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J Refract Surg 1999 Jan-Feb;15(1):38-45
Loss and recovery of corneal sensitivity following photorefractive
keratectomy for myopia.
Murphy PJ, Corbett MC, O'Brart DP, Verma S, Patel S, Marshall
Department of Vision Sciences, Glasgow Caledonian University, Glasgow, United
BACKGROUND: Photorefractive keratectomy affects corneal
innervation in a new, and drastic, way. This inevitably results in a significant
loss of corneal sensitivity. This paper investigates the pattern of sensitivity
loss and recovery following PRK for low to moderate myopia. METHODS: Patients
were recruited for two separate studies. Longitudinal Study: 10 patients,
treated with a -6.00 D/6 mm PRK ablation, were examined over a 1-year period.
Transverse Study: A comparison was made between 35 non-contact lens wearers,
80 contact lens wearers, and 60 patients who underwent five different PRK
treatments, 1 year previously. Corneal sensitivity was assessed using the
Non-Contact Corneal Aesthesiometer at four corneal locations: centrally,
temporally, medially, inferiorly, on all patients. RESULTS: Longitudinal
Study: Corneal sensitivity was significantly reduced at week 1, with a further
significant reduction at week 2. A gradual recovery in sensitivity then
followed to reach preoperative levels by 1 year. Transverse Study: There
was no significant difference in corneal sensitivity found as a result of
different PRK ablation depths. The depth of ablation was not a factor in
corneal sensitivity recovery in low to moderate myopic corrections. Corneal
sensitivity in the PRK treated eyes was significantly lower than in the
CONCLUSION: The immediate loss of corneal sensitivity
after surgery was due to the total removal of the corneal epithelial nerve
supply and a substantial portion of the underlying stromal nerves. The further
decrease at week 2 was probably due to the new epithelium acting as barrier
to stimulation. The gradual recovery of corneal sensitivity was most likely
caused by epithelial reinnervation within the ablation zone, but this was
still below normal levels at 1 year after surgery. Corneal nerve function
demonstrates a biphasic pattern of loss and recovery following the excimer
laser correction of low to moderate myopia.
Graefes Arch Clin Exp Ophthalmol 1999 Feb;237(2):161-5
PRK-induced anisometropia in the rabbit as a model of myopia.
Bryant MR, Kampmeier J, Er H, Kasetsuwan N, Sanchez-DiMartino
D, Shah SS, McDonnell PJ
University of Southern California School of Medicine, Doheny Eye Institute,
Los Angeles 90033, USA. firstname.lastname@example.org
BACKGROUND: Current animal models of myopia, such as the
chick and the tree shrew, have characteristics that limit their applicability
to human myopia and/or their use among researchers. The purpose of this
study was to establish a rabbit model of myopia based on photorefractive
keratectomy (PRK)-induced anisometropia. METHODS: A group of five pigmented
rabbits was treated with a monocular -5 D PRK at 5 weeks of age. At 10 weeks
of age, two of the eyes were retreated with a second -5 D PRK procedure
to compensate for partial regression of the refractive effect. A second
group of six pigmented rabbits was treated with a monocular -6 D PRK at
10 weeks of age. Longitudinal measurements of corneal curvature, refraction,
and axial length were performed until the rabbits were 13 and 21 weeks of
age in groups 1 and 2, respectively. The rabbits in each group were from
the same litter. RESULTS: Keratometry and retinoscopy measurements confirmed
the refractive effect of the PRK procedures. At the final measurement point
in group 1, the PRK-treated eyes were significantly longer than the untreated
eyes (16.01 +/- 0.45 mm vs 15.45 +/- 0.56 mm). In group 2, the PRK-treated
eyes were significantly longer by 0.19 mm and 0.20 mm at ages 19 and 21
2) CONCLUSIONS: PRK-induced anisometropia is an effective technique
to induce hyperopic error compensation in the rabbit as a model of myopic
development. The technique is effective if the PRK procedure is performed
at either 5 or 10 weeks of age. However, after PRK at 5 weeks of age, partial
retreatment may be necessary due to regression of the PRK effect.
Br J Ophthalmol 1998 Dec;82(12):1393-400
Confocal microscopy reveals persisting stromal changes after myopic
photorefractive keratectomy in zero haze corneas.
Bohnke M, Thaer A, Schipper I
University of Bern, Department of Ophthalmology, Switzerland.
AIMS: Micromorphological examination of the central cornea
in myopic patients 8-43 months after excimer laser photorefractive keratectomy
(PRK), using the slit scanning confocal microscope. METHODS: Patients were
selected from a larger cohort of individuals on the basis of full corneal
clarity (haze grading 0 to +1; mean 0.3) and their willingness to participate
in the study. 15 eyes of 10 patients with myopic PRK (-4 to -11 D; mean
6.7) and an uneventful postoperative interval of 8-43 months (mean 26) were
examined. Contact lenses had been worn by eight of the 10 patients for 4-11
years (mean 6.7) before surgery. Controls included the five untreated fellow
eyes of PRK patients, 10 healthy, age matched volunteers without a history
of ocular inflammation or contact lens wear, and 20 patients who had worn
rigid gas permeable (n = 10) or soft contact lenses (n = 10) for 2-11 years.
Subjects were examined with a real time flying slit, scanning confocal microscope
using x25 and x50 objectives. RESULTS: In PRK treated patients and contact
lens wearers, basal layer epithelial cells sporadically displayed enhanced
reflectivity. The subepithelial nerve plexus was observed in all individuals,
but was usually less well contrasted in the PRK group, owing to the presence
of a very discrete layer of subepithelial scar tissue, which patchily enhanced
background reflectivity. Within all layers of the stroma, two distinct types
of abnormal reflective bodies were observed in all PRK treated eyes, but
in none of the controls. One had the appearance of long (> = 50 microns),
slender (2-8 microns in diameter) dimly reflective rods, which sometimes
contained bright, punctate, crystal-like inclusions, arranged linearly and
at irregular intervals. The other was shorter (< 25 microns), more slender
in form (< 1 micron in diameter), and highly reflective; these so called
needles were composed of crystal-like granules in linear array, with an
individual appearance similar to the bright punctate inclusions seen in
rods, but densely packed. Both of these unusual structures were confined,
laterally, to the ablated area, but were otherwise distributed throughout
all stromal layers, with a clear predominance in the anterior ones. These
rods and needles were observed in all PRK treated corneas, irrespective
of previous contact lens wear. On the basis of qualitative inspection, the
incidence of rods and needles did not appear to correlate with either the
volume of tissue ablated or the length of the postoperative interval. In
contact lens wearing controls, highly reflective granules, reminiscent of
those from which the needles were composed, were found scattered as isolated
entities throughout the entire depth and lateral extent of the corneal stroma,
but rods and needles were never encountered. The corneal endothelium exhibited
no obvious abnormalities.
CONCLUSION: Confocal microscopy 8-43 months after
PRK revealed belated changes in the corneal stroma. These were manifested
as two distinct types of abnormal reflective bodies, which had persisted
beyond the stage when acute wound healing would have been expected to be
complete. The clinical significance of these findings in the context of
contrast visual acuity and long term status of the cornea is, as yet, unknown.
J Cataract Refract Surg 1999 Jan;25(1):140-3
Intraocular lens power calculation after decentered photorefractive
Speicher L, Gottinger W
Department of Ophthalmology, University of Innsbruck, Austria.
A 59-year-old patient who had photorefractive keratectomy
(PRK) to correct high unilateral myopia developed a progressive nuclear
cataract. Phacoemulsification and intraocular lens (IOL) implantation were
performed. However, determination of IOL power using automated keratometry
and computerized videokeratography was not successful in this case of high
axial myopia because of a decentered ablation zone, resulting in too-steep
keratometric readings. Postoperative hyperopia could only be corrected by
an IOL exchange. Because it may not be possible to determine the exact keratometric
values for IOL calculation after PRK, subtracting the change in refraction
induced by PRK from the preoperative keratometric readings might have been
more accurate in this patient.
J Cataract Refract Surg 1998 Dec;24(12):1571-4
Changes in corneal epithelial barrier function after excimer laser
Kim JY, Heo JH, Park SJ, Choi YS, Wee WR, Lee JH
Department of Ophthalmology, Seoul Municipal Boramae, Korea.
PURPOSE: To use fluorophotometry to measure corneal epithelial
barrier function after excimer laser photorefractive keratectomy (PRK).
SETTING: Seoul National University Hospital, Seoul, Korea. METHODS: Twenty-five
eyes of 21 patients (13 women, 8 men) had PRK to correct myopia. Corneal
epithelial healing time was measured and corneal epithelial permeability
to sodium fluorescein evaluated by fluorophotometry 1, 2, and 3 weeks after
surgery. RESULTS: Epithelial permeability showed a statistically significant
increase 1 week after surgery and returned to its preoperative level 1 week
later. Comparative studies according to epithelial healing day and corrected
diopter showed results that were not statistically significant (P > .05).
CONCLUSION: These results suggest that PRK delays
complete reconstruction of corneal epithelial barrier function. In humans,
the corneal epithelium regained its normal barrier function 2 weeks after
PRK. Thus, at least during these weeks, care should be taken to minimize
further epithelial trauma.
Arch Ophthalmol 1998 Nov;116(11):1425-31
In vivo confocal microscopy after photorefractive keratectomy in humans.
A prospective, long-term study.
Frueh BE, Cadez R, Bohnke M
Department of Ophthalmology, Inselspital, University of Berne, Switzerland.
OBJECTIVE: To assess corneal morphological characteristics
in vivo after photorefractive keratectomy (PRK) in humans. METHODS: Eighteen
eyes were examined before and after PRK by means of in vivo confocal microscopy.
Epithelial, stromal, and endothelial morphological characteristics were
recorded. Minimum follow-up was 12 months. RESULTS: Immediately after PRK,
the anterior stroma showed marked intercellular edema. At 1 month, fine
linear structures were noted in the anterior stroma and midstroma, and a
thin hyperreflective scar was present. The linear structures and the scar
tissue were more marked at 4 months but were still present up to 26 months.
Anterior stromal keratocyte density increased significantly 1 and 4 months
after PRK, whereas midstromal and posterior keratocytes and endothelial
cell densities did not change. Basal epithelial nerves were recognizable
as early as 1 month after PRK. Contact lens-related microdots in the stroma
6) CONCLUSIONS: The stromal linear structures represent a finding
that is detectable only by confocal microscopy at high magnification, is
not related to previous contact lens wear, and is still visible 26 months
after PRK. The extension of these structures as far as the midstroma indicates
that the permanent corneal changes caused by PRK affect deeper stromal layers
than the immediate subepithelial region.
Ophthalmologe 1998 Jun;95(6):420-6
[Change in twilight vision and glare sensitivity after PRK]. [Article
Katlun T, Wiegand W ALZ Augenklinik Hamburg.
BACKGROUND: Morphological changes in the corneal surface
after PRK may result not only in refraction fluctuations and reduction in
visual acuity, but also in changes of contrast sensitivity. The aim of this
study was to investigate whether PRK has an influence on contrast sensitivity
with and without glare with a subsequent effect on the ability to drive
cars. PATIENTS AND METHODS: Anonymous inquiries were made by means of a
questionnaire sent to 114 patients after bilateral PRK in which the patients
were asked to assess subjectly their driving ability. Additionally, in 66
eyes of 66 patients with a mean myopia of -5.3 D, an investigation on contrast
sensitivity was performed according to the recommendations of the DOG (German
Ophthalmological Society) using a Rodenstock nyctometer. RESULTS: Postoperatively,
55% of the patients felt more comfortable driving a car than preoperatively,
31% did not recognize any change, and 14% felt more uncomfortable driving
car. Contrast sensitivity with or without glare 2 weeks postoperatively
was so much reduced in 77% or 53%, respectively, of the patients that the
criteria for driving a car in Germany were not fulfilled. Within the first
12 months after PRK the number of impaired patients diminished but even
1 year after PRK the number of patients with reduced contrast sensitivity
with and without glare was higher than before PRK. Surprisingly, however,
the criteria for driving a car with respect to contrast sensitivity with
and without glare were not fulfilled even before PRK by as much as 44% and
24% of the patients, respectively.
7) CONCLUSIONS: All patients must be informed about the possible impairment
for driving a car before PRK is performed.
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Un interessante articolo BBC la
polizia, i pompieri etc non accettano più chi ha subito operazioni
laser: pessima visione notturna, troppi incidenti.
È anche una buona idea abbonarsi alle Newsletter,
che riportano novità e cose significative riguardo alle operazioni.
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e dispense Bibliografia Rasterbrille Laser:
luci ed ombre Testimonianza Personale
articolo BBC (ingl)