Hệ thống thị giác tạo
ra chất mang màu thị giác, 11- cis -retinal từ vitamin A trong chế độ ăn uống, all- trans -retinol làm cho vitamin này trở nên cần thiết
cho sức khỏe và chức năng của võng mạc. Các sự kiện trao đổi chất này được
thực hiện qua trung gian của một quá trình sinh hóa tuần tự được gọi là chu
trình thị giác. Retinol
dehydrogenases (RDHs) chịu trách nhiệm về hai phản ứng trong chu trình thị
giác được thực hiện trong các tế bào biểu mô sắc tố võng mạc (RPE), tế bào thụ
cảm ánh sáng và tế bào Müller trong võng mạc. RDH trong RPE có chức năng
như 11- cis -RDHs, oxy hóa 11- cis -retinol thành 11- cis -retinal in vivo. RDH trong
các tế bào thụ cảm ánh sáng hình que trong võng mạc hoạt động như all- trans -RDHs, làm giảm all- trans-retinal thành all- trans -retinol. Rối loạn chức năng của RDH có
thể gây ra các bệnh võng mạc di truyền ở người. Để tạo điều kiện cho sự hiểu
biết sâu hơn về các bệnh ở người, các mô hình chuột về các bệnh liên quan đến
RDH đã được kiểm tra cẩn thận và cho thấy sự đóng góp sinh lý của các RDH cụ thể
đối với chức năng chu kỳ thị giác và sức khỏe võng mạc tổng thể. Chức
năng của RDH trong RPE và võng mạc, đặc biệt là trong các tế bào cảm thụ ánh
sáng hình que, các đặc tính điều chỉnh của chúng đối với cân bằng nội môi
retinoid được mô tả và chiến lược điều trị trong tương lai để điều trị các bệnh
võng mạc.
Các vấn đề về mắt liên quan đến việc di chuyển bằng đường hàng
không
Burak Turgut -Department
of Ophthalmology, Yuksek Ihtisas University, Turkey. Citation: Turgut B. Ocular
problems associated air traveling. Adv Ophthalmol Vis Syst. 2018;8(2):80 – 83.
DOI: 10.15406/aovs.2018.08.00275
Du lịch hàng
không đã được tăng lên từng ngày. Do đó, cả phi hành đoàn và hành khách đã bị ảnh
hưởng bởi các điều kiện di chuyển trên không như nhiễu động nghiêm trọng, áp suất
thấp hoặc độ ẩm, sự hiện diện của ozone và không khí khô trong cabin. Do sự thay
đổi áp suất không khí trong cabin và các nguy cơ có thể xảy ra đối với mắt, việc
chậm chuyến bay của những người đã trải qua phẫu thuật thay thủy tinh thể hoặc
đục thủy tinh thể đã được khuyến cáo cho đến khi bác sĩ nhãn khoa làm rõ. Tuy
nhiên, những bệnh nhân mắc bệnh
tăng nhãn áp có thể đi máy bay một cách an toàn miễn là họ dùng thuốc chống
tăng nhãn áp.1‒6 Các phàn nàn về mắt thường gặp nhất ở những người đi máy bay là khô bề mặt mắt (20%) và
các triệu chứng liên quan. Ngoài ra, có thể gặp các vấn đề về mắt khác bao gồm ngứa mắt, đau quặn quặn thắt hoặc nhức
đầu, chảy nước mắt và không dung nạp kính áp tròng. 1,3,5‒7 Rối loạn tiền đình thần kinh mắt
(NOVD), bệnh thần kinh thị
giác do thiếu máu cục bộ, trầm trọng thêm Phù hoàng điểm do tiểu đường cũng đã được báo cáo
liên quan đến các rối loạn mắt xảy ra trong quá trình di chuyển bằng máy
bay.8‒11 Hơn nữa, người ta đã suy đoán rằng tắc động mạch võng mạc trung tâm hoặc các biến cố
thiếu máu cục bộ ở mắt khác có thể xảy ra do co mạch phản ứng hoặc thay đổi thiếu
máu cục bộ trong quá trình di chuyển ở độ cao. du khách là triệu chứng đáng lo
ngại và khó chịu nhất. Đau mắt xảy ra khi đi máy bay đã được Hiệp hội Đau đầu Quốc tế (IHS) phân
loại là một loại đau đầu kể từ năm 2013. (International Headache
Society (IHS) since 2013.)13 Tiêu chuẩn chẩn đoán đau đầu do đi máy bay (“đau đầu
trên máy bay”) (AHA headache attributed to airplane travel =“airplane
headache”) bao gồm đáp ứng tiêu chí ít nhất 2 cơn, bao gồm cả
'' 1. đau dữ dội khi di chuyển trên
máy bay kéo dài dưới 30 phút, với ít nhất 2 trong số các cơn đau một bên ‘’, vị
trí phía trước hôc mắt (có thể xảy ra đau vùng trán), đau do dao đâm hoặc chất
đâm (có thể xảy ra xung động) ’’
‘’ 2. không có
triệu chứng đi kèm '';
‘’ 3. không được
quy cho các rối loạn khác ''. 13
AHA đặc biệt
xuất hiện trong giai đoạn hạ cánh hoặc hạ cánh, đôi khi là giai đoạn đi lên hoặc
cất cánh trong các chuyến bay trên máy bay. Một đặc điểm điển hình nổi trội
khác của AHA là nó không xảy ra nếu không có bất kỳ triệu chứng rối loạn đồng
thời kèm theo nào trong hầu hết các trường hợp. Đặc điểm lâm sàng điển hình
khuôn mẫu của một cuộc tấn công AHA là một cơn đau một bên dữ dội và rất nghiêm
trọng khu trú ở vùng trán hoặc vùng quanh hốc mắt. Nó bắt đầu đột ngột và không
lâu sau khi lao xuống nhanh chóng từ độ cao trung bình 1.800 m. Cường độ đau
cao nhất diễn ra trong vài phút và AHA thường kéo dài 20-30 phút tương ứng với
thời gian máy bay cất cánh và hạ cánh cho đến khi giải quyết hoàn toàn. Hầu hết
các nghiên cứu trước đây đều báo cáo nam giới chiếm ưu thế đối với AHA. AHA thường
biểu hiện từ 25-30 năm. Cơ chế bệnh sinh của loại đau đầu này rất đa dạng, bao
gồm chủ yếu là chấn thương
xoang bướm hoặc có thể là
giãn mạch ở động mạch não do thay đổi áp suất cabin trong không khí di
chuyển. Người ta đã coi rằng chấn thương vùng kín liên quan đến các đầu dây thần
kinh sinh ba trong xoang ethmoid gây ra đau quặn thắt lưng trong thực thể lâm
sàng này.14–16 Người ta đã suy đoán rằng sự giãn mạch trong các động mạch não
phát triển trong một cuộc tấn công của AHA có thể được gây ra. bằng
prostaglandin E2.14,17 Mặc dù không có phương pháp điều trị hoặc dự phòng đặc
hiệu cho AHA, nhưng người ta đã chứng minh rằng một số loại thuốc bao gồm thuốc
giảm đau, thuốc chống viêm không steroid hoặc triptan có thể có tác dụng có lợi
như là liệu pháp dự phòng. Tuy nhiên, thuốc và thuốc làm thông mũi nên được
dùng dự phòng khoảng 30 phút và 30-60 phút, tương ứng trước giai đoạn kích hoạt
dự kiến (giai đoạn tăng hoặc giảm dần) của chuyến bay để đạt được kết quả tối
ưu. Một số thao tác bao gồm ép
vùng đau, vận động
Valsalva, mở rộng dái tai, nhai hoặc ngáp có thể giúp giảm 25% cường độ
đau..14–17
Khô mắt là vấn đề phổ biến nhất ở những người đi máy bay. Do độ ẩm không khí trong
khoang máy bay thường thấp hơn 20% tỷ lệ độ ẩm và không khí trong khoang điều
áp bị mất nước, nên thường xảy ra hiện tượng khô da và mắt. Đặc biệt, trong trường
hợp độ ẩm thấp, người sử dụng
kính áp tròng có nguy cơ bị khô vì nguồn oxy chính dưới ống kính bị triệt
tiêu. Sử dụng kem dưỡng ẩm da và dung dịch bôi trơn hoặc nước mắt nhân tạo, đeo
kính râm thay cho kính áp tròng, uống thêm nước, tắt hướng thổi của máy điều
hòa không khí sang một bên thay vì quay mặt và nghỉ ngơi khi đọc sách trong
chuyến bay có thể làm giảm hoặc ngăn ngừa khó chịu..1,3,5,6 Rối loạn tiền đình thần kinh
mắt hoặc say tàu xe có thể gặp phải đối với người đi máy bay trong trường hợp
sóng gió nghiêm trọng. Trong chuyến du lịch trên máy bay, việc có được chỗ ngồi
ngay gần cửa sổ và phần giữa của cabin hoặc những chiếc ghế vừa với cánh nơi ít
cảm nhận nhất có thể có lợi để tránh bị say tàu xe cho những người biết mình bị
NOVD. . Ngoài ra, một số loại thuốc có thể uống trước chuyến bay sẽ giúp ngăn
ngừa bệnh này, có thể có lợi.18–21 Không khí bất ổn trong chuyến bay cũng có thể
gây chấn thương mắt, đặc biệt đối với những mắt vừa mới phẫu thuật mắt như phẫu thuật thủy tinh thể
trong đó Khí nội nhãn giãn nở đã được sử dụng và phẫu thuật đục thủy tinh thể với
đặt thủy tinh thể nội nhãn. Bởi vì sự nhiễu loạn không khí có thể gây ra vết thương hở trong vùng rạch
giác mạc do nuốt nước bọt và nôn mửa hoặc nhãn áp tăng nghiêm trọng do
khí trong mắt giãn nở và hậu quả là tắc động mạch võng mạc trung tâm. Do đó, những
hành khách này không nên đi du lịch ngay sau khi phẫu thuật đục thủy tinh thể
và phải được thắt dây an toàn miễn là hành khách đã ngồi. Việc trì hoãn chuyến
đi trong khoảng hai đến sáu tuần sau khi tiêm vào mắt lưu huỳnh hexafluoride (SF6) và perfluoropropane
(C3F8), tương ứng đã được khuyến cáo.22 Những người đi máy bay bị bệnh tăng
nhãn áp thường không gặp bất kỳ vấn đề gì. Áp suất khí quyển giảm nhanh trong
khi bay có thể làm tăng nhãn
áp tương đối. Tuy nhiên, sự thay đổi này thường không gây ra vấn đề gì ở
bệnh nhân tăng nhãn áp trong quá trình di chuyển bằng máy bay vì cabin máy bay
có áp suất khí quyển nhân tạo được kiểm soát và điều này thường bù đắp cho sự
giảm áp suất phát triển ở độ cao lớn.22,23
PURPOSE:
To evaluate visual outcomes following epi-LASIK compared to photorefractive
keratectomy (PRK).
METHODS:
Of a total 294 patients aged ≥21 years, 145 (290 eyes) underwent epi-LASIK
and 149 (298 eyes) underwent PRK for low to moderate myopia or myopic
astigmatism. Epi-LASIK was performed with the Amadeus II epikeratome (Abbott
Medical Optics) and PRK with the Amoils rotary epithelial brush (Innovative
Excimer Solutions). All ablations were performed using the same excimer laser
system. Outcome measures included intraoperative complications, corneal
reepithelialization, postoperative pain, uncorrected distance visual acuity
(UDVA), manifest refraction spherical equivalent (MRSE), corrected distance
visual acuity (CDVA), corneal haze, and quality of vision.
RESULTS:
Mean preoperative MRSE was −2.97±1.19 diopters (D) for epi-LASIK versus
−2.95±1.06 D for PRK. Complete reepithelialization was achieved by postoperative
day 4 in 46.9% of epi-LASIK eyes versus 92.4% of PRK eyes, with superior UDVA at
postoperative day 1 in the PRK group (P=.002). Using Fisher exact test, a significantly higher
percentage of epi-LASIK eyes compared to PRK eyes achieved 20/15 or better at 1
month (25.8% vs 17.8%, P=.031), 3 months (62.3% vs 49.3%, P=.004), 6 months
(77.1% vs 57.9%, P<.001), and 12 months (75.9% vs 61.9%, P=.002).
A change in MRSE >0.50 D occurred in 8.4% of epi-LASIK eyes within the 3- and
12-month interval versus 17.7% of PRK eyes (P=.04). No differences were noted between the two
procedures in CDVA or clinically significant haze.
CONCLUSIONS:
Epi-LASIK showed superior refractive efficacy and stability but required more
time for wound healing, resulting in inferior early visual outcomes and a
tendency to overcorrect higher refractive errors compared to PRK. Both
treatments were safe and comparable in terms of pain and haze
formation.
From the Ophthalmology Service, Walter Reed Army
Medical Center, Washington, DC (Sia, Coe, Ryan); the Department of
Ophthalmology, University of Florida College of Medicine, Jacksonville, Florida
(Edwards); and The Wilmer Eye Institute, Johns Hopkins University, Baltimore,
Maryland (Bower).
Portions of this material were presented at the
Association for Research in Vision and Ophthalmology Annual Meeting, April
27–May 1, 2008, and May 3–7, 2009, Ft Lauderdale, Florida.
The authors have no financial interest in the
materials presented herein.
The opinions expressed in this manuscript are those
solely of the authors and do not represent the views or official policies of the
United States Army or Department of Defense. AUTHOR CONTRIBUTIONS Study concept and design (C.D.C., D.S.R.,
K.S.B.); data collection (C.D.C., D.S.R.); analysis and interpretation of data
(R.K.S., C.D.C., J.D.E., D.S.R., K.S.B.); drafting of the manuscript (R.K.S.,
C.D.C., J.D.E., K.S.B.); critical revision of the manuscript (R.K.S., C.D.C.,
D.S.R., K.S.B.); statistical expertise (C.D.C.); administrative, technical, or
material support (C.D.C.); supervision (C.D.C., D.S.R., K.S.B.)
Correspondence: Rose K. Sia, MD, Center for Refractive Surgery, Walter Reed
Army Medical Center, 6900 Georgia Ave, Washington, DC. Tel: 202.782.8327; Fax:
202.782.4653
Received: January 04,
2011
Accepted: August 08,
2011
Posted Online: October 10,
2011
Although LASIK is the most common refractive
surgery, surface ablation may be indicated in patients with thin corneas, dry
eyes, anterior basement membrane dystrophy, and in patients at risk for trauma
due to occupational or recreational considerations.1–3 However,
reepithelialization typically takes 3 to 5 days, during which time patients
frequently experience discomfort and fluctuating vision. In addition,
photorefractive keratectomy (PRK) can result in corneal haze in up to 2% to 4%
of patients.4,5
Alternative surface techniques have been developed
to overcome postoperative PRK pain and haze. Epi-LASIK uses a microkeratome-like
device to mechanically separate the epithelium from Bowman layer. The cell
morphology and physiology of the resulting epithelial sheet is less affected
compared to the chemical separation used in laser epithelial keratomileusis
(LASEK)6,7 and remains intact for at
least 24 hours postoperatively,7 acting as a mechanical barrier
to tear cytokine mediators8,9 and controlling the corneal
wound response. Preliminary studies have shown epi-LASIK to be a safe and
effective treatment in the short term.10–13 This study evaluates the
visual outcomes of epi-LASIK compared to PRK up to 12 months
postoperatively.
Patients and Methods
The present report compares data from two separate
non-randomized, prospective, clinical studies performed at Walter Reed Army
Medical Center after approval by the institutional review board and conducted in
accordance with the Declaration of Helsinki. After informed consent, consecutive
enrollment and treatment were done between May 2005 and July 2006 for PRK and
between November 2006 and December 2007 for epi-LASIK. Enrollment criteria and
all study methods pre- and postoperatively were identical between the two study
cohorts. All patients were aged ≥21 years with myopia or myopic astigmatism
between −0.50 and −6.25 diopters (D) of manifest refraction spherical equivalent
(MRSE), refractive cylinder up to 3.00 D, stable refraction for at least 12
months, and corrected distance visual acuity (CDVA) of 20/20 or better in both
eyes.
All treatments were performed with the LADAR Vision
6000 (Alcon Laboratories Inc, Ft Worth, Texas). Treatments were conventional
with a 6.5-mm optical zone; no wavefront-guided treatments were performed.
Stromal ablation in PRK was performed after epithelial debridement with the
Amoils rotary brush (Innovative Excimer Solutions, Toronto, Ontario). The
stromal bed was irrigated with chilled balanced saline solution (BSS),
moxifloxacin 0.5% ophthalmic solution and ketorolac 0.4% were administered, and
a bandage contact lens applied. In epi-LASIK, a nasal-hinged epithelial flap was
created using the Amadeus II epikeratome (Abbott Medical Optics, Santa Ana,
California), using manufacturer-recommended epikeratome parameters. After the
flap was reflected nasally with use of a microspatula, photoablation was
performed on the underlying stroma. During flap creation, if a complication
occurred in the first eye (right eye), a new epithelial separator was used for
the second eye. Immediately following ablation, the stromal bed was irrigated
with chilled BSS before repositioning the epithelial sheet, which was retained
whenever possible. After the epithelial sheet was in position and adherent
moxifloxacin 0.5% and ketorolac 0.4% were administered, a bandage contact lens
was applied.
Postoperative medications for both groups included
topical moxifloxacin 0.5% one drop four times daily for 1 week or until complete
reepithelialization; fluorometholone 0.1% one drop four times daily for 4 weeks,
followed by a 6-week taper; carboxymethylcellulose 0.5% one drop four to eight
times daily for 2 weeks and then as needed; topical ketorolac 0.4% up to four
times daily for the first 48 hours after surgery as needed; and
oxycodone/acetaminophen 5 mg/325 mg orally as needed for postoperative pain. The
bandage contact lens was removed on postoperative day 4 if there was no
epithelial defect or replaced as needed until complete reepithelialization.
Pain, corneal reepithelialization, uncorrected distance visual acuity (UDVA),
and any complications such as corneal infiltrates were assessed on postoperative
days 1, 4, and 7. Pain was assessed using a five-point scale10: 0 (none), 1
(minimal), 2 (mild), 3 (moderate), and 4 (severe/worst possible pain).
Uncorrected distance visual acuity, CDVA, MRSE,
wavefront aberrometry, patient satisfaction questionnaire, 5% and 25% low
contrast visual acuity, and slit-lamp microscopy were assessed at 1, 3, 6, and
12 months postoperatively. The questionnaire focused on visual difficulties and
the general satisfaction of postoperative vision using a 10-point scale ranging
from 1 (no symptoms) to 10 (severe, disabling symptoms).14 Low contrast
visual acuity was performed using back illuminated logMAR charts with 5% and 25%
contrast (Precision Vision Inc, La Salle, Illinois). Corneal haze was graded on
a standard 5-point scale: 0 (completely clear), 1+ (trace), 2+ (mild), 3+
(moderate), and 4+ (severe).15
Aberrometry was performed using the LADARWave
wavefront analyzer (Alcon Laboratories Inc) at 850 nm, and the wavefront error
at 550 nm was estimated using the instrument’s proprietary chromatic aberration
correction factor. Monochromatic aberrations were calculated using pupil
diameters of 3 and 6 mm and a Zernike polynomial series up to and including 4th
order was calculated for each measurement. For analysis, the absolute
root-mean-square (RMS) wavefront error of each Zernike mode was determined and
the absolute level of higher order aberrations calculated.
Visual outcomes of epi-LASIK and PRK were compared. Epi-LASIK eyes that had
intraoperative complications resulting in flap amputation were excluded from
comparative analysis. SPSS software version 16.0 (SPSS Inc, Chicago, Illinois)
was used for statistical analysis. Fisher exact test was performed to compare
visual outcomes, reepithelialization, and presence of clinically significant
haze between epi-LASIK and PRK. The Mann-Whitney test was used to compare early
postoperative UDVA, pain scores, and questionnaire data. Odds ratios (OR) were
used to determine likelihood of flap complications. P<.05 was
considered statistically significant for all testing.
Results
A total of 294 patients, mean age 34.2±7.8 years
(range: 21 to 52 years), were enrolled; 145 were consecutively assigned to
epi-LASIK and 149 to PRK. Age, gender, preoperative MRSE, UDVA, 25% low contrast
visual acuity, central corneal thickness, and keratometry were comparable
between groups (Table 1).
Table 1: Preoperative Demographics and Clinical
Characteristics of Eyes That Underwent Epi-LASIK and PRK for Low to Moderate
Myopia
Intraoperative Complications
A summary of intraoperative epi-LASIK complications
is shown in Table 2. Overall, a flap complication occurred in 102 (35%) of 290
epi-LASIK eyes, 57 of which resulted in flap amputation. A relative increase in
rate of complications was noted for age ≤34 years and the right eye, but only
age was statistically significant (P=.02). Odds
ratios are shown in Table 3. No
intraoperative complications occurred in the PRK group.
Table 2: Intraoperative Flap Complications That Occurred
During Epi-LASIK
Table 3: Preoperative Findings and Risk of Intraoperative
Epithelial Flap Complications in Epi-LASIK
Follow-Up Rate
Follow-up availability was comparable between the groups at 1 and 3 months.
Significantly fewer epi-LASIK (82.8%) patients returned for 6-month follow-up
compared with PRK patients (89.3%, P=.024),
whereas significantly more epi-LASIK (86.9%) than PRK patients (75.8%,
P=.001) were seen at 12 months. No significant differences were noted in
age, gender, baseline MRSE, UDVA, CDVA, or 5% and 25% low contrast visual acuity
between initial patients and those seen at each time point studied.
Pain, Epithelial Healing, and Early Visual
Recovery
Few patients reported significant pain on postoperative days 1, 4, or 7. Of
the 298 eyes treated with PRK and 233 eyes treated with epi-LASIK,
reepithelialization was significantly faster in PRK eyes compared with epi-LASIK
eyes by postoperative day 4 (92.4% vs 46.9%, P<.001) and postoperative day 7 (99.3% vs 86.3%, P<.001). Five epi-LASIK eyes required an
additional visit on postoperative day 10. Epi-LASIK was associated with
significantly worse UDVA at postoperative day 1 (P=.002); however, no
other significant difference was noted in UDVA in the early postoperative
period.
Visual Outcomes
Visual outcomes of eyes treated with epi-LASIK
(n=233) and PRK (n=298) were compared. Safety. Safety
indices progressively improved over time for both groups (Table 4). No eye
lost ≥2 lines of CDVA in either group at 12 months. Distribution of CDVA line
changes in epi-LASIK and PRK groups 12 months postoperatively are shown in Figure A.
Table 4: Safety and Efficacy Indices of Epi-LASIK and
PRK
Figure. Twelve-month outcomes of epi-LASIK and PRK. A) Change in corrected distance visual acuity. B) Uncorrected distance visual acuity. C) PRK spherical equivalent attempted vs achieved.
D) Epi-LASIK spherical equivalent attempted vs
achieved. E) Spherical equivalent refractive
accuracy. F) Stability of spherical equivalent
refraction.
Efficacy. Efficacy
index of epi-LASIK was consistently higher compared to PRK. A statistically
significant difference was noted in the number of eyes achieving UDVA of 20/20
or better at 3 months, favoring epi-LASIK (95.5% vs 86.9%, P=.001), but not at any other time point. A significantly
higher percentage of epi-LASIK eyes compared to PRK eyes achieved 20/15 or
better at 1 month (25.8% vs 17.8%, P=.031), 3
months (62.3% vs 49.3%, P=.004), 6 months
(77.1% vs 57.9%, P<.001), and 12 months
postoperatively (75.9% vs 61.9%, P=.002) (Fig B). Predictability. The
number of eyes within ±0.50 D of emmetropia was comparable between epi-LASIK and
PRK at 1 month (69.5% vs 68.5%, P=.85), 3
months (86.3% vs 81.5%, P=.157), and 6 months
(92.3% vs 89.2%, P=.295) but significantly
lower for epi-LASIK than PRK at 12 months postoperatively (86.2% vs 92.5%, P=.04). Figures C and D illustrate scatterplots of
12-month attempted versus achieved MRSE. A strong correlation was noted between
attempted and achieved MRSE in both groups, but with higher refractive errors,
epi-LASIK tends to overcorrect whereas PRK tends to undercorrect. The
distribution of final spherical equivalent refraction is shown in Figure E. Stability. Between
3 and 12 months postoperatively, 17 (8.4%) epi-LASIK eyes compared to 40 (17.7%)
PRK eyes had >0.50-D change in refractive spherical equivalent (P=.004). Mean MRSE at each time point is depicted
in Figure F.
Quality of Vision
Subjective Visual
Performance and Patient Satisfaction. Subjective optical quality was the
same between the two procedures at all time points for vision fluctuations,
double vision, glare, light sensitivity, halos, starbursts, patient
satisfaction, postoperative vision quality, and the chance to have the procedure
again. However, epi-LASIK patients reported more frequent artificial tear use at
3 (P<.001) and 6 (P<.001) months and slightly greater difficulty in their
daily activities when compared to PRK patients (P=.012). Low Contrast Visual
Acuity. Both 5% and 25% low contrast visual acuity results were comparable
between treatment groups at all time points except at 12 months postoperatively;
5% low contrast visual acuity was maintained or improved in 94% of epi-LASIK
versus 78.6% of PRK eyes (P<.001) whereas
25% low contrast visual acuity was unchanged or better than preoperative in 87%
of epi-LASIK versus 75.8% of PRK eyes (P=.024). Higher Order
Aberrations and Low Contrast Vision. Correlation analysis showed that for 3-
and 6-mm artificial pupils, epi-LASIK demonstrated a significant but weak
association between increasing higher order aberrations and diminished low
contrast visual acuity (3-mm pupil: 25% low contrast visual acuity: r=0.16, P=.019; 6-mm pupil: 5% low contrast visual acuity:
r=0.17, P=.015; 25% low contrast visual acuity:
r=0.25, P<.001) at 12 months postoperatively. No significant
correlation was noted for 3-mm pupils at 5% low contrast visual acuity. Optical Quality. Mean absolute higher order
aberrations increased postoperatively in PRK and epi-LASIK eyes. For a 3-mm
artificial pupil, epi-LASIK eyes increased from 0.068±0.029 μm to 0.095±0.036 μm
(P<.001) and PRK eyes increased from
0.075±0.10 μm to 0.089±0.043 μm (P=.03)
postoperatively. For a 6-mm artificial pupil, epi-LASIK eyes increased from
0.66±0.28 μm to 0.99±0.39 μm (P<.001) and
PRK eyes increased from 0.72±0.28 μm to 0.98±0.46 μm (P<.001) postoperatively. However, no significant difference
was noted between epi-LASIK and PRK in postoperative optical quality for either
a 3-mm pupil (P=.14) or 6-mm pupil
(P=.61).
Corneal Haze
Clinically significant haze was observed in two epi-LASIK eyes at 1 month,
one eye at 3 months, and one eye at 6 months postoperatively; each case
progressively improved and resolved. No PRK eye developed clinically significant
corneal haze at any time.
Visual Outcomes After Flap Complication
Two hundred ninety eyes planned to undergo
epi-LASIK were subgrouped by whether a quality flap was made (n=188), the flap
was removed by automatic amputation or surgeon amputation (n=57), or a
complication occurred where the flap was retained (n=45). Measurements of
safety, efficacy, predictability, and stability were found to be statistically
comparable among the subgroups. Stromal Incursion. Six (2.1%) of 290 epi-LASIK eyes had inadvertent
stromal incursion of the epikeratome during epithelial separation. All
treatments were completed during the same session as planned. Mitomycin C (MMC)
was not used in any case. Postoperatively, complete reepithelialization was
noted in 4 of 6 eyes at postoperative day 4, 1 eye at postoperative day 7, and 1
eye at postoperative day 10. One eye had clinically significant haze at 1 month
postoperatively, which subsequently improved with topical steroids. Although
midperipheral mild linear corneal scarring was observed in 2 eyes at 3 months
postoperatively, no eye lost ≥2 lines of CDVA at any time point. No irregular
astigmatism was detected in any of these patients. All eyes had UDVA 20/20 or
better starting at 3 months postoperatively.
Discussion
Previous studies of epi-LASIK have shown promising
results, with comparisons being made to off-flap versus on-flap epi-LASIK
procedures as well as with LASEK procedures.13,16,17 Our study is different
from previous studies as the comparison of epi-LASIK to PRK uses a rotating
brush for epithelial removal in the PRK eyes rather than an epikeratome or blunt
blade. Early postoperative results showed the two procedures to be equivalent
when comparing pain and vision, except for postoperative day 1 when PRK eyes had
significantly better UDVA. This is likely due to an edematous and hazy
epithelial sheet present in the epi-LASIK eyes. Epi-LASIK eyes were also
significantly slower to achieve reepithelialization than PRK eyes. This is
consistent with results reported by Torres et al,18 with epi-LASIK
requiring 4.75±1.44 days and PRK eyes requiring 3.95±1.39 days. In contrast,
O’Doherty et al16 reported 72±24 hours for
epithelial closure in epi-LASIK eyes, whereas PRK eyes took 96±24 hours. This
discrepancy may be a result of different techniques of epithelial removal in the
PRK eyes, as Torres et al18 used a beaver blade whereas
O’Doherty et al16 used an epikeratome.
In the present study, epi-LASIK and PRK were found
to be safe procedures but greater refractive stability and efficacy were seen in
epi-LASIK than PRK. Although a strong correlation between attempted and achieved
refraction was found in both treatments, epi-LASIK seemed to have a tendency to
overcorrect higher refractive errors. This observation was similar to the
initial results reported in LASEK,19,20 which were attributed to
the PRK nomogram-based treatment and the slower but modulated wound-healing
response probably due to the epithelial sheet acting as barrier between tear
cytokines and the ablated stroma.20,21 In contrast, myopic
regression and undercorrection tendencies in PRK are likely due to a more
intense wound-healing response as more tissues are removed, possibly as a
consequence of basement membrane disruption.7,21 Objective image quality in
epi-LASIK seemed to be superior over PRK in terms of retaining or improving low
contrast visual acuity but comparable to PRK in terms of absolute level of
higher order aberrations. Epi-LASIK patients reported experiencing greater
difficulty in performing daily activities but this may not be significantly
different from PRK given that the mean score for epi-LASIK patients was 1.5
(±1.0) and PRK was 1.36 (±0.89).
Corneal clarity as measured by clinically
significant haze was not detected in PRK eyes but was observed in some epi-LASIK
eyes. Kalyvianaki et al17 reported similar results, with
more on-flap epi-LASIK eyes developing haze at 1 and 3 months than off-flap
epi-LASIK eyes. The low level of haze is likely a result of mild to moderate
levels of myopia treated in the study.
In our study, 35% of epi-LASIK eyes had
intraoperative complications, with 20% resulting in amputated flaps. This is
similar to previous reports, including O’Doherty et al16 who reported
33% of eyes resulted in the failed creation of a flap and were converted to PRK.
Our data suggest a higher rate of flap complication occurs in younger patients
(≤34 years), which could be due to a more adherent epithelium in younger
patients.22 Results also suggested
complications were more likely to occur in the right eye than the left eye, but
this observation is likely biased because the right eye was treated first in all
cases. A new epithelial separator was used for the left eye every time a flap
complication occurred in the right eye.
Although the study was not designed to compare
onflap epi-LASIK versus off-flap techniques, our analysis showed retaining or
removing the flap following an unsuccessful creation did not appear to affect
the overall visual outcomes, which is consistent with the comparative study by
Kalyvianaki et al.17
Stromal incursion occurred in 2.1% of eyes treated
with epi-LASIK in our study, which is comparable to a previously reported 2.99%
rate.12 Despite the small number and
insignificant effect on visual outcomes found in our study, we cannot assume
that this complication could not be potentially sight-threatening. Two eyes in
our study developed midperipheral mild corneal scarring, which could have an
adverse effect on their vision if not managed carefully. Widely used in
refractive surgery to prevent postoperative haze and scarring, MMC21
was used by Katsanevaki et al12 following stromal incursion
whereas no eyes in our study were treated with MMC prophylactically.
In conclusion, epi-LASIK required more time for reepithelialization, had
inferior early visual acuity, a tendency to overcorrect higher refractive
errors, and a significant number of amputated flaps necessitating conversion to
PRK. However, when successful, epi-LASIK showed superior refractive efficacy and
stability compared to PRK. Both treatments were comparable in terms of safety
and haze formation. Despite being nonrandomized, the prospective design, large
sample size, identical study criteria and methods, as well as good follow-up
could provide considerable strength for the conclusion of this study. Because
this study was limited to myopia up to −6.00 D, the results cannot be
extrapolated to higher degrees of myopia or to hyperopic or mixed
astigmatism.
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Preoperative Demographics and Clinical
Characteristics of Eyes That Underwent Epi-LASIK and PRK for Low to Moderate
Myopia
Epi-LASIK
PRK
PValue*
No. of patients (eyes)
145 (290)
149 (298)
—
Female/male (%)
54/91 (62.8)
48/101 (67.8)
.225
Age (y)
34.1 (21 to 49)
34.8 (21 to 52)
.807
Sphere (D)
−2.68±1.18 (−0.50 to −6.25)
−2.65±1.04 (−0.25 to −5.75)
.716
Cylinder (D)
0.56±0.51 (0.00 to 2.50)
0.59±0.56 (0.00 to 2.75)
.588
MRSE (D)
−2.97±1.19 (−1.00 to −6.25)
−2.95±1.06 (−1.00 to −6.00)
.819
UDVA (logMAR [Snellen])
1.00 (20/200)±0.37
1.00 (20/200)±0.37
.678
CDVA (logMAR [Snellen])
−0.11 (20/16)±0.43
−0.10 (20/16)±0.48
<.001
5% LCVA (logMAR [Snellen])
0.30 (20/40)±0.11
0.33 (20/43)±0.11
.001
25% LCVA (logMAR [Snellen])
0.31 (20/41)±0.08
0.36 (20/46)±0.11
<.001
CCT (μm)
543±35
540±34
.258
Steep K (D)
44.39±1.58
44.36±1.46
.825
Flat K (D)
43.35±2.76
43.55±1.44
.257
Intraoperative Flap Complications That Occurred
During Epi-LASIK
Complication
No. of Eyes
(%)
None
188 (64.8)
Automatic flap amputation
43 (14.8)
Buttonhole flap
17 (5.9)
Hinge tear
14 (4.8)
Surgeon amputation (hinge in treatment
zone)
14 (4.8)
Incomplete flap/superficial
resection
8 (2.8)
Stromal incursion
6 (2.1)
Total
290 (100.0)
Preoperative Findings and Risk of Intraoperative
Epithelial Flap Complications in Epi-LASIK
Preop
Finding
Odds
Ratio (95% CI)
PValue*
Age ≤34 years
1.69 (1.04–2.76)
.02
Right eye
1.63 (1.00–2.65)
.07
Cylinder <1.00 D
1.26 (0.61–2.60)
.59
CCT ≤500 μm
1.23 (0.58–2.58)
.70
Flat K <42.00 D
1.21 (0.62–2.36)
.61
Steep K >46.00 D
0.57 (0.26–1.26)
.16
Safety and Efficacy Indices of Epi-LASIK and
PRK
Follow-up (mo)
Procedure
Safety Index
Efficacy
Index
1
Epi-LASIK
0.61
−0.16
PRK
0.72
0.39
3
Epi-LASIK
1.09
0.60
PRK
1.11
0.36
6
Epi-LASIK
1.33
0.78
PRK
1.18
0.59
12
Epi-LASIK
1.33
0.85
PRK
1.29
0.67
AUTHORS
From the Ophthalmology Service, Walter Reed Army
Medical Center, Washington, DC (Sia, Coe, Ryan); the Department of
Ophthalmology, University of Florida College of Medicine, Jacksonville, Florida
(Edwards); and The Wilmer Eye Institute, Johns Hopkins University, Baltimore,
Maryland (Bower).
Portions of this material were presented at the
Association for Research in Vision and Ophthalmology Annual Meeting, April
27–May 1, 2008, and May 3–7, 2009, Ft Lauderdale, Florida.
The authors have no financial interest in the
materials presented herein.
The opinions expressed in this manuscript are those
solely of the authors and do not represent the views or official policies of the
United States Army or Department of Defense.
Correspondence: Rose K. Sia, MD, Center for
Refractive Surgery, Walter Reed Army Medical Center, 6900 Georgia Ave,
Washington, DC. Tel: 202.782.8327; Fax: 202.782.4653
