin® (MHB preparation) applied topically to skin of the feet. Graded measurements were recorded on 4 efficacy variables including dryness, erythema, fissures, and itching and neurovascular assessments. Implications of the plant-based and mineral-based skin creams in the context of skin xerosis are contrasted. RESULTS: APP and MHB preparations were similar in effectiveness and safety. There was no significant difference among any of the 4 efficacy variables (P < .5) including neurovascular measurements. The APP preparation is absorbed into the skin, whereas the MHB skin cream leaves detectable residues after each application. CONCLUSION: Although the APP and MHB preparations were not significantly different in effectiveness and safety, distinctively, application of the APP skin cream preparation absorbed into the skin leaving no discernible residue in contrast to the MHB preparation leaving residues potentiating textile damage. Both of these technologies function in the hydration of skin; however, they differ in their modes of action. The plant-based APP preparation functions actively by phospholipid and triglyceride absorption, reparation of skin lamellae, and in the consequent delivery and organization of waters of hydration in skin. The MHB preparation functions passively, hydrating the skin it covers by sealing the skin against dehydration.

Intracellular ATP Concentration and Implication for Cellular Evolution.

Crystalline lens and striated muscle exist at opposite ends of the metabolic spectrum. Lens is a metabolically quiescent tissue, whereas striated muscle is a mechanically dynamic tissue with high-energy requirements, yet both tissues contain millimolar levels of ATP (>2.3 mM), far exceeding their underlying metabolic needs. We explored intracellular concentrations of ATP across multiple cells, tissues, species, and domains to provide context for interpreting lens/striated muscle data. Our database revealed that high intracellular ATP concentrations are ubiquitous across diverse life forms including species existing from the Precambrian Era, suggesting an ancient highly conserved role for ATP, independent of its widely accepted view as primarily "metabolic currency". Our findings reinforce suggestions that the primordial function of ATP was non-metabolic in nature, serving instead to prevent protein aggregation.

Guidelines for Reopening a Nation in a SARS-CoV-2 Pandemic: A Path Forward.

Background and Objectives: Action, not fear, is the path forward in the coronavirus infectious disease 2019 (COVID-19) pandemic. Since early 2020, the world's nations have faced conundrums over severe acute respiratory syndrome corona virus type 2 (SARS-CoV-2) infections resulting in COVID-19 resulting in national closures, and thus, a clear understandable plan that nations can implement is required to reopen. The healthcare benefits of reopening a nation more likely than not exceed the benefits of continued pandemic-related closure. Pandemic-related closures have resulted in countless delayed or avoided urgent care evaluations. Furthermore, routine care of acute and chronic illnesses, including evaluations, diagnoses, and treatments, has also been delayed. Isolation, loss of income, and fear have resulted in mental health conditions or exacerbated existing conditions. The magnitude of untoward ramifications is unknown and may ultimately represent an inestimable degree of danger and morbidity, and even death. The pandemic of SARS-CoV-2 has created an atmosphere of fear of COVID-19 that has directly and indirectly injured the world's population. Since this has resulted in increasing morbidity and mortality, creating economic chaos, and near systemic collapse of educational systems with no well described plan forward, it is the purpose of this study to provide guidelines that provide a path forward to safely open a nation. Physicians often equipped by their education, training, and experiences across disciplines are uniquely positioned to comprehend, coordinate, and teach other physicians, business owners, and municipal and government leaders from guidelines. As such, physicians may take the lead in a path forward to reopening a nation, including opening businesses, educational facilities, and religious establishments, while minimizing the risk of SARS-CoV-2 infection. Materials and Methods: Reviews of the literature among the disciplines of environmental air, sanitation, social interaction, medical testing, vaccination, protection, and disease prevention and safety allowed for the conceptualization and eventual genesis of identifiable interventions which either reduce the viral load in the environment or inactivate the virus from replication. Each of the guidelines was selected based on the principle that it involved the elimination or inactivation of the viral particle. With a reduction in viral load or inactivation of replication, the implementation of these guidelines is expected to allow for reopening a nation with an increased level of safety. Results: The guidelines identified, including air exchange (ventilation), air filtration, personal protective filtering devices (masks), hand hygiene, social distancing, screening and testing, vaccines, high-risk patient protection, medical management, and adjunctive therapies, are described and referenced. Conclusions: In that the pandemic is primarily a public health issue, the path forward is best coordinated by local, regional, and national physicians. Many physicians with a breadth of experiences are uniquely positioned to coordinate the implementation of these interdisciplinary guidelines. Using these guidelines as a planned, coordinated action, not fear, is a path forward. Nations have a decision to make: closuring versus opening.

Guidelines: Discharge Instructions for Covid-19 Patients.

INTRODUCTION/OBJECTIVES: Clinicians treating COVID-19 patients face a major challenge in providing an effective relationship with patients who are discharged to return to home in order to optimize patient self-management after discharge. The purpose of these discharge instructions is to assist and provide guidance for physicians, nurses, and other health care personnel involved in discharging COVID-19 patients to home after encounters at hospitals, emergency departments, urgent care settings, and medical offices. METHODS: A systematic literature-search of studies evaluating both symptoms and signs of COVID-19 was performed in order to establish specific optimal performance criteria in monitoring a patient's status with regard to disease safety. These optimal performance criteria parameters were considered with regard to the severity of morbidity and mortality. Strategies used to develop the discharge instructions included review of a broad spectrum of literature to develop the discharge criteria. RESULTS: These guidelines are presented for patient education and should achieve the essential goals including: enabling patients to understand their medical situation, preventing complications, supporting patients by providing instructions, helping patients make more effective use of available health services, and managing patient stress by giving patients comfort through the knowledge of specific recommendations including how to respond to situations. CONCLUSION: The COVID-19 pandemic requires clinicians to efficiently teach their patients self-management strategies and to provide a safe educated response to the patient and the surrounding community environment. The primary goal of the patient education discharge-instructions (PEDI) is to provide self-management strategies for preventing complications and disease transmission.

SARS-CoV-2 safety: Guidelines for shielding frontline nurses.

ABSTRACT: Protecting nurses in healthcare facilities from SARS-CoV-2 infection is essential for maintaining an adequate nursing force. Foundational guidelines, consistently utilized, protect the nursing staff from infection. This article describes guidelines designed to reduce acute infection and associated morbidity and mortality among nursing staff and improve compliance with infection prevention protocols.

A Comparison of Efficacy and Safety of Two Lipid-Based Lubricant Eye Drops for the Management of Evaporative Dry Eye Disease.

PURPOSE: The aim of this study was to compare the efficacy of two lipid-based lubricant eye drops in patients with lipid-deficient dry eye. METHODS: This Phase IV, multicenter, prospective, double-masked study enrolled adults (aged ≥18 years) who had a tear film breakup time (TFBUT) of ≤15 seconds(s), and unanesthetized Schirmer I test of ≥3 mm to ≤12 mm in at least one eye, at both screening and baseline visits. Eligible patients (n=231) were randomized (1:1) and received either Systane® Balance (SYSB; n=117) or Refresh® Optive Advanced (RFO-Ad, n=114), four-times a day, for 35 days. The primary endpoint was non-inferiority for change from baseline in TFBUT at Day 35 (non-inferiority was established if the lower limit of the 95% confidence interval (CI) for the difference between the treatment groups was > -1.0 s); secondary endpoints (test of superiority) were change in TFBUT and global ocular discomfort visual analog scale (VAS) score at Day 35. Other endpoints included the impact of dry eye on everyday life (IDEEL) treatment satisfaction scores (inconvenience and effectiveness) and safety. RESULTS: At Day 35, the mean change from baseline in TFBUT was 0.998 s in the SYSB and 0.868 s in the RFO-Ad groups with a treatment difference: 0.130 s; (95% CI -0.34, 0.60; P<0.0001) demonstrating non-inferiority of SYSB to RFO-Ad. The global ocular discomfort VAS scores improved in both groups, with a mean change from baseline of -9.7 and -8.8 in SYSB and RFO-Ad groups (treatment difference -0.8; P=0.62), respectively. No meaningful difference was observed in IDEEL treatment effectiveness and treatment inconvenience scores between SYSB vs RFO-Ad (P>0.05 for treatment difference). Both treatments were well tolerated. CONCLUSION: SYSB lubricant eye drops were non-inferior to RFO-Ad for improvement in TFBUT in patients with lipid-deficient dry eye. Both lubricant eye drops improved TFBUT and ocular discomfort scores in patients with lipid-deficient dry eye.

Guidelines for Frontline Health Care Staff Safety for COVID-19.

This document establishes safety guidelines for physicians, nurses, and allied health care and facility staff who may be exposed to patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in a health care facility. SARS-CoV-2 infection is highly contagious and places health care workers at risk for infection resulting in coronavirus disease (COVID-19). Physicians, nurses, and allied health care and facility staff in all frontline environments must be provided and utilize necessary personal protective equipment (PPE). It is important that health care staff adopt a universal set of guidelines in which to conduct themselves in order to minimize infection with the SARS-CoV-2 contagion. The establishment of these guidelines is necessary in this viral pandemic since such directives can create a standard of safety that is universally accepted. These guidelines establish a framework to provide consistency among health care facilities and staff from the time the staff member arrives at the health care facility until they return home. These guidelines provide a practical description of the minimum necessary protection for physicians, nurses, and allied health care and facility staff against SARS-CoV-2 infection.

Corneal absorption of glycerylphosphorylcholine.

This study documents the absorption of glycerylphosphorylcholine (GPC) into corneas ex vivo. Corneas in quadruplicate were incubated in preservation medium containing 30 mM GPC, which is used as a reference marker. The GPC reference marker is used to calibrate 31P nuclear magnetic resonance (NMR) spectral chemical-shift positions for identification of phosphatic metabolites and to calculate intracorneal pH in intact tissues ex vivo. Following baseline NMR ex vivo analysis, corneas were stored in eye bank chambers in preservation medium containing 30 mM GPC at 4 °C overnight for 8 h. After returning to room temperature, NMR analysis was repeated on the same corneas in fresh GPC-free preservation medium. NMR analysis also was performed on the 30 mM GPC preservation medium alone from the eye bank chambers for detection of the GPC signal. The elevated GPC signal unexpectedly persisted in corneas incubated at 4 °C overnight even though GPC was not present in the fresh GPC-free preservation medium. In fact, the concentration of GPC in the intact cornea was many times higher than that found in the cornea endogenously. The levels of phosphatic metabolites and the energy modulus, after subtracting the spectral contribution of the 30 mM exogenous GPC, as well as the intracorneal pH remained unchanged from pre-refrigeration analyses. Corneas also retained transparency through the time-course of this study irrespective of temperature or change in temperature. The GPC signal in the NMR analysis of the preservation medium from the eye bank chambers was nearly undetectable. GPC was unexpectedly absorbed into the corneal tissue without detectable metabolic or physical toxicity. The intracorneal uptake of GPC at reduced temperatures parallels the increase in GPC that occurs naturally in muscle tissue in animals during wintering periods and the very high concentration of GPC in sperm, a cryogenically compatible cell, suggestive of a potential role for GPC in cryopreservation.

SARS-CoV-2 safety guidelines for frontline nurses.

ABSTRACT: Protection of nurses in healthcare facilities from SARS-CoV-2 infection is essential for maintaining an adequate nursing force. Foundational guidelines consistently utilized, will protect the nursing staff from infection. This article provides guidelines that, when followed by frontline nursing staff, can reasonably be expected to reduce acute infection, associated morbidity, and mortality.

Hydrotropic function of ATP in the crystalline lens.

The hypothesis proposed herein is presented to explain the unexpectedly high concentration of ATP and provide evidence to support its hydrotropic function in the crystalline lens determined using 31P NMR. The lens, historically considered to be a metabolically quiescent organ, has the requisite machinery to synthesize ATP, such that the homeostatic level is maintained at about 3 mM. This relatively high concentration of ATP has been found to be consistent among multiple mammalian species including humans. This millimolar quantity is many times greater than the micromolar amounts required for the other known functions of ATP. The recent postulation that ATP at millimolar concentrations functions as a hydrotrope in various cell/tissue homogenates preventing protein aggregation coupled with observations presented herein, provide support for extending the hypothesis that ATP functions as a hydrotrope not only in homogenates but in an intact functioning organ, the crystalline lens. Concentrations of ATP of this magnitude are hypothesized to be required to maintain protein solubility and effectively prevent protein aggregation. This concept is important considering protein aggregation is the etiology for age-related cataractogenesis. ATP is a common ubiquitous intracellular molecule possessing the requisite hydrotropic properties for maintaining intracellular proteins in a fluid, non-aggregated state. It is proposed that the amphiphilic ATP molecule shields the hydrophobic regions on intralenticular fiber cell protein molecules and provides a hydrophilic interfacial surface comprised of the ATP negatively charged triphosphate side chain. Evidence is presented that this side chain is exposed to and has been reported to organize intracellular interstitial water to form an interfacial rheologically dynamic water layer. Such organization of water is substantiated with the effect of deuterium oxide (heavy water) on ATP line widths of the side chain phosphates measured ex vivo by 31P NMR. A novel model is presented to propose how this water layer separates adjacent lens fiber cell proteins, keeping them from aggregating. This hypothesis proposes that ATP can prevent protein aggregation in normal intact lenses, and with declining concentrations can be related to the disease process in age-related cataractogenesis, an affliction that affects every older human being.

Corneal Cryopreservation Using Glycerylphosphorylcholine-Enriched Medium.

PURPOSE: To determine the effects of prolonged cryopreservation at subzero-degree temperatures on corneal transparency and histology after treatment with preservation medium containing the phosphodiester glycerylphosphorylcholine (GPC). METHODS: Rabbit corneas (n = 30) were immersed for 3 hours in K-Sol preservation medium containing 30 mM GPC. Three groups with 6 corneas each were refrigerated at -8°C for 2 weeks and liquid nitrogen temperature for 2 and 6 weeks, respectively. Two groups with 6 corneas each immersed in K-Sol preservation medium only were refrigerated at -8°C for 2 weeks and liquid nitrogen temperature for 6 weeks, respectively. Postthawing corneal transparency was measured on a grading scale after which corneas were prepared for and analyzed by light and transmission electron microscopy. RESULTS: All 3 groups of corneas preserved with GPC maintained a greater degree of corneal transparency compared with corneas preserved without GPC. The number of corneas retaining epithelial and endothelial layers increased in all groups where corneas were preserved in medium containing GPC, in contrast to corneas preserved in medium without GPC. Cytoplasmic vacuolization or nuclear damage was greater in corneas preserved without GPC. Similar findings were found in corneas stored at -8°C and liquid nitrogen temperatures. CONCLUSIONS: This study demonstrates a cryoprotective effect of corneas preserved in K-Sol containing the phosphodiester GPC at subzero-degree temperatures. In corneas immersed in preservation medium containing GPC, a higher degree of transparency is maintained and a lesser degree of histopathologic changes is observed with storage at both -8°C and in liquid nitrogen.