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Purpose: In phakic silicone oil-filled eyes, removal of the silicone oil can be combined with phacoemulsification and intraocular lens (IOL) implantation. True axial length (AL) of the silicone oil-filled (viscosity 1300 centistokes) eye can be estimated from the measured AL (MAL) obtained on A and/or B scan echography, by multiplying MAL by a conversion factor of 0.71. IOL power can then be calculated using current biometry formulae (SRK/T). This study aims to evaluate the conversion factor in clinical practice., Methods: Eleven patients undergoing combined removal of silicone oil and phacoemulsification with IOL implant were studied. Patients were divided into two groups. In Group 1 (seven patients), the IOL was placed in the capsular bag and in Group 2 (four patients) the IOL was placed in the ciliary sulcus. Calculated AL (CAL) was obtained by multiplying the MAL of the silicone oil-filled eye (as measured on A or B scan ultrasonagraphy) by the conversion factor of 0.71. IOL power was then estimated using the CAL in the SRK/T formula. The spherical equivalent of the postoperative refractive error was compared to predicted refractive error., Results: The mean difference in actual and predicted refractive error was 0.74 dioptres (D) (standard deviation 0.75 D) for Group 1 and 1.31 D (standard deviation 1.4 D) for Group 2., Conclusions: The conversion factor of 0.71 corrects for the apparent increase in AL induced by silicone oil of viscosity 1300 centistokes. This allows accurate prediction of the required IOL power in eyes undergoing combined cataract extraction, removal of silicone oil and lens implant. Sulcus placement of the IOL gives a less predictable result than placement in the capsular bag.

Purpose: The advent of silicone oil tamponade has resulted in improved success rates in complicated retinal detachment surgery. Its use, however, can induce cataract formation in phakic eyes. In selected patients, removal of silicone oil can be combined with phacoemulsification of the cataract and intraocular lens (IOL) implantation, thus avoiding a further operation. This, however, poses a problem when trying to decide the power of IOL to be used, since the echographically measured axial length (AL) of an eye is greater in the presence of silicone oil. We performed ultrasound examination in the presence of silicone oil of viscosity 1300 centistokes, in order to determine whether the measured AL varied from the true AL by a constant factor., Methods: The ALs of 7 phakic eyes were measured by A-mode echography, with and without silicone oil of viscosity 1300 centistokes in the posterior segment. The retina was attached in all cases. The control group consisted of 6 phakic eyes with attached retinae undergoing vitrectomy without the use of silicone oil. The ALs in the control group were measured before and after vitrectomy., Results: The mean ratio of true AL to measured AL in the presence of silicone oil was 0.71 (standard deviation 0.01; range 0.70-0.73; median 0.71) in the 7 eyes in this study. In the control group, vitrectomy appeared to have no significant effect on AL., Conclusions: We have established a constant which corrects for the apparent increase in AL induced by silicone oil of viscosity 1300 centistokes. This conversion factor, when used in existing biometry formulae (SRK/T), allows estimation of the power of IOL required in eyes undergoing combined cataract extraction, removal of silicone oil and lens implantation.

Purpose: Fuchs' heterochromic cyclitis (FHC) is an inflammatory disease of unknown aetiology. Although anterior segment signs and vitreous changes are well recognised, retinal features are unusual. To assess the extent of retinal involvement, we performed electrophysiological testing in a group of FHC patients., Methods: Retinal function was assessed by means of flash electroretinogram (ERG) using a Ganzfeld stimulus, and pattern electroretinogram (PERG) using a checkerboard stimulus of spatial frequency 0.5 and 1.0 cycle per degree reversing at 6 Hz. A total of 21 patients with unilateral, normotensive FHC with visual acuities of 6/5 to 6/9 were studied., Results: In the flash ERG, selective scotopic b-wave abnormalities occurred in 9 (43%) of 21 FHC eyes. Despite clear media and no history of ocular surgery, 7 patients showed abnormalities of the PERG., Conclusions: These electrophysiological findings suggest subclinical damage to the inner retinal layers, but not involving the photoreceptors, in eyes with FHC.