Abstract
M.Sc. (Biochemistry)
Dry eye disease (DED) and keratoconus (KC) continue to affect the quality of life of
many South Africans (and elsewhere) and in the case of KC often leads to blindness.
It is estimated that DED affects 14% to 33% of the population worldwide, while 1
in 2000 of the worlds population is affected by KC. However, details of the etiology
of these diseases and their biochemical ‘fingerprint’ remain uncertain. In this
study, emphasis was placed on the investigation of immunological proteins in the
precorneal tear film of DED and KC subjects and meibomian lipids in these individuals.
Tear fluid and meibum were collected from control, DED and KC volunteers. Control
subjects were non-contact lens wearers and free from ocular diseases, whereas DED
subjects were diagnosed by means of an ocular surface disease index (OSDI) questionnaire.
DED subjects were divided into two groups: ‘moderate DED’ and ‘severe DED’ based on
OSDI. KC subjects were diagnosed by the use of a slit-lamp biomicroscopy exam. Enzymelinked
immunosorbent assays were performed to quantitate secretory immunoglobulin
A (sIgA), tumour necrosis factor-alpha (TNF-á) and matrix metalloproteinase-1
(MMP-1) in the collected tear fluid. Meibum was analysed with proton nuclear magnetic
resonance (1H-NMR) spectroscopy and Fourier transform infrared spectroscopy (FTIR).
Multivariate data analyses (PCA) were used to extract interpretable information from the
multidimensional data generated from the aforementioned techniques and used to build a
broad picture of the general lipidomic differences between DED, KC and healthy subjects.
Tear levels of sIgA and MMP-1 were significantly decreased in patients with KC compared
to control. In contrast, the tears of severe DED subjects were characterised by higher levels
of TNF-á and lower levels of sIgA. In subjects with moderate DED, TNF-á levels were
significantly elevated. The results of this study re-emphasize that KC and DED individuals
are associated with differential expression of specific tear proteins and support the view
that the severity of DED is reflected in the levels of immunological proteins present in basal
tears.
Differences in the chemical composition of meibum from subjects with severe DED and KC
compared to control were observed, more specifically in the aliphatic region of 1H-NMR
spectra and C-C rocking region of FTIR spectra. The results therefore point towards the
saturated components of fatty acids (and their chemical environments) as key targets for
future investigations to elucidate compositional differences between DED, KC and healthy
meibum.