Zg. Liu et Sc. Pflugfelder, Corneal surface regularity and the effect of artificial tears in aqueous tear deficiency, OPHTHALMOL, 106(5), 1999, pp. 939-943
Purpose: To evaluate corneal surface regularity and the effect of artificia
l tears on the regularity of the corneal surface in dry eye.
Design: A prospective, clinic-based, case-control study.
Participants: A total of 64 eyes of 33 normal subjects and 42 eyes of 22 pa
tients with aqueous tear deficiency were evaluated.
Methods: Indices of the TMS-I corneal topography instrument (Tomey Technolo
gy, Cambridge, MA) were used to evaluate corneal surface regularity and pot
ential visual acuity (PVA) in patients with aqueous tear deficiency dry eye
before and after the instillation of artificial tears and in normal subjec
ts. The TMS-I topographic maps were classified into round, oval, symmetric
bow-tie, asymmetric bow-tie, and irregular patterns.
Main Outcome Measures: The surface regularity index (SRI), surface asymmetr
y index (SAI), PVA index, and topographic pattern of the TMS-1 were compare
d between normal and dry eyes and in dry eyes before and after the instilla
tion of artificial tears.
Results: The SRI and SAI were significantly elevated and the PVA was signif
icantly reduced in dry eye patients compared with normal subjects: 0.31 +/-
0.22, 0.30 +/- 0.16, and 20/17.89 +/- 20/3.04, respectively, in normal sub
jects and 1.28 +/- 0.73, 1.05 +/- 1.17, and 20/33.45 +/- 20/13.99, respecti
vely, in patients with dry eye (P < 0.001 for all indices). The average amo
unt of astigmatism was also increased in dry eyes (2.10 +/- 1.96 prism diop
ters) compared with normal eyes (1.13 +/- 0.53 prism diopters, P = 0.02). I
n dry eyes, the SRI and SAI were positively correlated with corneal fluores
cein staining scores (P = 0.005 for SRI and P = 0.016 for SAI). The mean PV
A was not significantly different from the mean actual corrected visual acu
ity. The dry eyes had a significantly lower percentage of symmetric bow-tie
patterns and a greater percentage of irregular patterns on topographic map
s than normal eyes. After the instillation of artificial tears, the SRI, SA
I, and mean astigmatism all decreased significantly (P < 0.001 for SRI, P <
0.002 for SAI, P = 0.04 for astigmatism) and the PVA improved (P < 0.001)
in dry eyes. An irregular topographic pattern was observed in 45.24% of dry
eyes, and this decreased to 30.95% after the instillation of artificial te
ars (P < 0.005).
Conclusions: Patients with aqueous deficiency have an irregular corneal sur
face that may contribute to their visual difficulties. The SRI and SAI coul
d be used as objective diagnostic indices for dry eye as well as for evalua
ting the severity of this disease and the effect of artificial tears. Artif
icial tears have the secondary benefit of smoothing the corneal surface in
dry eye.