A comparative study on the viscoelastic properties of human and animal lenses.

A new method of compression between two parallel plates is used to measure the viscoelastic properties of whole and decapsulated human lenses and compare them with other animal species. Compressive load relaxation was performed by deforming the lens by 10% and measuring the force relaxation response for 100 s to obtain thickness, stiffness and relaxation of the induced loading force and Maxwell parameters for human, monkey, porcine and leporine whole and decapsulated lenses. Thickness and percentage loading force relaxation increased linearly with lens age, whereas stiffness and induced loading force increased exponentially. Human and monkey lenses aged at different rates. Loading force relaxation in a generalized Maxwell model was described by three time constants ranging from 1 to 1000 s. Compressive load relaxation is a very versatile method to study the viscoelastic properties of whole and decapsulated lenses and potentially also artificial accommodating lenses. The data presented in the study will help researchers choose the most suitable animal lenses based on the desired properties and age to be mimicked from the human lenses.

Ethambutol-induced optical neuropathy: risk of overdosing in obese subjects.

BACKGROUND: Ethambutol (EMB) is one of the first-line drugs in the treatment against tuberculosis (TB). Side-effects are infrequent, but its main adverse effect, optical neuropathy, has long been recognised. The mechanisms of action and predisposing factors have not yet been fully understood. METHOD: We conducted a retrospective study (1992--2007) in an attempt to find predisposing factors for optical neuropathy. RESULTS: Visual disturbance was reported in 1.3% of the 760 patients treated with EMB; of these, 0.8% were EMB-related. We present the six cases; four were clearly overdosed, but in two obese patients dosage was correctly calculated for total body weight (TBW). CONCLUSION: Analysis of the case histories and previous reports suggest that optical neuropathy may at least partly be caused by EMB overdosing due to daily dosing based on TBW instead of dosing on lean body mass.

[High-energy ocular trauma and changes in vision: a reason for a careful search for an intraocular foreign body]. / Hoogenergetisch oogletsel en visusveranderingen: reden voor nauwkeurig onderzoek naar een intraoculair corpus alienum.

A 50-year-old man visited his family physician one day after he had felt something entering his left eye following the blow of a metal hammer on metal, after which he began to see black spots. After the eye had been occluded for 4 days, his visual acuity had decreased to 0.1. Ophthalmologic examination revealed a defect in the cornea and iris, a foreign body in the vitreous and local cataract. Following surgical removal of the metal splinter and the lens, the visual acuity was restored to 0.8. Implantation of an artificial lens was planned. Ocular trauma is a major cause of permanent visual loss or blindness in (young) adults in the western world. Traumas in which a foreign body is propelled into the eye with high energy are most likely to penetrate the sclera. Damage and complications due to intraocular foreign bodies may lead to loss ofvision. The entry site of an intraocular foreign body may be difficult to find and the diagnosis may be missed. Therefore, an ophthalmologist should be consulted in case of a high-energy trauma in combination with visual loss.

Written case reports as assessment of the elective student clerkship: consistency of central grading and comparison with ratings of clinical performance.

The assessment of the elective clerkship at the University of Groningen consists of a written case report, graded by one of four independent reviewers, and a rating of clinical performance by the students' supervisors. This study analyses the grades of 710 case reports and 189 ratings. The grades were found to be normally distributed, similar for the reviewers and consistent over the years, but inter- or intra-observer variation was not studied. The ratings of clinical performance were skewed towards 'excellent'. There was a low correlation between the two assessments (Spearman's r = 0.25; p = 0.001). This may be attributed among other things to the large number of supervisors and the face-to-face assessment of clinical performance versus the distant assessment of a written document. A more relevant explanation, however, is that the case reports measure primarily cognitive aspects, as compared with overall clinical performance.

Quality of care from the perspective of the cataract patient: the reliability and validity of the QUOTE-cataract.

BACKGROUND/AIMS: To assess reliability and validity of the QUOTE-cataract, a questionnaire that measures the quality of care from the perspective of cataract patients. METHODS: The QUOTE-cataract was tested in a multicentre study among 540 cataract patients in three different hospitals. Reliability was represented by internal consistency (Cronbach's alpha), and repeatability (intraclass correlation coefficient (ICC)). Validity was evaluated qualitatively and by factor analyses. RESULTS: A strong internal consistency coefficient (0.89), and high repeatability (ICC = 0.76) demonstrated good reliability. Content validity was assured by involvement of patients in the development of the questionnaire. Factor analysis confirmed an underlying taxonomy of generic and disease specific items. CONCLUSION: The QUOTE-cataract has good reliability and provides a valid assessment of quality of care in cataract surgery.

Injectable intraocular lens materials based upon hydrogels.

The possibilities to develop an injectable hydrogel lens were investigated. Aqueous solutions of reactive polymers in combination with a water-soluble blue light photoinitiator were transformed into hydrogels by irradiation with blue light. Poly(ethylene glycol) diacrylates (PEGDA) with low molecular weights and an acrylate modified copolymer of N-vinylpyrrolidone and vinyl alcohol with a high molecular weight were used as reactive polymers. A copolymer of (4-vinyl-2,6-dimethylbenzoyl)diphenylphosphine oxide and dimethylacrylamide was used as a water-soluble blue light photoinitiator. PEGDA showed high reactivity and the hydrogels were more transparent than the natural lens. The mass loss and the additional swelling of the hydrogel were 1.0 and 4.0%, respectively. The refractive index of these hydrogels was 1.40, lower than that of natural lens. The viscosity of the solutions before cross-linking was too low for injection into the capsular bag. Hydrogels based upon the copolymer had a transmission comparable to a 25-year-old natural lens. The materials showed no mass loss and the additional swelling after curing was less than 1%. The refractive index was comparable to that of the natural lens (1.42). The viscosity of the polymer solutions was sufficient for injection into the capsular bag without leakage.

Cataract surgery and anticoagulants.

A questionnaire was sent to 240 members of the Netherlands Intraocular Implant Club (NIOIC) to register their policy followed in 1993 with regard to anticoagulant therapy (ACT) and the use of aspirin in patients having cataract surgery. Ninety-one (32%) forms were suitable for analysis. Most eye surgeons (76%) declared to discontinue anticoagulant therapy and the use of aspirin prior to cataract surgery, especially when using local anesthesia. After stopping anticoagulant therapy and the use of aspirin serious systemic complications were reported. Furthermore, ocular complications were reported due to continuation of ACT and the use of aspirin during surgery. Although the response rate to the enquiry was 32% only, we would suggest that continuation of ACT and the use of aspirin during surgery is to be recommended because of the possible life threatening complications related to discontinuing ACT and the use of aspirin. Risks of bleeding can be minimized further by using topical anesthesia, sub-tenon anesthesia and clear corneal surgery.

Clinical evaluation of two non-contact tonometers.

The precision and speed of two non-contact tonometers were examined and compared. The Goldmann applanation tonometer was used as the standard for precision. On the average the results obtained with the non-contact tonometers were not significantly different from those obtained with the Goldmann tonometer. The variation in the values obtained with the non-contact tonometers was greater. The speed of measurement differed between the two non-contact tonometers.

Fusional vergence in microstrabismus.

The fusional vergence velocity was studied in microstrabismus and in normal persons. In microstrabismus the system works less precisely in that small changes in disparity produce no response, while it is possible that the difference between the amplitude of the stimulus and the amplitude of the response is greater.