G M Thompson

The human anterior lens capsule--an attempted chemical debridement of epithelial cells by ethylenediaminetetracetic acid (EDTA) and trypsin.

The addition of edetic acid (EDTA) or trypsin to the infusion during a simulated extracapsular cataract extraction on cadaver eyes facilitates the removal of lens epithelial cells from the anterior capsule. Modification of the chemical composition of infusions used during extracapsular surgery may maximise lens epithelial cell removal and hence reduce the incidence of opacification of the posterior capsule after cataract extraction.

Hardness and ultrasonic characteristics of the human crystalline lens

Purpose: To evaluate the relationship between hardness of the human crystalline lens and its acoustic characteristics. Setting: St. Georges Hospital Medical School, University of London, London, United Kingdom. Methods: Cataractous lenses from patients who had extracapsular cataract surgery were studied for hardness and ultrasonic characteristics. Lens hardness was assessed with an automated guillotine. Ultrasound velocity and attenuation were measured with a scanning acoustic macroscope using the pulse transmission reflection method. Results: Thirty‐seven lenses from 37 patients (mean age 75.5 years) were evaluated. Lens hardness was associated with ultrasound attenuation (r = 0.65, P < .0001) and attenuation frequency gradient (r = 0.67, P < .0001). The correlation of hardness with mean ultrasound velocity was not significant (r = 0.22, P = .2). Conclusions: The attenuation of ultrasound waves by the human crystalline lens correlated with its hardness. Ultrasonography can be used to evaluate lens hardness.

The relationship between clinical classification of cataract and lens hardness.

‘Hardness’ of the cataractous lens is one of the major factors influencing the suitability of a patient for phacoemulsification. Surgeons should be able to estimate hardness when choosing patients for this method of cataract extraction. The aims of the study were to investigate the relationship between the clinical appearance of cataracts and their hardness. Ninety-one lenses were studied from patients undergoing endocapsular cataract extraction. Lenses were assessed using a classification based on the Lens Opacities Classification System II and hardness was assessed using an automated lens guillotine. The degree of nuclear sclerosis and the age of the patient were found to influence lens hardness. Regression analysis showed that 56% of the variation in hardness could be explained in terms of age and the degree of nuclear sclerosis. The presence of posterior subcapsular and cortical cataract did not influence hardness. These findings confirm our clinical suspicions and enable surgeons to make a more objective analysis of hardness prior to phacoemulsification.

Cytological factors relating to posterior capsule opacification following cataract surgery.

Simulated extracapsular cataract extractions on cadaver eyes were performed which demonstrated that the cells of the anterior capsule remain largely intact and that only a small amount of cortical lens matter remains postoperatively. Human lens epithelial cells from normal and cataractous lenses were grown in culture. There was no appreciable difference in growth rate between cells from normal and those from cataractous lenses or between equatorial and central capsule cells. The cells grew from the cut edges of the capsule, suggesting that release from contact inhibition is an important factor in stimulating proliferation. The daughter cells became increasingly abnormal and metaplastic in successive generations, but there was no evidence of differentiation into fibroblasts within the 35-day culture period, suggesting that a retinal growth factor may be involved with the fibrosis occurring in opacification of the posterior capsule. A small anterior capsulotomy will release fewer cells from contact inhibition and hence reduce cell proliferation after extracapsular cataract extraction.

Sickle retinopathy in patients with sickle trait

Sickle trait is traditionally considered a benign condition by ophthalmologists. Three cases of sickle retinopathy in subjects with sickle trait are reported. In all cases the onset of retinopathy was related to other contributing factors: in one case a traumatic hyphaema and raised intraocular pressure, in two others diabetes mellitus. Patients with sickle trait are at risk of retinopathy if coincident ocular or systemic disease is present.

The human lens epithelium; morphological and ultrastructural changes associated with steroid therapy.

A distinct disturbance to the structure of the lens epithelium was observed in cataract patients receiving steroid medication. Of those cataract patients receiving steroids, 83% exhibited a reticulated pattern of intercellular clefts compared to 5% in the control group. The reticulated pattern was shown to be due to the presence of gaps between the lateral borders of the epithelial cells by electron microscopy. A significant correlation between steroid therapy and epithelial disruption was demonstrated. The significance of such epithelial disruption to cataract formation is discussed.

The effects of steroids on the human lens epithelium

A study of anterior capsules from cataractous lenses revealed that there are marked abnormalities in epithelial structure associated with cataract. In certain cases a distinctive reticulated pattern was observed in whole mounts of the anterior capsule and of these a higher number than expected were from patients receiving steroid medication. In tissue culture experiments it was found that the presence of steroids in the growth medium (10 µM prednisolone) adversely affected the growth of human lens epithelial cells.These observations are consistent with the hypothesis that steroid-induced cataracts are the result of effects on anterior lens epithelial cell function.

Penetration of oral and topical ciprofloxacin into the aqueous humour

Aims: To investigate the penetration of ciprofloxacin via different modes of administration into the aqueous humour using capillary zone electrophoresis and to determine its prophylactic role in ophthalmic surgery.

Phenylephrine and pilocarpine in the treatment of post-operative irido-corneal adhesion

Following cataract surgery, entrapment of the iris within the surgical wound is often managed by intensive use of miotics. As the radial fibres stretch, only a small amount of traction is exerted upon the entrapped iris. Application of a combination of phenylephrine and pilocarpine drops causes simultaneous contraction of the pupil sphincter and the radial muscle fibres. This study investigated the relative magnitude of forces induced in the iris periphery by pilocarpine and phenylephrine and the effectiveness of adding g. phenylephrine 10% to g. pilocarpine 4% drops in the treatment of postoperative irido-corneal adhesions. The investigation was divided into two parts. First, the forces induced in the iris periphery upon exposure to pilocarpine and phenylephrine were measured in 6 cadaver irises. The mean force was 27.5 ± 5.7 X 10-3 N for pilocarpine and 23.3 ± 4.0 × 10-3 N for phenylephrine. The combination of the two drugs produced a force of 54.2 ± 6.6 × 10-3 N (p<0.05). In the second part of the study intensive pilocarpine 4% drops were administered to 17 patients who had iris-wound entrapment on the first post-operative day. Patients with persistent adhesion were commenced on intensive g. phenylephrine 10% and assessed after 90 minutes. Of the 17 patients, 6 responded to pilocarpine drops alone; in a further 7 the irido-corneal adhesion was released only by the addition of phenylephrine drops, and in 4 patients drops were ineffective in relieving the adhesion. This study indicates that addition of phenylephrine 10% to pilocarpine 4% drops enhances the effectiveness of pharmacological treatment of post-operative irido-corneal adhesion.

Lens hardness in mature cataracts

A cataract is said to be mature when all the cortical fibres become opaque. Depending on the pathophysiological processes that cause the cortical fibre opacification this phenomenon may be associated with a varying degree of nuclear sclerosis. A relationship between lens hardness and degree of nuclear sclerosis in non-mature cataracts has been demonstrated previously. This study aimed to investigate the relationship between the hardness of mature cataracts and the transmitted nuclear colour, age and rate of progression of the cataract. Thirty-eight patients with mature cataracts were assessed prior to extracapsular cataract surgery. The nuclear colour that was transmitted through the opaque cortex was graded using reference photographs. Age and duration of visual symptoms were recorded and lens hardness was measured by a specially designed lens guillotine. Multivariate analysis of data indicates a relationship between hardness of a mature cataract and the transmitted nuclear colour and age (adjusted R2 = 0.59). There is also a tendency for hardening of the lens as the duration of visual symptoms increases. By considering these clinical markers, the cataract surgeon can estimate the hardness of the lens and therefore its suitability for phacoemulsification.