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Gogate PM, Deshpande M, Wormald RP, Deshpande R, Kulkarni SR Br J Ophthalmol 2003; 87:667-72

Cataract is the chief cause of avoidable blindness in India and throughout the world. There are an estimated 9-12 million blind in India, half of which can be attributed to cataract. It is estimated that another three million develop visually disabling cataracts each year. Cataract extraction accounts for the majority of the workload of ophthalmic units worldwide. Extracapsular cataract extraction with posterior chamber intraocular lens implantation (PCIOL) was the most frequent surgical technique until the past decade.
The use of a smaller incision with the advantages of faster rehabilitation, less astigmatism and better postoperative vision without spectacles led to phacoemulsification becoming the preferred technique where resources are available. However, cost, both in terms of equipment and training has limited its use in the developing world. Thus there is a dichotomy with different standards of care between the developed and the developing world. Manual small incision surgery in which the nucleus is delivered through a 6-6.5 mm scleral tunnel is claimed to have similar advantages to phacoemul-sification.
High quality, high volume cataract surgery is needed in community eye care centers to effectively manage the large backlog of cataract blindness; but so far the effectiveness of manual small incision surgery has not been formally compared to the established extracapsular technique in this setting.
The purpose of this study was to study "manual small incision cataract surgery (MSICS)" for the rehabilitation of cataract visually impaired and blind patients in community based, high volume, eye hospital setting and to compare the safety and effectiveness of MSICS with conventional extracapsular cataract surgery (ECCE).
In this single masked randomized controlled clinical trial, 741 patients, aged 40-90 years, with operable cataract were randomly assigned to receive either MSICS of ECCE and operated upon by one of eight participating surgeons. Intraoperative and postoperative complications were graded and scored according to the Oxford Cataract Treatment and Evaluation Team recommendations. The patients were followed up at 1 week, 6 weeks, and 1 year after surgery and their visual acuity recorded.
This paper reports outcomes at 1 and 6 weeks. 706 of the 74 (95.3%) patients completed the 6 week follow up. 135 of 362 (37.3%) of ECCE group and 165 of 344 (47.9%) of MSICS group had uncorrected visual acuity of 6/18 or better after 6 weeks of follow up. 314 of 362 (86.7%) of ECCE group and 309 of 344 (89.8%) of MSICS group had corrected postoperative vision of 6/18 or better. Four of 362 (1.1%) of ECCE group and six of 344 (1.7%) of MSICS group had corrected postoperative visual acuity less than 6/60. There were no significant differences between the two groups for intraoperative and severe postoperative complications.
MSCIS and ECCE are both safe and effective techniques for treatment of cataract patients in community eye care settings. MSICS needs similar equipment to ECCE, but given better-uncorrected vision.

A clinical follow up of PRK and LASIK in eyes with preoperative abnormal corneal topographies
Schor P, Beer SMC, da Silva O, Takahashi R, Campos M
Br J Ophthalmol 2003; 87:682-5

Refractive surgery is an increasingly popular procedure to decrease spectacle or contact lens dependency. The risks of refractive surgery are low on an individual basis, but the impact on the population must be carefully evaluated by the medical community.
Photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) are two refractive procedures currently leading the field. The number of LASIK procedures has increased and far surpasses the number of PRK procedures owing to faster visual recovery, less pain, and greater ametropic range capability. The intraoperative risks related to LASIK are intrinsically greater than those related to PRK. Postoperative complications related to PRK include haze and regression which have become major limitations of the procedure. Long term complications related to LASIK include ectasia due to corneal weakening, which is not fully understood or well controlled.
The prevention of complications is a major goal in these elective procedures. Realistic patient expectations, night vision disabilities, and transient discomfort must be discussed with all patients before surgery, and a comprehensive ophthalmological examination should be performed. Current technology allows us to diagnose a limited range of corneal diseases; therefore the potential visual results of the procedures in abnormal eyes are not clear.
The purpose of this study was to assess the safety and predictability of photorefractive keratotomy (PRK) and laser in situ keratomileusis (LASIK) based on preoperative corneal topography.
A non-randomised comparative study was carried out on 84 eyes that presented with topographic abnormalities before undergoing PRK (n-44) or LASIK procedures were performed on 168 eyes using the Summit apex plus excimer laser. Topographic abnormalities, including apex displacement (AD), increased asphericity (AS), meridional irregularity (MI), increased inferior superior asymmetry (IS), increased curvature (CU), and combined features (CO), were assessed preoperatively using the Eye Sys analysis system. Safety and predictability of the two procedures were defined as a postoperative visual acuity of 20/40 or better and the loss of one or more lines of spectacle corrected visual acuity (SCVA).
All patients were followed for 6 months. There was a significant loss of best corrected visual acuity in the PRK-AD (p<0.001), PRK-CO (p<0.05), and LASIK-AS (p<0.001) patients. The number of eyes within plus or minus 1.0D of the surgical plan postoperatively was similar in all groups.
These data suggest that although predictability was similar, PRK and LASIK performed in corneas with topographic abnormalities might cause loss of vision.

Comparison of localized nerve fibre layer defects in normal tension glaucoma and primary open angle glaucoma
Woo SJ, Park KH, Kim DM
Br J Ophthalmol 2003;87:695-8

Many researchers have suggested a difference in pathogenesis between normal tension glaucoma (NTG) and primary open angle glaucoma (POAG). Among the evidence supporting this theory were the different patterns of visual field defect and optic nerve head configuration. The frequent occurrence of optic disc haemorrhage and the high incidence of systemic diseases in patients with NTG also suggested that a damaging mechanism other than high intraocular pressure contributed to the glaucomatous damage. Although retinal nerve fibre layer (RNFL) evaluation has become important in detecting glaucomatous nerve damage, quantitative comparison of RNFL photographs between NTG and POAG has been rare.
The purpose of this study was to compare the pattern of localized nerve fiber layer (NFL) defects in normal tension glaucoma (NTG) and primary open angle glaucoma (POAG).
50 NTG eyes and 36 POAG eyes, all with localized NFL defects, were enrolled. On retinal NFL photography, the proximity of the defect to the center of the fovea (angle a) and the sum of the angular width of the defects (angle ß) were determined. Angle a was the angle made by a line from the center of the fovea to the disc canter and a line from the disc center to the disc margin, where the nearest border of the defect met. The patterns of localized NFL defects in NTG and POAG were compared with angles a and ß . Independent t test was used for statistical analysis.
Angle a in NTG (35.1 (SD 20.0)o) was significant smaller than that of POAG (45.9 (21.9)o) (p=0.02), while angle ß in NTG (49.0 (31.9)o) was significantly larger than that of POAG (33.1 (23.9)o) (p=0.01).
The authors concluded that the pattern of NFL defects in NTG was different from that in POAG. Localised NFL defects in NTG were closer to the fovea and wider in width than those in POAG.

Features of abnormal Choroidal circulation in central serous chorioretinopathy

Kitaya N, Nagaoka T, Hikichi T, Sugawara R, Fukui K, Ishiko S, Yoshida A
Br J Ophthalmol 2003;87:709-12

Central serous chrioretinopathy (CSC) is characterized by a focal serous detachment of the neurosensory retina. Fluorescein angiography shows dye leakage from the retinal pigment epithelium (RPE) and subretinal dye pooling. However, fluorescein angiography has not been useful in determining the pathogenesis of CSC because of limitations in imaging the choroidal vessels. Thus, while the clinical features of CSC have been described, its pathogenesis is controversial.
Numerous recent reports have described abnormalities of the choroidal circulation using indocyanine green (ICG) angiography. ICG is a dye that has several advantages over sodium fluorescein for choroidal angiography, in that it binds tightly to plasma proteins and thus prevents marked leakage from fenestrated vessels such as the choriocapillaris. The dye also absorbs and fluoresces in the near infrared range, which enhances visualization of the fluorescence through hemoglobin, RPE, or xantophyll. Using ICG angiography, choroidal vascular abnormalities, such as filling delays of the choroidal arteries and choriocapillaris, venous dilation, and focal hyperfluorescence of the choroids, which indicate hyperpermeability of choroidal vessels, have been reported.
The purpose of this study was to evaluate abnormalities in the choroidal circulation in cases of central serous chorioretinopathy (CSC).
A complete clinical ophthalmological examination was performed using simultaneous fluorescein and indocyanine green (ICG angiography with a confocal scanning laser ophthalmoscopy and the digital images analysed in 36 consecutive patients with acute CSC. To quantify the choroidal circulation, the foveal choroidal blood flow was measured in 11 patients using laser Doppler flowmetry.
Fluorescein angiography showed focal leakage from the retinal pigment epithelium in all patients. ICG angiography revealed delays in arterial filling in 27 eyes (75%). Abnormal choroidal hyperfluorescence was observed in 30 eyes (83%). The choroidal blood flow in eyes with CSC was 45% lower than in fellow eyes (p<0.01).
The author concluded with remarks that decreased choroidal blood flow in CSC was demonstrated for the first time. The decreased choroidal blood flow might be correlated with the small, localized hypofluorescent areas, which may indicate non-perfused areas of the choriocapillaris that are frequently seen during ICG angiography.

Intraocular pressure and visual field loss in primary angle closure and primary open angle glaucomas
Gazzard G, Foster PJ, Devereux JG, Oen F, Chew P, Khaw PT, Seah S
Br J Ophthalmol 2003; 87:720-5

The aetiology of glaucomatous optic neuropathy (GON) is not fully understood. There are many implicated risk factors, the two most consistent of which appear to be intraocular pressure (IOP) and age. However, direct correlations between the extent of visual field loss (VFL) and the level of pretreatment IOP at presentation have been found to be weak for POAG. This probably reflects the multiple interacting risk factors for damage that modify the response of a particular nerve to a given IOP. The probability of developing glaucoma at a certain IOP may be different for different types of glaucoma. Stronger correlations between VFL and IOP have been seen in pseudoexfoliative glaucoma, which has been thought to be a more pressure dependent disease, than in POAG. Primary angle closure glaucoma (PACG) may also be considered to be a more purely pressure dependent disease than POAG.
A strong correlation between pretreatment IOP and the amount of visual field damage present may be an indicator of the extent to which a disease can be considered pressure dependent. Such an association may support the belief that the pathogenetic mechanisms involved in PACG are more pressure dependent. This in turn might have implications for prognosis and the need for clinical trials to explore the extent to which pressure lowering along may be successful in halting the progression of optic nerve damage and consequent VFL.
The purpose of this study was to compare the correlation between visual field loss and the pretreatment intraocular pressure (IOP) in primary angle closure glaucoma (PACG) and primary open angle glaucoma (POAG).
In a cross sectional observational study of 74 patients (43 PACG, 31 POAG), pretreatment IOP was measured at presentation, before treatment was initiated. The severity of visual field loss was assessed by AGIS score, mean deviation (MD), pattern standard deviation (PSD), and corrected pattern standard deviation (CPSD). Glaucomatous optic neuropathy was assessed from simultaneous stereo disc photographs.
There was a stronger correlation between pretreatment IOP and the extent of visual field loss in PACG subjects than in those with POAG for both MD (PACG: Pearson correlation coefficient (r) =0.43, p=0.002; r2=0.19), (POAG: r =0.21, p = 0.13; r2 = 0.04) and AGIS score (PACG: r = 0.41, p = 0.003; r2 = 0.17), (POAG: r = 0.23, p = 0.19; r2 = 0.05 respectively). No such associations were seen for pattern standard deviation (PSD) or corrected pattern standard deviation (CPSD) in either group (p> 0.29). Both horizontal and vertical cup-disc ratio were well correlated with severity of field loss but not with presenting IOP for either diagnosis.
The authors concluded with remarks that the results of the study are consistent with the hypothesis of a greater IOP dependence for optic nerve damage in PACG than POAG and, conversely, a greater importance of other, less pressure dependent mechanisms in POAG compared to PACG.

Interobserver agreement on visual field progression in glaucoma: a comparison of methods
Viswanathan AC, Crabb DP, McNaught AI, Westcott MC, Kamal D, Garway-Heath DF, Fitzke FW, Hitchings RA
Br J Ophthalmol 2003;87:726-30

Several scoring systems have been devised in order to identify visual field progression for the purposes of research but none has found widespread acceptance in general clinical practice. However, unaided clinical judgment is inconsistent: even expert observers show considerable disagreement about whether a given visual field series signifies progression or stability. One possible reason for this is that the standard output of most automated perimeters provides inadequate information relating to progression or stability. Thus, when the clinician is attempting to decide whether or not a given series of outputs constitutes progressive disease; the task involves manually comparing the decibel sensitivity values (or processed versions thereof) of graphical plots for all fields in the series. This task is further complicated by the contributions of "within test" variability (short term fluctuation) and "between test" variability (long term fluctuation), both of which are known to be increased above normal in glaucoma. For these reasons, and because the grids of numbers produced by automated perimeters are easily amenable to numerical analysis, a great variety of software and statistical approaches have been taken to aid in the determination of visual field progression in glaucoma. One set of methods rely on estimates of change in summary measures of the field such as regression analysis of the mean defect value, mean deviation, other global measures, measurement of whole field and quadratic sensitivity losses, and regression analysis of various estimates of the sensitivity of the whole field or parts of it. However, the analysis of summary measures, whether based on the whole field or on clusters of points within it, has been found to be "remarkably poor" and of little value" in detecting glaucomatous change. Summary measures largely or completely ignore the detailed spatial information contained within computerized field tests and are insensitive to early localized change. Furthermore, different regions of the visual field may deteriorate at different rates.
The purpose of this study was to examine the level of agreement between clinicians in assessing progressive deterioration in visual field series using two different methods of analysis.
Each visual field series satisfied the following criteria: more than 19 reliable fields, patient age over 40 years, macular threshold at least 30 db. The first three fields in each series were excluded to minimize learning effects: the following 16 were studied. Five expert clinicians assessed the progression status of each series using both standard Humphrey printouts and point wise linear regression (PRO-GRESSOR). The level of agreement between the clinicals was evaluated using a weighted kappa statistic.
A total of 432 tests comprising 27 visual field series of 16 tests each were assessed by the clinicians. The level of agreement between the clinicians was always higher when they used PROGRESSOR (median kappa = 0.59) than when they used Humphrey printouts (median kappa = 0.32). This was statistically significant (p = 0.006, Wilcoxon matched pairs signed rank sum test).
The authors concluded that the agreement between expert clinicians about visual field progression status is poor when standard Humphrey printouts are used even when the field series studied are long and consist solely of reliable fields. Under these ideal conditions, clinicians agree more closely about patients visual field progression status when using PROGRESSOR than when inspecting series of Humphrey printouts.

Extent of foveal tritanopia in diabetes mellitus
Davies N, Morland A
Br J Ophthalmol 2003;87:742-6.

Short wavelength sensitive (S) cones are fewer in number than medium wavelength (M) and long wavelength sensitive (L) cones, representing approximately 10% of the total cone population. An early study showed that the fovea was relatively insensitive to short wavelength light and that colour vision was impaired, colour matching being possible with two primaries instead of the usual three. It was thought initially that an absence of rods was responsible for the changes seen in visual function. Willmer and Wright1, however, demonstrated the tritanopic nature of the colour vision defect. They showed that dichromatic colour matches consistent with congenital tritanopia could be made for a 20 bipartite field. A similar tritanopic colour vision deficit was reported for small fields generally, suggesting that the fovea may not be unique in this respect. Other theories suggested that the apparent tritanopic deficit in the fovea might be due to Troxler fading or to preretinal screening of short wavelength light by the increasing density of the macular pigment. Anatomical study has also demonstrated that the center of the fovea appears to be devoid of S-cones in primates. The extent of the foveal tritanopic region is around 20-25 minutes of arc.
Studies of the Farnsworth Munsell 100 Hue test in diabetics have shown an increased error score. Some studies have shown generalized loss of hue discrimination with no specific axis, while others have demonstrated a red-green axis loss. However, three studies have shown a loss of colour discrimination on a tritanopic axis in patients with diabetes.
The purpose of this study was to use a colour matching technique to test the hypothesis that the foveal tritanopic zone is increased in size in diabetes mellitus.
A Wright tristimulus colorimeter was adapted for small field colour matching and colour matches were performed on bipartite fields in the range 12'to 60' of arc. The reference stimulus was 490 nm desaturated with 650 nm and the matching stimulus consisted of either two wavelengths (530 nm and 650 nm) or three (460 nm, 530 nm, and 650 nm). The size of the zone of foveal tritanopia was measured using two alternative forced choice presentations of dichromatic and trichromatic matches made by the observer for different field sizes. 21 diabetic and 12 controls performed the experiment.
The results for the controls show a normal distribution, with a median foveal tritanopic zone of 18' of arc. The median for the diabetic patients was also 18' of arc, but the distribution showed a significant skew to the right. A non-parametric test shows a significant difference in comparison with the controls (p = 0.01), with several subjects having extensive zones of foveal tritanopia, reaching up to 1 degree.
The authors concluded that the majority of diabetic subjects the extent of foveal tritanopia is normal; however, there is good evidence that in a small number of subjects the size of the zone is significantly increased. This indicates S-cone pathway damage that is sufficiently severe to lead to dichromatic colour vision in the fovea.
1. Willmer E, Wright W. Colour sensitivity of the fovea centralis. Nature 1945; 156:119-21.

Assessment of colour vision as a screening test for sight threatening diabetic retinopathy before loss of vision
Ong GL, Ripeley LG, Newsom RSB, Casswell AG
Br J Ophthalmol 2003;87:747-52

Despite effective treatments, diabetic retinopathy is still the most common cause of blindness in industrialized nations among the 20-60 years old age group.
The detection of presymptomatic sight threatening diabetic retinopathy (STDR) remains difficult. Early treatment of proliferative diabetic retinopathy and diabetic maculopathy improves visual outcome. However, STDR should be detected before visual damage has taken place as only a minority of patients have improvement in vision following laser treatment. With effective screening blind registrations for patients under the age of 70 could be reduced by 10%. Screening is clinically viable and cost effective and will be increasingly important as the incidence of diabetes rises over the next 10 years.
The purpose of this study was to assess the effects of sight threatening diabetic retinopathy (STDR) on colour vision and to evaluate automated tritan contrast threshold (TCT) testing for STDR screening before significant visual loss.
Patients were recruited from a hospital based photographic screening clinic. All subjects underwent best corrected Snellen visual acuity (BCVA) and those with 20/30 vision or worse were excluded. Automated TCT was performed with a computer controlled, cathode ray tube based technique. The system produced a series of sinusoidal, standardized equiluminant chromatic gratings along a tritan confusion axis. Grading of diabetic retinopathy was made by one of the team of experienced ophthalmic registrars (SpR) using slit lamp biomicroscopy and a 78D lens; HbA1c and urine albumin were also tested.
Patients with STDR had significantly worse TCT despite normal BCVA (p<0.0001). TCT yielded a sensitivity of 100% for detecting diabetic maculopathy and 94% for STDR with a specificity of 95%. Logistic regression analyses showed that TCT (p<0.001) and HbA1c (p<0.05) correlated significantly with he presence of STDR but duration of diabetes, urine albumin counts, and BCVA failed to show any significant correlation. No associations between TCT and duration of disease, TCT and HbA1c and TCT and urine albumin counts were found.
The authors concluded that tritan colour vision deficiency was observed in patients with STDR despite their normal BCVA. These results indicate that automated TCT assessment is an effective and clinically viable technique for detecting STDR, particularly diabetic maculopathy, before visual loss.

Impact of smoking on the response to treatment of thyroid associated ophthalmopathy
Eckstein A, Quadbeck B, Mueller G, Rettenmeier AW, Hoermann R, Mann K, Steuhl P, Esser J
Br J Ophthalmol 2003;87:773-6

Thyroid associated ophthalmopathy (TAO) occurs more frequently and tends to be more severe in smokers than non-smokers. Current but not lifetime tobacco use correlates with the severity of TAO. A prospective study revealed that smoking increases the risk of ophthalmopathy progression after radioiodine therapy. A retrospective study showed that smoking decreases the efficacy of orbital irradiation and of glucocoriticoid therapy. According to another retrospective investigation, however, the final outcome does not seem to be influenced by smoking habits.
In this prospective study, tobacco use was evaluated by quantitative analysis of the haemoglobin adduct N-2-hydroxyethylvaline (HEV). HEV is formed from hydroxyethylating agents of cigarette smoke and reflects the integrated "smoking dose" over the lifetime of erythrocytes. Although other sources of ethylene oxide (that is, exhaust fumes, endogenous ethylene production") influence the HEV concentration, a linear relation between the number of cigarettes smoked per day and the HEV levels has been observed (correlation coefficient r = 0.54) indicating that HEV is a suitable biomarker for active and passive smoking.
In patients with Groves' disease, smoking considerably increases the incidence and severity of thyroid associated ophthalmopathy (TAO). The authors sought to determine if smoking also influences the course of TAO during treatment, and the efficacy of therapy.
41 smokers and 19 non-smokers with moderate untreated TAO were included in this prospective study. All patients were treated with steroids and, 6 weeks after the beginning of drug therapy, with orbital irradiation. Follow up was performed 1.5,4.5, 7.5, and 12 months after beginning of the study. Proptosis, clinical activity score (CAS), and motility were evaluated. The extent of smoking was derived from the concentration of the haemoglobin adduct N-2-hydroxyethylvaline (HEV), a parameter of long term smoking.
There was no difference in the clinical manifestations of TAO between smokers and non-smokers at the beginning of treatment. However, CAS decreased (p<0.05) and motility improved (p<0.02) significantly faster and to a greater extent in non-smokers than smokers. Inverse correlations between the CAS decrease and the HEV levels observed 4.5 and 7.5 months after the beginning of treatment and between the improvement of motility and the HEV levels after 1.5, 4.5, and 7.5 months indicated a dose dependence. Mean HEV levels did not vary much during the follow up period and were significantly different in smokers (mean 5.4 (SD 2.7) ug/l) and non-smokers (mean 1.8 (1.3) ug/l; p<0.01).
The authors concluded that smoking influences the course of TAO during treatment in a dose dependent manner. The response to treatment is delayed and considerably poorer in smokers.