Neodymium-doped yttrium aluminum garnet (Nd: YAG) laser treatment in ophthalmology: a review of the most common procedures Capsulotomy and Iridotomy

Nowadays, lasers are used in various medical fields. Ophthalmology was the first medical specialty to utilize lasers in patient treatment and still remains the leading medical field that uses laser energy for both therapeutic and diagnostic purposes. The neodymium: yttrium-aluminum-garnet (Nd: YAG) laser is one of the most common lasers used in ophthalmology. It is a solid-state laser with a wavelength of 1064 nm that works on the principle of photodisruption. Since its introduction in ophthalmology over 40 years ago, it has found various applications, mainly for procedures where cutting or disruption of ocular tissue is required. Compared to surgical alternatives, the use of Nd: YAG lasers on ocular tissue is minimally invasive. In this review, we focus on the two most common ophthalmic applications of Nd: YAG laser - laser peripheral iridotomy and posterior capsulotomy. The history of the techniques, current trends, potential complications, and the prognosis for future use is discussed.

Corneal Endothelial Changes Following Early Capsulotomy Using Neodymium:Yttrium-Aluminum-Garnet Laser

We aimed to survey whether the timing of neodymium:yttrium–aluminum–garnet (Nd:YAG) laser capsulotomy would alter the corneal endothelial morphology and density. A retrospective cohort study was conducted, and 48 patients with unilateral posterior capsular opacity (PCO) and Nd:YAG laser capsulotomy performance were enrolled. The participants were divided into the early Nd:YAG group (timing ≤ 12 months, n = 20) and late Nd:YAG group (timing > 12 months, n= 28) depending on elapsed months between phacoemulsification and Nd:YAG laser capsulotomy. Endothelial cell density (ECD), coefficient of variant (CV), hexagonality (HEX), and central corneal thickness (CCT) between the two groups were collected. A generalized estimate equation was conducted to evaluate the corneal endothelial parameters between the two groups with an adjusted odds ratio (aOR) and 95% confidence interval (CI). The CDVA was improved after treatment in both groups (both p < 0.001). Chronically, ECD in the early group was significantly decreased one week after treatment (2221.50 ± 327.73/mm² vs. 2441.55 ± 321.80/mm², p < 0.001), which recovered to 2369.95 ± 76.37/mm² four weeks after the treatment but was still lower than the preoperative status (p < 0.001). In addition, the HEX percentage showed a significant reduction at four weeks after treatment (p = 0.028). The ECD in the early group was significantly lower than that in the late group (aOR: 0.167, 95% CI: 0.079–0.356, p = 0.003) in both week 1 (p < 0.001) and week 4 (p = 0.004) after laser treatment. In conclusion, the early application of Nd:YAG laser capsulotomy within one year after cataract surgery may be the reason for postoperative ECD decrement without known etiology.

The Effects of Glaucoma and Glaucoma Therapies on Corneal Endothelial Cell Density

A healthy corneal endothelium is required for corneal clarity. Both the glaucoma disease state and its various forms of treatment can have adverse effects on the corneal endothelium. Both the presence of glaucoma and the magnitude of intraocular pressure elevation are related to endothelial cell loss (ECL). Topical medical therapy, laser procedures, and both traditional surgeries-trabeculectomy and tube-shunts-and newer minimally invasive glaucoma surgeries have variable effects on ECL. This review will summarize the reported effects of glaucoma and its treatment on ECL. Concerns for corneal endothelial cell health should be part of the decision-making process when planning glaucoma therapy for lowering intraocular pressure, with added caution in case of planned device implantation in eyes with preexisting ECL and low endothelial cell density at high risk for corneal endothelial decompensation.

Long-Term Evaluation of Specular Microscopic Changes Following Nd: YAG Iridotomy in Chronic Primary Angle-Closure Glaucoma Eyes

AIM

The aim of this study was to evaluate specular microscopy of chronic primary angle-closure glaucoma (CPACG) eyes at least 1 year after Nd:YAG iridotomy, and compare them with CPACG eyes without an iridotomy and age-matched, normal eyes.

PATIENTS AND METHOD

Consecutive patients of CPACG at the Glaucoma service were screened. All patients underwent slit-lamp biomicroscopy, +90 D examination, and applanation tonometry. A total of 100 eyes of 100 consecutive patients of CPACG with an Nd:YAG iridotomy performed ≥1 year before, who met all inclusion/exclusion criteria, 60 consecutive CPACG eyes without an iridotomy, and 60 age and refraction-matched control eyes were enrolled. A specular microscopy was performed in one eye of each patient by an observer masked to diagnosis.

RESULTS

CPACG patients had a mean age of 62±8 years, a mean intraocular pressure of 18±5.3 mm Hg, a mean specular count of 2536±224 cells/mm, and mean duration after iridotomy of 3.2±2 years. There was a significant correlation of specular endothelial counts with age (r=-0.39; P<0.001) and interval after iridotomy (r=-0.25; P=0.01). CPACG eyes without an iridotomy had a mean age of 62±5 years and a mean specular count of 2469±199 cells/mm. Normal control eyes with a mean age of 61±6 years had a mean specular count of 2729±299 cells/mm. There was no significant difference in specular count between CPACG eyes with or without an iridotomy (P=0.19); however, both CPACG groups had a specular count significantly lower than controls (P=0.01 and 0.02, respectively). There was no statistically significant difference seen in polymegathism (coefficient of variation) and pleomorphism (% of hexagonal cells) in endothelial cells among the 3 groups.

CONCLUSIONS

An Nd:YAG iridotomy in CPACG eyes did not lead to any significant changes in central corneal specular microscopy in the long term as compared with patients who did not undergo iridotomy. Eyes with CPACG, without and after an iridotomy, had a lower specular count compared with age-matched controls.

Corneal graft failure following Nd:YAG laser membranotomy for inadvertent retained descemet's membrane after penetrating keratoplasty

Retained Descemet's membrane (DM) following penetrating keratoplasty (PKP) is a rare finding that may reduce visual acuity following opacification or endanger the graft endothelium. The association between Nd:YAG laser membranotomy and corneal graft failure is reported. Five of 1,350 patients (0.37%) undergoing PKP for pseudophakic bullous keratopathy or graft failure between 1986 and 2008 presented with inadvertent retained DM located close to the graft endothelium. The membrane opacified within 3 to 4 months, reducing the patients' vision. Nd:YAG laser membranotomy was performed using low energy and few pulses. Patients' visual acuity improved from 6/40 to 6/90 before treatment to 6/15(-) to 6/20 at 2 weeks following membranotomy. However, the corneal graft decompensated within 6 to 8 weeks following this procedure, necessitating repeat PKP, with removal of the retained DM. Nd:YAG laser membranotomy may lead to corneal graft failure due to shockwave damage created by the laser pulses, focused near the endothelial surface.

Neodymium:YAG laser peripheral iridotomy: cause of a visually incapacitating cataract?

Neodymium:YAG (Nd:YAG) laser peripheral iridotomy is the procedure of choice to treat and avoid further episodes of angle-closure glaucoma. A patient who developed a visually incapacitating posterior subcapsular lens opacity shortly after Nd:YAG laser peripheral iridotomy is described. The patient underwent cataract surgery and achieved a good level of visual acuity postoperatively. The intraocular pressure remained under control with no medical treatment. This case suggests a possible, albeit rare, potential complication of Nd:YAG laser peripheral iridotomy.

Dense membrane formation after combined phacoemulsification-trabeculectomy surgery

A case is reported of formation of a dense intraocular membrane following combined phacoemulsification-trabeculectomy surgery. The membrane might have originated from a loose piece of pigment epithelium or might have resulted from dense pigment deposition on a postoperative pupillary membrane. Postoperative membranes have been reported particularly after combined procedures. A combination of intensive topical dexamethasone, homatropine and a Nd:YAG laser was used to speed resolution of the membrane.

Effects of transcorneal iridal photocoagulation on the canine corneal endothelium using a diode laser

OBJECTIVE

To investigate the potential damage to the canine corneal endothelium following transcorneal iridal laser photocoagulation using a semiconductor diode laser.

ANIMALS STUDIED

Sixteen young mongrel dogs.

PROCEDURES

Baseline corneal endothelial cell counts and corneal thickness were measured in the central and temporal quadrants using a noncontact specular microscope under general anesthesia. Transcorneal iridal photocoagulation was applied using a semiconductor diode laser in a continuous mode with the use of an operating microscope. Fifteen dogs were treated, and the sixteenth dog served as a control. Fifteen different treatment combinations were randomly assigned to the 30 eyes; the fellow eye was treated differently. Three treatment factors were investigated: (1) laser energy intensity, (2) target tissue to endothelial distance, and (3) laser application duration. After 3 weeks the dogs were euthanized, specular microscopy was repeated, and the cornea was examined by scanning electron microscopy.

RESULTS

Dyscoria and focal iris darkening were noted in all eyes immediately following laser treatment. Focal corneal edema (n = 2) and an incipient anterior capsular cataract (n = 1) were also noted. Baseline mean corneal endothelial cell densities were 2530 cells/mm2 centrally and 2607 cells/mm2 temporally. Postlaser corneal endothelial cell densities were 2499 cells/mm2 centrally and 2523 cells/mm2 temporally. Mean prelaser corneal thickness measurements were 0.555 mm centrally and 0.549 mm temporally. Postlaser corneal thickness measurements were 0.580 mm centrally and 0.554 mm temporally. Statistical analyzes revealed no significant changes in endothelial cell densities (P > 0.05) or corneal thickness (P > 0.05) induced by any treatment combination. Aside from tissue handling and processing artifacts, scanning electron microscopy revealed no endothelial cell damage.

CONCLUSIONS

Our study demonstrated by specular and scanning electron microscopy that diode laser iridal photocoagulation had no significant effect on the canine corneal endothelium within the parameters described. However, one must take into consideration the young age of the dogs and the potential for corneal endothelial cell regeneration in young dogs, and the relatively short period of postoperative study.

Two-site phacotrabeculectomy with intraoperative mitomycin-C: fornix- versus limbus-based conjunctival opening in fellow eyes

To prospectively compare the influence of fornix-based and limbus-based conjunctival flaps on the final outcome and complications of 2-site phacotrabeculectomy with mitomycin-C in fellow eyes of patients with bilateral open-angle glaucoma (OAG). Glaucoma Unit, Department of Ophthalmology, University of Crete, Crete, Greece.Twenty-two patients with bilateral primary OAG and 8 patients with bilateral exfoliative glaucoma had 2-site phacotrabeculectomy in both eyes. Eyes were randomly assigned to the fornix-based flap or limbus-based flap group by the use of random tables. The intraocular pressure (IOP) decreased significantly in both groups (P <.01); however, there was no statistically significant difference between the groups in the amount of IOP decrease or the number of postoperative antiglaucoma medications after a 1-year follow-up. Faster improvement in visual acuity was observed in the fornix-based group during the first week. The mean time of surgery was 3.5 minutes less in the fornix-based group. An increased incidence of fibrin exudation, pupillary membrane formation, and capsule opacification was found in eyes with exfoliative glaucoma. The early bleb leakage was 3 times more frequent in the fornix-based group. The type of conjunctival flap in a 2-site phacotrabeculectomy did not seem to influence the final outcome. The main advantage of the fornix-based conjunctival flap is the shorter surgical time and the relatively faster improvement in vision postoperatively. The main disadvantage is more frequent early bleb leakage.