Conjunctival squamous cell neoplasia is a serious problem with a high impact on public health owing to its relatively high prevalence and the potential to cause severe disability. We conducted a study to find the association of sun exposure and HPV infection and the neoplasm.
The study was designed in such a way to minimise biases. Sampling bias may occur if only selected cases were included. In this study we searched the archival tissue for the most recent cases. We found a variety of stages of diagnosis. However, these cases were from a hospital based population, which is an unrepresentative sample of the general population. In order to obtain a comparable group of samples with equal opportunity to reach medical attention, the controls were recruited from the same hospital.
With a further attempt to minimise any unknown confounders, control specimens were age and sex matched to the cases. Matching increased the power of the comparison between groups by balancing the number of cases and controls at each level of the constitutional factors. Elastic staining and HPV DNA detection were compared with the positive and negative controls to enhance the validity of measurement. Two pathologists interpreted the results to increase the reliability of the study. We blinded the outcome assessors of the case-control status in order to prevent ascertainment bias.
Solar elastosis is a pathological manifestation of actinic damage to the tissue where collagen, ground substance, and fibrocytes alter to abnormal “elastotic” material. This finding was used as a pathognomonic sign in the pathological diagnosis of degenerative diseases of the conjunctiva such as pinguecula and pterygia.18
Solar elastosis can be demonstrated in routine haematoxylin and eosin stain as blue-grey, wavy, and irregular sizes of strands in the subconjunctival areas. This material changes its colour to dark brown after elastic staining. We found different proportions of positive solar elastosis between neoplastic cases and non-diseased conjunctival controls. The odds ratio showed that solar elastosis is related to malignant changes of the conjunctiva. Owing to the small sample size, the confidence interval of the odds ratio was rather large.
The dose-response relation is one of the criteria to establish a causal effect of exposure to the disease. We, however, did not measure the solar elastosis quantitatively because the retrieved specimens were previously sectioned to generate pathological reports, and later to detect HPV infection.
We extracted DNA from paraffin embedded specimens with the most appropriate technique as previously described by Chan et al
Unfortunately, we could not find any positivity on HPV infection in the study. This might be because of low prevalence of the viral infection.
Multiple factors may contribute to the development of the disease. Further studies to explore all factors in a single situation would contribute to more useful information. Since HIV infection is a possible confounding factor,26–30
the investigation on HPV and HIV infections together with special characteristics on pathological figures will predict the diseases more definitely.
In conclusion, sun exposure, as demonstrated by pathologically proved solar elastosis of the subconjunctival tissue, is one of the risk factors to develop conjunctival squamous cell neoplasia. More studies need to be performed to explore the relation of this tumour to multiple factors.