Parwez Hossain

Recent advances in ophthalmic anterior segment imaging: a new era for ophthalmic diagnosis?

Anterior segment imaging is a rapidly advancing field of ophthalmology. New imaging modalities, such as rotating Scheimpflug imaging (Pentacam-Scheimpflug) and anterior segment optical coherence tomography (Visante OCT and Slit-Lamp OCT), have recently become commercially available. These new modalities supplement the more established imaging devices of Orbscan scanning slit topography and ultrasound biomicroscopy (UBM). All devices promise quantitative information and qualitative imaging of the cornea and anterior chamber. They provide a quantitative angle estimation by calculating the angle between the iris surface and the posterior corneal surface. Direct angle visualisation is possible with the OCT devices and UBM; they provide images of the scleral spur, ciliary body, ciliary sulcus and even canal of Schlemm in some eyes. Pentacam-Scheimpflug can measure net corneal power, a feature particularly useful for cataract patients having undergone previous corneal surgery. Anterior segment OCT can measure corneal flap depth following LASIK and anterior chamber width prior to phakic intraocular lens implantation. The arrival of the new imaging devices may herald the dawn of a new era for ophthalmic diagnosis, particularly in view of the ease and non-contact nature of examination.

Geographic variations in microbial keratitis: an analysis of the peer-reviewed literature.

The epidemiology of microbial keratitis has been investigated in several studies by analysis of organisms cultured from corneal scrapes. However, a comparison of the frequency of different organisms causing keratitis in different parts of the world is lacking. The authors present a review incorporating an analysis of data from studies worldwide. The data provide a comparison of the frequency of culture-positive organisms found in different parts of the world. Associations between a countrys gross national income and types of causative organism are explored. The highest proportion of bacterial corneal ulcers was reported in studies from North America, Australia, The Netherlands and Singapore. The highest proportion of staphylococcal ulcers was found in a study from Paraguay, while the highest proportion of pseudomonas ulcers was reported in a study from Bangkok. The highest proportions of fungal infections were found in studies from India and Nepal. The Spearman correlation coefficient demonstrated statistically significant correlations between gross national income and percentages of bacterial (0.85 (95% CI 0.68 to 0.91, p<0.0001)), fungal (–0.81 (95% CI −0.90 to −0.66, p<0.0001)) and streptococcal (−0.43 (95% CI −0.66 to −0.12, p=0.009)) isolates.

The management of retinal vein occlusion: is interventional ophthalmology the way forward?

Retinal vein occlusions (RVO) are the second commonest sight threatening vascular disorder. Despite its frequency treatments for RVO are unsatisfactory and include several that have not been tested by large, well designed, prospective, randomised controlled trials. There is also the lack of long term follow up in many of the available small uncontrolled studies, and the timings of interventions are haphazard. This review aims to evaluate the current knowledge relating to the pathogenesis, suggested treatments for the different types of RVO, and their complications. Isovolaemic haemodilution is of limited benefit and should be avoided in patients with concurrent cardiovascular, renal, or pulmonary morbidity. Evidence to date does not support any therapeutic benefit from radial optic neurotomy, optic nerve decompression, or arteriovenous crossing sheathotomy on its own. Vitrectomy combined with intravenous thrombolysis may offer promise for central RVO. Similarly, vitrectomy combined with arteriovenous sheathotomy intravenous tissue plasminogen activator may offer benefits for branch RVO. RVOs occur at significantly high frequency to allow future prospective randomised controlled studies to be conducted to evaluate the role of different therapeutic modalities singly or in combination.

The journey to femtosecond laser-assisted cataract surgery: new beginnings or a false dawn?

Femtosecond laser-assisted cataract surgery (FLACS) represents a potential paradigm shift in cataract surgery, but it is not without controversy. Advocates of the technology herald FLACS as a revolution that promises superior outcomes and an improved safety profile for patients. Conversely, detractors point to the large financial costs involved and claim that similar results are achievable with conventional small-incision phacoemulsification. This review provides a balanced and comprehensive account of the development of FLACS since its inception. It explains the physiology and mechanics underlying the technology, and critically reviews the outcomes and implications of initial studies. The benefits and limitations of using femtosecond laser accuracy to create corneal incisions, anterior capsulotomy, and lens fragmentation are explored, with reference to the main platforms, which currently offer FLACS. Economic considerations are discussed, in addition to the practicalities associated with the implementation of FLACS in a healthcare setting. The influence on surgical training and skills is considered and possible future applications of the technology introduced. While in its infancy, FLACS sets out the exciting possibility of a new level of precision in cataract surgery. However, further work in the form of large scale, phase 3 randomised controlled trials are required to demonstrate whether its theoretical benefits are significant in practice and worthy of the necessary huge financial investment and system overhaul. Whether it gains widespread acceptance is likely to be influenced by a complex interplay of scientific and socio-economic factors in years to come.

Impact of graft thickness on visual acuity after Descemet's stripping endothelial keratoplasty

Objective To evaluate the relationship, over time, between central graft thickness and visual acuity following Descemets stripping endothelial keratoplasty (DSEK). Methods A retrospective analysis of 70 consecutive cases of DSEK. All donor lenticules were dissected manually. Serial postoperative measurements of central graft and total corneal thicknesses were made using anterior segment optical coherence tomography. Visual acuity, refraction and patient demographics were collected from case notes. The correlation between central graft thickness and visual acuity at serial time points was calculated. Results The median age at surgery was 75 years (lower quartile (LQ) 66, upper quartile (UQ) 83, range 36–90 years). Nineteen eyes were excluded from statistical analysis, leaving 51 eyes of 46 patients remaining. Last follow-up occurred a median of 12 months postoperatively (LQ 6, UQ 23, range 4–38 months). The median preoperative visual acuity was 0.71 logarithm of the minimum angle of resolution (logMAR), improving to 0.34 logMAR postoperatively (p<0.001, n=43). Median graft thickness decreased from 209 μm at day 1 to 142 μm at last follow-up (p<0.001). No statistically significant correlation was found between central total corneal thickness and visual acuity at any time point. Except for a single time point, no statistically significant correlation was found between central graft thickness and visual acuity. Conclusion There is no clear association between central graft, or total corneal, thickness and visual acuity following DSEK.

Clinical applications of corneal confocal microscopy.

Corneal confocal microscopy is a novel clinical technique for the study of corneal cellular structure. It provides images which are comparable to in-vitro histochemical techniques delineating corneal epithelium, Bowman’s layer, stroma, Descemet’s membrane and the corneal endothelium. Because, corneal confocal microscopy is a non invasive technique for in vivo imaging of the living cornea it has huge clinical potential to investigate numerous corneal diseases. Thus far it has been used in the detection and management of pathologic and infectious conditions, corneal dystrophies and ecstasies, monitoring contact lens induced corneal changes and for pre and post surgical evaluation (PRK, LASIK and LASEK, flap evaluations and Radial Keratotomy), and penetrating keratoplasty. Most recently it has been used as a surrogate for peripheral nerve damage in a variety of peripheral neuropathies and may have potential in acting as a surrogate marker for endothelial abnormalities.

Assessment of the use of anterior segment optical coherence tomography in microbial keratitis.

PURPOSE To investigate the imaging capabilities of anterior segment optical coherence tomography (AS OCT) in microbial keratitis and to assess whether measurements of the quantitative parameters, infiltrate thickness and corneal thickness, were possible. DESIGN Prospective, noncomparative, observational case series. METHODS The study was conducted at a university hospital clinical setting. Seven patients (eyes) with suspected microbial keratitis underwent standard clinical examination and treatment based on slit-lamp clinical findings. AS OCT scanning was performed on presentation and at two follow-up appointments. All scans were carried out with the scanning beam passing through the center of the infiltration and at a specific meridian. Examination was carried out by the same operator. RESULTS Corneal infiltration was imaged as a hyperreflective area in the corneal stroma on high-resolution AS OCT scans. Retrocorneal pathologic features and anterior chamber inflammatory cells could be imaged. Corneal and infiltrate thickness could be measured with calipers in six cases. In one case, corneal and infiltrate thickness could not be measured because of a thick inflammatory plaque attached to the endothelium. In this case, the width of the plaque was measured on serial scans. CONCLUSIONS AS OCT imaging provides a range of parameters that can be used to assess microbial keratitis and the treatment response objectively.

Expression of haematopoietic stem cell markers, CD133 and CD34 on human corneal keratocytes

Aim: To study the expression of CD133 and CD34 antigens on cultured human keratocytes over time. Methods: Primary cultures of human corneal stromal cells were established from explants derived from cadaver eye donors. The cultures were sorted for CD133+ and CD34+ cells using magnetic beads. Both the primary cultures and secondary passages of sorted cells were further analysed by flow cytometry and western blot analysis for expression of the same antigens over time. Results: Four different cell populations—namely, CD133+, CD133−, CD34+ and CD34−, were identified in the culture samples. Two further specific subgroups were identified by flow cytometry: CD133+/CD34− cells and CD133+/CD34+ cells. Expression of CD133 declines more than CD34 with time in cell cultures. Although most cells lost expression of these markers, small populations retained staining up to 5 weeks in culture. Conclusion: Human keratocytes express the haematopoietic stem cell markers CD133 and CD34. This expression decreases with time in culture, with most but not all cells losing expression. On the basis of these markers, the corneal stroma shows a heterogeneous population of cells. Expression or down regulation of expression of these molecules could represent different stages of activation of these cells.

Artificial means for restoring vision

Degeneration of the retina occurs in age related macular degeneration and retinitis pigmentosa, resulting in loss of vision. Age related macular degeneration is a major cause of visual impairment among people over 65 in Western countries1; in the United Kingdom its incidence has increased by 30-40% over the past 40 years.2 Retinitis pigmentosa generally occurs in a younger age group (incidence 1 per 4000 live births) and affects 1.5 million people worldwide.3 In both conditions patients are visually impaired due to loss of photoreceptors. At present few treatments can remedy this and lead to recovery of vision.4 5 Photodynamic laser therapy has been beneficial in some patients with age related macular degeneration, but this therapy does not address photoreceptor loss. Different gene and drug therapies have been tried,4 5 but their ability to replace lost photosensitive tissue is limited. Researchers are therefore investigating the possibility of using prostheses to restore vision. Advances in microtechnology have facilitated the development of a variety of prostheses that can be connected to the brain or implanted in the eye. Some of these approaches have improved the eyesight of patients with visual impairment. This article gives an overview of the methods that are being assessed to restore vision in patients with severe sight loss. We carried out a comprehensive search through Medline and PubMed using the terms “age related maculopathy”, “visual prosthesis”, “retinitis pigmentosa”, “retina”, and “eye”. We also searched for the latest developments in artificial vision through the website of the Association for Research in Vision and Ophthalmology. Efforts to develop visual prostheses are not new. Attempts at artificial vision began in the 18th century with direct electrical stimulation of blind eyes.6 In the 1920s, the German neurosurgeon Otfrid Foerster developed this approach further by investigating direct …

Herpes simplex virus keratitis: an update of the pathogenesis and current treatment with oral and topical antiviral agents.

Ophthalmic herpes simplex viral keratitis is responsible for a range of ocular manifestations from superficial epithelial disease to stromal keratitis and endotheliitis. The Herpetic Eye Disease Study has guided the management of herpetic eye disease for almost twenty years, but newer medications such as valacyclovir are now available and are considered to have better bioavailability than acyclovir. In this review, we examine the existing evidence on the pathogenesis of different ophthalmic herpes simplex viral keratitis disease modalities and the role of oral and topically administered antiviral drugs in the treatment of herpes simplex viral keratitis.