Polyacrylic Acid Gel in Patients with Dry Eyes: A Randomised Comparison with Polyvinyl Alcohol

Purpose

To compare the safety and efficacy of polyacrylic acid 0.2% (PAA) gel and polyvinylalcohol 1.4% (PVA) in the treatment of patients with dry eyes.

Methods

Eighty-nine patients with dry eyes were randomly allocated to treatment with either PAA (48) or PVA (41) in a prospective, investigator-masked study in two centres. The parameters assessed were daily frequency of instillation of the study medications, ocular signs and symptoms, tear film break up time, Schirmer's test values, local tolerance and global assessment of the improvement following treatment.

Results

The two groups were similar in patient demographics and study parameters at baseline. The total score of symptoms (gritty or foreign body sensation, burning sensation, dry eye sensation, photophobia, others) and signs (conjunctival hyperaemia, ciliary injection, corneal and conjunctival epithelial staining) was reduced significantly more by treatment with PAA than with PVA at both three and six weeks (p<0.0001). The daily frequency of instillation of PAA was significantly less than that PVA on 38 of the 41 (93%) study days. Both PAA and PVA were safe and equally well-tolerated except for blurred vision, usually mild and transient, on PAA. On global assessment of the improvement in their dry eye condition, significantly more PAA patients felt better on treatment at six (p=0.02) weeks compared with those on PVA.

Conclusions

Polyacrylic acid gel was as safe as and more effective than polyvinylalcohol in the treatment of patients with dry eyes.

Basal Tear Osmolarity as a metric to estimate body hydration and dry eye severity

The osmolarities of various bodily fluids, including tears, saliva and urine, have been used as indices of plasma osmolality, a measure of body hydration, while tear osmolarity is used routinely in dry eye diagnosis, the degree of tear hyperosmolarity providing an index of disease severity. Systemic dehydration, due to inadequate water intake or excessive water loss is common in the elderly population, has a high morbidity and may cause loss of life. Its diagnosis is often overlooked and there is a need to develop a simple, bedside test to detect dehydration in this population. We hypothesize that, in the absence of tear evaporation and with continued secretion, mixing and drainage of tears, tear osmolarity falls to a basal level that is closer to that of the plasma than that of a tear sample taken in open eye conditions. We term this value the Basal Tear Osmolarity (BTO) and propose that it may be measured in tear samples immediately after a period of evaporative suppression. This value will be particular to an individual and since plasma osmolarity is controlled within narrow limits, it is predicted that it will be stable and have a small variance. It is proposed that the BTO, measured immediately after a defined period of eye closure, can provide a new metric in the diagnosis of systemic dehydration and a yardstick against which to gauge the severity of dry eye disease.

The ageing lens and cataract: a model of normal and pathological ageing

Cataract is a visible opacity in the lens substance, which, when located on the visual axis, leads to visual loss. Age-related cataract is a cause of blindness on a global scale involving genetic and environmental influences. With ageing, lens proteins undergo non-enzymatic, post-translational modification and the accumulation of fluorescent chromophores, increasing susceptibility to oxidation and cross-linking and increased light-scatter. Because the human lens grows throughout life, the lens core is exposed for a longer period to such influences and the risk of oxidative damage increases in the fourth decade when a barrier to the transport of glutathione forms around the lens nucleus. Consequently, as the lens ages, its transparency falls and the nucleus becomes more rigid, resisting the change in shape necessary for accommodation. This is the basis of presbyopia. In some individuals, the steady accumulation of chromophores and complex, insoluble crystallin aggregates in the lens nucleus leads to the formation of a brown nuclear cataract. The process is homogeneous and the affected lens fibres retain their gross morphology. Cortical opacities are due to changes in membrane permeability and enzyme function and shear-stress damage to lens fibres with continued accommodative effort. Unlike nuclear cataract, progression is intermittent, stepwise and non-uniform.

NADPH-diaphorase expression in the meibomian glands of rat palpebra in postnatal development

In the current study, we aimed at investigating the presence of nitric oxide synthase (NOS) positive nerve fibers in rat meibomian glands (MGs) at various stages of development. There is good evidence to suggest that nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) is a surrogate for neuronal nitric oxide synthase (NOS). Sections of the central, upper eyelids of Wistar rats were processed histochemically for NADPH-d to investigate the presence and distribution of NOS-positive nerve fibers at the following time points: day 1 and weeks 1, 2 and 3 post partum, and in adult controls. At day 1, MG acini were lightly stained and located at a distance from the mucosal border. Vessels were accompanied by intensely stained NADPH-d positive nerve fibers. At the week 1 time point, both the vessels and the NADPH-d positive fibers were still present, but less numerous. MGs were now closer to the mucosa, so that the submucosa was thinner. The acini were mostly pale but occasionally darker. At week 3, there were fewer blood vessels in both the sub-mucosa and within the septa. Darker acini were more common than lightly stained acini. NADPH-d positive dots were observed in the vicinity of the MGs. At the week 3 time point, MGs were adjacent to the mucosal border and stained more intensely than at earlier times; almost all acini were stained. The microscopic appearances were almost identical with those of adult palpebra. Submucosal and septal blood vessels and NADPH-d positive nerve fibers were less numerous. NADPH-d histochemical staining confirmed differences in the density of stained nerve fibers at different developmental stages. The greatest density of NADPH-d -positive nerve fibers occurred in 1-day-old rats whereas they were less numerous in adult rat eyelids. Nerves innervating MGs utilize nitric oxide (NO) as a neurotransmitter mostly in early developmental stages and this need thereafter decreases and stabilizes at 3 weeks postnatally.

Role of keratan sulphate (sulphated poly -N-acetyllactosamine repeats) in keratoconic cornea, histochemical, and ultrastructural analysis

AIMS

Keratan sulphate (KS) is the predominant glycosaminoglycan (GAG) present in the corneal stroma where it is thought to regulate collagen fibril diameter. In this study we investigated the distribution of KS in normal and keratoconic corneas.

METHODS

Four normal, one mild, and four severe keratoconic corneas were used for the study. Distribution of keratan sulphate proteoglycans (KS-PG) was investigated using a primary monoclonal antibody (5-D-4) that recognizes disulphated disaccharides in the poly-N-acetyllactosamine repeats of KS. The immuno-reactivity of 5-D-4 was analyzed by immunohistochemistry and immuno-electron microscopy.

RESULTS

Immuno-histochemistry showed diffuse 5-D-4 staining in keratoconic cornea compared to the punctuate staining in normal corneas. In the single cornea with mild keratoconus, immunogold microscopy revealed a very high density of KS-PG staining, especially in the posterior stroma, compared to severe keratoconic and normal cornea. The amount of KS-PG in the stroma in severe keratoconus was slightly less compared to the normal cornea. In the mild keratoconic cornea, a higher quantity of KS-PG was present around the keratocytes. In severe keratoconic corneas, a higher quantity of KS-PG was present within the keratocytes compared to normal cornea.

CONCLUSIONS

The finding of an altered expression of KS in our keratoconic corneas, in particular the strong expression of KS in keratocytes, is in keeping with reports of an altered expression of proteoglycan metabolism in keratoconus. KS-PG plays an important role in stromal collagen fibril assembly and a dysregulation of KS-PG synthesis or catabolism could explain changes in collagen fibril spacing and diameter, which we have reported elsewhere.

A hypothesis to suggest that light is a risk factor in glaucoma and the mitochondrial optic neuropathies

The authors propose that light entering the eye interacts with retinal ganglion cell (RGC) axon mitochondria to generate reactive oxygen intermediates (ROI) and that when these neurons are in an energetically low state, their capacity to remove these damaging molecules is exceeded and their survival is compromised. They suggest that in the initial stages of glaucoma, RGCs exist at a low energy level because of a reduced blood flow at the optic nerve head and that in the mitochondrial optic neuropathies (MONs), this results from a primary, genetic defect in aerobic metabolism. In these states RGCs function at a reduced energy level and incident light on the retina becomes a risk factor. Preliminary laboratory studies support this proposition. Firstly, the authors have shown that light is detrimental to isolated mitochondria in an intensity dependent manner. Secondly, light triggers apoptosis of cultured, transformed RGCs and this effect is exacerbated when the cells are nutritionally deprived. Detailed studies are under way to strengthen the proposed theory. On the basis of this proposal, the authors suggest that patients with optic neuropathies such as glaucoma or at risk of developing a MON may benefit from the use of spectral filters and reducing the intensity of light entering the eye.

Gelatinous drop-like corneal dystrophy in a child with developmental delay: clinicopathological features and exclusion of the M1S1 gene

AIMS

Gelatinous drop-like corneal dystrophy (GDLD) is an early-onset, autosomal recessive condition characterised by amyloid deposits within the cornea. We report the histopathological and molecular genetic findings in a Caucasian child with GDLD who also exhibited global developmental delay.

METHODS

Bilateral lamellar keratoplasty was carried out at age 6 and 7 years. Tissue was fixed for light and electron microscopy, including immunoelectronmicroscopy. The coding region of the M1S1 gene was screened for mutations in the affected proband and available relatives, using DNA extracted from mouthwashes.

RESULTS

Nodular deposits, which were present subepithelially and in the central superficial stroma, stained typically for amyloid with PAS and Congo red. A nodular deposit of amyloid, together with large amounts of lactoferrin and sparse amounts of keratoepithelin (betaig-h3), was present in the central superficial stroma, causing destruction of Bowman's layer and elevation of the thinned, degenerate epithelium. Around the deposit zone, the stroma exhibited large numbers of thick filamentous proteoglycan deposits. While the affected child was homozygous for a novel A1133 C single-nucleotide polymorphism (SNP) that resulted in an aspartic acid to alanine substitution at position 173 of the M1S1 coding sequence, this polymorphism was also found at relatively high frequency in a sample of normal controls, enabling exclusion of the M1S1 gene as the disease locus.

CONCLUSION

Increased epithelial permeability in GDLD may be explained in part by an altered membrane permeability of the superficial epithelial cells. An association with developmental delay has not been reported previously.

Clinical and ultrastructural findings in mare's tail lines of the corneal epithelium

AIMS

Mare's tail lines are uncommon, grey, parallel, tapering epithelial lines, which may give rise to discomfort or to visual symptoms. The authors report the clinical and ultrastructural findings in two patients

METHODS

Therapeutic debridement was performed in two patients suffering from mare's tail disorder. The loosely attached epithelium was removed and fixed in glutaraldehyde containing cuprolinic blue and processed in a standard fashion for electron microscopy.

RESULTS

Ultrastructural studies showed an avascular, collagenous pannus extending under the whole of the excised epithelium in each case and separated from it by a thickened basal lamina like zone. The basal laminar material extended into the epithelium in folds, in keeping with the clinical features. Interesting ultrastructural features included: (1) a lack of hemidesmosomes in relation to the basal laminar material; (2) trapping of degenerate keratocytes within the invaginating basal laminar folds; (3) an unusual regularity and fine dimensions of the collagen fibrils and proteoglycans making up the subepithelial pannus. The basal laminar material contained proteoglycans and small fibres similar in appearance to long spacing collagen.

CONCLUSIONS

Mare's tail lines are caused by basal laminar material, assumed to be chiefly of epithelial origin, which invaginates the corneal epithelium. The presence of occasional keratocytes within the invaginating folds suggests that there may be a stromal contribution to the disorder. The visibility of mare's tail lines in the focal beam of the slit lamp is likely to be related to the thickness and light scattering properties of the invaginations and of the subepithelial deposits. Tractional forces, imposed by lid action, could explain their horizontal disposition.

Functional aspects of the tear film lipid layer

The lipid layer is an essential component of the tear film, providing a smooth optical surface for the cornea and retarding evaporation from the eye. The meibomian lipids which compose it are well adapted for this purpose. They form a thin, smooth film whose thickness, and probably composition, influences the rate of evaporation. Their melting range ensures sufficient fluidity for delivery to the tear film from the lid margin reservoirs, while the film itself may exhibit a higher viscosity at the cooler temperature of the ocular surface. The factors governing lipid film formation during the blink are not fully understood, but one view is that the polar lipids, interacting with the aqueous sub-phase of the tear film, spread in advance of the non-polar components, which form the bulk of the film. The meibomian lipids stabilise the tear film by lowering its free energy; they carry water into the film during its formation and interact with lipid-binding proteins in the aqueous phase, such as tear lipocalin. The lipocalins, complexed with other tear components, may also contribute to the high, non-Newtonian viscosity of the tear film and its low surface tension, features which are essential for tear film stability. Formation of the lipid film is a complex process. Lipid is delivered to the tear film in the up-phase of the blink, more from the lower than the upper reservoir. The lipid layer comes to a stop well after completion of the blink and remains relatively immobile until it is compressed in the down-phase of the blink that follows. Then, it either retains its structure in a series of subsequent blinks, or is completely re-constituted after mixing with the reservoir lipids. Delivery of meibomian lipid to the marginal reservoirs is mainly the result of continuous secretion, under neural and hormonal control, supplemented by lid action. The reservoirs provide a hydrophobic barrier to tear overspill and to contamination by skin lipids which might destabilise the tear film. They probably also provide the chief route for meibomian lipid excretion.

The Contribution of Meibomian Disease to Dry Eye

The tear film lipid layer is the major barrier to evaporation from the ocular surface. A decrease in its thickness or functional integrity may cause evaporative dry eye (EDE). Obstructive meibomian gland dysfunction (MGD) is the most common cause of EDE and occurs as a primary disorder or secondary to acne rosacea, seborrheic or atopic dermatitis, and with cicatrizing conjunctival disorders, such as trachoma, erythema multiforme, and cicatricial pemphigoid. MGD may be an incidental finding in asymptomatic eyes, or it may be responsible for irritative lid symptoms in the absence of dry eye. MGD-dependent EDE is diagnosed on the basis of a defined degree of MGD in a symptomatic patient showing typical ocular surface damage in the absence of an aqueous tear deficiency. When MGD occurs in a background of aqueous tear deficiency (ATD), then an additional evaporative component may assumed, depending on the extent of meibomian obstruction. However, definitive criteria are not yet established. The clinical severity of dry eye is greatest when ATD and EDE occur together, particularly in Sjogren syndrome. A hypothesis is proposed to explain the steps leading to primary, simple MGD and subsequent EDE.

Differential effects of aging on transport properties of anterior and posterior human sclera

The transport properties and composition of 44 pairs of human sclera, 37-91 years were compared. Solute transport, diffusion and partition coefficients of posterior sclera for solutes ranging in mass from 0.023-70kDa were higher than those of anterior sclera; the posterior region was also more hydrated. The differences in partition coefficient between anterior and posterior sclera became more pronounced as solute molecular weight increased. Partition coefficients and hydration of both regions decreased with increasing age. Chondroitinase ABC digestion, which removed the majority of glycosaminoglycans, increased partition coefficients of both regions significantly. These results suggest that for regions of equal scleral thickness, neglecting the influence of vascular factors, drug delivery will be more readily achieved across the posterior sclera than the anterior sclera in the age group studied and that, for both regions, ease of delivery will decrease with decreasing age.

Intraocular vancomycin levels after intravitreal injection in post cataract extraction endophthalmitis

PURPOSE

Intravitreal antibiotics are the mainstay of treatment of endophthalmitis following cataract surgery. The purpose of this study is to determine the range of intraocular vancomycin found after intravitreal therapy and assess the optimum time for repeat injections.

METHODS

Aqueous and vitreous vancomycin was assayed at the time of reinjection in 14 patients with endophthalmitis showing a poor clinical response after their primary injection. Nine patients received vancomycin 2 mg and another five received vancomycin 1 mg. In six patients the injection was repeated at 48 hours and in seven at 72 hours. Two patients received three injections.

RESULTS

Aqueous vancomycin varied from 8.4 to 170 mg/L and the vitreous vancomycin level ranged from 21.2 to 220 mg/L.

CONCLUSIONS

In the current study vitreous vancomycin levels were variable, but well within the therapeutic range for sensitive Gram-positive organisms. At times they exceeded the putative retinotoxic levels (100 mg/L). Higher aqueous levels were found after an injection of 2 mg than after 1 mg. Vancomycin levels were still very high 3 days after injection of 2 mg where results were available. Assay at the time of repeat injection may provide insight into the adequacy of vitreous levels and guide future therapy.

Ultrastructural morphology and expression of proteoglycans, betaig-h3, tenascin-C, fibrillin-1, and fibronectin in bullous keratopathy

AIMS

To investigate the ultrastructural localisation of proteoglycans (PG), betaig-h3 (keratoepithelin), tenascin-C (TN-C)), fibrillin, and fibronectin in bullous keratopathy (BK) corneas.

METHODS

Five corneas from cases of pseudophakic bullous keratopathy (BK) were examined by electron microscopy. PG were demonstrated using cuprolinic blue, and the proteins betaig-h3, TN-C, fibrillin, and fibronectin were immunolocalised with rabbit anti-betaig-h3, mouse anti-TN-C (BC10 and TN2), mouse anti-fibrillin-1 (MAB2502), mouse anti-fibrillin (MAB1919), and rabbit anti-fibronectin by using a standard immunogold technique.

RESULTS

Epithelial cells contained numerous vacuoles. Epithelial folds and large, electron lucent subepithelial bullae were present. Basal lamina was thickened and traversed by disrupted anchoring filaments. In the stroma, interfibrillar collagen spacing was increased and abnormally large PG were present. Descemet's membrane (DM) contained lucent spaces in which there were small filaments. Keratocyte and endothelial cells contained melanin granules. A posterior collagenous layer (PCL) contained numerous microfilaments and wide spacing collagen fibres with a periodicity of 100 nm. Large quantities of abnormal PG were observed at the endothelial face of the PCL. Very strong labelling with betaig-h3 antibody was observed in the basement membrane, Bowman's layer, stroma, DM, and PCL, but not in keratocytes and endothelial cells. Strong labelling with BC10 and TN2 was seen below the epithelium, in electron lucent spaces where the hemidesmosomes were absent, in the fibrotic pannus, in parts of Bowman's layer, the stroma, and Descemet's membrane. Labelling with BC10 was stronger and more evenly distributed than with TN2. Fibrillin-1 (MAB2502) and fibrillin (MAB1919) labelling was similar to TN-C labelling. Fibrillin (MAB1919) labelling was stronger than fibrillin-1 (MAB2502) labelling.

CONCLUSIONS

Immunoelectron microscopy showed precise labelling of proteins at both the cellular and the subcellular level. Expression of proteins betaig-h3, TN-C, fibrillin, and fibronectin was highly increased compared with normal cornea. In the oedematous stroma, increased collagen fibril separation may facilitate a wider distribution of some soluble proteins, such as betaig-h3, throughout stroma. The modified expression of the proteins studied in these cases of BK may be regarded as part of an injury response.

Congenital hereditary endothelial dystrophy and band keratopathy in an infant with corpus callosum agenesis

PURPOSE

To report the features of a syndrome of endothelial failure and band-shaped keratopathy in an infant with corpus callosum agenesis.

METHODS

The clinical and histopathologic features of an infant presenting with bilateral corneal clouding and corpus callosum agenesis are reported. The patient underwent bilateral penetrating keratoplasty at ages 28 months and 4 years. Light and electron microscopy were used to characterize the structural changes.

RESULTS

The epithelium was thin and degenerate. Bowman's membrane contained spherical aggregates that were present also within a connective tissue pannus. The midstroma was normal, but there were floral and rope-like aggregations of collagen in the pre-Descemet's membrane region. Under electron microscopy, the spherules formed target-shaped lesions with a central focus of alternating electron-dense and lucent material. Numerous microfilaments in the pannus and anterior stroma labeled with fibrillin-1 antibody. Microfilaments within fibroblasts were stained with vimentin antibody. Posteriorly, the endothelium was mainly absent and Descemet's membrane showed a fetal layer and a posterior collagenous layer.

CONCLUSION

Corneal appearances in this patient were in keeping with those of congenital hereditary endothelial corneal dystrophy. However, there was no family history and neither parent showed a clinical endothelial abnormality. The presence of fetal, banded material in Descemet's membrane suggested that endothelial loss began at or near the time of birth. The band keratopathy was regarded as a secondary change. The association with corpus callosum agenesis does not appear to have been described previously.

Diagnosis of dry eye

Dry eve disease is characterized by symptoms, ocular surface damage, reduced tear film stability, and tear hyperosmolarity. There are also inflammatory components. These features can be identified by various kinds of diagnostic tests (symptom questionnaires, ocular surface staining, tear break-up time, and osmometry), although there may not be a direct correlation between the number or severity of symptoms and the degree of ocular surface damage or tear deficiency. Once the diagnosis of dry eye disease has been established, further tests can be used to classify the condition into tear-deficient or evaporative dry eve. The two forms of dry eye are not mutually exclusive and often co-exist. The optimal diagnosis of dry eye disease, therefore, depends on the results of several tests, and this article suggests an appropriate order for performing these tests at a single clinic visit.

Posterior subcapsular and nuclear cataract after vitrectomy

PURPOSE

To examine the morphological changes in the postvitrectomy lens and to monitor the development of these changes over time.

SETTING

Oxford Eye Hospital, Oxford, United Kingdom.

METHODS

In this prospective study, 33 consecutive phakic patients having pars plana vitrectomy were recruited. Cataract development was quantified by clinical grading and digital Scheimpflug image analysis. Slitlamp biomicroscopy and photography were used to document the morphological appearance. The main outcome measures were the incidence, morphology, and development of posterior subcapsular and nuclear cataract.

RESULTS

A characteristic, transient posterior subcapsular cataract (PSC) was present in 89% (17 of 19) of tamponade patients within 24 hours of surgery. Of the patients who had vitrectomy without tamponade, 9% (1 of 11) developed similar changes. Nuclear opacity developed in 61% (11 of 18) of tamponade patients and in 50% (3 of 6) of nontamponade patients. A longer term retrospective review of the same patients' case notes revealed nuclear cataract in 67% (12 of 18) of tamponade cases and 30% (3 of 10) of nontamponade cases. Eighteen percent (2 of 11) of nontamponade cases and 67% (14 of 21) of tamponade cases had cataract surgery after a 10.7 month and a 12.4 month follow-up, respectively.

CONCLUSIONS

Vitrectomy and tamponade produced a characteristic transient PSC in the immediate postoperative period. Disruption of fluid balance in the region of the posterior lens was suggested by the morphological appearance. The acute changes resolved but were followed by accelerated nuclear opacification.

Tear meniscus changes during cotton thread and Schirmer testing

PURPOSE

To elucidate the effect of the cotton thread test (CT-T) and Schirmer test (S-T) on the tear reservoir by evaluating the radius of tear meniscus curvature.

METHODS

The radii (R) of the central lower tear menisci were measured by a newly developed video meniscometer in 11 eyes of 11 normal volunteers (6 men, 5 women; mean age, 27.7 +/- 3.6 years [SD]) and 9 eyes of 9 patients with tear deficiency and severe dry eye in whom the puncta had been therapeutically occluded (9 women; mean age, 50.6 +/- 10.4 years). In this dry eye group, the absence of reflex tearing, coupled with the absence of lacrimal drainage due to punctal occlusion allowed more precise observation of the removal of tears from the meniscus. A 1-minute CT-T was performed, followed after an interval of 10 minutes by a 1-minute S-T. Tear meniscus curvature was documented before (R:(0)) and during the tests at 30 seconds (R(30)) and 60 seconds (R:(60)).

RESULTS

In the normal group, respective R values (CT-T; S-T; mean +/- SD mm) were R(0) (0.26 +/- 0.11; 0.26 +/- 0. 07), R(30) (0.27 +/- 0.16; 0.20 +/- 0.13), and R(60) (0.29 +/- 0.15; 0.23 +/- 0.21); and in the dry eye group, respective R: values (CT-T; S-T) were R(0) (0.59 +/- 0.23; 0.51 +/- 0.19), R(30) (0.52 +/- 0.25; 0.22 +/- 0.09), and R(60) (0.51 +/- 0.19; 0.21 +/- 0.08). It was demonstrated in the dry eye group that R was diminished more by the S-T than by the CT-T in the time course of the measurement (P = 0.01). In the dry eye group alteration of R occurred within the first 30 seconds, and in this group significant correlation was found between R(0) and the S-T result (r = 0.67; P = 0.05), and between R(60)- R(0) and the S-T result (r = -0.81; P = 0.01). Also, there was a significant correlation between R(60)- R(0) and the S-T result in the normal group (r = 0.71; P = 0.02). There were no significant correlations between R(0) or R(60)- R(0) and the CT-T results in either group.

CONCLUSIONS

These studies afford some insight into the dynamics of the Schirmer test, suggesting that wetting is influenced by the negative hydrostatic pressure within the tear meniscus. With the protocol used, no conclusion could be drawn about the relation between meniscus radius and wetting of the cotton thread.

The effect of hydration and matrix composition on solute diffusion in rabbit sclera

There is increasing interest in the possibility for drug delivery into the vitreous humor across the conjunctiva and sclera as an alternative route to the conjunctiva-cornea pathway. As a preliminary to human studies we have investigated the influence of scleral composition and hydration on solute transport in the rabbit sclera. Intermuscular sclera was excised from adult New Zealand rabbits. Tissue samples were either examined directly (controls), digested using chondroitinase ABC or crosslinked using glutaraldehyde. The effect of these treatments on the ultrastructural appearance of the sclera was assessed. Diffusion and partition coefficients for solutes of different molecular weights [sodium chloride (23 MW),(14)C sucrose (342 MW) and dextran-fluoresceins (3, 10, 40 and 70 kDa)] were measured in relation to tissue treatment. The results were used to determine the effect of tissue structure and composition on solute movement. We have found that: (1) diffusion and partition coefficients are sensitive to solute MW, decreasing as MW increases; (2) diffusion and partition coefficients are sensitive to tissue hydration, increasing as hydration increases; (3) crosslinking of the sclera by glutaraldehyde reduced the partition coefficients significantly for solutes with MW over 3 kDa; and (4) removal of glycosaminoglycans has only a small effect on either diffusion or the partition coefficient.

Genetics of the corneal dystrophies: what we have learned in the past twenty-five years

PURPOSE

To indicate important changes in our understanding of the corneal dystrophies.

METHODS

A review of the literature of the last quarter of a century.

RESULTS

The earliest clinical classifications of the corneal dystrophies were based on the application of clinical, biological, histochemical, and ultrastructural methods. Since then, the first great impetus to our understanding has come from the application of techniques to map disorders to specific chromosome loci, using polymorphic markers. More recently, using candidate gene and related approaches, it has been possible to identify genes causing several of the corneal dystrophies and the mutations responsible for their phenotypic variation. A notable success has been to show that several important "stromal" dystrophies result from mutations in the gene beta ig-h3, which encodes for the protein keratoepithelin (beta ig-h3).

CONCLUSIONS

For the corneal dystrophies, as with other inherited disorders, there is room for two sorts of classification system, one based mainly on clinical presentation and the other on an up-to-date understanding of the genetic mechanisms. They are not mutually exclusive. Some developmental corneal disorders are also discussed.

5-Hydroxytryptamine1A agonists: potential use in glaucoma. Evidence from animal studies

Various classes of compounds exist to lower intraocular pressure (IOP) in the treatment of glaucoma. None of them is ideal since some patients respond better than others and the side effects vary between individuals. New classes of compounds need to be introduced to allow the clinician greater scope for effective treatment of all patients. It is now generally agreed that the cause of ganglion cell dysfunction in glaucoma is likely to be multifactorial and that concentrating solely on reducing IOP is inadequate. Irrespective of the reason for the dysfunction, the future goal must be to attenuate cell death. This may be achieved with drugs that interact with components of the retina, and is termed 'neuroprotection'. Thus, drugs that can both reduce IOP and act as neuroprotectants would be ideal for the treatment of glaucoma. In this article we summarise studies on animals which show serotonergic 5-HT1A agonists to both reduce IOP when topically applied to the rabbit eye and blunt the damaging effect to the rat retina and ganglion cells induced by glutamate toxicity or ischaemia. Reduction of IOP occurs via stimulation of 5-HT1A receptors associated with the ciliary processes. Neuroprotection of retinal neurones appears to involve the interaction of 5-HT1A agonists with membrane sodium channels and/or 5-HT1A or even possibly 5-HT7 receptors. Various 5-HT1A agonists are used in patients to treat depression, so classes of these drugs have a proven safety profile for use in patients. The animal studies summarised in this article suggest that 5-HT1A agonists need to be considered as a new class of drugs for the treatment of glaucoma.

Reflective meniscometry: a new field of dry eye assessment

PURPOSE

To report a newly developed noninvasive method to measure the radius of tear meniscus curvature (reflective meniscometry) and its application to normal eyes, dry eyes, and other ocular surface conditions.

METHODS

Two types of meniscometer--photographic and video--were devised. Both use tear meniscus as a concave mirror, and a specular reflex of an illuminated target at the meniscus was photographed or videotaped to obtain the radius of tear meniscus curvature. The photographic system was applied to 45 normal and 32 dry eyes; in the dry eyes, the radius of tear meniscus curvature was compared to the results of other dry eye examinations. The video system was used to examine meniscus formation on the ocular surface in patients with ocular surface irregularities.

RESULTS

The radii of tear meniscus curvature were significantly lower in dry eyes (0.250 +/- 0.086 mm, mean +/- SD) than in normal eyes (0.365 +/- 0.153; p = 0.0003). There were significant correlations between the radius and fluorescein staining score (p = 0.0032) and the grading of interference colors on the precorneal oil film (p = 0.0125). Videomeniscometry demonstrated the tear meniscus to be very stable and proved to be useful in the study of menisci at the edge of rigid contact lenses and other menisci encountered in ocular surface disorders.

CONCLUSIONS

Measurement of the radius of tear meniscus curvature may be useful in the diagnosis of dry eyes. Reflective meniscometry is expected to find wide applications in the analysis of tear meniscus in ocular surface disorders.

Post-operative changes in the capsulorhexis aperture: a prospective, randomised comparison between loop and plate haptic silicone intraocular lenses

PURPOSE

There is disagreement regarding whether the capsulorhexis aperture always decreases or may increase post-operatively. The aim of this study was to settle the controversy concerning loop haptic silicone lenses and to learn more of the dynamics of the capsulorhexis relating to plate haptic lenses.

METHODS

We performed a prospective randomised study comparing the post-operative changes in capsulorhexis aperture in two groups of eyes implanted with either plate or loop haptic silicone intraocular lenses. All the surgery was performed, at a teaching hospital in the United Kingdom, by a single surgeon, using a standard technique of phacoemulsification. Patients were reviewed at 2 weeks and 6 months post-operatively. Digital retroillumination images of the anterior segment were captured. The area of the capsulorhexis aperture was determined by manually detecting its edge on a computer monitor.

RESULTS

Forty-eight cases were randomised. The groups were comparable for demographic variables and mean initial aperture size (p > 0.05). There was an 8.4% mean decrease in aperture size for the loop haptics, contrasting with 4.5% expansion for the plate haptics (p < 0.05). Sixty-five per cent of patients with the plate haptic underwent enlargement of the aperture, contrasting with 25% for the loop haptic lens (p < 0.05).

CONCLUSIONS

Silicone lenses with plate haptics undergo expansion of the capsulorhexis aperture more frequently than those with Prolene loop haptics.

The ageing lens

The human lens grows by a process of epithelial cell division at its equator and the formation of generations of differentiated fibre cells. Despite the process of continuous remodelling necessary to achieve growth within a closed system, the lens can retain a high level of light transmission throughout the lifetime of the individual, with the ability to form sharp images on the retina. Continuous growth of the lens solves the problem imposed by terminal differentiation within a closed, avascular system, from which cells cannot be shed. The lens fibre tips arch over the equator to meet anteriorly and posteriorly and form branching sutures of increasing complexity. The stages of branching may create the optical zones of discontinuity seen on biomicroscopy. The lens is exposed to the cumulative effects of radiation, oxidation and postranslational modification. These later proteins and other lens molecules in such a way as to impair membrane functions and perturb protein (particularly crystallin) organisation, so that light transmission and image formation may be compromised. Damage is minimised by the presence of powerful scavenger and chaperone molecules. Progressive insolublisation of the crystallins of the lens nucleus in the first five decades of life, and the formation of higher molecular weight aggregates, may account for the decreased deformability of the lens nucleus which characterises presbyopia. Additional factors include: the progressive increase in lens mass with age, changes in the point of insertion of the lens zonules, and a shortening of the radius of curvature of the anterior surface of the lens. Also with age, there is a fall in light transmission by the lens, associated with increased light scatter, increased spectral absorption, particularly at the blue end of the spectrum, and increased lens fluorescence. A major factor responsible for the increased yellowing of the lens is the accumulation of a novel fluorogen, glutathione-3-hydroxy kynurenine glycoside, which makes a major contribution to the increasing fluorescence of the lens nucleus which occurs with age. Since this compound may also cross-link with the lens crystallins, it may contribute to the formation of high-molecular-weight aggregates and the increases in light scattering which occur with age. Focal changes of microscopic size are observed in apparently transparent, aged lenses and may be regarded as precursors of cortical cataract formation.

Postoperative intraocular lens rotation: a randomized comparison of plate and loop haptic implants

OBJECTIVE

To compare the postoperative rotation of plate and loop haptic implants of spherical power to ascertain the optimal design appropriate for toric intraocular lenses (IOLs).

DESIGN

Randomized, controlled trial.

PARTICIPANTS

Forty-eight patients attending for routine cataract surgery by phacoemulsification.

METHOD

Patients with cataract as the only ocular disease were randomly implanted with plate or loop haptic implants after uncomplicated phacoemulsification. The baseline position of the IOL was determined from a video frame acquired at the conclusion of surgery. Postoperative IOL position was documented using digital retroillumination images at 2 weeks and 6 months after surgery. Capsular fusion patterns were recorded using slit-lamp biomicroscopy. Correlation of IOL rotation with axial length, capsular contraction, and fusion was attempted.

MAIN OUTCOME MEASURES

Early IOL rotation, occurring between surgery and 2 weeks after surgery, was graded as mild (<10 degrees), moderate (10 degrees < to <30 degrees), or severe (>30 degrees) by a semiobjective online comparison of the images. Late IOL rotation, occurring between 2 weeks and 6 months, was measured more precisely using software developed specifically for the study.

RESULTS

Twenty-three patients were allocated the loop haptic and 25 the plate haptic IOL. The groups were comparable for demographic variables and numbers of patients excluded from analysis (P > 0.05). Five (24%) of 21 of plate haptic IOLs underwent severe early rotation compared to 2 (9%) of 22 loop haptics (P = 0.36). The median late rotation was 6.8 degrees for loop haptics compared to 0.6 degrees for plate haptics (P = 0.0073). Between 2 weeks and 6 months, anticlockwise rotation had occurred in 16 (89%) of 18 loop haptic IOLs compared to 11 (52%) of 21 plate haptic IOLs (P = 0.0081).

CONCLUSIONS

Plate haptic IOLs show greater rotational stability than do loop haptics made from polypropylene once capsular fusion has taken place. Loop haptics invariably rotate anticlockwise after 2 weeks.

Sugars including erythronic and threonic acids in human aqueous humour

PURPOSE

Sugars in the aqueous humour of the eye serve both as a source of nutrients to the lens and other anterior ocular tissues, and potentially as an indicator of waste products from these tissues. In this work we intended to measure the levels of sugars in human blood and aqueous humour from cataract patients with and without diabetes. After initial results we decided to identify an unknown sugar component.

METHODS

Sugars were measured by hplc. The unknown sugar peak was identified by gas chromatography/mass spectrometry

RESULTS

Very little fructose and sorbitol were found. Glucose levels were higher in both blood and aqueous from diabetic patients. During these analyses we found a major component that did not correspond to any sugar reported previously in aqueous humour. This was identified as a mixture of threonic and erythronic acids.

CONCLUSIONS

Glucose levels increase in human aqueous humour in diabetes without markedly raised levels of sorbitol or fructose. Erythronic and threonic acids are normal components of aqueous humour and blood. They may be derived from glycated proteins or from degradation of ascorbic acid.

The development and maintenance of emmetropia

The human eye is programmed to achieve emmetropia in youth and to maintain emmetropia with advancing years. This is despite the changes in all eye dimensions during the period of growth and the continuing growth of the lens throughout life. The process of emmetropisation in the child's eye is indicated by a shift from the Gaussian distribution of refractive errors around a hypermetropic mean value at birth to the non-Gaussian leptokurtosis around an emmetropic mean value in the adult. Emmetropisation is the result of both passive and active processes. The passive process is that of proportional enlargement of the eye in the child. The proportional enlargement of the eye reduces the power of the dioptric system in proportion to the increasing axial length. The power of the cornea is reduced by lengthening of the radius of curvature. The power of the lens is reduced by lengthening radii of curvature and the effectivity of the lens is reduced by deepening of the anterior chamber. Ametropia results when these changes are not proportional. The active mechanism involves the feedback of image focus information from the retina and consequent adjustment of the axial length. Defective image formation interferes with this feedback and ametropia then results. Heredity determines the tendency to certain globe proportions and environment plays a part in influencing the action of active emmetropisation. The maintenance of emmetropia in the adult in spite of continuing lens growth with increasing lens thickness and increasing lens curvature, which is known as the lens paradox, is due to the refractive index changes balancing the effect of the increased curvature. These changes may be due to the differences between nucleus and cortex or to gradient changes within the cortex.

Assessment of meibomian gland function in dry eye using meibometry

OBJECTIVE

To study meibomian gland function in dry eyes using meibometry.

METHODS

Forty-two patients with clinically diagnosed dry eye that was reclassified as meibomian gland dysfunction (MGD [n = 12]), aqueous-tear deficiency (AD [n = 10]), MGD combined with AD (n = 2), "incomplete" dry eye (n = 12), and non-dry eye (6 eyes) were compared with 41 healthy control subjects. The following 2 techniques of meibometry were applied: direct meibometry (DM) measuring lipid imprints using the Meibometer, and integrated meibometry (IM) using image-scanning and computer densitometry. Tear film lipid layer thickness was assessed using interference microscopy.

RESULTS

Imprints were homogeneous for all subjects except those with MGD. Mean+/-SE readings on results of DM were 127.24+/-24.4 for MGD, 306.4+/-9.2 for AD, 248.6+/-13.2 for incomplete dry eye, and 268.5+/-6.3 for controls, showing lower values in the MGD group relative to all others (P<.001). Results of IM gave similar results (P<.001, P =.01, and P<.001, respectively). Lipid layers appeared lower for the MGD group than others.

CONCLUSIONS

Compared with controls, lid lipid levels are reduced in patients with MGD, and increased in women with AD. Lipid layer thickness is increased in women with AD compared with patients with MGD. Both meibometric techniques may be useful for evaluating MGD. Although DM requires special equipment (the Meibometer), it provides a record of immediate diagnostic value. Although IM is less effective than DM, it offers visual documentation of the lipid imprint, which may itself be of diagnostic value, and uses equipment available in many laboratories.

Comparison of the efficacy and safety of two eye gels in the treatment of dry eyes: Lacrinorm and Viscotears

PURPOSE

To compare the efficacy and safety of two carbomer 940 eye gels in the treatment of dry eyes: Lacrinorm (also called GelTears), a recently introduced eye gel, and Viscotears (also called Vidisic or Lacrigel), used as a reference gel. The main difference between the two gels is in the preservative, respectively benzalkonium chloride and cetrimide.

METHODS

A double-masked, randomised, parallel-group study was conducted in 16 centres in four European countries. A total of 179 patients suffering from aqueous-deficient dry eye were enrolled, of whom 92 were randomised to treatment with Lacrinorm and 87 to the reference gel. Gel was instilled four times a day for a period of 30 days.

RESULTS

After 30 days of treatment, subjective symptoms (the combined scores of foreign body sensation, ocular dryness, burning or pain, and photophobia) had improved by 50% in the Lacrinorm group and by 45% in the reference gel group, and objective test results (break-up time, fluorescein test, Schirmer test, Lissamine Green test) by 35-36% in the Lacrinorm group and 25-45% in the reference group. The improvements were significant in both treatment groups (p < 0.001), with no significant differences between the treatment groups. Subjective local tolerability upon instillation on day 30 was rated 'good' or 'very good' by 91% of patients in both treatment groups. Adverse events were reported for 21 patients in the Lacrinorm group and 17 in the reference group, the most frequent being discomfort, blurred vision, hyperaemia, burning and itching. The frequency and descriptions of adverse events did not differ significantly between the two treatment groups. No serious adverse events were reported.

CONCLUSIONS

Over the period of study, Lacrinorm eye gel was as effective and safe as Viscotears/Lacrigel in the treatment of dry eye.

Deposits and proteoglycan changes in primary and recurrent granular dystrophy of the cornea

OBJECTIVE

To investigate the origin and distribution of granular deposits in the corneas of 3 patients with granular dystrophy, 1 of whom had previously received a lamellar keratoplasty in which the granular dystrophy had recurred.

METHOD

Corneal tissue from 2 patients with primary granular dystrophy (patients 1 and 2) and from a patient with recurrent granular dystrophy (patient 3) was examined. Corneal graft tissue was fixed in (1) 3% glutaraldehyde in sodium cacodylate buffer, (2) 2.5.% glutaraldehyde in sodium acetate buffer containing cuprolinic blue, and (3) 4% paraformaldehyde in phosphate-buffered saline.

RESULTS

In patient 1 (aged 48 years), electron-dense granular structures were observed in epithelium, Bowman layer, and throughout the stroma. Bowman layer was absent in several places. Patient 2 (aged 78 years) showed similar features except with more deposits in the stroma. In patient 3 (aged 48 years), granular structures were heavily deposited in the epithelium; there were also some deposits in the posterior (host) stroma, some of which were associated with partially degenerated keratocytes. Bowman layer appeared normal. In all 3 patients, the intracellular or extracellular granular structures were surrounded by fine fibrillar material and abnormal proteoglycans. Electron-lucent spaces within the corneal stroma contained large quantities of abnormal proteoglycan filaments that were attached in part to collagen fibrils.

CONCLUSIONS

Results from patient 3 support an epithelial origin for the deposits, presumably from keratoepithelin, aggregated with other proteins. The role of keratocytes is less clear, although the presence of deposits in the stroma of all 3 patients, some associated with keratocytes, suggests that these cells might produce granular material in addition to abnormal proteoglycans.

Physical properties of stimulated and unstimulated tears

It has long been assumed that unstimulated tears are more thoroughly equilibrated with epithelial secretions than stimulated tears, since they are in contact with tarsal, bulbar and corneal surfaces for longer. It was also believed from results with model solutions that soluble mucin is responsible for the observed surface tension and viscosity of tears. If longer contact means more mucin is dissolved in the aqueous tears, then the surface activity (surface tension lowered by mucin) and viscosity (raised by mucin) of tears should therefore be enhanced in unstimulated over stimulated tears. Pools of stimulated and minimally-stimulated tears were collected from a group of healthy adult volunteers by glass capillary. Viscosities were measured in the Contraves Low Shear 30 rheometer over the range of shear rates 0-130 sec-1. Surface tension was measured in the collection capillaries by a micro-technique, before and after refrigerated storage. Both surface tension and viscosity were determined for a variety of tear proteins and mucins. No significant difference was found between the viscosity/shear rate plots of stimulated and unstimulated tear samples. The viscosities of solutions of individual tear proteins were low, except for the combination of lysozyme and secretory IgA. Surface tensions were also similar in both cases, and unchanged by storage at room temperature or refrigeration, indicating no significant loss of surface-active material by adsorption on the capillary walls. Results with model mucin solutions gave a variety of results indicating either little surface activity or losses due to wall adsorption. Tear proteins, individually or in combination, did not lower surface tension to the level of tears. Tear viscosity seems not to depend on the level of dissolved mucins. This suggests either that a constant level of these is picked up even by short-term contact with ocular surfaces, or that viscosity arises from currently unknown materials which vary little with tear flow rate. This type of shear-dependent viscosity is most easily simulated in model solutions with polyionic linear macromolecules, including mucins. The contribution of individual proteins to overall viscosity is small, but combinations including lysozyme show tear-like characteristics, and may indicate that proteins whose concentration is relatively independent of tear flow rate combine with other tear components (possibly including mucins or lipids) to produce their full effect on tear viscosity. The surface tension results suggest that mucins are not of primary importance. Theories of tear film structure and performance need revision.

The meibomian glands and tear film lipids. Structure, function, and control

Meibomian gland disease--and, in particular, obstructive meibomian gland disease--makes an important contribution to ocular surface disease, in the form of meibomian keratoconjunctivitis. With improved methods for the study of meibomian oil composition and function, we are moving closer to the possibility of distinguishing the contribution of meibomian deficiency, as opposed to inflammatory events, to this disorder. More importantly, where aqueous tear deficiency and meibomian gland disease coincide in patients with dry eye, we are closer to the possibility of distinguishing their relative contributions to the dry eye state. This has implications for future therapies.

Nutrition supplements and the eye

PURPOSE

A review of the role of vitamins, minerals, carotenoids and essential fatty acids in relation to eye health. The mode of action may be directly on the eye or by promoting bodily health on which the eye depends.

RESULTS

The lens and retina suffer oxidative damage and the anti-oxidant vitamins A, C and E are implicated as protective. Studies in man give indifferent support to the role of nutrition in the development of cataract. In the elderly, vitamin intake may be inadequate, so that a vitamin supplement may be reasonable. Zinc has a role in retinal metabolism and may be beneficial in macular degeneration. Selenium has an anti-oxidant role. Other minerals including copper have a less defined role. Carotenoids are concentrated at the macula and have an anti-oxidant role. A reduced risk of macular degeneration is found in relation to a high serum level. The essential fatty acid, gamma-linolenic acid (GLA), is useful in Sjögren's syndrome and may help in other dry eye conditions. Omega-3 fatty acids are important in retinal development and have a role in preventing cardiovascular disease.

CONCLUSION

All persons should be encouraged to maintain healthy nutrition. Middle-aged and elderly patients may benefit from a supplement. An intake in excess of the recommended daily intake may be beneficial, but this is not proven. Further clinical trials are indicated to define the advisability of vitamin, mineral and other supplements. Dosages for recommended intake and for supplements are given.

Cavernous-dural fistula with secondary angle-closure glaucoma

PURPOSE

To report a rare case of angle-closure glaucoma, secondary to the rapid development of a choroidal effusion, in a patient with a long-standing cavernous-dural shunt.

METHODS

Case report. Investigations included computed tomographic scan, magnetic resonance imaging, and carotid angiography.

RESULTS

The development of the choroidal effusion occurred because of partial thrombosis of the ipsilateral superior ophthalmic vein and cavernous sinus. Drainage of the choroidal effusion resolved the angle-closure glaucoma.

CONCLUSIONS

The combination of worsening signs and evidence of thrombosis indicates impending resolution of a cavernous-dural shunt. However, if a choroidal effusion causes angle-closure glaucoma, prompt surgical drainage should be considered to prevent permanent peripheral anterior synechiae formation, with the expectation that the effusion will not recur.

Decentration of 5.1 mm intraocular lenses after continuous curvilinear capsulorhexis and in-the-bag fixation

PURPOSE

To determine the incidence of decentration in eyes with 5.1 mm optic intraocular lenses (IOLs) and to assess the effect on vision.

SETTING

Clinical Cataract Research Unit, Oxford Eye Hospital, Oxford, England.

METHODS

Patients having phacoemulsification and small IOL implantation over 12 months were identified and invited for assessment. Intraocular lens decentration was measured geometrically using a modified, digital, retroillumination camera. The expected incidence of symptoms caused by decentration was estimated by determining the presence of an IOL edge within an artificial pupil overlaid on the digital image.

RESULTS

In 13 eyes (20%), IOL decentration was more than 0.5 mm. Symptoms were expected in 38 patients (59%) but occurred in only 14 (22%).

CONCLUSION

Decentration of the 5.1 mm optic IOL caused fewer clinical problems than anticipated, although the results raise concerns that such IOLs may be inappropriate in patients who need excellent vision in scotopic illumination.

The ocular blood flow tonograph: a new instrument for the measurement of intraocular pressure in rabbits

The Ocular Blood Flow Tonograph (OBFT) and Digilab Pneumatonograph (PTG) were calibrated for use on New Zealand White rabbits using a pressure manometer and performing tonometry at varying known pressures. The calibration experiments showed that a good correlation exists between OBFT measurements and manometric readings of IOP. Moreover, no difference between open and closed stopcock measurements were observed. Corrective equations for conversion of OBFT readings to mm Hg are documented. The OBFT was compared with the PTG and the results showed there was no significant difference between the IOP measured by either instrument in a group of rabbits displaying a range of different IOPs. Regression analysis of the data gave a slope of 0.88 and a correlation co-efficient of 0.78. The OBFT proved easier to use than the PTG under restricted lighting conditions. The OBFT was also used to measure the circadian variation in IOP and to measure the IOP after the topical application of prostaglandin E2 and various serotonergic agonists. The combined data demonstrated that the OBFT is an accurate and reliable tonometer for the measurement of IOP in rabbits.

Corneal dystrophies and keratoconus

This year's reports have given us a better understanding of several dystrophies as well as improvements in diagnosis and treatment. Eight corneal dystrophies have now been mapped to specific chromosomes and of these lattice, granular, Avellino, and Reis Bückler's dystrophies map to the same region of chromosome 5q, raising the question whether they are the result of mutations in separate genes or of mutations within alleles of a single gene. Phototherapeutic keratoplasty appears to offer an advantage in the initial treatment of several dystrophies whose symptoms arise from superficial corneal change. Some success has been reported in reducing the degree of hyperopic shift that accompanies deeper ablations. Further support for the genetic basis of keratoconus comes from a study in monozygotic twins and from improvements in quantitative videokeratographic indices, which have also improved our ability to distinguish keratoconus from other topographic abnormalities of the cornea. A new hypothesis for the mechanism of keratoconus proposes that an increased expression of interleukin-1 receptors, acting through a paracrine pathway, may disturb keratocyte activity and turnover, leading to a loss of stromal mass.

Ultrastructural study of the cornea in a bone marrow-transplanted Hurler syndrome patient

This case report describes a 14-year-old girl with Hurler syndrome, who had received a successful bone marrow-transplant at the age of two. Corneal clouding was present at the time of transplant and has only partially cleared. A right penetrating keratoplasty was performed and the corneal specimen was examined by light microscopy, transmission electron microscopy with Cuprolinic blue staining for proteoglycans, and low-angle X-ray diffraction. The results show the corneal stroma to be disrupted by vacuolated stromal cells. There is abnormal accumulation of proteoglycans in the vacuolated stromal cells and nearby stroma. These proteoglycans mainly contain chondroitin/dermatan sulphate glycosaminoglycans since they are susceptible to chondroitinase ABC. There are a large range of fibril diameters (12.5-50.1 nm) and there is an abnormal distribution of the fibril diameters measured from micrographs. Both are confirmed by X-ray diffraction results (the mean collagen fibril diameters are in a range between 29.7 and > 51.1 nm). X-ray diffraction also shows that the mean centre-to-centre distance of the fibrils slightly increases. These findings suggest that proteoglycans play a role in modelling the stromal structure and can also explain the corneal clouding. Many long-spacing collagen structures with a mean periodicity of 91.8 nm are observed in the corneal stroma. The finding that the long-spacing collagen consists of fine collagen fibrils and that very few proteoglycans filaments bind to them suggests that some change in the interaction of proteoglycans and collagen is responsible for the formation of long-spacing collagen. To our knowledge, this is the first ultrastructural study of the cornea from a bone marrow-transplant patient with Hurler syndrome. The structural features documented here relate to a cornea incompletely corrected by bone marrow transplantation.

The penetration of topical cysteamine into the human eye

The penetration of cysteamine into human aqueous was measured to assess its suitability as a topical agent for the prevention of radiation-induced cataract. Cysteamine drops (0.5% and 1.0%) were administered preoperatively to cataract patients every half hour, for two, four, six or eight hours. Aqueous humor was collected at the start of surgery and assayed for total free thiol. There was no significant difference in the aqueous thiol level of any of the treatment groups compared with the controls. No side effects were observed.

Absence of effect of simvastatin on the progression of lens opacities in a randomised placebo controlled study. Oxford Cholesterol Study Group

AIMS

A detailed assessment of ophthalmic effects of an HMG CoA reductase inhibitor, simvastatin, was performed.

METHODS

Six hundred and twenty one individuals considered to be at increased risk of coronary heart disease were randomised, following an 8 week placebo 'run in' period, to receive 40 mg daily simvastatin, 20 mg daily simvastatin, or matching placebo. Patients with a baseline corrected visual acuity better than 6/24 and without a history of cataract were eligible for detailed ophthalmic assessment at 6 months (539 patients assessed) and at 18 months (474 patients assessed).

RESULTS

No significant differences between the treatment groups were detected at the 6 month or 18 month visit in the refractive condition of the eye or in the mean intraocular pressure. Nor were there clear differences in the Oxford grading system scores for various measures of the major types of cataract (cortical spokes, posterior subcapsular cataract, nuclear brunescence, white scatter) or for other morphological features visible within the lens (fibre folds or focal dots). Scheimpflug slit image photographs and retroillumination analysis of the percentage of cataract within a defined region of the lens were also performed at each visit, with no clear differences observed between the treatment groups.

CONCLUSION

This single centre double blind study found no good evidence of any adverse effects of 18 months of simvastatin treatment on lens opacity formation, using a variety of validated techniques to assess cataract development. Routine clinic follow up of visual symptoms and admission to hospital for ophthalmic procedures over 5 years of treatment was also reassuring, with no excess adverse outcomes observed with simvastatin.

Heterogeneity in ultrastructure and elemental composition of perinuclear lens retrodots

PURPOSE

To unravel the cataractogenic process(es) leading to the birefringent lenticular bodies known as perinuclear retrodots.

METHODS

Ten human lenses containing biomicroscopically verified perinuclear retrodots were systematically screened and analyzed using scanning electron microscopy and energy dispersive x-ray microanalysis to verify their ultrastructure and elemental composition.

RESULTS

Three types of retrodots were distinguished, different in size, ultrastructure, and origin. Two of them contained calcium phosphate, the third probably contained calcium oxalate. All three types were separated from surrounding normal fibers and the crystalline inclusions were sequestered within membrane-lined bodies.

CONCLUSIONS

Because of these observations and data found in the literature it is postulated that elevated free calcium is the initiating factor in the formation of retrodots, trapped by either oxalate or phosphate and sequestered in the retrodots. It is suggested that the oxalate is derived from ascorbate because of impaired protection against oxidative stress in the older lens. Phosphoric acid is believed to be released by calcium-induced hydrolysis of membrane phospholipids.