Use of polymerase chain reaction in detection of Mycobacterium tuberculosis complex DNA from vitreous sample of Eales’ disease
- Dr Jyotirmay Biswas.
Editor,—Eales’ disease, first described by Henry Eales in 1880 is a primary retinal perivasculitis that predominantly affects the peripheral retina of young and otherwise healthy adults in the age group 15–40 years. Of the several aetiologies proposed, most favoured are tuberculosis and hypersensitivity to tuberculoprotein.1 Since polymerase chain reaction (PCR) using primers for the insertion sequence of IS6110 consisting of upstream primer: 5′ CCTGCGAGCGTAGGCGT CGG3′ and downstream primer: 5′CTC GTCCAGCGCCGCTTCGG 3′ coding for 123 bp product, has found a universal acceptance for detection of Mycobacterium tuberculosis complex DNA in clinical specimens,2 we applied it on vitreous fluid samples obtained from clinically diagnosed patients with Eales’ disease and controls (undergoing vitreous surgery for proliferative diabetic retinopathy and proliferative vitreoretinopathy).
Uncontaminated vitreous fluid from 12 cases of Eales’ disease and 45 non-Eales’ disease control patients collected at the beginning of vitrectomy were subjected to PCR using IS6110 primers for the presence of M tuberculosis complex DNA.2-4 PCR was found to be specific and sensitive enough to detect 2.5 pg of M tuberculosis complex DNA. Five (41.6%) among 12 vitreous fluid samples from Eales’ disease (Fig 1) and only one (2.2%) out of 45 vitreous fluid samples from the control group were positive by PCR and this difference was statistically significant (Pearson-χ2 <0.001). Vitreous fluid from both groups of patients did not reveal the presence of acid fast bacilli by direct smear and culture by standard conventional techniques.
Results of PCR using IS6110 primers on vitreous aspirates of Eales’ cases. Lanes: 1, case 1 (positive); 2, case 2 (negative); 3, case 3 (negative); 4, case 4 (positive); 5, case 5 (positive); 6, positive control (H37Rv); 7, negative control (reagents); 8, molecular weight marker (Phi x 174 Hinf 1 digest).
The presence of M tuberculosis complex DNA in a statistically significant number of vitreous fluid samples of Eales’ disease patients compared with the control group leads us to hypothesise the presence of sequestrated mycobacterium in the eyes of Eales’ disease patients and a probable role of this bacterium in the pathogenesis of this enigmatic clinical condition.
Acknowledgments
Part of the study has been presented at the annual meeting of the Association of Research in Vision and Ophthalmology, 1997.
