Influence of LASIK on scanning laser polarimetric measurement of the retinal nerve fibre layer with fixed angle and customised corneal polarisation compensation.

BACKGROUND/AIM: Retinal nerve fibre layer thickness (RNFLT), as measured with scanning laser polarimetry using the fixed angle corneal polarisation compensator (SLP-F), has been found to be reduced after uncomplicated laser assisted in situ keratomileusis (LASIK) compared to the pre-LASIK measurement. Since this virtual RNFLT thinning is attributed to the corneal changes induced by the LASIK, the authors investigated whether customised corneal polarisation compensation (SLP-C), which compensates for the actual corneal polarisation during each measurement, can avoid the LASIK induced, virtual changes of the polarimetric RNFLT values. METHODS: Scanning laser polarimetry using both the SLP-F and SLP-C methods (GDx-Access, software version 5.0) was performed on 15 consecutive healthy subjects with no eye disease who underwent LASIK for ametropia correction. The SLP measurements were performed before the surgery, then on day 1 and day 6 after LASIK. Thickness data from images of one randomly selected eye per subject were analysed using the ANOVA and Scheffe multiple comparison tests. RESULTS: Superior maximum, inferior maximum, normalised superior area, and normalised inferior area (SLP parameters representing the RNFLT at the superior and inferior poles of the optic nerve head) remained unchanged with SLP-C (ANOVA, p>0.05) but decreased (superior maximum, normalised superior area, Scheffe test, p<0.05) or tended to decrease (inferior maximum) after LASIK, when measured using SLP-F. In contrast, certain other parameters-namely, superior ratio and inferior ratio (representing the ratios between the superior or the inferior sector and the temporal sector), maximal modulation, and ellipse modulation decreased with SLP-C (Scheffe test, p<0.05), but remained stable with SLP-F (ANOVA, p>0.05) after LASIK. Superior to nasal ratio, symmetry of the superior and inferior RNFLT as well as the parameter showing the probability of having glaucoma (called "the number") remained unchanged with both types of corneal compensation (ANOVA, p>0.05). With SLP-C the parameter ellipse average thickness increased after LASIK (Scheffe test, p = 0.021). No parameter value altered between day 1 and day 6 after LASIK, for either method. CONCLUSION: The results suggest that the LASIK induced decrease of the polarimetric RNFLT, which is consistently detected with polarimeters when using the fixed angle corneal polarisation compensator, is due to alterations of the corneal polarisation. The use of customised corneal polarisation compensation avoids this virtual decrease of the polarimetric RNFLTHowever, our results suggest an increase of the measured retardation in the temporal quadrant of the SLP-C image after LASIK. Since ratios of parameters using the temporal RNFLT in the denominator are important in the polarimetric glaucoma diagnosis algorithm, their decrease as a consequence of using SLP-C needs further investigation.

Orbital malignancy in Papua New Guinea: a 21 year review.

BACKGROUND: Information about orbital malignancies in Papua New Guinea (PNG) is limited to reports published 20 years ago. The present retrospective study was performed to establish the pattern of malignant orbital lesions occurring in PNG and to see whether the pattern is any different from that reported in the earlier series and in other countries. Papua New Guinea is special in that it has a large and relatively homogenous population unaffected,to a large extent, by contact with the'outside world'. METHODS: The records of 176 proven cases of orbital malignancy treated between 1975 and 1996 were studied with respect to type of tumour, age, gender; mode of presentation and, where possible, treatment and its outcome. RESULTS: Orbital tumours were found to be uncommon relative to other malignancies. The most common orbital tumour encountered in the present study was orbital extension of retinoblastoma (40.3%). These tumours were all unilateral and were associated with a very high mortality. No bilateral or familial cases were seen. Squamous cell carcinomas were the second most common tumours (25.6%) and were seen in young adults (average age 36.6 years). Basal cell carcinomas (9.1%) occurred later (average age 54 years) and were more common in the lighter-skinned Southern Highlanders and expatriates. The other malignancies seen included lacrimal gland tumours (3.4%), malignant melanomas (4.5%), lymphomas (3.4%), rhabdomyosarcomas (1.7%), meibomian cell carcinomas (1.7%) and soft tissue sarcomas. CONCLUSIONS: Most patients presented late and the mortality rate was high. This could also reflect the relative paucity of ophthalmic and oncological services in the country as well as psychosocial attitudes to disease. Many patients live far from medical services and may be treated by traditional healers before coming to a hospital.

Intraoperative use of mitomycin C in the treatment of recurrent pterygium.

The prevalence rate of pterygium in Papua New Guinea (PNG) is as high as 15%. Recurrence rates up to 50% are encountered after primary excision. In a country such as PNG where resources in terms of funds and manpower are limited, a simple procedure had to be identified to reduce this alarmingly high rate of pterygium recurrence. This article compares the results of a randomized masked study involving the single intraoperative application of 0.02% mitomycin C solution in 65 eyes undergoing surgery for recurrent pterygium using the bare sclera technique with a similar group of 65 patients in which the drug was not used. The results indicate that a single intraoperative application of mitomycin C solution was enough to reduce the recurrence rate of pterygium to 3% in the treated group as compared to 48% in the untreated group at the end of a 12-month follow-up. In the study it was also seen that, in PNG, pterygia were more common in females and that recurrences tended to occur early and were obvious in the first few weeks following surgery.