Fred K. Chen

RPE transplantation and its role in retinal disease.

Retinal pigment epithelial (RPE) transplantation aims to restore the subretinal anatomy and re-establish the critical interaction between the RPE and the photoreceptor, which is fundamental to sight. The field has developed over the past 20 years with advances coming from a large body of animal work and more recently a considerable number of human trials. Enormous progress has been made with the potential for at least partial restoration of visual function in both animal and human clinical work. Diseases that have been treated with RPE transplantation demonstrating partial reversal of vision loss include primary RPE dystrophies such as the merTK dystrophy in the Royal College of Surgeons (RCS) rat and in humans, photoreceptor dystrophies as well as complex retinal diseases such as atrophic and neovascular age-related macular degeneration (AMD). Unfortunately, in the human trials the visual recovery has been limited at best and full visual recovery has not been demonstrated. Autologous full-thickness transplants have been used most commonly and effectively in human disease but the search for a cell source to replace autologous RPE such as embryonic stem cells, marrow-derived stem cells, umbilical cord-derived cells as well as immortalised cell lines continues. The combination of cell transplantation with other modalities of treatment such as gene transfer remains an exciting future prospect. RPE transplantation has already been shown to be capable of restoring the subretinal anatomy and improving photoreceptor function in a variety of retinal diseases. In the near future, refinements of current techniques are likely to allow RPE transplantation to enter the mainstream of retinal therapy at a time when the treatment of previously blinding retinal diseases is finally becoming a reality.

Repeatability of manual subfoveal choroidal thickness measurements in healthy subjects using the technique of enhanced depth imaging optical coherence tomography.

PURPOSEnThe aim of this study was to investigate the repeatability of manual measurements of choroidal thickness in healthy subjects imaged on spectral domain optical coherence tomography (OCT) using the enhanced depth imaging (EDI) technique.nnnMETHODSnFifty consecutive, healthy, young, adult volunteers with no known eye disease were enrolled prospectively. Two good-quality horizontal and vertical line scans through the fovea were obtained for each eye. Using the manual calipers provided by the software of the proprietary device, two experienced OCT readers measured the subfoveal choroidal thickness (SFCT) of the horizontal and vertical line scans for all eyes. The readers were masked to each others readings. Intraobserver, interobserver, and intrasession coefficients of repeatability (CRs) were calculated.nnnRESULTSnMean (standard deviation [SD]) age of the study subjects was 38 (5) years (range, 30-49 years). Mean (SD) subfoveal choroidal thickness was 332 (90) μm (right eyes) and 332 (91) μm (left eyes). Intraobserver CR was approximately 23 (95% confidence interval [CI], 19-26) μm, whereas interobserver and intrasession CRs were greater at 32 (95% CI, 30-34) and 34 (95% CI, 32-36) μm, respectively. There was no significant difference in SFCT between all pairs of SFCT measurements except for the two intrasession vertical line scans.nnnCONCLUSIONnA change of >32 μm was likely to exceed interobserver variability in SFCT. Future studies are required to estimate the repeatability of SFCT measurements in patients with chorioretinal pathology.

Test-Retest Variability of Microperimetry Using the Nidek MP1 in Patients with Macular Disease

PURPOSEnTo determine the test-retest variability of the retinal sensitivity of the Nidek MP1 microperimeter in patients with macular disease.nnnMETHODSnIn this prospective study, 50 patients were enrolled with a range of macular diseases. One examiner performed two consecutive microperimetry tests for all patients using the same test strategy. Test-retest variability for mean sensitivity (MS), mean deviation (MD), point-wise sensitivity (PWS), local defect classification (LDC), average sensitivity for the central macula (CMS, 16 loci inside 10 degrees ), paracentral macular sensitivity (PMS, 52 loci in the 10 to 20 degrees ring), and dense scotoma size (DSS) were analyzed by calculating the 95% coefficients of repeatability or percentage agreement.nnnRESULTSnMean (SD) age and visual acuity were 61 (15) years and 0.34 (0.32) logMAR, respectively. The mean difference in MS between tests 1 and 2 was +0.2 dB (SD, 0.9 dB; P = 0.127). The coefficients of repeatability for MS, MD, CMS, and PMS were 1.81, 2.56, 2.13, and 1.93 dB, respectively. The mean (SD) of coefficients of repeatability for PWS across all 68 loci was 5.56 (0.86) dB. Of all test loci in all patients 76% had perfect agreement in LDC, and 94% of patients had a change in DSS of four or fewer test loci.nnnCONCLUSIONSnTest-retest variability was lowest for MS and highest for PWS. However, MS does not provide spatial information. The authors recommend the use of CMS and PMS for monitoring macular function and consider a change of greater than 2.56 and 2.31 dB (the upper limit of the 95% confidence interval of their coefficients of repeatability), respectively, to exceed test-retest variability.

Intersession Repeatability of Visual Acuity Scores in Age-Related Macular Degeneration

PURPOSEnTo describe the intersession repeatability of visual acuity measures obtained with Early Treatment of Diabetic Retinopathy Study (ETDRS) charts in patients with age-related macular degeneration.nnnMETHODSnVisual acuity was measured in four sessions over 12 weeks using a standardized protocol with ETDRS charts in 107 nontreated eyes of 107 patients with age-related macular degeneration enrolled in an ongoing clinical trial.nnnRESULTSnData from 90 patients were included in the analysis. The 95% coefficient of repeatability (CR) was 12 ETDRS letters and ranged from 9 letters for 29 eyes with small to intermediate drusen only to 17 letters for 25 eyes with late AMD (macular scars or geographic atrophy). Ten (11%) eyes had a 5-letter reduction or more in visual acuity at the week 1 visit compared with baseline. Excluding seven eyes with visual acuity measurements potentially affected by measurement-related factors (a change in testing distance between visits) the revised CR was 10 letters for the cohort (n = 83) and 11 letters for the late-AMD subgroup (n = 18).nnnCONCLUSIONSnIntersession ETDRS visual acuity measurements are subject to considerable variability in patients with AMD. The variability may be due to both measurement- and disease-related factors. The variable readings have implications for AMD clinical trial design and for the assessment and treatment of patients with neovascular AMD. Further work is needed to determine both the sources of variability in visual acuity measurements and the optimal change criterion for visual acuity measurements in this important group of patients.

Repeatability of stratus optical coherence tomography measures in neovascular age-related macular degeneration

PURPOSEnTo determine the repeatability of Stratus optical coherence tomography (OCT) measures of retinal thickness and volume in patients with neovascular age-related macular degeneration (nAMD) METHOD: Fifty-one eyes of 51 consecutive patients with nAMD underwent an OCT imaging session in which two fast macular thickness map (FMTM) protocol scans sets were acquired by a single experienced operator certified for clinical trials work. Coefficients of repeatability for each of nine Early Treatment of Diabetic Retinopathy Study (ETDRS)-like regions, foveolar center-point retinal thickness (CPT) and total macular volume (TMV), were calculated. Scans were analyzed retrospectively for errors in retinal boundary placement by two observers, with revised coefficients of repeatability calculated after excluding any scan sets with significant segmentation error.nnnRESULTSnThe coefficient of repeatability for the central 1-mm macular subfield was 67 mum (23%) and was less than 75 mum for all macular subfields. There was much larger variability in the center-point thickness measure, with a coefficient of repeatability of 88 mum (32%) for the automated center-point thickness (ACPT). After excluding nine scan set pairs with significant segmentation error, the coefficient of repeatability for the central 1-mm macular subfield was reduced to 50 mum (19%).nnnCONCLUSIONSnOCT-derived retinal thickness measurements are subject to considerable measurement variability in patients with nAMD. Changes in central macular thickness of more than 50 mum may better reflect true clinical change in scan sets without significant segmentation error and may be used to guide the retreatment of patients with nAMD in clinical trials and clinical practice.

Segmentation error in stratus optical coherence tomography for neovascular age-related macular degeneration.

PURPOSEnTo describe the rate of automated segmentation error in Stratus optical coherence tomography (OCT) scans in consecutive patients with neovascular age-related macular degeneration (nAMD) receiving treatment and to investigate the effect of the segmentation error on automated retinal thickness measures and whether further imaging reduces the rate of segmentation error.nnnMETHODSnA retrospective analysis of fast macular thickness map (FMTM) protocol OCT scans of 50 eyes of 50 consecutive patients with nAMD. Each line scan was analyzed for segmentation error with manual measurement of the center-point retinal thickness allowing calculation of the percentage error in automated thickness. OCT scanning was repeated to overcome segmentation error.nnnRESULTSnSegmentation error was detected in 45 (90%) of the 50 patients with 37 (74%) patients having an error affecting the central 1-mm subfield. Scan sets with a high central segmentation error score (two or more line scans affected of six) had a significantly greater error in automated center-point retinal thickness than scan sets with a low error score (20% compared with 3%, P < 0.000005). Central subfield segmentation error persisted in 30 (60%) patients despite repeat scanning.nnnCONCLUSIONSnThere is a high rate of segmentation error in OCT scans of patients with nAMD who are undergoing treatment, leading to errors in automated central retinal thickness measurement. The authors recommend manual measurement of central macular thickness when two or more line scans are affected by segmentation error in the central 1-mm subfield. Repeated scanning reduced the rate of error but did not eliminate the problem.

Long-term visual and microperimetry outcomes following autologous retinal pigment epithelium choroid graft for neovascular age-related macular degeneration.

Background:u2002 To describe the 2‐ to 4‐year visual and microperimetry outcomes of autologous retinal pigment epithelium (RPE)‐choroid graft in patients with neovascular age‐related macular degeneration (AMD).

Induction of Differentiation by Pyruvate and DMEM in the Human Retinal Pigment Epithelium Cell Line ARPE-19

PURPOSEnCultured retinal pigment epithelium (RPE) may become a therapeutic option for transplantation in retinal disease. However maintaining a native RPE phenotype in vitro has proven challenging. The human RPE cell-line ARPE-19 is used widely as an alternative to primary RPE. It is grown in DMEM/F12 medium as standard, but its phenotype is dependent on culture conditions, and many differentiation markers are usually absent. The purpose of this study was to examine how this sensitive phenotype of ARPE-19 can be modulated by growth media with or without the metabolite pyruvate to elucidate better RPE growth conditions.nnnMETHODSnARPE-19 cells at passages p22 to p28 were cultured on filters for up to 3 months in DMEM/F12 or DMEM media with or without pyruvate and 1% fetal calf serum. Assessment of differentiation was performed using pigmentation, immunocytochemistry, protein/mRNA expression, transepithelial resistance, VEGF secretion, and ultrastructure.nnnRESULTSnPyruvate, in combination with DMEM, induced dark pigmentation and promoted differentiation markers such as CRALBP and MerTK. Importantly, RPE65 protein was detected by Western blotting and was enhanced by pyruvate, high glucose, and DMEM. ARPE-19 cells maintained in this medium could also phagocytose human photoreceptor outer segments (POS). VEGF secretion was greater in DMEM cultures and was affected by glucose but not by pyruvate. Pigmentation never occurred in DMEM/F12.nnnCONCLUSIONSnThis study demonstrated important differentiation markers, including pigmentation and Western blots of RPE65 protein, and showed human POS phagocytosis in ARPE-19 cultures using a simple differentiation protocol. The results favor the use of high-glucose DMEM with pyruvate for future RPE differentiation studies.

Effects of Retinal Morphology on Contrast Sensitivity and Reading Ability in Neovascular Age-Related Macular Degeneration

PURPOSEnTo investigate the effect of changes in retinal morphology on contrast sensitivity and reading ability in patients with neovascular age-related macular degeneration (AMD) in the Avastin (bevacizumab; Genentech, South San Francisco, CA) for choroidal neovascularization (ABC) Trial.nnnMETHODSnContrast sensitivity obtained with Pelli-Robson charts, reading ability assessed with Minnesota Reading charts, and Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuity (VA) obtained by protocol refraction, were recorded. Raw Stratus optical coherence tomography (OCT; Carl Zeiss Meditec, Inc., Dublin, CA) images were analyzed with the publicly available software OCTOR, which allows precise delineation of any retinal compartment of interest. Thickness and volume were calculated for neurosensory retina, subretinal fluid (SRF), subretinal tissue, and pigment epithelium detachment, and the resulting measurements were correlated with each visual function parameter.nnnRESULTSnOne hundred twenty-two patients with newly diagnosed neovascular AMD and enrolled in the ABC Trial, were evaluated. Increased subretinal tissue volume correlated with decreased contrast sensitivity (Pearsons correlation coefficient, r = -0.4944, P = 0.001). A modest correlation was detected between SRF volume and contrast sensitivity (r = -0.2562, P = 0.004). Increased retinal thickness at the foveal center also correlated with decreased visual function (ETDRS VA: r = -0.4530, P < 0.001).nnnCONCLUSIONSnThe strongest correlation detected between the functional parameters assessed and any of the OCT-derived morphologic parameters was that between decreased contrast sensitivity and increased subretinal tissue. In the future, assessment of contrast sensitivity and reading ability, in combination with quantitative subanalysis of retinal compartments, may lead to the identification of parameters relevant to functional improvement and ultimate prognosis in patients with newly diagnosed neovascular AMD (www.controlled-trials.com number, ISRCTN83325075).

Macular function assessed by microperimetry in patients with enhanced S-cone syndrome

PURPOSEnEnhanced S-cone syndrome (ESCS), also known as Goldmann-Favre syndrome, is a progressive retinal degeneration that frequently presents with night blindness and nummular pigment clumping around the vascular arcades and is caused by recessive mutations in the photoreceptor-specific NR2E3 transcription factor. A unique feature of this disease is the development of retinoschisis of the macula. This study used fine anatomic and functional assessments within this region to determine whether the loss of retinal function was due to progressive schisis or a primary photoreceptor loss, similar to other rod-cone dystrophies.nnnDESIGNnCross-sectional, prospective study.nnnPARTICIPANTSnNine probands (n=18 eyes) and 3 controls (n=6 eyes) were studied at Moorfields Eye Hospital in London, United Kingdom.nnnMETHODSnHistories were obtained and visual acuity was measured using Early Treatment Diabetic Retinopathy Study protocol. Autofluorescence (AF), fundus photography, and spectral domain optical coherence tomography (OCT) imaging were co-registered to detailed microperimetry (Nidek MP1; NAVIS software version 1.7.2; Nidek Technologies, Padova, Italy) data for statistical analysis.nnnMAIN OUTCOME MEASURESnRetinal sensitivity (decibels) in a customized test grid of the macula; retinal structure assessed with OCT and AF.nnnRESULTSnPatients were divided into 3 cohorts roughly based on life span and documentation of schisis: (1) no schisis, childhood; (2) macular schisis, young adults; (3) resolved schisis, older adults. Retinal sensitivity was significantly attenuated in those with schisis and did not recover in those whose schisis had resolved despite retinal thickness comparable to that of controls. All probands exhibited loss of AF peripherally (and corresponding loss of retinal sensitivity), but there was relative preservation of AF within the macula.nnnCONCLUSIONSnDevelopment of macular retinoschisis in ESCS is an important feature of the disease and contributes to attenuated retinal sensitivity that persists after resolution of retinoschisis. The central macula appears to be compromised more by foveoschisis than photoreceptor loss. In contrast, the peripheral retina (ordinarily a rod-rich region) is affected early in the disease process and degenerates rapidly because of photoreceptor loss. Thus, 2 distinct mechanisms of retinal degeneration may exist in ESCS, corresponding to regions of the retina that may experience either normal or abnormal photoreceptor development.