There is little reported information on repeatability of clinical methods of assessment in ophthalmology or of questionnaire data on visual disability.2 It was therefore thought desirable, while carrying out a 2-centre study into the relative severity of cataract in groups of patients,3 also to investigate the amount of variability which occurred in examination findings and questionnaire responses so that the repeatability of the currently employed methods might be assessed.Disagreements in repeated observations on the same subjects by the same observer are termed 'within-observer error'. This may be due to inconsistency in technique or interpretation of results, and the variation tends to be random. Variation which occurs between different observers when they assess the same subjects is termed 'between-observer error', is usually due to differences in technique or interpretation, and tends to be systematic. PATIENTS AND INTERVIEWSThree hundred patients over 65 years old attending the outpatient department of the Royal United Hospital, Bath, and the Bristol Eye Hospital, who were noted on examination to have lens opacities which reduced the visual acuity to 6/9 or less, were interviewed and had an ophthalmic examination. All interviews were conducted by H.F.S., who also abstracted clinical data from the hospital notes and supplemented them by direct questioning of the clinician who had examined the patient. Patients who were fit enough to travel by car and who lived close to one or other of the 2 hospitals were invited to attend for re-examination; of the 300, 64 agreed to do so. Statistical examination of the data obtained about these 64 patients showed that this method of selection did not introduce bias.3At the return visit all the 64 patients had an ophthalmic examination performed by R.A.G. with equipment similar to that used at the first examination. Interview was carried out by H.F.S. Re-examination and interview were performed without reference to the previous records in order to minimise possible bias introduced by knowledge of the original findings. The time that elapsed between first and second examination varied between three weeks and two months. Records of the first and 457 on 7 May 2018 by guest. Protected by copyright.

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SUMMARY Corneal sensitivity measurements were performed on both eyes of 57 patients after they were subjected to unilateral retinal detachment surgery, the unoperated eyes acting as controls. A marked decrease in corneal sensitivity was found in eyes that were treated with encircling bands, but no significant change of sensitivity could be detected in eyes in which localised radial or circumferential silicone sponge explants alone had been employed. It would appear that encirclement procedures lower the sensitivity of the cornea, and this may continue as a long-term effect.Sensory impulses from the cornea are conducted in the long and short ciliary nerves which lie in the suprachoroidal space prior to piercing the sclera at the posterior pole of the eyeball.' While in the suprachoroidal space the ciliary nerves are potentially vulnerable to the trauma, both thermal and mechanical. which is deliberately applied as part of the surgical therapy for rhegmatogenous retinal detachments. There is evidence from both experimental2 and human studies3 that cooling of nervous tissue may interfere with impulse conduction. However, there is little published information about the effects on ciliary nerve function of mechanically distorting the choroid by the explants used in retinal detachment surgery.To determine whether corneal sensitivity does indeed become impaired following retinal detachment surgery a study was instituted in which corneal sensation was recorded with the Cochet-Bonnet corneal aesthesiometer4 in patients who had undergone previous unilateral retinal detachment surgery. Materials and methodsPatients who had undergone strictly unilateral retinal detachment surgery in the Bristol Eye Hospital during a 2-year period from January 1978 to December 1979 were recalled for corneal sensitivity measurements in each eye. The formed acted as a control. Factors which included variations between individuals, humidity, age,7 menstruation,8 pregnancy,9 and diurnal variation of sensitivitv'°could therefore be neglected.To avoid observer bias" the type of retinal detachment procedure was not known to the examiner until after corneal sensitivitv measurements had been determined.The patients were seated at a slit-lamp, and the fellow eye was stabilised with the fixation light attachment of the slit-lamp. Under a x 12'5 magnification the nylon filament of a hand-held aesthesiometer was applied at a slow, constant speed to the cornea at right-angles to this tissue's surface until the filament was seen to just bend. All studies began with the filament extended to its longest length of 6 cm and subsequently retracted by centimetre decrements until at each point tested 50% of the touches were reported by the subject. Each corneal point was touched 4-6 times with at least one blank to test the subject's reliabilitv. Five corneal points were stimulated,'2 first at the corneal centre and then midway between centre and limbus at the 6. 9. 3. and 12 o'clock positions on the cornea; the sensitivitv measurements were plotted on charts a...

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