The aim of the DEWS Definition and Classification Subcommittee was to provide a contemporary definition of dry eye disease, supported within a comprehensive classification framework. A new definition of dry eye was developed to reflect current understanding of the disease, and the committee recommended a three-part classification system. The first part is etiopathogenic and illustrates the multiple causes of dry eye. The second is mechanistic and shows how each cause of dry eye may act through a common pathway. It is stressed that any form of dry eye can interact with and exacerbate other forms of dry eye, as part of a vicious circle. Finally, a scheme is presented, based on the severity of the dry eye disease, which is expected to provide a rational basis for therapy. These guidelines are not intended to override the clinical assessment and judgment of an expert clinician in individual cases, but they should prove helpful in the conduct of clinical practice and research.

The definition and classification of dry eye disease: Report of the definition and classification subcommittee of the international Dry Eye WorkShop (2007)

Background Lamellar refractive surgery reduces the biomechanical strength of the cornea which may lead to mechanical instability and keratectasia. Methods Three eyes had laser in situ keratomileusis (LASIK) for myopia from -10.00 to -13.50 D. The procedures were performed with two different wide-field excimer lasers and two different microkeratomes. The patients were followed up to 1 year after surgery. Results Central steep areas developed between 1 and 8 months after surgery. In contrast to conventional central steep islands, these showed rapid progression and were interpreted as keratectasia. Conclusion Iatrogenic keratectasia represents a complication after LASIK that may limit the range of myopia correction. Based on biomechanical considerations we recommend a residual corneal thickness of the stromal bed of at least 250 microm.

Iatrogenic keratectasia after laser in situ keratomileusis.

http://voi.opt.uh.edu/1999-AJO-Comparisonofcornealwavefrontaberrationsafterprk.pdf

Comparison of corneal wavefront aberrations after photorefractive keratectomy and laser in situ keratomileusis

Purpose To demonstrate the functional vision and corneal changes following laser in situ keratomileusis (LASIK) determined by contrast sensitivity, glare testing, and corneal topography. Setting University of Texas Medical School, Houston, Texas, USA. Methods Seven patients ranging in age from 20 to 61 years who had bilateral LASIK were evaluated preoperatively and 1 day, 1 week, and 1 and 6 months postoperatively. Visual acuity, using letters on the Baylor Visual Acuity Testor (BVAT) at 98% (standard acuity) and 13% contrast, and the contrast threshold were determined at 3 light levels (darkness, medium brightness acuity testor [BAT], high BAT). Pupil sizes were measured at each level, and corneal topography was performed at each visit. Results The greatest changes were found 1 day postoperatively: The contrast threshold worsened by a mean of 0.6 lines ± 1.0 (SD) (P = .05) in darkness, 0.4 ± 0.7 lines (P = .05) at medium BAT, and 0.8 ± 0.7 lines (P = .002) at high BAT. The 98% contrast acuity decreased a mean of 1.4 ± 1.6 lines (P = .01) in darkness, 1.0 ± 2.0 lines (P = .09) at medium BAT, and 0.8 ± 2.3 lines (P = .22) at high BAT. The 13% contrast acuity decreased a mean of 2.2 ± 2.6 lines (P = .01) in darkness, 1.3 ± 1.9 lines (P = .02) at medium BAT, and 1.4 ± 2.5 lines (P = .07) at high BAT. The predicted corneal acuity (PCA) obtained from corneal topography decreased by a mean of 3.3 ± 3.1 lines (P = .002), and the asphericity (Q-value) increased by an average of +0.35 ± 0.67 (P = .07). All values returned to the preoperative levels by 1 week except PCA, asphericity, visual acuity at 13%, and contrast threshold in darkness, which improved slightly but had not returned to baseline by 6 months. The 98% contrast acuity at medium BAT improved by 0.2 ± 1.0 lines (P = .34) and 0.3 ± 0.8 lines (P = .16) at high BAT at 1 month. The 98% contrast acuity values remained 0.3 lines over baseline through 6 months. Corneal topography showed that all corneas became oblate after LASIK to a mean Q-value of +0.47 ± 0.40 (P Conclusions Functional vision changes do occur after LASIK. The optical quality of the cornea is reduced and the asphericity becomes oblate. Changes in functional vision worsen as the target contrast diminishes and the pupil size increases. These findings indicate that the oblate shape of the cornea following LASIK is the predominant factor in the functional vision decrease.

Functional vision and corneal changes after laser in situ keratomileusis determined by contrast sensitivity, glare testing, and corneal topography.

LASIK complications: etiology, management, and prevention.

In this study, we report the results of a prospective, double-blind trial to determine whether high-dose topical corticosteroids have an effect on refractive outcome or anterior stromal haze after photorefractive keratectomy. A total of 113 patients were allocated randomly to either placebo- or steroid-treated groups (0.1% dexamethasone metasulphobenzoate for 3 months) and underwent either -3.00-diopter (D) or -6.00-D procedures. At 6 weeks, the mean change in refraction was significantly greater in the steroid-treated group than in the placebo-treated group (-3.00-D group, P = .0015; -6.00-D group, P = .0011). However, when corticosteroids were discontinued at 3 months, this difference became statistically insignificant. There was no statistically significant effect on anterior stromal haze at any stage. Since long-term use of corticosteroids to maintain the initial beneficial effect on refraction would be unacceptable, we conclude that these agents should not be used after photorefractive keratectomy.

The effect of topical corticosteroids on refractive outcome and corneal haze after photorefractive keratectomy. A prospective, randomized, double-blind trial.

Corneal Light Scattering and Visual Performance in Myopic Individuals With Spectacles, Contact Lenses, or Excimer Laser Photorefractive Keratectomy

BACKGROUND: To date, there has been no systematic study of the effects of ablation zone diameter on the outcome of photorefractive keratectomy. To address these issues, we examined a series of eyes with bilateral corrections using different-sized ablation zones. METHODS: Thirty-three patients underwent bilateral photorefractive keratectomy (Summit Excimed UV200, Waltham, Mass) with identical dioptric corrections in both eyes, except first eyes had 4.00-millimeter and second eyes had 5.00-millimeter ablation zones. Identical postoperative eyedrop regimens were used in both eyes of each subject and the interval between treatments was 12 months. The mean depth of the programmed central ablation was 24 microns in eyes treated with 4.00-millimeter and 39 microns with 5.00-millimeter zones. RESULTS: There was no statistically significant difference in the preoperative refraction between first and second eyes. Mean changes in refraction at 1, 3, 6, 9, and 12 months were significantly greater in eyes treated with 5.00-millimeter ablation diameters (p < .001). No eyes treated with 4.00-millimeter zones were overcorrected, but five eyes (15%) treated with 5.00-millimeter beams had a refraction greater than +1.00 diopter (D) at 12 months postoperatively. There was no significant difference in the amount of anterior stromal haze between the two eyes at any stage. In 14 patients, less night halo was noticed in the eye treated with a 5.00-millimeter zone. Using a computer program, halo measurements were made in both eyes of 12 patients whose pre- and postoperative refractions were within 0.50 D. The magnitude of halo was significantly less in eyes treated with 5.00-millimeter zones (p < .01). CONCLUSIONS: Despite greater depths of stromal ablation with 5.00-millimeter diameters, there was no increased anterior stromal haze or postoperative regression of refraction. The biological and physical constraints governing the optimum size of the photorefractive keratectomy ablation zone are discussed.

Excimer Laser Photorefractive Keratectomy for Myopia: Comparison of 4.00- and 5.00-Millimeter Ablation Zones

• The records of 66 patients with the iridocorneal endothelial (ICE) syndrome were retrospectively reviewed. Glaucoma occurred in 33 (50%) of the patients with ICE syndrome and was most common in the variants in which abnormal cells involve the entire posterior corneal surface (disseminated ICE and total ICE). Of 25 patients with glaucoma, the diagnosis of ICE syndrome was overlooked initially in 17 (68%). Medical glaucoma treatment was generally ineffective. Of 22 patients (88%) who underwent surgery (typically trabeculectomy), 10 (45%) required more than one procedure. The success rates of first operations at 1 and 5 years were 60% and 21% and those of second and third operations at 1 year were 20% and 17%. During the course of their management, 11 patients (44%) developed visual field loss. The diagnosis of ICE syndrome should be considered in younger patients with unilateral glaucoma and confirmed by specular microscopy. Management of glaucoma due to ICE syndrome is surgical, and means of improving its long-term success need to be addressed.

Glaucoma and the iridocorneal endothelial syndrome.

Recurrent corneal erosion may be a difficult disorder to treat, with a number of patients suffering persistent symptoms despite conventional therapy. We present a series of 15 patients (17 eyes) who underwent excimer laser phototherapeutic keratectomy (PTK) for recurrent corneal erosion. In 9 patients a previous episode of corneal trauma could be identified, while in 6 (8 eyes) the problem had occurred spontaneously. The mean duration of symptoms prior to PTK was 13 months (range 6-60 months). All patients had received lubricant ointments, 7 had tried bandage contact lenses and 4 had undergone epithelial debridement with no amelioration of their symptoms. The affect area of epithelium was removed and a 20-30 pulse (5-7 microns) ablation was performed to Bowman's membrane. Great care was taken to avoid the edges of treatment zones from encroaching on the axial cornea. In 11 patients (13 eyes) there was a marked improvement in symptoms post-operatively with no recurrences. The mean follow-up was 11 months (range 6-24 months). Four patients experienced recurrent episodes 3-6 months after PTK and 2 have subsequently been retreated, 1 of whom has been symptom-free for 12 months. Post-operative best corrected visual acuity was unaltered in 9 eyes and improved by at least one Snellen line in 8 eyes. Excimer laser PTK appears to be a safe and promising procedure for recurrent corneal erosion in cases refractory to medical treatment. Further studies are indicated to compare its effectiveness with established surgical procedures.

/pdf/phototherapeutic-keratectomy-for-recurrent-corneal-erosions-4rpf3lpxyt.pdf

Malcolm G. Kerr Muir

Papers

The effect of topical corticosteroids on refractive outcome and corneal haze after photorefractive keratectomy. A prospective, randomized, double-blind trial.

Corneal Light Scattering and Visual Performance in Myopic Individuals With Spectacles, Contact Lenses, or Excimer Laser Photorefractive Keratectomy

Excimer Laser Photorefractive Keratectomy for Myopia: Comparison of 4.00- and 5.00-Millimeter Ablation Zones

Glaucoma and the iridocorneal endothelial syndrome.

Phototherapeutic keratectomy for recurrent corneal erosions.