Hydraulic conductivity of fixed retinal tissue after sequential excimer laser ablation: barriers limiting fluid distribution and implications for cystoid macular edema.

OBJECTIVES: To measure the hydraulic conductivity (HC) of human retina and to determine the presence and location of high-resistance barriers to fluid movement through the retina. METHODS: Forty-one pairs of human eyes were investigated using an HC chamber. Once baseline HC had been determined, the effect of ablating through varying thickness of retina from the vitreous or photoreceptor surface using an excimer laser (193 nm) was investigated. Tissue samples were then processed for histological investigation. RESULTS: The HC of fixed intact human retina was 2.54 x 10(-10) m/s per pascal at 539 Pa (range, 0.6 x 10(-10) to 3.3 x 10(-10) m/s per pascal; SD, 0.6 x 10(-10) m/s per pascal [1 mm Hg equals 133 Pa]). Ablation from either surface resulted in little change in HC until a critical depth was reached, at which point there was an order of magnitude increase. The critical depth was approximately 170 microm from the inner limiting membrane when ablating from the vitreous surface and 70 microm from the inner limiting membrane when ablating from the photoreceptor surface. Histological specimens showed that these barriers were the synaptic portion of the outer plexiform layer, and the inner plexiform layer, respectively. CONCLUSIONS: The 2 high-resistance barriers to fluid flow through the retina are the synaptic portion of the outer plexiform layer, and the inner plexiform layer. CLINICAL RELEVANCE: These observations help to explain the distribution of cystoid macular edema seen in histological studies and with optical coherence tomography.

Intravitreal triamcinolone for uveitic cystoid macular edema: an optical coherence tomography study.

PURPOSE: To investigate the use of intravitreal injection of triamcinolone acetonide (TA) for the treatment of refractory uveitic cystoid macular edema (CME). DESIGN: Prospective, nonrandomized, self-controlled comparative trial. PARTICIPANTS: Six patients with chronic CME resistant to treatment with systemic steroids, orbital floor steroids, and cyclosporine A. Three patients were followed for more than 1 year, and the other three for between 3 and 9 months. INTERVENTION: Injection of 2 mg of TA into the vitreous cavity. TESTING: Optical coherence tomography scanning of the fovea before and after injection and logarithmic minimal angle of resolution visual acuity. MAIN OUTCOME MEASURES: Visual acuity, retinal thickness, cystoid space height, and intraocular pressure. RESULTS: There was complete anatomic resolution of CME in five of the six cases within 1 week after injection. Cystoid spaces began to return between 6 weeks and 3 months after injection. Two patients with longer term follow-up responded to further orbital floor steroid injection and had no CME 1 year later. One patient had raised intraocular pressure develop, requiring a trabeculectomy. Mean improvement in visual acuity after 12 months was 0.27 (range, 0.14-0.42). CONCLUSIONS: Complete anatomic and, to some extent, functional recovery can be induced by intravitreal TA despite long-term refractory inflammatory CME. Optical coherence tomography aids in the management of these cases.

Optical coherence tomography of melanocytoma.

PURPOSE: To evaluate the use of optical coherence tomography in differentiating between melanocytoma and choroidal melanoma. METHODS: Case reports. Three consecutive patients with melanocytoma were scanned using optical coherence tomography. RESULTS: Optical coherence tomography showed lesions with a high reflectance signal anteriorly and optical shadowing behind, corresponding to the melanocytomas. The high signal was continuous with the retinal nerve fiber layer, consistent with known growth patterns of melanocytoma. CONCLUSION: Optical coherence tomography may be useful in differentiating melanocytoma from choroidal melanocytic lesions.

Comparison between optical coherence tomography and fundus fluorescein angiography for the detection of cystoid macular edema in patients with uveitis.

PURPOSE: To compare optical coherence tomography (OCT) with fundus fluorescein angiography (FFA) for the detection of cystoid macular edema (CME) in patients with uveitis. DESIGN: Prospective comparative observational series. PARTICIPANTS: One hundred twenty-one eyes of 58 patients with uveitis of varied causes (seven patients were studied twice). TESTING: Patients with suspected CME underwent OCT scanning followed by FFA at the same visit. MAIN OUTCOME MEASURES: Detection and distribution of macular edema. RESULTS: One hundred eight eyes had similar results on both OCT and FFA in that 67 eyes had CME and 41 eyes had no CME. In 10 eyes subretinal fluid was detected on OCT but not FFA. Five of these eyes had CME on FFA but not OCT. Three other eyes had CME that was detected by FFA but not by OCT. Compared with FFA, the OCT sensitivity for detecting CME was 96% (including the eyes with subretinal fluid), and the OCT specificity was 100%. CONCLUSIONS: OCT is as effective at detecting CME as is FFA but is superior in demonstrating axial distribution of fluid.

Papillofoveal traction in macular hole formation: the role of optical coherence tomography.

OBJECTIVES: To determine the validity of the assumption that optical coherence tomographic scans of macular holes have a discrete linear signal (DLS) that represents a detached posterior vitreous face, and to analyze the DLS in macular hole pathogenesis. METHODS: Optical coherence tomographic scans were taken of 3 situations in which the vitreous conditions were known: (1) dissected intact vitreous, (2) clinically evident Weiss rings, and (3) maculae before and after saccades in eyes without a biomicroscopic posterior vitreous detachment. In addition, 70 eyes of 35 patients with macular holes underwent clinical examination and optical coherence tomographic scanning that passed through the optic disc and the fovea or macular hole. RESULTS: Spatial properties of the DLS matched those of the posterior vitreous face in the situations examined. Of the 70 eyes, 16 (23%) had a biomicroscopic posterior vitreous detachment, whereas a DLS was demonstrated in 40 (57%). Of the 54 eyes without a biomicroscopic posterior vitreous detachment, 18 (33%) had a DLS attached focally to the optic disc margin and the fovea or macular hole. All 7 of the "can opener" holes examined had a nasally "hinged" central flap, 6 with a focally attached DLS. CONCLUSIONS: The DLS corresponds to the posterior vitreous face. Anteronasal papillofoveal traction may generate some macular holes.

Are optic disc drusen inherited?

OBJECTIVE: To conduct family studies of the incidence of optic disc drusen and related optic disc anomalies among relatives of those affected. DESIGN: Retrospective case series with prospective examination of patients and their relatives using B-scan ultrasonography and color photography. PARTICIPANTS: A total of 27 relatives of 7 probands with bilateral optic disc drusen were examined. MAIN OUTCOME MEASURES: Presence of optic disc drusen on clinical examination or B-scan ultrasonography and presence of related anomalies, including absence of optic disc cup and presence of anomalous vasculature. RESULTS: Only 1 of 27 relatives had optic disc drusen (3.7%). Thirty of 53 eyes had anomalous vessels (57%), and 26 eyes had no optic cup (49%). CONCLUSION: The primary pathology of optic disc drusen is likely to be an inherited dysplasia of the optic disc and its blood supply, which predisposes to the formation of optic disc drusen.

The effect of fluorescein on the accuracy of blood glucose determination by glucose meters.

PURPOSE: To investigate whether intravenous fluorescein significantly affected the accuracy of a glucose meter. METHODS: Thirty-four consecutive patients undergoing fluorescein angiography were recruited. Venous blood was removed immediately before and 1 hour after injection of 5 mls of 20% Sodium Fluorescein solution (1 mg). Whole blood glucose was measured with a glucose meter and plasma glucose levels were measured by the Department of Biochemistry for both samples. The results were analysed using Wilcoxon matched pairs test. RESULTS: Mean glucose results before fluorescein injection were 7.4 mmol/l (SD 4.5) with the glucose meter and 8.1 mmol/l (SD 5.0) biochemically (p=0.02). The post dose levels were 7.2 mmol/l (SD 4.7) and 8.5 mmol/l (SD 4.8), respectively (p=0.001). The difference between the mean results of the two tests was 0.7 mmol/l before fluorescein and 1.3 mmol/l after fluorescein (p=0.001) CONCLUSION: Intravenous fluorescein appears to influence minimally the difference between glucose levels measured in the laboratory and by glucose meter. The degree of difference, whilst achieving statistical significance, should not affect insulin dosage clinically.

The pathogenesis of edema in diabetic maculopathy.

Diabetic maculopathy is characterized by the accumulation of extracellular fluid in Henle's layer and the inner nuclear layer of the retina. The localization of the edema is likely to be due, in part, to the relative barrier properties of the inner and outer plexiform layers. The origin of the extracellular fluid is from the intravascular compartment. Although changes to retinal blood flow may partly explain the extravasation of fluid, the most important mechanism is breakdown of the blood retinal barriers. Both the inner blood retinal barrier formed by the retinal capillary endothelial cell tight junctions and the outer barrier formed by the retinal pigment epithelial cell tight junctions can be affected. The mechanism of breakdown of the blood retinal barriers is likely to be changes to the tight junction proteins including occludin and ZO-1. The biochemical messenger inducing these changes may be vascular endothelial growth factor. The origin of this or other cofactors may be the retinal glial cells. The underlying biochemical stimulus to the production of vascular endothelial growth factor is chronic hyperglycaemia, but it is uncertain by what pathway this is effected.

The maintenance of per-operative mydriasis in phacoemulsification with topical diclofenac sodium.

PURPOSE: To determine whether the use of topical diclofenac sodium (diclofenac) pre-operatively improves the maintenance of per-operative mydriasis, in conjunction with irrigating solutions containing adrenaline. METHODS: Sixty-four consecutive patients undergoing phacoemulsification were randomised to receive either diclofenac or no diclofenac in conjunction with cyclopentolate 1% and phenylephrine 10% pre-operatively. They subsequently underwent routine phacoemulsification by one consultant surgeon. Irrigating solutions of balanced salt solution contained adrenaline 1:10(6). Pupil diameters were measured pre-sclerostomy, post-phacoemulsification, post-irrigation/aspiration and on day 1 post-operatively. These were then compared by Student's t-test. RESULTS: The two groups were statistically similar in age and sex. The mean pre-sclerostomy pupillary diameters were 8.1 mm in both groups. The mean post-phacoemulsification diameters were 7.6 mm in those receiving diclofenac and 7.2 mm in those not (p = 0.03). The mean diameters after infusion/aspiration were 7.7 mm in those receiving diclofenac and 7.1 mm in those not (p = 0.008). The mean pupillary diameters on day 1 were 5.3 mm in those receiving diclofenac and 4.6 mm in those not (p = 0.003). CONCLUSION: Diclofenac improves the maintenance of per-operative mydriasis, in the presence of irrigating solutions containing adrenaline.

Phacoemulsification in diabetics.

In a retrospective study we examined a consecutive group of diabetic patients (74 operated eyes) who underwent phacoemulsification and intraocular lens implantation over a 2 year period ending in June 1994. We compared this group with 66 diabetic eyes who underwent extracapsular surgery and lens implantation and who were examined for a previous study. There were no significant differences in progression of the retinopathy, complications, or final visual acuity. Seventy-two per cent of the phacoemulsification group improved by at least 2 lines of Snellen acuity postoperatively compared with 76% of the extracapsular group. Seventy-four per cent of the phacoemulsification group achieved an acuity of 6/12 or better compared with 68% of the extracapsular group. Overall there were fewer post-operative complications in the phacoemulsification group though there was an increased incidence of transient corneal oedema. The major cause of poor visual acuity in the phacoemulsification group was maculopathy, particularly in the presence of proliferative retinopathy in older patients. Use of a small intraocular lens did not prevent adequate fundal examination or photocoagulation. It is concluded that the outcome of cataract surgery in diabetics is largely determined by the degree of maculopathy. Phacoemulsification and extracapsular cataract surgery give similar visual results. Diabetic retinopathy should not be considered a contraindication to small-incision cataract surgery and phacoemulsification.