Nowadays excimer laser surgery is one of the most popular procedures in ophthalmology. Thousands of patients are operated on annually in US to correct different refractive errors.[1] In this field, LASIK (Laser-assisted in situ keratomileusis) and PRK (Photorefractive keratectomy) have become the most commonly performed surgical procedures due to their safety and efficacy, but both have some disadvantages. In the case of PRK, post operative pain, haze, slower visual recovery are some of the commonly complications. On the other hand, LASIK has disadvantages, such as potential flap related complications (intra and post operative), interface related complications and ectasia post lasik.[2]

HeNe laser class

The LASOS® Helium Neon lasertubes and modules have a robust mechanical design, excellent beam quality and long service life of up to 30,000 hours. Standard and customized models are available in a large variety in the spectral range red, green and yellow with output powers between 0.5 and 20 mW. Options are single mode or multimode, randomly or linear polarized and Brewster window tubes for educational and scientific purposes.

Helium-neon laser spectrum

LASEK (Laser epithelial keratomileusis) can theoretically combine all the advantages of LASIK and PRK and potentially avoid some of their complications.

Ruby laser

Unwanted emission besides the nominal wavelength value, often disturbing in spectroscopy and interferometry. Can be suppressed by special mirror technology.

The Helium Neon lasers are designed for multipurpose applications such as confocal laser scanning microscopy, spectroscopy, digital imaging, metrology, industrial measurement, positioning, alignment, aiming, testing, code scanning, medical, basic research, education or entertainment.

Tube supports exact two orthogonally polarized longitudinal modes. Required for special methods of frequency stabilization.

Thorlabs HeNe Laser

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The history of LASEK dates back to 1996 , when the first LASEK procedure was performed at the Massachusetts Eye and Ear Infirmary by Dr. Dimitri Azar; [3] but it was Dr. Massimo Camellin who introduced the term LASEK and popularized this procedure[4] [5] [6]

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Tobaigy et al matched each LASEK-treated eye to a LASIK-treated eye using specific criteria. 122 LASEK eyes were matched with 122 LASIK eyes. This group concluded, although there were some differences in the visual and refractive results favoring LASEK, they were not clinically significant. Both procedures seemed safe, effective, and predictable for the treatment of low and moderate myopia [2]. Zhao et al found in their meta-analysis that there were no significant differences in visual and refractive outcomes between the LASEK and LASIK for low to moderate myopia in the midterm and long-term follow-up, and suggest new randomized and prospective studies to know the benefits of this technique [30] Kaya et al reported the results of LASEK and LASIK in a prospective study for myopia of less than -6.0 D. Based on 6-month results, they found no statistical difference in UCVA, BSCVA, and spherical and cylindrical refractive error between the groups and considered LASEK an alternative for LASIK. [31] Also Kim compared the visual and refractive results of LASEK and LASIK for high myopia in 470 eyes up to 1 year post-operatively. They found an UCVA of 20/25 was achieved in 83% of the eyes that underwent LASIK compared with 76% that underwent LASEK. More eyes lost more than one line of vision in LASEK (14.3%) than LASIK (1.2%). This group concluded that LASIK provided superior and more favorable results for high myopia.[32] In summary, both techniques are safe and effective. Finally, every surgeon has to take an decision based in the characteristic of the patient such as activities and lifestyle, cornea thickness and requirement of visual rehabilitation.

helium-neon laser pdf

After instillation of topical ophthalmic anesthesia, a notched micro-trephine is used to create an epithelial incision (with a 90° hinge at 12:00). An 18% ethanol solution (using distilled water for dilution instead of balanced salt solution) is applied over an area of 8.5 mm diameter for 20 seconds. The surface of the eye is then rinsed with diclofenac sodium. The flap edge is detached and moved superiorly toward the 12:00 position. Laser ablation is performed and then the epithelium is then repositioned and a soft contact lens is placed on the cornea for 3 to 4 days. Postoperatively, antibiotic and cortisone eye drops are administered for a few days, and a mild cortisone treatment is continued for up to a month.[10]

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This is an alcohol-free technique. The epithelium is marked and then coated with GenTeal® gel. Trephination of the cornea is then performed. Scoring of the epithelium down to Bowman’s layer (a distance of 1–2 mm) is performed using a 2.25 rounded knife (ASICO). Ten drops of 5% NaCl ophthalmic solution are applied to the corneal epithelium (to stiffen the epithelium) and then blotted dry with eye spears. A microkeratome head (upside down) is placed on the eye and the stalk/stem is held by a surgical assistant (as the surgeon must use both hands to continue operating); suction is then applied. A cannula is then slipped under the epithelium and used as a fulcrum to sweep and to loosen the epithelium. Suction is then released and GenTeal® gel is then injected under the loosened epithelium. A LASEK flap is then created via the Vinciguerra butterfly technique. Using Vannas scissors, a cut is made through the center of the sheet of epithelium and the two halves of the sheet are reflected to the side. Alternatively, the sheet of epithelium may be quadrisected rather than bisected. An eye spear is then used to remove the gel from Bowman’s and excimer laser ablation is applied. The epithelium is then replaced and a bandage contact lens is placed. [9][15] [16]

In this technique, with a Vinciguerra spatula (ASICO, Westmont IL), a thin abrasion (0.75 mm) is performed on the paracentral cornea from the 8:00 to 11:00 positions, and 20% alcohol in BSS is placed in contact with the cornea for 5–30 seconds. With the same spatula, the epithelium is separated from Bowman’s layer, proceeding from center to periphery on both sides. Vinciguerra LASEK butterfly protector/retractor (ASICO) is used to move the two sheets of loose epithelium sideways toward the limbus and hold them in place. After drying the surface, excimer laser ablation is performed. Smoothing with a hyaluronic acid masking solution (Laservis; Cheme- dica, Munchen, Germany) is then carried out, followed by repositioning of the stretched epithelial flaps with the margins overlapping. [13] [14]

When this method was initially reported, 76 eyes with mean refractive error of -11.00 +/- 3.00 D (range -8.00 to -22.00) were treated. Post operatively, visual stability was noted at approximately 60 days. 62.7% of the patients reported no post operative pain. No significant subepithelial haze was seen in 95% of eyes. Thus, the study concluded that LASEK had the advantage of being able to treat a larger diameter ablation zone in thinner corneas without problems of stromal flap compared to LASIK. Less post operative pain and minimal subepithelial haze was the advantage of LASEK over PRK in these cases.[10]

Sudden changes of the polarization of different modes espacially in short tubes. Particularly disturbing when HeNe laser tubes are used in frequency stabilized operation. Can be eliminated by special selection process.

All our laser models can be provided with adequate OEM and laboratory power supplies, meeting the European and American standard with the availability of approvals and certificates CDRH, IEC, CSA, CE, TÜV, UL.

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Frequency split of He-Ne laser modes in the presence of a strong magnetic field (> 200 G). Can be used for obtaining extremely high frequency stability. LASOS® has been successful in developing tubes with specific split frequencies for defi ned magnetic fields.

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Hashemi et al performed a prospective, randomized and paired comparison between LASEK and PRK for myopia less than -6.50 diopters and reported similar predictability, efficacy, safety, and patient satisfaction of LASEK and PRK in the treatment of low to moderate myopia.[26]. Lee et al compared LASEK and PRK, for low to moderate myopia (–3.00 to –6.50 diopters) in 27 patients and reported during 3 month follow-up, there were no significant between-eye differences in epithelial healing time, UCVA, or refractive error. However, they reported that LASEK-treated eyes had lower postoperative pain scores and corneal haze scores than PRK-treated eyes. From a patient perspective, in this study, seventeen patients (63%) preferred the LASEK procedure[27]. On the other hand, Litwak et al found less discomfort in PRK eyes than LASEK eyes in the 25 patients studied.[28] An interesting meta-analysis was performed by Cui et al comparing PRK and LASEK according to the available data, they reported there is no difference between PRK and LASIK for correcting myopia from 0 to -9.0 D. This study mainly focused on the comparison of the early, mid-term and mid-long term results of the two methods.[29]. Even though some authors found more advantages in LASEK than PRK, we need more studies to know if there is a real and significant advantage of one over the other between these two techniques.

After application of topical 0.05% proparacaine (Ophthetic; Allergan, Inc., Irvine, CA) and 4% tetracaine (formulated in the Massachusetts Eye and Ear Infirmary pharmacy), a lid speculum is applied. The cornea is then marked with overlapping 3mm circles around the corneal periphery, simulating a floral pattern. An alcohol dispenser consisting of a customized 7 or 9mm semi-sharp marker (ASICO, Westmont, IL) attached to a hollow metal handle serves as the reservoir for 18% alcohol. After 25–30s, the ethanol is absorbed using an aspiration hole followed by dry sponges (Weckcel or Merocel). If necessary, the ethanol application may be repeated for an additional 10–15s. Epithelial removal is performed with an arm of a modified Vannas scissors (ASICO) to delineate the epithelial margin and fashion a hinged epithelial flap. The modified Vannas scissors also allow for creative variations of the LASEK incision to be customized for different corneal types. After pushing aside the epithelial flap, the underlying stromal bed is ablated with an excimer laser. After ablation, an anterior chamber cannula is used to hydrate the stroma and float the epithelial flap over a layer of balanced salt solution. The epithelial flap is then replaced under intermittent irrigation and with careful attention to realignment of the epithelial flap margins using the previous marks. The epithelial flap is then allowed to dry for 2–5min. Topical steroids and antibiotic medications are applied, and a bandage contact lens placed. The bandage contact lens is removed after complete reepithelialization (generally postoperative day 3 or 4).[7][11] [12]

LASEK involves producing an epithelial detachment with application of diluted alcohol solution (18-20%) on the cornea. The alcohol is then rinsed off and the, epithelium is scraped. An epithelial flap is created by folding the epithelium on a nasal or superior hinge. Laser ablation is then performed on the bed. The epithelium is replaced on the stroma with special attention to achieve correct alignment to avoid future complications. Finally, topical steroids and antibiotic are applied and a soft contact lens is placed. The soft contact lens is removed after complete re-epithelialization (typically 3 or 4 days post op). [7] [8] [9]