higher-order aberrations, contrast sensitivity:

Invest Ophthalmol Vis Sci. 2004 Nov;45(11):3986-90.

Ocular higher-order aberrations and contrast sensitivity after conventional
laser in situ keratomileusis.

Yamane N, Miyata K, Samejima T, Hiraoka T, Kiuchi T, Okamoto F, Hirohara Y,
Mihashi T, Oshika T.

Department of Ophthalmology, Institute of Clinical Medicine, University of
Tsukuba, Tsukuba, Japan; the.

PURPOSE: To investigate prospectively the relation between induced changes in
higher-order aberrations of the eye and changes in contrast sensitivity by
conventional laser in situ keratomileusis (LASIK) for myopia. METHODS: In 200
eyes of 110 consecutive patients (mean age, 32.7 8.4 years) undergoing
LASIK, ocular aberrations and contrast sensitivity function were determined
before and 1 month after surgery. The amount of myopic correction was 5.2
2.8 D (range, 1.0-13.0). Ocular higher-order aberrations were measured for a
4-mm pupil using the Hartmann-Shack wavefront analyzer (KR-9000PW; Topcon,
Tokyo, Japan). The root mean square (RMS) of the third- and fourth-order Zernike
coefficients was used to represent coma- and spherical-like aberrations,
respectively. Total higher-order aberrations were calculated as the RMS of the
third- and fourth-order coefficients. Contrast sensitivity and low-contrast
visual acuity were measured. From the contrast sensitivity data, the area under
the log contrast sensitivity function (AULCSF) was calculated. RESULTS: LASIK
significantly improved logMAR best corrected visual acuity (Wilcoxon signed-rank
test, P < 0.001), but significantly reduced AULCSF (P < 0.001) and low-contrast
visual acuity (P = 0.007). Total higher-order (P < 0.001), coma-like (P <
0.001), and spherical-like (P < 0.001) aberrations were significantly increased
after LASIK. The greater the amount of achieved myopia correction was, the more
the changes in contrast sensitivity function and ocular higher-order aberrations
were. The induced changes in AULCSF by LASIK showed significant correlations
with changes in total higher-order (Pearson r = -0.221, P = 0.003), coma-like (r
= -0.205, P = 0.006), and spherical-like (r = -0.171, P = 0.022) aberrations.
The changes in logMAR low-contrast visual acuity by surgery significantly
correlated with changes in total higher-order (r = 0.222, P = 0.003), coma-like
(r = 0.201, P = 0.007), and spherical-like (r = 0.207, P = 0.005) aberrations.
CONCLUSIONSConventional LASIK significantly increases ocular higher-order aberrations, which compromise the postoperative contrast sensitivity function.



nerves demage:

Invest Ophthalmol Vis Sci. 2004 Nov;45(11):3991-6.

Corneal Reinnervation after LASIK: Prospective 3-Year Longitudinal Study.

Calvillo MP, McLaren JW, Hodge DO, Bourne WM.

Departments of Ophthalmology and.

PURPOSE: To measure the return of innervation to the cornea during 3 years after
LASIK. METHODS: Seventeen corneas of 11 patients who had undergone LASIK to
correct myopia from -2.0 D to -11.0 D were examined by confocal microscopy
before surgery, and at 1, 3, 6, 12, 24, and 36 months after surgery. In all
available scans, the number of nerve fiber bundles and their density (visible
length of nerve per frame area), orientation (mean angle), and depth in the
cornea were measured. RESULTS: The number and density of subbasal nerves
decreased >90% in the first month after LASIK. By 6 months these nerves began to
recover, and by 2 years they reached densities not significantly different from
those before LASIK. Between 2 and 3 years they decreased again, so that at 3
years the numbers remained <60% of the pre-LASIK numbers (P < 0.001). In the
stromal flap most nerve fiber bundles were also lost after LASIK, and these
began recovering by the third month, but by the third year they did not reach
their original numbers (P < 0.001). In the stromal bed (posterior to the LASIK
flap interface), there were no significant changes in nerve number or density.
As the subbasal nerves returned, their mean orientation did not change from the
predominantly vertical orientation before LASIK. Nerve orientation in the
stromal flap and the stromal bed also did not change. CONCLUSIONSBoth subbasal
and stromal corneal nerves in LASIK flaps recover slowly and do not return to
preoperative densities by 3 years after LASIK. The numbers of subbasal nerves
appear to decrease between 2 and 3 years after LASIK. The orientation of the
regenerated subbasal nerves remains predominantly vertical.

Good finds! Thanks for posting these.