Guillermo Rocha

A comparison of Scheimpflug imaging simulated and Holladay equivalent keratometry values with partial coherence interferometry keratometry measurements in phakic eyes

OBJECTIVE To evaluate the interchangeability of a Scheimpflug camera (Pentacam, Oculus) and a partial coherence interferometry keratometer (IOLMaster, Zeiss) for measures of keratometry and anterior chamber depth (ACD). A particular focus was to determine which Pentacam keratometry value best correlates with the IOLMaster and if these results can be used interchangeably in clinical practice. STUDY DESIGN Retrospective comparative study using data from the GRMC Vision Centre and ImagePlus Laser Eye Centre. PARTICIPANTS Fifty-two eyes from 27 patients (11 male, 16 female) of normal general health with no history of ocular disease. METHODS Each eye was assessed by an IOLMaster as part of a complete eye examination, and later by the Pentacam, prior to laser in situ keratomileusis (LASIK) surgery. RESULTS The differences in the mean keratometry readings of the IOLMaster and those of the simulated and equivalent Pentacam measurements were 0.35 D and 0.23 D, respectively. The Bland-Altman plots showed 95% limits of agreement (LOA) of 0.92 D and 1.68 D for the same parameters. A comparison of ACD measurements revealed a 0.03 mm difference in mean measurements with a 95% LOA of 0.33 mm. CONCLUSIONS The interdevice variability was significantly lower than that reported previously but still warrants caution if the 2 instruments are to be used interchangeably. With an appropriate correction for mean differences, the Pentacams simulated keratometry values would be within 0.46 D of the IOLMaster, 95% of the time. When the Holladay equivalent keratometry values were compared with the IOLMaster, a greater interdevice variability was seen.

Cataract surgery and optimal spherical aberration: as simple as you think?

This paper reviews the optics of higher-order and spherical aberrations and discusses aspheric intraocular lenses, attempting to address 2 questions that, despite an abundance of information, remain unanswered: what amount of ocular spherical aberration has been correlated with optimum visual performance, and for what final amount of spherical aberration should the cataract surgeon aim? Finally, the paper briefly reviews recent publications and makes suggestions for future studies in the area.

Two-Year follow-up of noncontact holmium laser thermokeratoplasty for the correction of low hyperopia

PURPOSE To summarize the 2-year results of laser thermal keratoplasty with a holmium:yttrium-aluminum-garnet (Ho:YAG) laser and the Sunrise Corneal Shaping System and assess the procedures safety, efficacy and predictability in correcting hyperopia in a phase III clinical intervention case series. METHODS The Ho:YAG laser was used to correct low hyperopia (manifest spherical equivalent of +0.75 to +2.50 dioptres [D], with manifest cylinder of 1.00 D or less) in 38 eyes of 28 patients 40 years of age or older. Laser pulses were delivered to the cornea in 2 radially placed, concentric, 8-spot rings 6.0 and 7.0 mm in diameter. The last follow-up was at 2 years. RESULTS The preoperative uncorrected visual acuity (UCVA) at distance was less than 20/40 in 82% of the eyes and at near was less than 20/32 in 42%. At 2 years the distance UCVA was 20/40 or better in 100% of the eyes and 20/20 or better in 84%, and the near UCVA was 20/32 or better in 97% of the eyes and 20/20 or better in 8%. The difference between the preoperative and postoperative UCVA was statistically significant (p < 0.01). The correction at 2 years was within 0.50 D of that intended in 92% of the eyes and within 1.00 D in 100%. The reduction in mean spherical equivalent at 2 years was statistically significant (p < 0.0001). No loss of 2 lines or more in best-corrected visual acuity occurred after the 1st month of follow-up. INTERPRETATION The Ho:YAG Sunrise Corneal Shaping System is safe and effective for the treatment of low hyperopia and astigmatism. It provides a predictable refractive outcome at 2 years of follow-up. However, our results show a tendency towards regression by 2 years.

Effect of femtosecond laser on efficiency of cataract surgery in public setting

OBJECTIVE To determine the time needed to perform a femtosecond laser-assisted cataract surgery (FLACS) and its effect on the efficiency of cataract surgery flow in a Canadian public health centre. DESIGN Retrospective chart review. PARTICIPANTS Patients who had cataract surgery performed in the first 3 months of femtosecond laser (FSL) technology use were compared with patients who had conventional phacoemulsification in the 3 months before FSL installation at Brandon Regional Health Centre (Brandon, Man.). METHODS The primary outcome measure was the time needed to complete FLACS versus the time needed to complete conventional phacoemulsification. Secondary outcome measures were the time the patient spent in the operating room (time in and time out) and the number of cataract surgeries done per surgical day before and after FSL was implemented systemwide. RESULTS There were 235 FSL cases and 199 conventional cases. Operating room time, total surgery time, and manual time were significantly longer in patients who underwent FLACS compared with patients who underwent conventional phacoemulsification (p < 0.001). Manual times and FSL suction times on the first day of implementing FLACS surgery were significantly longer than those on day 23 (p < 0.03), which suggests a learning curve effect. The number of cases per surgical day dropped by 28.6% in the first operative day and by 7.1% in the second and third operative days of FSL use, then reverted to pre-FSL levels. CONCLUSION The addition of FLACS results in longer time per case than traditional cataract surgery. Although statistically significant, the results may not be indicative of practical differences.

Intraoperative outcomes and safety of femtosecond laser-assisted cataract surgery: Canadian perspective

OBJECTIVE To report the intraoperative surgical outcomes and safety of femtosecond laser-assisted cataract surgery (FLACS) during surgeon learning curve and compare those outcomes with those of conventional phacoemulsification in a Canadian public hospital setting. DESIGN Retrospective chart review. PARTICIPANTS FLACS and phacoemulsification patients at Brandon Regional Health Centre, Brandon, Manitoba, Canada. METHODS Intraoperative surgical outcomes and safety (rates of intraoperative complications and phacoemulsification parameters) were compared among 3 groups: the first consecutive 197 cases using femtosecond laser (FSL) pretreatment to ultrasound phacoemulsification in cataract surgery (group 1; early FLACS), the second consecutive 165 cases using FSL (group 2; later FLACS), and 80 consecutive conventional cataract surgery cases (group 3; conventional phaco). RESULTS There was a statistically significant difference for phacoemulsification parameters (actual phaco time [APT], effective phaco time [EPT], and ultrasound average) among the 3 groups (all p-values < 0.05). The mean phacoemulsification parameters (APT and EPT) for the early FLACS and the conventional phaco groups were significantly longer than those for the later FLACS group (p < 0.05). The mean FSL time for the early FLACS group was significantly longer than that for the later FLACS group. There was no statistical difference among the rates of intraoperative complications (suction breaks, capsular tags, FSL-induced miosis, posterior capsular tears, and anterior vitrectomy) for the 3 groups. CONCLUSIONS During the learning curve, the intraoperative outcomes and safety of FLACS are comparable to the conventional phacoemulsification technique. After the learning curve, FLACS is significantly superior to conventional surgery in all measured phacoemulsification parameters.

Femto-second laser (FSL) techniques and consistency in corneal surgery: experimental study

OBJECTIVE To investigate the feasibility, effectiveness, and reproducibility of femtosecond laser (FSL) technology in different corneal cuts. DESIGN Experimental study at the Brandon Regional Health Centre. PARTICIPANTS Twenty two Human Cadaver eyes donated for research and supplied by the eye bank of Manitoba university. METHODS In this experimental study, the effectiveness and reproducibility of FSL were investigated in different corneal cuts. The corneas were divided into 5 groups: group I for penetrating keratoplasty; group II for anterior lamellar keratoplasty; group III for corneal pockets for inlays; group IV for intracorneal ring tunnels; and group V for corneal cross-linking pockets. Our primary endpoint was the repeatability of planned versus obtained thickness and diameter of the cuts with FSL. A secondary endpoint was the effectiveness and ease of dissection, rated from 0-4, with 4 being the easiest and 0 the most difficult to dissect. RESULTS There was a high correlation between planned and obtained thickness (r = 0.997, p < 0.001) and diameter (r = 0.998, p < 0.001). Both were statistically significant. Linear regression analyses showed that the obtained thickness of corneal cuts in micrometers was significantly predicted by the planned thickness of corneal cuts in micrometers (β = 0.996, t = 56.47, p < 0.001). Likewise, the obtained diameter of corneal cuts in millimeters was significantly predicted by the planned diameter of corneal cuts in millimeters (β = 0.971, t = 70.85, p < 0.001). The surgeons gave 15 out of a total of 22 corneas (68.2%) the maximum score for ease of dissection (Grade 4), where no adhesions were found and the dissection was smooth and steady. Five corneas out of a total of 22 (22.7%) were given a score of 3 of 4 where minor adhesions were found. Two corneas out of a total of 22 (9.1%) were given a score of 2 of 4 where >1 adhesion was found, with some difficulty in separating the cut cornea from the bed. No corneas were given grade 1 or grade 0. No significant differences were obtained for the ease of dissection among the 5 surgery types using Kruskal-Wallis H test (H [4] = 4.971, p > 0.05). CONCLUSION The measured corneal-cut geometry correlated well with laser settings in a variety of full- and partial-thickness FSL corneal patterns, including different depths and diameters. This reproducible efficacy and measurement accuracy of the planned versus obtained cuts could have a favourable result on a variety of corneal surgeries. It also yields a favourable ease of dissection of the cut lenticule from the stromal bed.

Electronic screens and children’s vision: development of a joint position statement

Electronic screens are everywhere. Televisions, computers, tablets, smartphones, video game consoles, et cetera. We use them at work, at school, at home, and in public spaces. They have become an integral part of our lives — and the lives of our children. As ophthalmologists, we are often faced with questions from patients, parents, and the public about the effects of too much screen time on children. While some research suggests that the prevalence of electronic screen-related ocular symptoms is as high as 50%–90% in adults, there is little scientific literature examining the effect of electronic screens on children’s oculovisual systems. In 2017, the Canadian Ophthalmological Society (COS), in collaboration with the Canadian Association of Optometrists (CAO), developed a position statement on the Effects of Electronic Screens on Children’s Vision and Recommendations for Safe Use. The statement was drafted by Dr. Christine Law, a pediatric ophthalmologist from Queen’s University, and Shamrozé Khan, OD, an optometrist from the University of Waterloo. These dedicated authors conducted a thorough search of the literature to ensure the recommendations were evidence-based. Given the shortage of research in this area, this was no small task, and we thank the authors for their tireless work on this important topic. The position statement acknowledges that the current state of the literature in this area is lacking. It provides a review of the literature that does exist, and makes the following recommendations based on that evidence:

Comparison of visual and refractive outcomes following Intacs implantation in keratoconus eyes with central and eccentric cones.

OBJECTIVE To compare visual and refractive outcomes after Intacs implantation in keratoconus eyes with central and eccentric cones and to validate the current nomogram used to select Intacs size. DESIGN Comparative study. PARTICIPANTS The charts of 20 patients in a single practice, who had symmetric (15 eyes) or asymmetric (16 eyes) implants, were retrospectively reviewed. METHODS Intacs were implanted by a single surgeon using a femtosecond laser. Based on Scheimpflug imaging, central and eccentric cone patterns received symmetric and asymmetric Intacs, respectively. Uncorrected distance visual acuity (UDVA) and best-corrected distance visual acuity (CDVA), manifest refraction spherical equivalent (MRSE), and keratometry (K) values were measured pre- and postoperatively. RESULTS The mean improvement in UDVA and CDVA in the symmetric group was 3.8 ± 0.9 and 0.6 ± 0.5 lines, and in the asymmetric group was 3.4 ± 0.7 and 1.8 ± 0.3 lines, respectively. The mean change in manifest refraction spherical equivalent (MRSE), refractive cylinder, and average K in the symmetric group was 2.40 ± 0.71 D, 0.02 ± 0.90 D, and -2.71 ± 0.50 D, and in the asymmetric group was 2.67 ± 1.21 D, 0.05 ± 0.47 D, and -2.35 ± 0.40 D, respectively. In CDVA, asymmetric Intacs showed statistically significant and better results than symmetric Intacs (p = 0.0016). There was no statistically significant difference between the means of symmetric and asymmetric implantation for UDVA, MRSE, average K, or corneal astigmatism (p > 0.05). CONCLUSIONS The implantation of symmetric and asymmetric Intacs segments in keratoconus eyes with central and eccentric cones, respectively, was found to have comparable visual and refractive outcomes except for CDVA, which improved significantly more in the asymmetric group. This study also demonstrates the validity of the nomogram used.