Creutzfeldt-Jakob disease and the eye. I. Background and patient management

Basic and translational neuro-ophthalmology of visually guided saccades: disorders of velocity

INTRODUCTION

Saccades are rapid, yoked eye movements in an effort to direct a target over fovea. The complex circuitry of saccadic eye movements has been exhaustively described. As a result clinicians can elegantly localize the pathology if it falls on the neuraxis responsible for saccades. Traditionally saccades are studied with their quantitative characteristics such as amplitude, velocity, duration, direction, latency and accuracy.

AREAS COVERED

Amongst all subtypes, the physiology of the visually guided saccades is most extensively studied. Here we will review the basic and pertinent neuro-anatomy and physiology of visually guided saccade and then discuss common or classic disorders affecting the velocity of visually guided saccades. We will then discuss the basic mechanism for saccade slowing in these disorders.

EXPERT COMMENTARY

Prompt appreciation of disorders of saccade velocity is critical to reach appropriate diagnosis. Disorders of midbrain, cerebellum, or basal ganglia can lead to prolonged transition time during gaze shift and decreased saccade velocity.

Improved infection control in the prevention of variant Creutzfeldt-Jakob disease in Australia: costs and benefits

OBJECTIVE

To evaluate the costs and benefits of infection control strategies to prevent the transmission of variant Creutzfeldt-Jakob disease (vCJD) in ophthalmic surgery in Australia.

METHODS

The reduction in the risk of iatrogenic transmission of vCJD from feasible infection control strategies was calculated using decision analytic models. A static model calculated the direct secondary transmission for surgical eye procedures, and a simple dynamic model estimated the change in the risk of a subsequent sustained epidemic over the longer term. The expected number of vCJD infections, their cost of care and years of life lost and the estimated cost of strategies included the direct costs of infection control measures were calculated taking a health system perspective.

RESULTS

The dynamic model (Markov process) predicted that from a hypothetical pool of as many as 100 primary vCJD cases there would be less than five iatrogenic infections in the next 30 years. If there are fewer than five primary cases the model predicted no secondary cases of vCJD. The costs of providing care for a vCJD case is estimated to be about $50,000, subject to considerable uncertainty. The minimum cost for using a partial infection control strategy to prevent an iatrogenic infection is likely to be in the order of several millions of dollars.

CONCLUSIONS

Substantial public health investment would need to be made in order to reduce a low risk of iatrogenic transmission of vCJD. Given the likely number of cases of iatrogenic infection, and the order of magnitude of the costs of caring for cases of vCJD, it may be difficult to justify the high cost of risk reduction strategies.

Accuracy of the Tonosafe disposable tonometer head compared to the Goldmann tonometer alone

PURPOSE

To assess the accuracy of the Tonosafe disposable prism tonometer head via a randomised controlled prospective trial.

METHODS

The intraocular pressure (IOP) of 69 patients (31 men, 38 women) involving 137 eyes was measured using both the Tonosafe disposable and the Goldmann tono-meter head. The average age of patients was 66.5 years (range 23-93 years). The two examiners (PM and SL) who performed tonometry were masked while a separate observer read the IOP measurements. The order was randomised between Tonosafe and Goldmann devices. The minimum interval between the two measurements was 15 min. Patients with corneal and external diseases were excluded from the study.

RESULTS

The mean IOP using the Goldmann tonometer head was 17.44 +/- 4.97 mmHg. The mean IOP using the Tonosafe disposable head was 17.58 +/- 5.03 mmHg. The mean difference was 0.14 +/- 1.73 mmHg (95% CI -0.44, 0.16, P= 0.36). Subgroup analysis on eyes with IOP > 21 mmHg showed the Tonosafe disposable head was on average 0.15 +/- 2.40 mmHg higher than the Goldmann tonometer head. There was a high level of correlation between the IOPs obtained with the Goldmann and Tonosafe heads. Pearson's coefficient of correlation was 0.94 (P < 0.0001).

CONCLUSION

The Tonosafe disposable prism head was found to be accurate in IOP measurement, even in the higher range.

Creutzfeldt-Jakob disease following corneal transplantation

OBJECTIVE

To report a case of possible iatrogenic Creutzfeldt-Jakob many years following penetrating keratoplasty.

DESIGN

Observational case report.

METHODS

We reviewed the patient's chart, available literature on Creutzfeldt-Jakob disease, and current recommendations from the Eye Bank of America Association.

RESULTS

An 80-year-old woman with a history of granular dystrophy underwent penetrating keratoplasty in 1978 (OS) and 1987 (OD) for decreased visual acuity. In early July 2002 the patient developed rapidly progressive dementia. Attempts were made to procure information regarding the corneal donors. No information was available. The patient expired slightly less than 1 month after her onset of symptoms. Review of the EBAA medical standards before October 2002 reveal that donor records were to be kept for a minimum of 10 years.

CONCLUSION

Creutzfeldt-Jakob disease occurred 15 to 24 years after bilateral penetrating keratoplasy, but donor-to-host transmission was uncertain because no information on the corneal donor could be retrieved. Eye-bank records should be kept indefinitely because CJD may occur decades after iatrogenic exposure.

Comparison between standard Goldmann applanation prism and disposable applanation prism in tonometry

BACKGROUND

Disposable devices are increasingly becoming the preferred choice where possible in contact medical equipment.

AIM

To evaluate the accuracy of the disposable applanation tonometer head as a potential substitute to the standard Goldmann applanation head.

METHODS

The study was prospective. The intraocular pressure recordings in 80 eyes of 42 patients were compared using the disposable and standard Goldmann applanator heads. The Bland and Altman method of assessing agreement between two methods of clinical measurement was used in the analysis.

RESULTS

The difference in the readings between the two types of tonometer heads was highly variable (mean difference=0.78 mm Hg, range=-1 to 11 mm Hg). This was because of the distortions on the applanating surface of the disposable device. When the readings associated with the defective heads were excluded, very strong agreement was obtained (mean=0.07 mm Hg, range=-1 to 2 mm Hg).

CONCLUSION

Good agreement with standard Goldmann applanation is achieved with the disposable heads except where surface distortions induce significant errors. Careful inspection to ensure well-structured disposable units is imperative in disposable applanation tonometry.

Prions and the human transmissible spongiform encephalopathies

The last 5 years have seen the emergence of a new disease in humans (vCJD), mainly in the United Kingdom. This emergence has been accompanied by an explosion of scientific data on a novel group of the responsible infectious agents called prions and has profound implications for infection control and transfusion policies. Also of concern is the finding of prions in neural, gingival, pulpal, and salivary tissue in animal models and significant titers of infectivity from extraneural organs (particularly, in cases of vCJD, in lymphoreticular tissues). There is limited information on the presence of prion proteins in the oral tissues from human studies. Because of the differences in patterns of disease in animal models and in strains of prion protein, it is difficult to extrapolate directly these findings to humans, but it illustrates a potential for transmission by way of the dental route. High levels of infectivity may be present in tissues early in the incubation period and before clinical signs and symptoms. The dental profession must turn its attention to the routine decontamination of dental instruments to ensure that these procedures are performed to the highest regulatory standard. Clinicians and manufacturers must work closely together to develop instruments that are either single use or can be presented in a form that can be more easily decontaminated. Clinicians must pay close attention to manufacturers' decontamination instructions and must not reuse items designated as single use, such as endodontic files. Improvements in compliance with these requirements will not only reduce the risk of transmission of TSEs but also other less tenacious infectious agents.

Retention of corneal epithelial cells following Goldmann tonometry: implications for CJD risk

AIMS

To assess the adequacy of current decontamination methods for the Goldmann tonometer in the context of variant Creutzfeldt-Jakob disease (vCJD).

METHODS

Reusable Goldmann tonometer prisms were used to perform applanation tonometry on different groups of patients. Following tonometry, retained materials were collected from the tonometer prism head and examined using cytological methods. The used tonometers were subjected to a series of conditions to evaluate their effect on the residual cell numbers found on the tonometer heads. These included wiping alone and wiping or washing followed by disinfection of the tonometer prism. The effect on cell counts of drying the prism overnight was studied, as well as drying overnight and then wiping and disinfecting. All disinfections were performed with sodium hypochlorite (0.05% w/v).

RESULTS

The cytology specimens of 69 patients were studied. Patients using eye drops regularly desquamated significantly more corneal epithelial cells with Goldmann tonometry than patients not using regular eye drops. The mean number of cells was 156 (range 0-470) for patients using eye drops and 14 (4-57) for patients not using eye drops (p = 0.004). Wiping or washing the tonometer head reduced the cell number significantly but neither method completely eliminated cells. The two methods were not significantly different (p=0.3). Drying left a large number of cells (23-320 cells).

CONCLUSIONS

Retained corneal epithelial cells, following the standard decontamination routine of tonometer prisms, may represent potential prion infectivity. Manual cleaning was the most important step in reducing epithelial cell retention.

The risk of transmission of variant Creutzfeldt–Jakob disease via contact lenses and ophthalmic devices

This review collated the available information regarding the risk of transmission of variant Creutzfeldt-Jakob disease (vCJD) via contact lenses and other ophthalmic devices. The topics examined include: the emerging background science of the unconventional infective agent, the prion, particularly those factors affecting transmission; the estimates of the number of undiagnosed infective individuals; and evidence of infectivity in the external eye. Despite many uncertainties in the literature, we conclude that cross-infection is theoretically possible. An assessment of the extensive search for a complete inactivation procedure resulted in the recommendation of the use of sodium hypochlorite (NaOCl), which does not appear to distort rigid lenses. Further tests are required for other devices.

Debris on processed ophthalmic instruments: a cause for concern

PURPOSE

To assess the quality of processed ophthalmic instruments and look for the presence of foreign material on the surface of these instruments.

METHODS

Data were prospectively collected on the presence of debris on processed instruments in the trays used for phacoemulsification surgery. All instruments were examined under an operating microscope before use and details of the types of debris on the various instruments were noted. If debris was found, a new tray was opened to obtain a clean instrument.

RESULTS

Forty-seven trays were opened for use during the study period. Deposits on instruments were found in 29 (62%) trays. These were mainly present on the intraocular lens introducers. Loose fibres were found on instruments from eight (17%) trays. Debris was found in the aspiration channels of three (6%) hand pieces.

CONCLUSIONS

A significant number of processed ophthalmic instruments had debris on their surfaces. To reduce the risk of intraocular inflammation and of transmission of prion diseases the instruments should go through a thorough decontamination process before sterilization. Routine mechanical cleaning at the end of surgery and ultrasonic cleaning before sterilization should reduce the occurrence of debris on the instruments. Instruments should also be inspected under the operating microscope before use.

The sclera, the prion, and the ophthalmologist

Prions have emerged in the past 5 years as serious transmissible infective agents. Ocular tissue transplantation has come under scrutiny after potential infected tissue was transplanted into healthy patients. In this review we examine the evidence for the risk of transmission of prions after scleral transplantation and explore alternative materials that may be used in ocular surgery.

Evaluation of a disposable prism for applanation tonometry

BACKGROUND

Recently the Medical Devices Agency recommended that 'ophthalmic devices that touch the surface of the eye should be restricted to single use'.

AIM

To evaluate one such device: a disposable tonometer prism for routine applanation tonometry.

METHODS

The intraocular pressure (IOP) of 100 consecutive patients from a general eye clinic (197 eyes) was measured with both a disposable and the standard Goldmann tonometer (Goldmann). The level of agreement between the two methods of clinical measurement was assessed and the sensitivity and specificity of the disposable prism in detecting clinically significant raised IOP estimated.

RESULTS

The mean difference in IOP measured by the two different prisms was 0.44 mmHg with a standard deviation (SD) of 1.54. The mean IOP for the disposable prism was 19.51 mmHg (SD 6.53 mmHg). The mean IOP for the standard Goldmann tonometer prism was 19.07 mmHg (SD 6.64 mmHg). The sensitivity to detect IOP > 21 mmHg was 95.9% (95% confidence interval (CI): 86.0-99.5%) and the specificity of 93.9% (95% CI: 88.8-97.2%). It gave a positive predictive value of 83.9% (95% CI: 71.7-92.4%).

CONCLUSION

There was close agreement between the IOP measurements obtained by the disposable tonometer prism and the Goldmann device for high and low pressures. If replicated, the high sensitivity and specificity would justify its use in screening.