Faculty Bibliography

BACKGROUND:To determine the average amount of mechanical forces applied to the lids of keratoconus patients during eye rubbing. METHODS:Fifty-seven patients (41 male, 16 female, average age 34.8 years) with a clinically and topographically diagnosed keratoconus and a history of eye rubbing were prospectively asked to perform their individual eye rubbing movement on a high-precision balance. The type of eye-rubbing movement and the force applied, represented in newtons (N), were recorded and analyzed. RESULTS:We detected three different types of eye rubbing. Rubbing with the fingertip was most frequent (51%), followed by rubbing with the knuckle (44%) and rubbing with the fingernail (6%). Each type of eye rubbing showed different average forces, with knuckle type eye rubbing applying significantly more force (9.6 ± 6.3 N) on the lids than fingertip (4.3 ± 3.1 N) and fingernail (2.6 ± 3.3 N) types (p < 0,001 and p = 0,016, respectively). CONCLUSIONS:There were major variations in the force exerted on the lids, depending on the type of eye rubbing employed. This data will help determine the forces that need to be applied in future experimental eye rubbing models.

PURPOSE:Quasi-static optical coherence elastography (OCE) is an emerging technology to investigate corneal biomechanical behavior in situations similar to physiological stress conditions. Herein OCE was applied to evaluate previously inaccessible biomechanical characteristics of human corneal tissue and to study the role of Bowman's layer in corneal biomechanics. METHODS:Human corneal donor buttons (n = 23) were obtained and Descemet's membrane and endothelium were removed. In 11 corneas, Bowman's layer was ablated by a 20 µm stromal excimer laser ablation. Buttons were mounted on an artificial anterior chamber and subjected to a pressure modulation from 10 to 30 mm Hg, and back to 10 mm Hg, in steps of 1 mm Hg. At each step, a spectral-domain optical coherence tomography scan was obtained. Displacements were analyzed by optical flow tracking, and strain over the entire stromal depth was retrieved from the phase gradient of the complex interference signal. RESULTS:During pressure increase, corneal tissue moved upward (486-585 nm/mm Hg) but did not fully recover (Δ= 2.63 to 8.64 µm) after pressure decrease. Vertical corneal strain distribution was negative in the anterior and positive in the posterior cornea, indicating simultaneous corneal compression and expansion, respectively. Bowman's layer caused minor localized differences in corneal strain distribution. CONCLUSIONS:Corneal strain distribution is more complex than previously assumed, with a fundamental difference in mechanical response between the anterior and posterior stroma. Clinically, OCE technology might be used to monitor the progression of corneal ectatic diseases and to determine the success of corneal cross-linking.

BACKGROUND:Middle vault asymmetry is a common reason for retained postoperative deviations. Although minor deformities can be camouflaged with cartilage, soft-tissue materials, or injectable fillers, comprehensive observation of upper lateral cartilage and subsequent topographic classification in major anatomical anomalies will help surgeons better plan their procedures to obtain better symmetry. METHODS:Photographs of 71 randomly selected primary open rhinoplasty patients were analyzed for anatomical presentation of their upper lateral cartilage. Photographs were taken before and after separation of upper lateral cartilage from the septum. Upper lateral cartilage was classified from class I to class V according to the width of the transverse subunits and curvature of the vertical subunits. RESULTS:The authors observed 142 upper lateral cartilages of 71 rhinoplasty patients. Upper lateral cartilage was classified as follows: class I, 53 cases; class II, three cases; class III, 40 cases; class IV, 36 cases; and class V, 10 cases. CONCLUSIONS:Upper lateral cartilage asymmetry is a common occurrence in rhinoplasty, and the upper lateral cartilage itself may be the source of nasal deviation. The middle vault requires special attention, and establishment of a classification system could enable surgeons to devise an effective plan for correction and prevention of retained postoperative nasal deviation.

PURPOSE/OBJECTIVE:To compare the outcomes of accelerated photoactivated chromophore for keratitis corneal cross-linking (PACK-CXL) as an adjunct treatment for bacterial keratitis (PACK-CXL plus standard antibiotic therapy) for patients receiving only standard antibiotic therapy. METHODS:Retrospective cohort study of outcomes of patients with moderate infectious presumed bacterial keratitis (ulcer diameter 2 to 7 mm and stromal depth < 300 µm) were compared before and after initiation of a new treatment protocol of PACK-CXL in addition to standard antibiotic treatment. RESULTS:A total of 70 eyes of 70 patients were included: 39 eyes in the PACK-CXL plus antibiotic (PACK-ABX) group and 31 eyes in the antibiotic only (ABX) control group. The PACK-ABX group showed shorter times to complete reepithelialization (9.3 ± 6.0 vs 16.0 ± 12.7 days, P = .01) and did not require tectonic emergency keratoplasty (0% versus 19.4%, P = .006). The PACK-ABX group also showed a higher percentage of eyes with complete reepithelialization in 6 days or less (46.2% vs 6.5%, P < .001) and a trend for shorter hospitalizations (6.3 ± 5.0 vs 8.5 ± 4.5 days, P = .06). A multivariate analysis controlling for age showed that PACK-ABX treatment remained significantly associated with early ulcer reepithelialization (odds ratio = 0.09, 95% confidence interval = 0.02 to 0.48, P = .005). CONCLUSIONS:This study validates previous findings regarding the use of accelerated PACK-CXL in the treatment of bacterial keratitis. Adding PACK-CXL improved clinical outcomes (reducing healing time) when compared to antibiotics alone. [J Refract Surg. 2020;36(4):258-264.].

BACKGROUND:Facial and cranial asymmetry is common in bilateral vertebrates, particularly human beings. Through years of injecting fillers and performing face-lift operation on patients, we began to observe that more fillers were required on the right side to reach symmetry and also more loose skin and soft tissue was observed on the right side in the majority of patients (Fig. 5). Here, we conducted an analytical study to comprehensively measure human skulls in order to observe and quantify this difference. METHODS:We collected forty-one natural skulls available from five medical schools of Tehran province in Iran. Standard photography was conducted from the front, lateral, and superior views. Measurements and statistics were completed using Image J software (National Institutes of Health) for exact comparison of fixed-point distances on the samples. RESULTS:Comparison of right and left dimensions on the skulls revealed several fixed asymmetries. The most significant differences were measurements around the orbit. The distance between the upper orbit point and zygion (zy), zygion to sub-nasal, and orbital areas were significantly larger on the left side. Measuring the anterior gonion-pogonion distance showed a wider mandibular body on the left side. We did not find any considerable differences between any other left-sided and right-sided skull dimensions. CONCLUSIONS:Asymmetry of the face and body is a general rule in human anatomy, but correlation and consistency of this asymmetry between the left and right sides is a novel finding based on our measurements. Our findings showed that the orbit was significantly bigger in width, height, and surface area on the left side. We also quantified a narrower mandible on the right side. We hope these findings can be translated to aesthetic surgery practice to make the plastic surgeon and patient more familiar with the patient's specific anatomy in order to better predict, plan, and successfully implement aesthetic procedures such as injecting fillers or doing peri-orbital procedures. NO LEVEL ASSIGNED:This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266.

PURPOSE/OBJECTIVE:To evaluate the biomechanical effect of corneal cross-linking (CXL) in paired human corneas following small incision lenticule extraction (SMILE) or photorefractive keratectomy (PRK) in an ex vivo model for postoperative ectasia. METHODS:) in both groups. The elastic modulus was evaluated using two-dimensional stress-strain extensometry. RESULTS:Following accelerated CXL, the ectatic cornea model showed a mean effective elastic modulus of 17.2 ± 5.3 MPa after PRK and 14.1 ± 5.0 MPa after SMILE. Although the elastic modulus in corneas previously subjected to PRK was higher, there was no significant biomechanical difference between the two groups (P = .093). CONCLUSIONS:Under similar conditions, both experimental groups (PRK followed by CXL and SMILE followed by CXL) were characterized by similar biomechanical stability as measured experimentally on ex vivo human fellow corneas. The data suggest that, in the event of postoperative ectasia, the biomechanical improvement achieved by CXL may be similar after PRK and SMILE. [J Refract Surg. 2020;36(1):49-54].

BACKGROUND:The purpose of our study is to examine the long (5-year) efficacy of the all surface laser ablation (ASLA) combined with accelerated cross-linking (CXL) for the treatment of myopia without the use of mitomycin-C (MMC). METHODS:This retrospective study consisted of 202 eyes of 118 myopic (SD: 2.41, range: - 1.50 to - 12.75 D) patients (44 males, 74 females). Mean age was 28.50 years (SD: 6.45, range: 18 to 51 years) that underwent ASLA with accelerated CXL for the treatment of their myopia. RESULTS:The patients underwent routine postoperative assessment on the 1st, 3rd, 7th day and in the 1st, 3rd, 6th and 12th month, 30th month (±6 months), 4th and 5th year. The mean spherical equivalent (SEq) refractive error changed from - 6.41 ± 2.41 D preoperatively to - 0.02 ± 0.53 D at 5 years postoperatively. The haze score was 0.18, 0.25 and 0.28 at 1, 3 and 6 months postoperatively. At 12 months after the treatment, no eyes had significant corneal haze and in all the following postoperative time intervals the haze traces were gone. CONCLUSION/CONCLUSIONS:ASLA combined with accelerated CXL (ASLA-XTRA) appears to be safe, efficacious and offering very good refractive results. The potential additional benefits of this modality are the stabilizing effect of the refraction and its sterilization effect on the treated cornea without the potential side effects of MMC.

PURPOSE/OBJECTIVE:To determine the relative impact of contact lens- assisted corneal cross-linking (CACXL) and standard protocol CXL (CXL) on regional corneal stiffness using Brillouin microscopy. METHODS:CXL and CACXL were performed on 30 intact fresh porcine eyes (15 per group). Depth profile of stiffness variation and averaged elastic modulus of anterior, middle, and posterior stroma were determined by Brillouin maps. Corneas were cut into strips to conduct mechanical stress-strain tests after Brillouin microscopy to evaluate stiffness difference between CXL and CACXL. Each eye served as its own control. RESULTS:CXL had a greater impact on corneal stiffness, with a maximum increase of 5.74% compared to 3.99% for CACXL (P < .001). CXL increased longitudinal modulus by 7.8% in the anterior, 1.7% in the middle, and -0.7% in the posterior regions compared to CACXL, which increased longitudinal modulus by 5.5% in the anterior (P < .001), 1.2% in the middle (P = .15), and -0.4% in the posterior regions (P = .60). Mechanical stress-strain tests showed that at 10% strain averaged Young's modulus was 5 MPa for CXL and 2.97 MPa for CACXL (P < .001). CONCLUSIONS:Both CACXL and standard protocol CXL induced significant corneal stiffening primarily concentrated in the anterior cornea. CACXL leads to less stiffening compared with CXL. An attenuated but continuous stiffening effect can be observed through the whole cornea for both CACXL and CXL, although CACXL has a smaller stiffness gradient. [J Refract Surg. 2019;35(11):721-728.].

PURPOSE/OBJECTIVE:To investigate the biomechanical properties of the ex vivo human paired corneas after completion of photorefractive keratectomy (PRK) versus small incision lenticule extraction (SMILE) in the same donor. METHODS:In this experimental study, 13 pairs of human corneas unsuitable for transplantation were equally divided into two groups. Corneal thickness was measured in each eye directly before laser refractive surgery. Corneas from the right eye were treated with PRK and corneas from the left eye with SMILE. All corneas were subjected to a refractive correction of -10.00 diopters (D) sphere and -0.75 D cylinder at 0° with a 7 mm zone, using either surface ablation (PRK) or 130 µm cap (SMILE). For two-dimensional biomechanical measurements, corneoscleral buttons underwent two testing cycles (preconditioning stress-strain curve from 0.03 to 9.0 N and stress-relaxation at 9.0 N during 120 seconds) to analyze the elastic and viscoelastic material properties. The effective elastic modulus was calculated. Statistical analysis was performed with a confidence interval of 95%. RESULTS:In stress-strain measurements, the effective elastic modulus was not significantly different (P = .081) between SMILE (9.58 ± 4.26 MPa) and PRK (11.9 ± 4.90 MPa). The effect size was medium (Cohen's d = 0.58). In stress-relaxation measurements, the remaining stress was not significantly different (P = .878) between SMILE (122 ± 33 kPa) and PRK (123 ± 30 kPa). CONCLUSIONS:The lenticule extraction procedure (SMILE) and the surface ablation technique (PRK) may be considered equivalent in terms of biomechanical stability when measured experimentally in ex vivo human fellow eye corneas. [J Refract Surg. 2019;35(8):501-505.].