To evaluate the effects of inferior oblique muscle recession (IOR) in cases of laterally incomitant hypertropia <10 prism dioptres (PD) in central gaze thact 2t are clinically consistent with superior oblique palsy (SOP).
We retrospectively reviewed patients with SOP and hypertropias <10 PD in central gaze who underwent graded IOR. Primary outcomes were reduction of lateral incomitance and number of overcorrections in central gaze.
Twenty-five patients were included. Mean follow-up was 13.8 months (range 1.4–66). Mean central gaze hypertropia decreased from 5.6±2.1 to 0.2±1.6 PD (p<0.001). Contralateral gaze hypertropia decreased from 15.9±7.6 to 2.3±3.3 PD (p<0.001). Lateral incomitance (central vs contralateral gaze) was 10.3±6.9 PD preoperatively and 2.0±3.0 PD postoperatively (p<0.001). There were two patients overcorrected in central gaze, and one patient overcorrected in downgaze. One patient necessitated further surgery for overcorrection.
Although small hypertropias can be treated with prisms or small, adjustable inferior rectus recessions, IOR collapses incomitance without causing much overcorrection. IOR is a reasonable treatment for small, laterally incomitant hypertropia due to SOP.
Three types of open-angle glaucoma (OAG) – primary, pigmentary, and pseudoexfoliative – are frequently encountered. The aim of this study was to compare demographic, ocular, and systemic medical information collected on people with these three OAG types at diagnosis, and determine if the OAG type affected prognosis.
Information on 607 participants of the Collaborative Initial Glaucoma Treatment Study was accessed. Descriptive statistics characterized their demographic, ocular, and medical status at diagnosis. Comparisons were made using analysis of variance (ANOVA), and chi-square or Fisher exact tests. Multinomial, mixed, and logistic regression analyses were also performed.
Relative to people with primary OAG, those with pigmentary OAG were younger, more likely to be white, less likely to have a family history of glaucoma, and were more myopic. Those with pseudoexfoliative OAG were older, more likely to be white, more likely to be female, less likely to have bilateral disease, and presented with higher IOP and better VA. The type of glaucoma was not associated with intraocular pressure or visual field progression during follow-up.
Characteristics of newly-diagnosed enrollees differed by the type of OAG. While some of these differences relate to the pathogenesis of OAG type, other differences are noteworthy for further evaluation within population-based samples of subjects with newly-diagnosed OAG.
Macula; retina; choroid; angiogenesis; drugs
Gelatinous drop-like corneal dystrophy (GDLD), also known as familial subepithelial corneal amyloidosis, is an autosomal recessive disorder that causes progressive corneal opacity due to accumulation of amyloid fibrils in the corneal stroma. Genetic analyses have revealed that a mutation in membrane component chromosome 1 surface marker 1 gene is responsible for GDLD. However, the mechanism of amyloid formation in the corneal stroma remains unclear. The present study attempted to reveal the role of advanced glycation end products (AGE) and d-amino acids in amyloid formation in GDLD.
Informed consent was obtained from five patients with GDLD, three patients with bullous keratopathy and three patients with interstitial keratitis and all the specimens were analysed. Localisation of amyloid fibrils was analysed using Congo-red and thioflavin T staining. In addition, the localisation of AGE (Nɛ-carboxy(methyl)-l-lysine, pyrraline and pentosidine) and d-β-aspartic acid-containing proteins, a major form of d-amino acid-containing proteins, was analysed immunohistochemically.
In all GDLD specimens, strong immunoreactivity to AGE and d-β-aspartic acid-containing proteins was detected in the subepithelial amyloid-rich region. In contrast, amyloid fibrils, AGE, or d-amino acid-containing proteins were slightly detected in the corneal stroma of patients with bullous keratopathy and interstitial keratitis.
Abnormally accumulated proteins rich in AGE and d-β-aspartic acid co-localise in the amyloid lesions in GDLD. These results indicate that non-enzymatic post-translational modifications of proteins, including AGE formation and isomerisation of aspartyl residues, will be the cause as well as the result of amyloid fibril formations in GDLD.
Advanced glycation end products; biochemistry; cornead-amino acids; d-β-aspartic acid; familial subepithelial corneal amyloidosis; GDLD; gelatinous drop-like corneal dystrophy; M1S1; Nɛ-(carboxy)methyl-l-lysin; optics and refraction; pathology; pentosidine; physiology; pyrraline; treatment surgery; tumour-associated calcium signal transducer 2 (TACSTD2)
Retinal endothelial cells are crucially involved in the genesis of diabetic retinopathy which is treated with vascular endothelial growth factor (VEGF) inhibitors. Of these, ranibizumab can completely restore VEGF-induced effects on immortalised bovine retinal endothelial cells (iBREC). In most experiments supporting diabetic retinopathy therapy with bevacizumab, only non-retinal EC or retinal pigment epithelial cells have been used. Also, bevacizumab but not ranibizumab can accumulate in retinal pigment epithelial cells.
To investigate the effects of bevacizumab on VEGF-induced changes of iBREC properties and potential uptake and accumulation of both inhibitors.
Uptake of VEGF inhibitors by iBREC with or without pretreatment with VEGF165 was visualised by immunofluorescence staining and western blot analyses. Measured transendothelial resistance (TER) of iBREC (±VEGF165) showed effects on permeability, indicated also by the western blot-determined tight junction protein claudin-1. The influence of bevacizumab on proliferation and migration of iBREC was studied in the presence and absence of VEGF165.
Bevacizumab strongly inhibited VEGF-stimulated and basal migration, but was less efficient than ranibizumab in inhibiting VEGF-induced proliferation or restoring the VEGF-induced decrease of TER and claudin-1. This ability was completely lost after storage of bevacizumab for 4 weeks at 4°C. Ranibizumab and bevacizumab were detectable in whole cell extracts after treatment for at least 1 h; bevacizumab accumulated during prolonged treatment. Ranibizumab was found in the membrane/organelle fraction, whereas bevacizumab was associated with the cytoskeleton.
Both inhibitors had similar effects on retinal endothelial cells; however, some differences were recognised. Although barrier properties were not affected by internalised bevacizumab in vitro, potential adverse effects due to accumulation after repetitive intravitreal injections remain to be investigated.
Retinal endothelial cells; VEGF inhibition; diabetic macular oedema; diabetic retinopathy; biochemistry; diagnostic tests/investigation; macula; neovascularisation; retina
Cornea; lens and zonules
To investigate age-related lesions in the far-anterior retina that migrate from the ciliary body (CB) and how they affect the neural retina and retinal pigmented epithelium (RPE).
One eye from three healthy subjects aged 87, 92 and 93 years were used. Retinae were photographed, embedded in resin and then sectioned at 2 μm.
Multiple elliptically shaped lesions were present in the CB. Larger lesions extended into the peripheral retina. Lesions resulted from deposits that had lenticular qualities. These develop centrally along Bruch's membrane sweeping away the RPE, such that piles of RPE cells were present around the deposits that resulted in retinal atrophy. The internal composition of the deposits revealed large numbers of spherical bodies, unlike those seen in drusen. RPE cells adjacent to these deposits and their underlying lesions became highly irregular, with melanin granules spacing themselves out within the cell and adopting similar orientations. This is a highly distinctive feature.
These far-anterior deposits were different in nature from drusen in terms of morphology, composition and origin. They swept away the RPE, exposing the Bruch's membrane and isolating the retina, leading to atrophy. They appeared to originate from the CB and progressed centrally. The deposits may have developed from the ciliary muscle, which would account for their elongated orientation. Their impact on melanin distribution in RPE cells was unexpected and unusual, implying that they release a signal that influences melanin organisation.
Lesions/deposits; far-peripheral retina; RPE; retina; ciliary body; degeneration; pathology
To determine the relationship between retinal ischaemia and the presence of macular oedema (DMO) in patients with diabetic retinopathy (DR) using ultra-widefield fluorescein angiography (UWFA) imaging.
A retrospective review of 122 eyes of 70 treatment-naïve diabetic patients who underwent diagnostic UWFA using the Optos 200Tx imaging system. Two independent, masked graders quantified the area of retinal ischaemia. Based on clinical examination and optical coherence tomography (OCT), each patient was given a binary classification as either having DMO or no DMO. McNemar's test (with Yates' correction as indicated) and a two-sample test of proportions were used to determine the relationship between DMO and ischaemia for binary and proportional data, respectively. Linear and logistic models were constructed using generalised estimating equations to test relationships between independent variables, covariates and outcomes while controlling for inter-eye correlation, age, gender, haemoglobin A1c, mean arterial pressure and dependence on insulin.
Seventy-six eyes (62%) exhibited areas of retinal ischaemia. There was a significant direct correlation between DMO and peripheral retinal ischaemia as seen on UWFA (p<0.001). In addition, patients with retinal ischaemia had 3.75 times increased odds of having DMO compared with those without retinal ischaemia (CI 1.26 to 11.13, p<0.02).
Retinal ischaemia is significantly correlated with DMO in treatment-naïve patients with DR. UWFA is a useful tool for detecting peripheral retinal ischaemia, which may have direct implications in the diagnosis, follow-up and treatment such as targeted peripheral photocoagulation.
Ultra-wide field imaging; fluorescein angiography; diabetes; diabetic retinopathy; diabetic macular oedema; retina; epidemiology; retina
To evaluate the cost-effectiveness of ranibizumab as either monotherapy or combined with laser therapy, compared with laser monotherapy, in the treatment of diabetic macular oedema (DME) causing visual impairment from a UK healthcare payer perspective.
A Markov model simulated long-term outcomes and costs of treating DME in one eye (BCVA ≤75 letters) based on data from the RESTORE Phase III trial. Outcomes measured in quality-adjusted life-years (QALYs) were simulated for a 15-year time horizon based on 12-month follow-up from RESTORE and published long-term data. Costs included treatment, disease monitoring, visual impairment and blindness (at 2010 price levels).
Ranibizumab monotherapy resulted in a 0.17 QALY gain at an incremental cost of £4191 relative to laser monotherapy, yielding an incremental cost-effectiveness ratio (ICER) of £24 028. Probabilistic sensitivity analysis showed a 64% probability of being cost-effective at a threshold of £30 000 per QALY. Combined ranibizumab and laser therapy resulted in a 0.13 QALY gain at an incremental cost of £4695 relative to laser monotherapy (ICER £36 106; 42% probability of ICER <£30 000).
Based on RESTORE 1-year follow-up data, ranibizumab monotherapy appears to be cost-effective relative to laser monotherapy, the current standard of care. Cost-effectiveness of combination therapy is less certain. Ongoing studies will further inform on disease progression and the need for additional ranibizumab treatment.
Ranibizumab; diabetic macular oedema; visual impairment; cost-effectiveness; macula; treatment medical; clinical trial; epidemiology; public health; vision; retina
UK estimates of age related macular degeneration (AMD) occurrence vary.
To estimate prevalence, number and incidence of AMD by type in the UK population aged ≥50 years.
Age-specific prevalence rates of AMD obtained from a Bayesian meta-analysis of AMD prevalence were applied to UK 2007–2009 population data. Incidence was estimated from modelled age-specific prevalence.
Overall prevalence of late AMD was 2.4% (95% credible interval (CrI) 1.7% to 3.3%), equivalent to 513 000 cases (95% CrI 363 000 to 699 000); estimated to increase to 679 000 cases by 2020. Prevalences were 4.8% aged ≥65 years, 12.2% aged ≥80 years. Geographical atrophy (GA) prevalence rates were 1.3% (95% CrI 0.9% to 1.9%), 2.6% (95% CrI 1.8% to 3.7%) and 6.7% (95% CrI 4.6% to 9.6%); neovascular AMD (NVAMD) 1.2% (95% CrI 0.9% to 1.7%), 2.5% (95% CrI 1.8% to 3.4%) and 6.3% (95% CrI 4.5% to 8.6%), respectively. The estimated number of prevalent cases of late AMD were 60% higher in women versus men (314 000 cases in women, 192 000 men). Annual incidence of late AMD, GA and NVAMD per 1000 women was 4.1 (95% CrI 2.4% to 6.8%), 2.4 (95% CrI 1.5% to 3.9%) and 2.3 (95% CrI 1.4% to 4.0%); in men 2.6 (95% CrI 1.5% to 4.4%), 1.7 (95% CrI 1.0% to 2.8%) and 1.4 (95% CrI 0.8% to 2.4%), respectively. 71 000 new cases of late AMD were estimated per year.
These estimates will guide health and social service provision for those with late AMD and enable estimation of the cost of introducing new treatments.
Prevalence; incidence; AMD; UK; epidemiology; clinical trial
Currently, the border of idiopathic epiretinal membranes (iERM) is outlined intraoperatively using vital dyes. Therefore, the authors set out to investigate the role of the preoperative retinal thickness map (RTM) of the optical coherence tomography (OCT) in identifying the shape and the size of the iERMs.
15 eyes of 15 patients with iERM who underwent vitrectomy with indocyanine green-assisted membrane peeling were included in this study. The authors analysed the intraoperative fundus images and preoperative Cirrus HD-OCT to detect the shape and the size of the iERM as well as the shape and the size of each thickness-indicating colour (white, red, orange and yellow) on the RTM, respectively. The correlation of areas and morphologic characteristics between both groups was explored.
Analysis of iERM morphologic characteristics (shape) showed a similarity between the iERM contour and the corresponding RTM in 13 cases (86.6%). Furthermore, retinal folds were found in six iERMs and in their corresponding RTMs. Analysis of iERM size (area) revealed a positive correlation between the iERM area and each studied coloured area in RTM. The most significant correlation was between iERM and the red area (440–480 μm; r=0.87, p<0.0001).
The iERM-related retinal folds are clearly distinguishable on the HD-OCT. The red area in RTM representing the 440–480 μm retinal thickness can be a reliable predictor of the extent and the shape of the iERM.
Optical coherence tomography; epiretinal membrane; indocyanine green; retinal thickness map; retina; vitreous; treatment surgery; imaging; neovascularisation; treatment lasers
In proliferative diabetic retinopathy (PDR), vascular endothelial growth factor (VEGF) and connective tissue growth factor (CTGF) may cause blindness by neovascularisation followed by fibrosis of the retina. It has previously been shown that a shift in the balance between levels of CTGF and VEGF in the eye is associated with this angiofibrotic switch. This study investigated whether anti-VEGF agents induce accelerated fibrosis in patients with PDR, as predicted by this model.
CTGF and VEGF levels were measured by ELISA in 52 vitreous samples of PDR patients, of which 24 patients had received intravitreal bevacizumab 1 week to 3 months before vitrectomy, and were correlated with the degree of vitreoretinal fibrosis as determined clinically and intra-operatively.
CTGF correlated positively, and VEGF correlated negatively with the degree of fibrosis. The CTGF/VEGF ratio was the strongest predictor of fibrosis. Clinically, increased fibrosis was observed after intravitreal bevacizumab.
These results confirm that the CTGF/VEGF ratio is a strong predictor of vitreoretinal fibrosis in PDR, and show that intravitreal anti-VEGF treatment causes increased fibrosis in PDR patients. These findings provide strong support for the model that the balance of CTGF and VEGF determines the angiofibrotic switch, and identify CTGF as a possible therapeutic target in the clinical management of PDR.
Angiogenesis; choroid; CTGF; diabetic retinopathy; drugs; fibrosis; imaging; macula; retina; VEGF; vitreous
To elucidate the morphological features of optic neuropathy in an ischaemic model of glaucoma in macaque monkeys.
The regional degenerative process was investigated by experimentally occluding the paraoptic branches of the lateral short posterior ciliary artery, that is, the circle of Haller and Zinn, in 11 eyes. Morphological changes in nerve fibres in the lamina cribrosa were evaluated by histopathology, immunocytochemistry and angiography, and the findings were compared with those observed in an aged macaque with spontaneous glaucomatous optic neuropathy.
Retinal ganglion cell axons were grouped in bundles and traversed through pores in columns of the lamina cribrosa. The processes of astrocytes extended to the bundles, and capillaries branched in surrounding connective tissue from the circular arterioles. Experimental ischaemia induced time-dependent anoxic deterioration of phosphorylated fibres in the temporal arcuate zone, accompanied by glial proliferation. A monkey with spontaneous visual impairment had nerve fibre loss and gliosis with collagenous proliferation in the temporal hemisphere, suggesting glaucomatous neuropathy.
Circulatory interference in the circle of Haller and Zinn caused time-dependent deterioration in the area where anoxic segmental degeneration is associated with pathogenesis of open-angle glaucoma.
Experimental glaucoma; circle of Haller and Zinn; ischaemic optic neuropathy; macaque glaucoma; glaucoma
Keratoprosthesis (KPro) devices are prone to long-term corrosion and microbiological assault. The authors aimed to compare the inflammatory response and material dissolution properties of two candidate KPro skirt materials, hydroxyapatite (HA) and titania (TiO2) in a simulated in vitro cornea inflammation environment.
Lipopolysaccharide-stimulated cytokine secretions were evaluated with human corneal fibroblasts on both HA and TiO2. Material specimens were subjected to electrochemical and long-term incubation test with artificial tear fluid (ATF) of various acidities. Topography and surface roughness of material discs were analysed by scanning electron microscopy and atomic force microscopy.
There were less cytokines secreted from human corneal fibroblasts seeded on TiO2 substrates as compared with HA. TiO2 was more resistant to the corrosion effect caused by acidic ATF in contrast to HA. Moreover, the elemental composition of TiO2 was more stable than HA after long-term incubation with ATF.
TiO2 is more resistant to inflammatory degradation and has a higher corrosion resistance as compared with HA, and in this regard may be a suitable material to replace HA as an osteo-odonto-keratoprosthesis skirt. This would reduce resorption rates for KPro surgery.
OOKP; microbial infection; material dissolution; artificial tear fluid; cornea; biochemistry; prosthesis; microbiology; contact lens; stem cells; lens and zonules; treatment surgery; epidemiology; experimental and animal models; ocular surface; genetics; imaging; treatment lasers
To study tissue remodelling and wound healing after retinal pigment epithelium (RPE) tears due to age-related macular degeneration.
Retrospective longitudinal study of 36 eyes (33 patients) with RPE tears. Imaging was performed using fundus autofluorescence (FAF) (λ=488 nm) and spectral-domain optical coherence tomography (SD-OCT). Presence of intraretinal hyper-reflective dots in SD-OCT, which correlated with hyperfluorescent dots in FAF, indicating RPE migration was studied. Morphology of subretinal mass and RPE layer integrity in the RPE denuded area over time were examined.
7 of 36 eyes (19.4%) showed patchy or hazy hyperfluorescent areas in FAF, and the majority of eyes (83.3%) showed hyper-reflective dots, which possibly represent intraretinal RPE migration and hard exudates. Homogenous subretinal mass was encountered in about half of all cases. In one case (2.8%), the RPE layer proliferated and covered the defect.
SD-OCT and FAF showed a considerable amount of RPE proliferation, migration and repopulation. Intraretinal RPE migration did not form a functional RPE layer. A small defect might be repaired by cell proliferation. But this RPE proliferation is not sufficient to cover large defects.
Retinal pigment epithelium tear; pigment migration; spectral-domain optical coherence tomography; fundus autofluorescence; macula; pharmacology; neovascularisation; drugs; clinical trial; treatment surgery
To compare the efficacy and safety of 3% diquafosol ophthalmic solution with those of 0.1% sodium hyaluronate ophthalmic solution in dry eye patients, using mean changes in fluorescein and rose bengal staining scores as endpoints.
Trial design and methods
In this multicenter, randomised, double-masked, parallel study of 286 dry eye patients with fluorescein and rose bengal staining scores of ≥3 were randomised to the treatment groups in a 1 : 1 ratio. Efficacy and safety were evaluated after drop-wise instillation of the study drug, six times daily for 4 weeks.
After 4 weeks, the intergroup difference in the mean change from baseline in fluorescein staining score was −0.03; this verified the non-inferiority of diquafosol. The mean change from baseline in rose bengal staining score was significantly lower in the diquafosol group (p=0.010), thus verifying its superiority. The incidence of adverse events was 26.4% and 18.9% in the diquafosol and sodium hyaluronate groups, respectively, with no significant difference.
Diquafosol (3%) and sodium hyaluronate (0.1%) exhibit similar efficacy in improving fluorescein staining scores of dry eye patients, whereas, diquafosol exhibits superior efficacy in improving rose bengal staining scores. Diquafosol has high clinical efficacy and is well tolerated with a good safety profile.
Clinical Trial; Conjunctiva; Cornea; Drugs; Tears
Choroid; Neoplasia; Genetics; Imaging; Diagnostic tests/Investigation
To compare the retinal sensitivity and frequency of microscotomas found by spectral domain optical coherence tomography (SD-OCT) combined with scanning laser ophthalmoscopy (SLO) microperimetry after idiopathic macular hole closure, in eyes that underwent internal limiting membrane (ILM) peeling and eyes that did not.
This was a retrospective, non-randomised, comparative study. Combined SD-OCT and SLO microperimetry was performed in 16 consecutive eyes after closure of an idiopathic macular hole. A customised microperimetry pattern with 29 measurement points was used. The ILM was peeled in 8/16 eyes. The main outcome measure was mean retinal sensitivity.
Mean retinal sensitivity (in dB) was lower after peeling: 9.80±2.35 dB with peeling versus 13.19±2.92 without (p=0.0209). Postoperative microscotomas were significantly more frequent after ILM peeling: 11.3±6.6 points with retinal sensitivity below 10 dB in eyes that underwent peeling versus 2.9±4.6 in those that did not (p=0.0093).
These results suggest that ILM peeling may reduce retinal sensitivity, and significantly increase the incidence of microscotomas. Until a prospective trial confirming or not these results, it seems justified to avoid peeling the ILM when its potential benefit seems minor or unproved, and when peeling is carried out, to limit the surface peeled to the bare minimum.
Retina; Macula; Treatment Surgery; Imaging; Vision
To describe subretinal debris found on ultrastructural examination in an eye with macular telangiectasia (MacTel) type 2 and on optical coherence tomography (OCT) in a subset of patients with MacTel type 2.
Blocks from the mid-periphery and temporal perifovea of an eye with clinically documented MacTel type 2 were examined with electron microscopy (EM). Cases came from the Sydney centre of the MacTel project and the practices of the authors.
On EM examination, subretinal debris was found in the perifovea with accumulation of degenerate photoreceptor elements in the subretinal space. Despite the substantial subretinal debris, there was minimal retinal pigment epithelial (RPE) reaction. Focal defects were seen in the inner limiting membrane in the perifovea. Of the 65 Sydney MacTel project participants, three (5%) had prominent yellow material at the fovea. OCT revealed smooth mounds between the RPE and the ellipsoid region. The material was hyperautofluorescent.
This study suggests that subretinal accumulation of photoreceptor debris may be a feature of MacTel type 2. Ultrastructural and OCT evidence of disease beyond the vasculature, involving photoreceptors and Muller cells, is presented.
Retina; Macula; Pathology; Imaging; Degeneration
The aim of the study was to describe the clinical and genetic features of 15 Italian patients with Bietti crystalline dystrophy (BCD).
All study participants underwent a complete ophthalmological examination, including standard electroretinogram (ERG), optical coherence tomography, microperimetry, autofluorescence and multifocal electroretinogram. The 11 exons of the CYP4V2 gene were sequenced. The effect of mutations on protein function was estimated by a combination of web based programs.
15 patients (eight women, 7 men, aged 29–60 years) with BCD were recruited into this study. Sequencing of CYP4V2 revealed nine sequence variants in four unrelated families and six isolated individuals with BCD. Seven of these variants were novel. Among the patients, even with the same genotype, considerable variability in phenotypic expression with different degrees of accumulation of the typical intraretinal crystalline deposits was detected. Moreover, we found that more than 50% of patients had recordable standard ERG responses and in two patients the responses were within normal limits after 20 years of symptom onset.
In conclusion, we have reported seven new mutations and illustrated the large range of genotypic and phenotypic variability in BCD, highlighting the lack of a clear genotype–phenotype correlation and underlining the existence of less severe clinical manifestations, probably linked to relatively mild mutations.
Retina; Genetics; Degeneration
To study the variability of central retinal thickness (CRT), its concordance to the fellow eye, and the implications for designing future clinical trials using spectral-domain optical coherence tomography (SD-OCT).
Cross-sectional retrospective analysis of European Genetic Database. 632 eyes of 316 subjects over 60 years of age without macular pathology were examined using SD-OCT.
Mean CRT was 280.22 µm and 281.02 µm for the right and left eyes, respectively. There was a strong concordance for all measured values between right and left eyes. Men had significantly thicker CRT than women. Variation up to 23 µm difference between both eyes was seen. To detect a change of at least 30 µm in CRT, a sample size of 90 or 176 per group is needed for a single-arm or double-arm study, respectively (α=0.05, power=0.80, no loss to follow up, assuming SD in future studies=100 µm).
Clinical trials using CRT as an endpoint are feasible in terms of sample size needed.
Imaging; Macula; Retina