Macular oedema (MO) is an established complication of intraocular surgery and is one of the leading causes of poor post-operative visual acuity after keratoplasty.1–7 MO is a localised expansion of the retinal intracellular and/or extracellular space in the macular area. This tendency towards the macular region is probably associated with the loose binding of innerconnecting fibres in Henle’s layer, allowing accumulation of fluid leaking from peri-foveal capillaries.
The aim of this study8 was to assess the incidence of MO following keratoplasty and to identify factors that are associated with oedema using optical coherence tomography (OCT). The device utilised was an OCT 3 (Stratus, Carl Zeiss Meditec, Dublin, California), the only device capable of providing a detailed analysis of retinal tissue, and an objective, reproducible and reliable measurement of retinal thickness.7,9 OCT is a highly sensitive tool that allows reproducible measurements of retinal thickness with reproducibility of ±5%. It is a more powerful investigative tool than the biomicroscopic or angiographic examinations previously reported in the literature: both are qualitative and insensitive to small changes in retinal thickness.
Materials and Methods
This prospective study involved 62 patients who were all operated on by the same surgeon. Informed consent was obtained from all patients. Forty-three (69.35%) underwent penetrating keratoplasty and 19 (30.65%) deep anterior lamellar keratoplasty (using the big-bubble technique). We realised a deep anterior keratoplasty with pathologies involving the corneal stroma and sparing the Descemet membrane. Combined surgery was performed for 20 patients. Of this number there were secondary implantations for nine patients, cataract extractions for eight and iris plasties for three. The indications for surgery were as follows: keratoconus in 18 cases, pseudophakic or aphakic keratopathy in 18 cases, Fuchs dystrophy in 10 cases, viral corneal scar in seven cases, re-graft in five cases and corneal oedema following closed angle glaucoma in four cases.
We analysed the morphological characteristics of the macula by OCT 3 one and three months after surgery using ‘line group’ mode, with 6mm sections centred on the patient’s fixation point along various axes. We also measured central macular thickness (CMT). CMT was defined as the average thickness of a central macular region 1000μm in diameter, centred on the patient’s foveola and automatically measured by OCT 3 and A5 mapping software (Humphrey Instruments, Dublin, California).
MO was defined as increased central retinal thickness, to more than 250μ (retinal thickness in healthy eyes is 212±20μ)8 with intra-retinal cystoid-like spaces that appeared as round or oval areas of low reflectivity. OCT investigations before keratoplasty were not possible due to corneal transparency. Student’s t-test and Fisher’s test were used for statistical analysis.