Site-directed tryptophan fluorescence reveals the solution structure of tear lipocalin: evidence for features that confer promiscuity in ligand binding

The solution structure of human TL was deduced from the position of the emission peaks after site-directed tryptophan fluorescence (SDTF). The fluorescent amino acid tryptophan was sequentially substituted for each native amino acid in the sequence. Characteristic periodicities for eight beta-strands that comprise the beta-barrel and three alpha-helices were identified. The putative beta-strand I was relatively exposed to solvent, suggesting it does not participate in the formation of the beta-barrel. The beta-strands A and F contain beta-bulges. The average lambda(max) of emission maxima reveals that strand D is at the edge of the barrel and beta-strand H interacts with the main alpha-helical domain. On the basis of the SDTF data, a 3D homology model was constructed for TL and compared to the known crystallographic structures of RBP and beta-lactoglobulin. The small size and splayed open configuration of the E-F hairpin facilitate access of ligands into the cavity mouth of TL as compared to that of RBP with a long overhanging loop that restricts access. In the model of TL, four alanine residues are positioned in the binding site as compared to bulkier residues in the corresponding positions of beta-lactoglobulin. Substitution of A51, A66, A86 to Trp results in a 3-4-fold decrease in binding affinity. The data suggest that the smaller side chains of Ala provide more capacity in the cavity of TL than the bulkier side chains (I56, I71, V92) in the cavity of beta-lactoglobulin. The structural features provide an explanation for the promiscuous binding characteristics exhibited by TL. SDTF provides a general approach for determining the solution structure of many proteins and enhances homology modeling in the absence of high sequence identity.

North Carolina macular dystrophy: clinicopathologic correlation

PURPOSE

To describe the clinical and histopathologic findings of a 72-year-old female with North Carolina macular dystrophy.

METHODS

Observational case report with histopathologic correlation. Clinical examination includes slit-lamp biomicroscopy, indirect ophthalmoscopy, color fundus photography, and focal electroretinography. Histopathologic examination of the enucleated left eye performed with light microscopy.

RESULTS

Light microscopy demonstrated a discrete macular lesion characterized by focal absence of photoreceptor cells and retinal pigment epithelium with attenuation of the Bruch membrane and focal atrophy of the choriocapillaris. Adjacent to the macular lesion, some lipofuscin was identified in the retinal pigment epithelium.

CONCLUSION

North Carolina macular dystrophy has both clinical and microscopic appearances of a well-demarcated lesion confined to the macula, which involves the retina, pigment epithelium, and choriocapillaris.

Acanthamoeba keratitis associated with fungal keratitis

PURPOSE

To report fungal infection complicating Acanthamoeba keratitis.

METHODS

Case report. A 45-year-old woman with contact lens-related bilateral Acanthamoeba keratitis developed corneal ulcer, corneal perforation, and mature cataract in the left eye, which was managed by penetrating keratoplasty, lensectomy, and vitrectomy.

RESULTS

Histopathologic examination of the keratoplasty specimen from the left eye revealed extensive lamellar stromal necrosis with the coexistence of both empty cysts and branching hyphae. Cultures from the keratoplasty specimen grew Scedosporium apiospermum.

CONCLUSION

Keratomycosis caused by S. apiospermum may complicate protracted Acanthamoeba keratitis.

Secretory lipophilins: a tale of two species

Secretory lipophilins are "lipid-loving" proteins that are major constituents of several mammalian secretions, including the prostatic fluid of rats and the tears of humans and rabbits. These proteins form covalent heterodimers that are stabilized by three intramolecular cystine disulfide bonds. The heterodimers, some of which are glycosylated, may undergo additional non-covalent assembly to form tetramers. The peptide components found in secretory lipophilins are from two subfamilies: lipophilins A/B and lipophilin C. The C subfamily members described in this report are three rabbit and one human lipophilin, plus human mammaglobin and the C3 subunit of rat prostatein. Human A/B and C lipophilins are expressed by many tissues and are especially prominent in endocrine-responsive organs. The gene for human lipophilin B resides at chromosome 10q22-23. This region harbors the PTEN/MMAC1 gene and is believed to contain additional tumor suppressor genes. Although the functions of secretory lipophilins are imperfectly understood, their abundance in glandular secretions and in hormone-responsive tissues suggests that they deserve considerably more attention than they have received to date.

Ocular involvement in patients with posttransplant lymphoproliferative disorder

OBJECTIVES

To describe ocular disease in 3 patients with posttransplant lymphoproliferative disorder (PTLD) and to identify the frequency of such ocular involvement.

METHODS

Medical record reviews. Using Kaplan-Meier analysis, we calculated the frequency of ocular involvement among pediatric patients with systemic PTLD after liver transplantation.

RESULTS

Each patient had bilateral anterior chamber cells. Biopsy of an iris nodule from a patient who had undergone cardiac transplantation confirmed the diagnosis of PTLD, but no signs of systemic PTLD were found. The other 2 patients had systemic PTLD after liver transplantation; 1 presented with iris nodules in both eyes and a subretinal mass in the left eye, while the other had bilateral anterior chamber cells only. Ocular signs improved slowly after reduction of immunosuppressive drug therapy. Ophthalmological examinations were performed on 22 of 25 pediatric patients with PTLD after liver transplantation; 2 had ocular disease. Kaplan-Meier analysis indicated a 20% risk of ocular involvement at 3 years after development of PTLD (95% confidence intervals, 0%-50%).

CONCLUSIONS

Posttransplant lymphoproliferative disorder should be considered in the differential diagnosis of uveitis after organ transplantation. Anterior chamber cells and iris nodules are the most common ocular signs, but the posterior segment can be involved. Ocular involvement can occur without evidence of systemic disease and can be asymptomatic. Reduction of immunosuppressive drug therapy is an appropriate treatment.

North Carolina macular dystrophy: clinicopathologic correlation

PURPOSE

To describe the clinical and histopathologic findings in a 72-year-old woman with North Carolina macular dystrophy.

METHODS

Clinical examination was performed by slit-lamp biomicroscopy, indirect ophthalmoscopy, color fundus photography, and focal electroretinography. Histopathologic examination of the enucleated left eye consisted of light microscopy.

RESULTS

Light microscopy demonstrated a discrete macular lesion characterized by focal absence of photoreceptor cells and retinal pigment epithelium. Bruch's membrane was attenuated in the center of the lesion and associated with marked atrophy of the choriocapillaris. Adjacent to the central lesion, some lipofuscin was identified in the retinal pigment epithelium.

CONCLUSIONS

North Carolina macular dystrophy has both clinical and microscopic appearances of a well-demarcated retinal and pigment epithelial lesion confined to the macula. This is consistent with the clinical impression that it is a focal macular dystrophy.

Functional cavity dimensions of tear lipocalin

PURPOSE

We calibrated the cavity of tear lipocalin with a series of fluorescent labeled lipids of increasing chain length and varying diameter.

METHODS

Cavity length was assessed with competitive fluorescent assays in which DAUDA was displaced from apo-tear lipocalin with ligands of increasing carbon chain lengths from C12-C24. The concentrations of competitors that inhibit 50% of the binding of DAUDA (IC(50)) were compared. Functional diameters of tear lipocalin and beta-lactoglobulin were estimated with fatty acids bearing fluorescent labels of various diameters. The cavity dimensions of other lipocalins were derived from their published crystal structure coordinates.

RESULTS

In tear lipocalin, the binding affinities of fatty acids increased up to a carbon chain length of 18 (22.5 A) but remained constant from C18-C24. The cavity length of other lipocalins in crystal form were similar to tear lipocalin in solution. Tear lipocalin showed decreased binding affinities with progressively increasing ring dimensions of the ligand. In contrast to beta-lactoglobulin and retinol binding protein, tear lipocalin bound DAUDA and cholesterol in the calyx. Neither tear lipocalin nor beta-lactoglobulin bound P646 in their respective cavities. The calculated inter-sheet distances at the mouth of the crystallized lipocalins ranged from 16-22A.

CONCLUSIONS

Tear lipocalin is more promiscuous than beta-lactoglobulin or retinol binding protein because of a greater functional diameter. Differences in ligand specificity of the various lipocalins can not be explained simply by variation in cavity length or the intersheet distances at the calyx mouths as determined by crystal structure. Other factors may influence ligand specificity such as size and/or dynamic motion of loops between the beta strands.

Bilateral blindness and lumbosacral myelopathy associated with high-dose carmustine and cisplatin therapy

PURPOSE

To report the early ocular pathologic findings associated with high-dose carmustine and cisplatin therapy.

METHODS

A patient with metastatic breast carcinoma developed an acute onset of branch retinal artery occlusion, bilateral blindness, and a myelopathy involving the lower extremities after high-dose chemotherapy and bone marrow transplant.

RESULTS

Histopathologic examination of the eye and optic nerves at autopsy disclosed nerve fiber layer infarction secondary to right inferior temporal retinal artery thrombosis. Patchy necrosis of both optic nerves, medulla oblongata, and spinal cord was associated with focal small-vessel thrombosis.

CONCLUSIONS

The syndrome of retinal vascular occlusion, optic neuropathy, and myelopathy is associated with the high-dose chemotherapeutic agents carmustine and cisplatin. The distribution of necrosis suggests an ischemic event rather than direct neurotoxic effects.

Endonuclease activity in lipocalins

Several lipocalins contain conserved amino acid sequences similar to the phosphodiester bond cleavage domain of sugar non-specific magnesium-dependent nucleases of the Serratia marcescens type. His-89 and Glu-127 of the S. marcescens endonuclease are believed to have a role in the active catalytic site by the attack of a water molecule at the phosphorus atom of the bridging phosphate. Tear lipocalin contains both amino acids in analogous regions, and is active as a nuclease. Two forms of beta-lactoglobulin contain only Glu-134 (analogous to Glu-127 of the Serratia nuclease) yet retain nuclease activity equal to or greater than that of tear lipocalin. However, retinol-binding protein lacks both of these motifs and shows no detectable activity. DNA-nicking activity is decreased by 80% in the mutant of tear lipocalin that replaces Glu-128 but is unchanged by mutations of His-84. The endonuclease activity of tear lipocalin is dependent on the bivalent cations Mg(2+) or Mn(2+) but is decreased at high concentrations of NaCl. These findings indicate that some lipocalins have non-specific endonuclease activity similar in characteristics to the Mg(2+)-dependent nucleases and related to the conserved sequence LEDFXR (where 'X' denotes 'any other residue'), in which the glutamic residue seems to be important for activity.

Chronic exposure of hydroxyapatite orbital implants: cilia implantation and epithelial downgrowth

PURPOSE

To describe previously unreported histologic findings in two patients who developed chronic implant exposure and abscess formation within hydroxyapatite orbital implants.

METHODS

Surgically removed implant specimens were processed for histopathologic examination and stained for microorganisms. Each patient's clinical course, socket appearance, and exposure management were reviewed.

RESULTS

Histopathologic examination of case 1 showed a channel of necrosis leading from the anterior surface of the implant to its center. Hair shafts were discovered embedded within this channel. Histopathologic examination of the site of chronic exposure in case 2 showed epithelial ingrowth into the pores of the implant. Both spheres in this report indicated limited fibrovascular ingrowth and abscess formation.

CONCLUSIONS

Chronic exposure of hydroxyapatite implants allows a portal of entry for extraneous hair shafts and also can lead to epithelial downgrowth. Both of these may be contributing factors in the development of serious implant infections.

Corneal transplantation in a patient with mucopolysaccharidosis type VII (Sly disease)

PURPOSE

To illustrate a good visual outcome following penetrating keratoplasty in a patient with Sly disease, a rare mucopolysaccharidosis (MPS) caused by a deficiency of beta-glucuronidase.

METHODS

A 15-year-old male with progressive bilateral corneal opacification had a complete medical, genetic, and ophthalmic evaluation followed by a penetrating keratoplasty.

RESULTS

The cornea has remained clear for two years following surgery. Histopathology of the corneal button demonstrated vacuoles and granular inclusions consistent with this lysosomal storage disease.

CONCLUSION

While research is ongoing in the fields of enzyme replacement and bone marrow transplantation, these treatments may not alleviate or reverse the corneal clouding. This case illustrates that cornea transplantation may be a valuable treatment option for visually rehabilitating such patients.

Resolution of ligand positions by site-directed tryptophan fluorescence in tear lipocalin

The lipocalin superfamily of proteins functions in the binding and transport of a variety of important hydrophobic molecules. Tear lipocalin is a promiscuous lipid binding member of the family and serves as a paradigm to study the molecular determinants of ligand binding. Conserved regions in the lipocalins, such as the G strand and the F-G loop, may play an important role in ligand binding and delivery. We studied structural changes in the G strand of holo- and apo-tear lipocalin using spectroscopic methods including circular dichroism analysis and site-directed tryptophan fluorescence. Apo-tear lipocalin shows the same general structural characteristics as holo-tear lipocalin including alternating periodicity of a beta-strand, orientation of amino acid residues 105, 103, 101, and 99 facing the cavity, and progressive depth in the cavity from residues 105 to 99. For amino acid residues facing the internal aspect of cavity, the presence of a ligand is associated with blue shifted spectra. The collisional rate constants indicate that these residues are not less exposed to solvent in holo-tear lipocalin than in apo-tear lipocalin. Rather the spectral blue shifts may be accounted for by a ligand induced rigidity in holo-TL. Amino acid residues 94 and 95 are consistent with positions in the F-G loop and show greater exposure to solvent in the holo- than the apo-proteins. These findings are consistent with the general hypothesis that the F-G loop in the holo-proteins of the lipocalin family is available for receptor interactions and delivery of ligands to specific targets. Site-directed tryptophan fluorescence was used in combination with a nitroxide spin labeled fatty acid analog to elucidate dynamic ligand interactions with specific amino acid residues. Collisional quenching constants of the nitroxide spin label provide evidence that at least three amino acids of the G strand residues interact with the ligand. Stern-Volmer plots are inconsistent with a ligand that is held in a static position in the calyx, but rather suggest that the ligand is in motion. The combination of site-directed tryptophan fluorescence with quenching by nitroxide labeled species has broad applicability in probing specific interactions in the solution structure of proteins and provides dynamic information that is not attainable by X-ray crystallography.

Tear lipocalins: potential lipid scavengers for the corneal surface

PURPOSE

To investigate the dynamic effect of tear lipocalins (TLs), the major lipid-binding protein in tears, at aqueous-cornea and lipid-aqueous interfaces, and their potential contribution to surface tension in the tear film.

METHODS

Human apo- and holo-TLs were applied to the aqueous subphase in a Langmuir trough, and changes in surface pressure were measured. Changes in the contact angle of tear components were observed on Teflon and ferric-stearate-treated surfaces. A nitroxide-labeled derivative of lauric acid and a fluorescence-labeled derivative of palmitic acid were used to monitor the dynamic interaction of lipid removed from a hydrophobic surface by the major tear components in solution.

RESULTS

TLs increase the surface pressure at the aqueous-air interface by penetrating, spreading, and rearranging on the surface. Apo-TLs show a longer diffusion-dependent induction time than holo-TLs due to more extensive oligomerization of the apoprotein. Kinetic analysis of relaxation time suggests that apo-TLs have more rapid surface penetration and rearrangement than holo-TLs, indicative of a more flexible structure in apo-TLs. TLs reduce the contact angle of solutions on lipid films, a property that is greater with TLs than other tear proteins. TLs, unlike lysozyme and lactoferrin, remove labeled lipids from hydrophobic surfaces and deliver them into solution.

CONCLUSIONS

TLs are potent lipid-binding proteins that increase the surface pressure of aqueous solutions while scavenging lipids from hydrophobic surfaces and delivering them to the aqueous phase of tears. These data suggest important functional roles for TLs in maintaining the integrity of the tear film.

Interaction of tear lipocalin with lysozyme and lactoferrin

The interaction of human tear lipocalin with lysozyme and lactoferrin was studied by electron paramagnetic resonance (EPR) spectroscopy. TL mutants I98C and F99C were spin labeled with MTSL and its derivative. The spectra demonstrated that at sites C98 and C99 the mobility of the nitroxides was reduced in the presence of lysozyme, lactoferrin, but not albumin. The reduced mobility was manifested as a reduction in side chain motion and backbone fluctuations. The overall correlation time of tear lipocalin, measured by MTSL derivative-labeled F99C, was prolonged in the presence of lysozyme and lactoferrin indicating that the interaction involves direct contact. The effect was mitigated at high salt concentration suggesting an electrostatic interaction of the molecules. The reduction in side chain mobility at C98 and C99 of tear lipocalin was observed in tears. Taken together, the data indicate that tear lipocalin interacts with both lysozyme and lactoferrin and suggest that they may function in concert with one another.

Side chain mobility and ligand interactions of the G strand of tear lipocalins by site-directed spin labeling

Side chain mobility, accessibility, and backbone motion were studied by site-directed spin labeling of sequential cysteine mutants of the G strand in tear lipocalins (TL). A nitroxide scan between residues 98 and 105 revealed the alternating periodicity of mobility and accessibility to NiEDDA and oxygen, characteristic of a beta-strand. Residue 99 was the most inaccessible to NiEDDA and oxygen. EPR spectra with the fast relaxing agent, K(3)Fe(CN)(6), exhibited two nitroxide populations for most residues. The motionally constrained population was relatively less accessible to K(3)Fe(CN)(6) because of dynamic tertiary contact, probably with side chain residues of adjacent strands. With increasing concentrations of sucrose, the spectral contribution of the immobile component was greater, indicating a larger population with tertiary contact. Increased concentrations of sucrose also resulted in a restriction of mobility of spin-labeled fatty acids which were bound within the TL cavity. The data suggest that sucrose enhanced ligand affinity by slowing the backbone motion of the lipocalin. The correlation time of an MTSL derivative (I) attached to F99C resulted in the lack of side chain motion and therefore reflects the overall rotation of the TL complex. The correlation time of F99C in tears (13.5 ns) was the same as that in buffer and indicates that TL exists as a dimer under native conditions. TL-spin-labeled ligand complexes have a shorter correlation time than the protein alone, indicating that the fatty acids are not rigidly anchored in the cavity, but move within the pocket. This segmental motion of the ligand was modulated by protein backbone fluctuations. Accessibility studies with oxygen and NiEDDA were performed to determine the orientation and depth of a series of fatty acid derivatives in the cavity of TL. Fatty acids are oriented with the hydrocarbon tail buried in the cavity and the carboxyl group oriented toward the mouth. In general, the mobility of the nitroxide varied according to position such that nitroxides near the mouth had greater mobility than those located deep in the cavity. Nitroxides positioned up to 16 carbon units from the hydrocarbon tail of the ligand are motionally restricted and inaccessible, indicating the cavity extends to at least this depth. EPR spectra obtained with and without sucrose showed that the intracavitary position of lauric acid in TL is similar to that in beta-lactoglobulin. However, unlike beta-lactoglobulin, TL binds 16-doxyl stearic acid, suggesting less steric hindrance and greater promiscuity for TL.

Binding studies of tear lipocalin: the role of the conserved tryptophan in maintaining structure, stability and ligand affinity

The principal lipid binding protein in tears, tear lipocalin (TL), binds acid and the fluorescent fatty acid analogs, DAUDA and 16-AP at one site TL compete for this binding site. A fluorescent competitive binding assay revealed that apo-TL has a high affinity for phospholipids and stearic acid (Ki) of 1.2 microM and 1.3 microM, respectively, and much less affinity for cholesterol (Ki) of 15.9 of the hydrocarbon chain. TL binds most strongly the least soluble lipids permitting these lipids to exceed their maximum solubility in aqueous solution. These data implicate TL in solubilizing and transporting lipids in the tear film. Phenylalanine, tyrosine and cysteine+ were substituted for TRP 17, the only invariant residue throughout the lipocalin superfamily. Cysteine substitution resulted in some loss os secondary structure, relaxation of aromatic side chain rigidity, decreased binding affinity for DAUDA and destabilization of structure. Mutants of TL, W17Y, and W17F showed a higher binding affinity for DAUDA than wild-type TL. Comparison of the results of the tryptophan 17 substitution in lipocalin with those of tryptophan 19 substitution in beta-lactoglobulin revealed important differences in binding characteristics that reflect the functional heterogeneity within the lipocalin family.

Bilateral periopticointrascleral hemorrhages associated with traumatic child abuse

PURPOSE

To report a case of bilateral periopticoscleral hemorrhages associated with traumatic child abuse.

METHODS

Postmortem gross examination and histopathologic studies of both eyes and the optic nerves of a 6-month-old infant who died from subdural hematoma.

RESULTS

Gross examination and histopathologic step sections disclosed bilateral intrascleral hemorrhages around both optic nerves. In addition, bilateral diffuse multilayered retinal, vitreous, and sublaminar (beneath the internal limiting membrane) hemorrhages were present.

CONCLUSION

Periopticointrascleral hemorrhages are characteristic of blunt head trauma and may constitute important forensic evidence in cases of suspected child abuse.

Lipophilins: human peptides homologous to rat prostatein

Lipophilin components A, B and C are human homologues of prostatein, the major secreted protein of rat prostate. This report describes their cDNA sequences, tissue expression and chromosomal localization. Lipophilin gene products were widely expressed in normal tissues, especially in endocrine-responsive organs. The gene for lipophilin C (also called mammaglobin b) is located on chromosome 11q12-q13.1, near the mammaglobin gene, a homologue overexpressed in many breast cancers. The lipophilin B gene resides on chromosome 10q23, a region deleted in many tumors, and the lipophilin A gene is on chromosome 15q12-q13.

Fine-needle aspiration: comparison of smear, cytospin, and cell block preparations in diagnostic and cost effectiveness

We compared the results of smears to those of cytospin and cell block preparations from fine-needle aspirations to determine the cost effectiveness of each and to determine which should be routinely obtained. We reviewed 844 cases, 361 of which had both smears and cytospins, and 483 of which had both smears and cell blocks. Smears alone were diagnostic in 94% of cases (796/844 cases), cytospins alone diagnostic in 43% of cases (154/361 cases), and cell blocks alone diagnostic in 57% of cases (277/483 cases). Cytospins contributed additional information beyond that obtained from smears in 2% (7/361) and cell blocks in 12% (57/483) of cases. When smears were nondiagnostic, cytospins contributed additional information in 10% (2/21) of cases and cell blocks contributed additional information in 44% (12/27) of cases. The cost of providing a diagnosis from smear alone is $212, from cytospin alone is $352, and from cell block alone is $392. The cost for additional information established by cytospin is $7,736 and by cell block the cost is $1,906. Smears are superior to either cytospins or cell blocks in providing a diagnosis. It is not cost-effective to obtain either cytospins or cell blocks in addition to smears on all cases. However, it is cost-effective to obtain cell blocks when the immediate smear evaluation is nondiagnostic.

Nonvascular contractile cells in sclera and choroid of humans and monkeys

PURPOSE

To investigate by histochemistry and immunohistochemistry the distribution and innervation of nonvascular contractile cells in the sclera and choroid of humans and monkeys.

METHODS

Globes were obtained from 2 macaque monkeys and 19 human cadavers that ranged in age from fetal life to 94 years. Immunohistochemistry was performed using monoclonal antibody against human smooth muscle (SM) alpha-actin and tyrosine hydroxylase (TH). The nicotinamide-adenine dinucleotide phosphate (NADPH)- diaphorase reaction was used as a marker for nitric oxide synthase.

RESULTS

The scleras of all but fetal, newborn, and infant globes exhibited myofibroblasts, amelanotic, fibroblastlike cells having SM alpha-actin immunoreactivity. In the choroid of all but fetal eyes, SM cells were present in the suprachoroidal layer, forming a reticulum of flattened laminae, and in the choriocapillaris where ovoid-to-spindle-shaped SM cells were arrayed in parallel layers immediately adjacent to Bruch's membrane. Contractile cells in the sclera and choroid were most concentrated subfoveally and were sparse anteriorly. Nerve terminals positive for NADPH- diaphorase were colocalized with SM alpha-actin-positive cells in the sclera and choroid, whereas TH-positive nerve terminals colocalized with SM cells in the choroid. Clusters of ganglion cells were present on the posterior surface of globes near SM cells.

CONCLUSIONS

The posterior choroid and sclera of humans and monkeys contain nonvascular contractile cells. The presence of nerve terminals and adjacent ganglion cells suggests neural control of these contractile cells. The absence of such contractile cells in fetal, newborn, and infant eyes is an argument against a major role of these cells in promoting ocular enlargement. These contractile cells may instead participate in regulation of refractive state by maintenance of ocular size in the face of intraocular pressure or in intermediate-term regulation of choroidal thickness.

Lipophilin, a novel heterodimeric protein of human tears

We identified a novel heterodimeric protein, lipophilin AC, in human tears. One of its components, lipophilin A (69 residues; mass, 7575.1; pI, 9.47) was homologous to the C1 and C2 components of prostatein ('estramustine-binding protein'), the major secreted protein of rat prostate. Human lipophilin C (77 residues; mass, 8854.1; pI, 4.94) was homologous to the rat prostatein C3 component and to human mammaglobin, a protein overexpressed in some mammary carcinomas. Tear lipophilins A and C expand the roster of human uteroglobin superfamily members and provide models for exploring these typically steroid-regulated and steroid-binding molecules.

Structural changes in human tear lipocalins associated with lipid binding

Structural and conformational changes in tear lipocalins were detected in association with ligand binding and release. Circular dichroism measurements demonstrated that ligand binding induces beta structure formation, aromatic side chain asymmetry, and a more rigid state in tear lipocalins (TL). The exposure of the tyrosyl component is less in apo-TL than in holo-TL. The sole tryptophan residue, Trp17, is buried in both holo- and apo-TL. The steady state exposure of Trp17 is the same in holo- and apo-TL, but the dynamic exposure is two-fold greater in apo-TL. Maneuvers to unfold the protein with urea or incubation in an acidic environment resulted in increased exposure of aromatic amino acids. Electron paramagnetic resonance studies verified that lipids are liberated from TL in an acidic environment. Acidic pH promotes conformational changes in TL involving aromatic residues, particularly the conserved residue Trp17. These changes are associated with lipid release. The liberation of lipid from the cavity of TL under acidic conditions involves a molten globule state of the protein. We postulate that TL, exposed to the steep surface pH gradient that exists at lipid-aqueous interfaces, would release lipid in association with a molten globule transition. The data suggest a plausible regulatory mechanism for lipid delivery from lipocalins at the tear film surface.

Fine-needle aspiration: comparison of smear, cytospin, and cell block preparations in diagnostic and cost effectiveness

We compared the results of smears to those of cytospin and cell block preparations from fine-needle aspirations to determine the cost effectiveness of each and to determine which should be routinely obtained. We reviewed 844 cases, 361 of which had both smears and cytospins, and 483 of which had both smears and cell blocks. Smears alone were diagnostic in 94% of cases (796/844 cases), cytospins alone diagnostic in 43% of cases (154/361 cases), and cell blocks alone diagnostic in 57% of cases (277/483 cases). Cytospins contributed additional information beyond that obtained from smears in 2% (7/361) and cell blocks in 12% (57/483) of cases. When smears were nondiagnostic, cytospins contributed additional information in 10% (2/21) of cases and cell blocks contributed additional information in 44% (12/27) of cases. The cost of providing a diagnosis from smear alone is $212, from cytospin alone is $352, and from cell block alone is $392. The cost for additional information established by cytospin is $7,736 and by cell block the cost is $1,906. Smears are superior to either cytospins or cell blocks in providing a diagnosis. It is not cost-effective to obtain either cytospins or cell blocks in addition to smears on all cases. However, it is cost-effective to obtain cell blocks when the immediate smear evaluation is nondiagnostic.

Carcinoma of the male breast metastatic to both orbits

We report the case of a 43-year-old man who presented with painless proptosis of the right eye of 6 weeks' duration. Examination demonstrated a tense right orbit and decreased vision and extraocular motility bilaterally. Diagnostic evaluation included computed tomographic imaging of the head and orbits, a therapeutic trial of high-dose systemic corticosteroids, and orbital biopsy, which revealed the presence of metastatic adenocarcinoma. The primary tumor was found to be an estrogen-receptor-positive, infiltrating ductal adenocarcinoma of the right breast. Therapy included lumpectomy of the breast mass, orbital irradiation, and hormonal therapy. Metastatic carcinoma of the breast should be considered in the differential diagnosis of orbital neoplastic disease in the male patient.

A conserved disulfide motif in human tear lipocalins influences ligand binding

Structural and functional characteristics of the disulfide motif have been determined for tear lipocalins, members of a novel group of proteins that carry lipids. Amino acid sequences for two of the six isolated isoforms were assigned by a comparison of molecular mass measurements with masses calculated from the cDNA-predicted protein sequence and available N-terminal protein sequence data. A third isoform was tentatively sequence assigned using the same criteria. The most abundant isoform has a measured mass of 17 446.3 Da, consistent with residues 19-176 of the putative precursor (calculated mass 17 445.8 Da). Chemical derivatization of native and reduced/denatured protein confirmed the presence of a single intramolecular disulfide bond in the native protein. Reactivity of native, reduced, and denatured protein with 4-pyridine disulfide and dithiobis(2-nitrobenzoic acid) indicated that access to the free cysteine is markedly restricted by the intact disulfide bridge. Mass measurements of tryptic fragments identified C119 as the free cysteine and showed that the single intramolecular disulfide bond joined residues C79 and C171. Circular dichroism indicated that tear lipocalins have a predominant beta-pleated sheet structure (44%) that is essentially retained after reduction of the disulfide bond. Circular dichroism in the far-UV showed reduced molecular asymmetry and enhanced urea-induced unfolding with disulfide reduction indicative of relaxation of protein structure. Circular dichroism in the near-UV shows that the disulfide bond contributes to the asymmetry of aromatic sites. The effect of disulfide reduction on ligand binding was monitored using the intrinsic optical activity of bound retinol. The intact disulfide bond diminishes the affinity of tear lipocalins for retinol and restricts the displacement of native lipids by retinol. Disulfide reduction is accompanied by a dramatic alteration in ligand-induced conformational changes that involves aromatic residues. The disulfide bridge in tear lipocalins is important in conferring protein rigidity and influencing ligand affinity. The disulfide bond appears highly conserved so that these findings may have implications for the entire lipocalin superfamily.

Solution structure by site directed tryptophan fluorescence in tear lipocalin

The solution structure of the G strand of human tear lipocalin was deduced by site directed tryptophan fluorescence (SDTF). The fluorescent amino acid, tryptophan, was sequentially substituted for each native amino acid in the sequence of the G strand. The fluorescent properties resolved alternating periodicity as predicted for beta sheet structure, twists in the beta sheet, strand orientation in the lipocalin cavity, and the relative depth of residues in the cavity. A distribution of microstates with various orientations of dipoles in the side chain environments of the G strand revealed mobility on the nanosecond time scale. SDTF is broadly applicable to most proteins and will complement x-ray crystallography, site directed spin labeling by electron paramagnetic resonance (EPR), and nuclear magnetic resonance (NMR) in the determination of solution structure.

Epibulbar hemangiopericytoma

PURPOSE

To report a case of an epibulbar hemangiopericytoma that appeared clinically as a firm nodule.

METHODS

We examined a 28-year-old man with a 5-year history of a gradually enlarging red, firm epibulbar nodule. Excisional biopsy was performed.

RESULTS

Histopathology identified an encapsulated hemangiopericytoma. Eight-year follow-up showed no recurrence postresection.

CONCLUSIONS

Epibulbar hemangiopericytoma is rare and has a good prognosis after resection. The smaller size and more conspicuous location of epibulbar hemangiopericytomas may lead to relatively early treatment and account for a more favorable prognosis.

Intramammary lymph nodes: cytologic findings and implications for fine-needle aspiration cytology diagnosis of breast nodules

The recognition of intramammary lymphoid proliferations is important because smears of these proliferations would be judged as insufficient by several of the published criteria for specimen adequacy. Alternatively, some might be confused with medullary carcinoma of the breast or adenocarcinomas with a "single-cell" pattern. We found 19 intramammary lymphoid proliferations in a series of 887 fine-needle aspirates of palpable breast nodules. Six were lymphomas and 13 were benign intramammary lymph nodes. Smear cellularity ranged from scant to high, but in all cases, lymphocytes dominated the cell population. The cytology of intramammary lymph nodes and lymphoma did not differ from those occurring at other sites.

Salivary gland lesions with a prominent lymphoid component: cytologic findings and differential diagnosis by fine-needle aspiration biopsy

Fine-needle aspiration (FNA) is an accepted technique for the preoperative diagnosis of salivary gland nodules. The majority of salivary gland nodules are pleomorphic adenomas and offer little difficulty in diagnosis. Most diagnostically difficult lesions fall into one of four morphologic categories represented by squamous-cell-containing lesions, clear cell neoplasms, neoplasms with a prominence of stromal material, and lymphocyte-containing lesions. Herein, we describe our experience with a series of 61 histologically confirmed cases in which the smears contained a prominent or predominant number of lymphocytes. The differential diagnosis is discussed and points of diagnostic aid enumerated.

Evidence for breaches of the retinal vasculature in acquired immune deficiency syndrome angiopathy. A fluorescent microsphere study

PURPOSE

The author studied the retinal vasculature in patients with acquired immune deficiency syndrome (AIDS) by infusion of microspheres impregnated with fluorescent dye.

METHODS

Experimental study of the structural integrity of the retinal microvasculature in 14 autopsy patients with AIDS was compared with age- and gender-matched control retinas.

MATERIALS

Fourteen autopsy eyes from patients with AIDS, eight autopsy eyes from immunosuppressed control patients, and four autopsy eyes from nonimmunosuppressed control patients were studied.

EXPERIMENTAL METHOD

The central retinal arteries of autopsy eyes were perfused with fluorescent microspheres of 10 and 200 nm in diameter. The retinas were dissected from the eyes and viewed by fluorescence microscopy.

RESULTS

Vascular breaches permeable to 200-nm microspheres were discovered in eyes from patients with AIDS. Ruptured microaneurysms were identified at the center of retinal hemorrhages in 7 of 14 eyes from patients with AIDS and 5 of 8 immunosuppressed control eyes. Leakage around microaneurysms occurred even in the absence of hemorrhage and were more frequent in eyes from patients with AIDS (11/14) than in control eyes (3/12). Cotton wool patches were surrounded by tortuous retinal vessels and microaneurysms.

CONCLUSIONS

Ruptured microaneurysms are a frequent cause of retinal hemorrhage in immunosuppressed patients. Breaches in microaneurysms occur even in the absence of hemorrhage. These breaches are often at least 200 nm in diameter, a size that is permissive to capsids and virions of cytomegalovirus (CMV). Ruptured and/or leaky microaneurysms are potential sources of CMV permeation of the blood-retinal barrier. Breaches of the retinal microvasculature are not specific to patients with AIDS and occur frequently in other immunosuppressed patients.

Cavitation in ciliary body melanoma

PURPOSE

To report a case of a cystic ciliary body melanoma that appeared clinically as a solid mass.

METHODS

A 59-year-old woman underwent an iridocyclectomy for removal of a ciliary body melanoma in the right eye. The tumor was analyzed histopathologically for acid mucopolysaccharide production.

RESULTS

Histopathology identified a ciliary body melanoma with cystic cavities. Contents of the cystic spaces did not stain with alcian blue. Histologic findings suggested exudation, cavitary necrosis, or both rather than acid mucopolysaccharide production as pathogenic factors for cyst formation.

CONCLUSION

Cystic cavities can develop in a solid, malignant tumor and therefore should not be considered signs of a benign lesion.

Chiasmal infarction and sudden blindness caused by mucormycosis in AIDS and diabetes mellitus

PURPOSE

To report rapidly progressive rhino-orbitocerebral mucormycosis in a 47-year-old woman with both diabetes mellitus and the acquired immunodeficiency syndrome (AIDS).

METHOD

Case report including postmortem examination of the eyes, orbit, and brain of a patient with rhino-orbitocerebral mucormycosis, diabetes mellitus, and AIDS.

RESULTS

Invasion by hyphae of the Rhizopus species produced an occlusive vasculitis and massive infarction of the optic chiasm. Fungal organisms were discovered in multiple granulomata of the optic nerve.

CONCLUSION

Infarction at the optic chiasm probably caused sudden blindness in this patient.

Bilateral endogenous Fusarium endophthalmitis associated with acquired immunodeficiency syndrome

A 51-year-old man with acquired immunodeficiency syndrome and cytomegalovirus retinitis had bilateral endogenous fungal endophthalmitis. Cultures yielded Fusarium species. Histopathologic examination showed a severe necrotizing acute and granulomatous reaction, with numerous fungal elements in the retina and uveal tract. Fungal elements were seen in the lens, sclera, and emissarial vessels. Angiopathic infiltration by fungus and widespread thrombosis produced retinal and choroidal infarction. In some areas, fungal infection coexisted with cytomegalovirus retinitis. The bilateral distribution suggests hematogenous seeding of the eyes. The eye findings were the first clinically apparent manifestations of fungal disease in this patient.

Draining cutaneous fistula associated with infection of hydroxyapatite orbital implant

The implantation of an orbital hydroxyapatite implant was complicated by conjunctival dehiscence, cutaneous fistula formation, and infection with Staphylococcus aureus. Pathologic examination of the sphere 2 years after its implantation revealed reduction in the size of the implant, peripheral lamellar bone formation and central necrosis. This is the first report of this constellation of complications with hydroxyapatite spheres positioned in the orbit. The 2-year interval between implantation and removal of the sphere is the longest reported in a case with histopathologic analysis.

Contact and noncontact transscleral neodymium:YAG laser cyclophotocoagulation in a rabbit model

PURPOSE

Contact versus noncontact transscleral neodymium:YAG laser cyclophotocoagulation was compared in a rabbit model with respect to the effects on intraocular pressure and pathologic findings.

METHODS

Thirty-two rabbits received comparable energy levels (2 joules) of contact and noncontact cyclophotocoagulation. Pneumotonometry was performed every other day following treatment.

RESULTS

For both the 2-week and 8-week periods following treatment, intraocular pressure was significantly lower in eyes receiving contact cyclophotocoagulation than in eyes receiving noncontact cyclophotocoagulation (for the 2-week period, mean difference in intraocular pressure was 5.3 mm Hg, n = 22, p < 0.001; for the 8-week period, mean difference in intraocular pressure was 4.3 mm Hg, n = 17, p < 0.013). Pathologic findings include acute ciliary body hemorrhage and inflammation (1 day), chronic inflammation (1 week), granulation tissue within laser lesions (2 weeks), and marked ciliary body atrophy (8 weeks).

CONCLUSIONS

In our rabbit model, contact cyclophotocoagulation was more effective in lowering intraocular pressure than noncontact cyclophotocoagulation. Both contact and noncontact cyclophotocoagulation produced a variety of pathologic lesions in the rabbit eye, including cataract, phthisis bulbi, and anterior synechiae.

Aspergillus endophthalmitis. An unrecognized endemic disease in orthotopic liver transplantation

PURPOSE

The authors discovered an unusually high incidence of Aspergillus endophthalmitis in an autopsy series of orthotopic liver transplantation recipients. This study was conducted to discern the frequency, topographic distribution, and potential significance of the infections.

METHODS

Autopsy reports from liver transplant patients were reviewed. All patients with Aspergillus endophthalmitis were studied by gross and histologic examination. Histologic sections were stained with Grocott-Gomori methenamine-silver nitrate and periodic acid-Schiff stains. Some Grocott-Gomori methenamine-silver nitrate stained sections were counterstained with hematoxylin-eosin. The distribution of ocular infections in the eye was determined for each patient. The organs infected were determined at autopsy.

RESULTS

The authors found seven patients with Aspergillus endophthalmitis. Six of these seven patients were from a group of 85 (7.1%) orthotopic liver transplantation recipients. Fourteen (16.5%) orthotopic liver transplantation recipients had invasive pulmonary aspergillosis and ten (11.8%) had disseminated disease. The eyes were the second most common site of infection. Two patients had ocular involvement as the only nonpulmonary site of infection. Aspergillus endophthalmitis was diagnosed in only one patient before death. Infection was located posterior to the equator in all patients; three patients were anterior to the equator as well. The retina (5/7), vitreous (5/7), and choroid (3/7) were common sites of infection.

CONCLUSIONS

This is the first report of Aspergillus endophthalmitis associated with orthotopic liver transplantation recipients. Patients with orthotopic liver transplants are unusually susceptible to invasive aspergillosis and Aspergillus endophthalmitis. Aspergillus infection is frequently bilateral, begins posteriorly in the retina or choroid, and has vitreous involvement. Recognition of this entity is important because many patients die of disseminated Aspergillus infection that may be detected early with bedside funduscopic examination.

Corneal scarring after photorefractive keratectomy in a penetrating keratoplasty

PURPOSE

To report severe scarring in a corneal graft after excimer laser photorefractive keratectomy.

METHODS

A 35-year-old man underwent photorefractive keratectomy twice for severe compound myopic astigmatism and anisometropia after penetrating keratoplasty.

RESULTS

Corneal opacity corresponded to areas of irregular epithelial thickness, focal absence of the basement membrane, loss of Bowman's layer, and stromal scarring in the ablation zone.

CONCLUSION

There may be an increased risk of severe corneal stromal scarring from photorefractive keratectomy in eyes that have had previous penetrating keratoplasty.

Immunopathologic features of Staphylococcus aureus endophthalmitis in the rat

PURPOSE

To study the clinical, histopathologic, and immunologic responses to Staphylococcus aureus endophthalmitis in rats.

METHODS

Experimental Lewis rats received an intravitreal injection of viable S. aureus (65 organisms), and control rats received sterile saline. The clinical scores, cellular infiltrate, delayed hypersensitivity reaction in skin tests, and serum and vitreous enzyme-linked immunosorbent assay titers of immunoglobulin (Ig) M, IgG, and IgA to ribitol teichoic acid (RTA), the major antigenic determinant of S. aureus cell wall, were measured and compared on days 3, 7, 10, 14, 21, and 30. The differences were statistically assessed using Mann-Whitney nonparametric t-tests and analysis of variance.

RESULTS

The red reflex was abolished in the majority of rats between days 3 and 21. Ocular inflammation resolved by day 30. The vitreous of eyes injected with S. aureus showed bacterial growth on days 3 and 7, followed by a decrease in numbers on days 10 and 14 and disappearance on days 21 and 30. In the vitreous, a peak neutrophil count was observed at day 3 that rapidly declined by day 7. The number of lymphocytes and plasma cells peaked on day 3 but declined more slowly. Plasma cells and Mott cells were seen on days 10 and 14, suggesting intraocular antibody production. IgM titers to RTA increased progressively in serum and vitreous, reached a peak on day 21, and declined on day 30. A weak IgG but absent IgA response to RTA was observed in serum and vitreous. S. aureus endophthalmitis was not associated with delayed hypersensitivity to the bacteria in skin tests.

CONCLUSIONS

S. aureus endophthalmitis is associated with the infiltration of neutrophils, lymphocytes, monocytes, and plasma cells in vitreous. Neutrophils, the predominant infiltrating cells, may be involved in bactericidal activity and opsonophagocytosis. In rat staphylococcal endophthalmitis, IgM rather than IgG may be the protective antibody.

Tissue expression of lipocalins in human lacrimal and von Ebner's glands: colocalization with lysozyme

BACKGROUND

Tear-specific prealbumin is a group of proteins recently renamed as the tear lipocalins. These proteins were initially described as unique to lacrimal fluid. The tissue distribution and localization have never been thoroughly studied.

METHODS

The distribution of purified tear lipocalins was studied in many human secretions and tissues by western blots, immunohistochemistry and immunoelectron microscopy.

RESULTS

Tear lipocalin species of the same molecular weights were observed in western blot lanes loaded with tears, saliva, and protein extracts from the lacrimal and lingual von Ebner's glands. Lacrimal and von Ebner's glands contained tear lipocalins; other human tissues and secretions, including other salivary glands and taste buds, did not. Tear lipocalins colocalized with lysozyme in serous acinar cells of lacrimal and von Ebner's glands. Ultrastructurally, tear lipocalins were present on polyribosomes, endoplasmic reticulum, and Golgi areas. Lipocalins were concentrated in lacrimal secretory granules in amounts commensurate with a regulated pathway.

CONCLUSION

Tear lipocalins are expressed and truncated similarly in lingual von Ebner's and lacrimal glands, but not at all in other human tissues. Lipocalins are expressed and secreted with lysozyme. Lipocalins are concentrated in secretory granules in an amount consistent with a regulated secretory pathway.

Rupture of radial and arcuate keratotomy scars by blunt trauma 91 months after incisional keratotomy

PURPOSE/METHODS

We studied a case in which blunt trauma caused dehiscence of radial and arcuate corneal scars 91 months after incisional keratotomy. The ruptured incisions did not extend beyond the corneoscleral limbus.

RESULTS/CONCLUSIONS

Incisional refractive surgery renders the cornea susceptible to blunt traumatic rupture. This vulnerability results from the intrinsic weakness of the keratotomy wounds. Our case documents that this weakness persists up to 91 months after the operation.

Vortex vein exit sites. Scleral coordinates

PURPOSE

The authors determined the frequency and scleral coordinates of vortex vein exit sites in 46 autopsy eyes to provide topographic data that will enable surgeons to locate these vessels more precisely.

METHODS

Forty-six autopsy eyes were examined under a dissecting microscope to measure the frequency of vortex veins and the cord lengths between the vortex vein scleral exit sites and the limbus, rectus muscle insertions, and oblique muscle insertions.

RESULTS

Data from this study showed that 32 (70%) of the 46 individual eyes studied had more than four vortex veins. The number of second or third vortex veins found in the nasal quadrants was significantly higher than the number found in the temporal quadrants (P < 0.01). Statistical analyses of the measurements provided mean values for distances between vortex vein scleral exit sites and the three nearest extraocular muscle insertions; these positions among eyes were found to be relatively uniform (standard deviation, 0.7-2.5 mm).

CONCLUSION

The authors suggest that the majority of adult eyes encountered by a surgeon will have more than four vortex vein exit sites and that more vortex veins may be expected in the nasal quadrants than in the temporal quadrants. This study delineates the locations of vortex vein exit sites so that surgeons can reliably predict their surface positions to avoid vessel laceration and its ensuing complications.

Evidence for fibromuscular pulleys of the recti extraocular muscles

PURPOSE

Magnetic resonance imaging (MRI) shows that the paths of recti extraocular muscle (EOM) bellies remain fixed in the orbit during large ocular rotations and across large surgical transpositions of their insertions. These findings imply that recti EOMs pass through pulleys coupled to the orbit and anterior to the muscle bellies, because the insertions must move with the globe. The present study was conducted to locate anatomically and to characterize histologically the pulley tissues.

METHODS

High-resolution MRI images were collected from volunteers, using multiple gaze directions to infer the locations of, and occasionally to visualize, recti EOM pulleys. Fresh cadaver orbits were exenterated and dissected to evaluate mechanical and structural properties of the orbital connective tissues. Lipid was cleared from whole specimens to reveal tissue relationships. Other specimens were selectively step- and serial-sectioned for histochemical and immunohistochemical staining.

RESULTS

Magnetic resonance imaging demonstrated dense connective tissue structures within posterior Tenon's fascia near the equator of the globe adjacent to the recti EOMs. Histochemistry showed these structures to be pulleys--fibroelastic EOM sleeves consisting of dense bands of collagen and elastin, suspended from the orbit and adjacent EOM sleeves by bands of similar composition. A monoclonal antibody to human smooth muscle alpha-actin demonstrated substantial smooth muscle in the pulley suspensions and in posterior Tenon's fascia. Tenon's fascia itself was seen to be suspended at its periphery from the orbital walls like a drumhead.

CONCLUSIONS

The human orbit contains specialized musculofibroelastic tissues in and just posterior to Tenon's fascia that serve as compliant pulleys and determine the pulling directions of recti EOMs. In this sense, the pulleys are the functional origins of the recti EOMs and are determinants of ocular motility.

Tear lipocalins bind a broad array of lipid ligands

To identify the native ligands of tear lipocalins, tear proteins were separated by size exclusion chromatography and the lipid content in the major protein fractions identified. Lipids extracted from native tears and purified tear lipocalins comigrated with fatty acids, fatty alcohols, phospholipids, glycolipids, and cholesterol on thin layer chromatograms. Abundant stearic and palmitic acids as well as cholesterol, and lesser amounts of lauric acid were specifically identified in extracts of purified lipocalins by gas chromatography-mass spectroscopy. A preliminary study of the ligand-protein interaction was carried out using nitroxide spin-labeled lipids.

Cuterebra Ophthalmomyiasis

PURPOSE/METHODS

We used a simple laboratory method to identify the first instar stage of a Cuterebra larva that emerged from the conjunctiva of a 14-year-old boy with ipsilateral decreased vision, subretinal hemorrhages, and linear streaks in the fundus. The maggot was removed from the conjunctiva and cleared in glycerol solutions.

RESULTS/CONCLUSIONS

Light microscopy disclosed spines characteristic of Cuterebra larvae. Scanning electron microscopy is not necessary for diagnosis of Cuterebra ophthalmomyiasis even if samples are limited to the larval thorax.

A quantitative and cartographic study of retinal microvasculopathy in acquired immunodeficiency syndrome

We quantified the retinal microvascular abnormalities in 57 eyes from autopsy patients with the acquired immunodeficiency syndrome (AIDS) and in 24 eyes from gender- and age-matched control subjects. We related retinal vascular changes to the topography of cytomegalovirus retinitis. Analysis of retinal trypsin digests revealed more vascular attenuation (P = .005), increased ratio of endothelial cells to pericytes (P = .001), and more microaneurysms (P = .02) in eyes of AIDS patients without cytomegalovirus retinitis than in those of control subjects. Cytomegalovirus retinitis was frequently bilateral, extensive, and distributed along blood vessels. Peripheral retinitis was more frequent than macular infection. Lymphocytes aggregated focally in arterioles, venules, and capillaries leading to areas infected with cytomegalovirus. Acquired immunodeficiency syndrome microvasculopathy occurs in the absence of cytomegalovirus retinitis and is not accounted for by immunosuppression alone. The location and character of these vascular changes in AIDS indicate an ischemic pathogenesis. In AIDS patients with cytomegalovirus retinitis, the vascular changes are more profound and include capillary destruction.

Corneal ectasia as a complication of repeated keratotomy surgery

BACKGROUND

Staged keratotomy surgery, or "enhancement surgery," may allow a more predictable outcome, but also subjects the patient to additional surgical risks.

METHODS

A 39-year-old man underwent astigmatic keratotomy for myopic astigmatism, followed by 12 enhancement procedures for residual astigmatism.

RESULTS

These procedures effectively resulted in a double hexagonal keratotomy. The patient's best spectacle-corrected acuity deteriorated to counting fingers. Clinically, a conically-shaped protrusion of the central cornea, Munson's sign, diffuse subepithelial scarring, and central corneal thinning were noted. Penetrating keratoplasty was performed. Histopathologic examination showed central thinning, epithelial edema, disruption of Bowman's layer, marked stromal scarring, and focal areas of endothelial attenuation--findings consistent with keratoconus.

CONCLUSION

This case illustrates that multiple keratotomy procedures may result in corneal ectasia in apparently normal eyes and suggests that hexagonal keratotomy may be more likely to cause iatrogenic keratoconus.

GLUT1 glucose transporter expression in the diabetic and nondiabetic human eye

PURPOSE

The GLUT1 glucose transporter is expressed in endothelial and epithelial barriers, including the retinal capillary endothelium and the retinal pigment epithelium (RPE) of the eye. The present studies were undertaken to determine whether GLUT1 is expressed in additional cell types within the human eye and whether retinal endothelial GLUT1 is aberrantly expressed in diabetic proliferative retinopathy in humans.

METHODS

Immunohistochemical staining of sections of human eyes obtained at surgery or autopsy from patients with and without diabetes was performed with polyclonal antisera directed against the human GLUT1 glucose transporter.

RESULTS

In the course of this study, an unexpected multicellular localization of GLUT1 in different cellular barriers of the human eye was observed. In the nondiabetic eye, specific staining for GLUT1 was seen in the nerve fiber layer, the ganglion and photoreceptor cell bodies, the capillaries and the RPE of the retina, the basal infoldings of the pigmented and nonpigmented layers of the ciliary body, the capillary endothelium and posterior epithelium of the iris, the corneal epithelium and endothelium, and the endothelium lining of the canal of Schlemm. Müller cells, a type of retinal glial cell identified by morphology and by parallel staining for glial fibrillary acidic protein, also stained intensely positive for GLUT1. The pattern of GLUT1 immunoreactivity in the diabetic eyes was virtually identical to that in the nondiabetic specimens, with the notable exception that the neovascular endothelium of proliferative retinopathy did not stain for GLUT1.

CONCLUSIONS

These studies describe the heretofore unrecognized expression of immunoreactive GLUT1 in the ganglion cell layer of the retina, the endothelium lining the canal of Schlemm, the corneal endothelium, and the basal cells of the corneal epithelium of the human eye. The present study also provides evidence for immunoreactive GLUT1 in glial cells of the central nervous system. Because the expression of GLUT1 is characteristic of tissues that possess a barrier function, the absence of GLUT1 immunoreactivity in the neovascular tissue of proliferative diabetic retinopathy suggests that the loss of selective permeability is associated with an absence of facilitated glucose transport in this disorder.