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.