Refractive surgery for iatrogenic and congenital anisometropia and mild visual impairment

In anisometropia, the two eyes have unequal refractive power. Anisometropia is a risk factor for amblyopia. The visual deficiencies are thought to be irreversible after the first decade of life. There is, however, accumulating evidence that neural plasticity exists also in adult brains. The aim of this study was to investigate functional outcome of excimer laser refractive surgery in adult anisometropic and visually impaired patients. Additional goal was to examine changes in the primary visual cortex (V1) using multifocal functional magnetic resonance imaging (mffMRI) after laser refractive surgery. Study I comprised of 57 anisometropic patients (anisometropia of ≥3.25 diopters) and 174 isometropic myopic subjects formed the control group. A significant improvement in best-spectacle-corrected visual acuity (BSCVA) among myopic control subjects was evident 3 months postoperatively. The improvement in BSCVA was significantly slower for anisometropic patients and the improvement appeared to persist to the end of the follow-up (24 months). In study II we found that refractive surgery may be also successfully used for iathrogenic anisometropia. In Study III we evaluated mildly visually impaired adult patients after refractive surgery. There was a statistically significant improvement in BSCVA among visually impaired patients and the difference in the mean BSCVA between visually impaired patients and isometropic myopic control subjects diminished during follow-up. Study IV was a prospective follow-up trial examining the changes in the primary visual cortex after refractive surgery. Two anisometropic patients and two isometropic myopic patients were examined with a 61-region mffMRI before refractive surgery and at three, six, nine and twelve months postoperatively. In this study, a dramatic decrease in the number of active voxels in the fovea was found among anisometropic patients. The results presented in this thesis revealed that refractive surgery may be successfully used for the treatment of anisometropic adults with both congenital and iatrogenic anisometropia and for mildly visually impaired adults. The findings in conclusion strengthen our hypothesis of plastic changes in the visual cortex of adult anisometropic and mildly visually impaired patients after refractive surgery.

Corneal nerves in refractive surgery and dry eye

This study aimed to investigate the morphology and function of corneal sensory nerves in 1) patients after corneal refractive surgery and 2) patients with dry eye due to Sjögren's syndrome. A third aim was to explore the possible correlation between cytokines detected in tears and development of post-PRK subepithelial haze. The main methods used were tear fluid ELISA analysis, corneal in vivo confocal microscopy, and noncontact esthesiometry. The results revealed that after PRK a positive correlation exists between the regeneration of subbasal nerves and the thickness of regenerated epithelium. Pre- or postoperative levels of the tear fluid cytokines TGF-β1, TNF-α, or PDGF-BB did not correlate with the development of corneal haze objectively estimated by in vivo confocal microscopy 3 months after PRK. After high myopic LASIK, a discrepancy between subjective dry eye symptoms and objective signs of dry eye was observed. The majority of patients reported ongoing dry eye symptoms even 5 years after LASIK, although no objective clinical signs of dry eye were apparent. In addition, no difference in corneal sensitivity was observed between these patients and controls. Primary Sjögren's syndrome patients presented with corneal hypersensitivity, although their corneal subbasal nerve density was normal. However, alterations in corneal nerve morphology (nerve sprouting and thickened stromal nerves) and an increased number of antigen-presenting cells among subbasal nerves were observed, implicating the presence of an ongoing inflammation. Based on these results, the relationship between nerve regeneration and epithelial thickness 3 months after PRK appears to reflect the trophic effect of corneal nerves on epithelium. In addition, measurement of tear fluid cytokines may not be suitable for screening patients for risk of scar (haze) formation after PRK. Presumably, at least part of the symptoms of "LASIK-associated dry eye" are derived from aberrantly regenerated and abnormally functioning corneal nerves. Thus, they may represent a form of corneal neuropathy or "phantom pain" rather than conventional dry eye. Corneal nerve alterations and inflammatory findings in Sjögren's syndrome offer an explanation for the corneal hypersensitivity or even chronic pain or hyperalgesia often observed in these patients. In severe cases of disabling chronic pain in patients with dry eye or after LASIK, when conventional therapeutic possibilities fail to offer relief, consultation of a physician specialized in pain treatment is recommended.

Excimer laser refractive surgery : corneal wound healing and clinical results

Although the first procedure in a seeing human eye using excimer laser was reported in 1988 (McDonald et al. 1989, O'Connor et al. 2006) just three studies (Kymionis et al. 2007, O'Connor et al. 2006, Rajan et al. 2004) with a follow-up over ten years had been published when this thesis was started. The present thesis aims to investigate 1) the long-term outcomes of excimer laser refractive surgery performed for myopia and/or astigmatism by photorefractive keratectomy (PRK) and laser-in situ- keratomileusis (LASIK), 2) the possible differences in postoperative outcomes and complications when moderate-to-high astigmatism is treated with PRK or LASIK, 3) the presence of irregular astigmatism that depend exclusively on the corneal epithelium, and 4) the role of corneal nerve recovery in corneal wound healing in PRK enhancement. Our results revealed that in long-term the number of eyes that achieved uncorrected visual acuity (UCVA)≤0.0 and ≤0.5 (logMAR) was higher after PRK than after LASIK. Postoperative stability was slightly better after PRK than after LASIK. In LASIK treated eyes the incidence of myopic regression was more pronounced when the intended correction was over >6.0 D and in patients aged <30 years.Yet the intended corrections in our study were higher for LASIK than for PRK eyes. No differences were found in percentages of eyes with best corrected visual acuity (BCVA) or loss of two or more lines of visual acuity between PRK and LASIK in the long-term. The postoperative long-term outcomes of PRK with two different delivery systems broad beam and scanning laser were compared and revealed no differences. Postoperative outcomes of moderate-to-high astigmatism yielded better results in terms of UCVA and less compromise or loss of two more lines of BCVA after LASIK that after PRK.Similar stability for both procedures was revealed. Vector analysis showed that LASIK outcomes tended to be more accurate than PRK outcomes, yet no statistically differences were found. Irregular astigmatism secondary to recurrent corneal erosion due to map-dot-fingerprint was successfully treated with phototherapeutic keratectomy (PTK). Preoperative videokeratographies (VK) showed irregular astigmatism. However, postoperatively, all eyes showed a regular pattern. No correlation was found between pre- and postoperative VK patterns. Postoperative outcomes of late PRK in eyes originally subjected to LASIK showed that all (7/7) eyes achieved UCVA ≤0.5 at last follow-up (range 3 — 11 months), and no eye lost lines of BCVA. Postoperatively all eyes developed and initial mild haze (0.5 — 1) into the first month. Yet, at last follow-up 5/7 eyes showed a haze of 0.5 and this was no longer evident in 2/7 eyes. Based on these results, we demonstrated that the long-term outcomes after PRK and LASIK were safe and efficient, with similar stability for both procedures. The PRK outcomes were similar when treated by broad-beam or scanning slit laser. LASIK was better than PRK to correct moderate-to-high astigmatism, yet both procedures showed a tendency of undercorrection. Irregular astigmatism was proven to be able to depend exclusively from the corneal epithelium. If this kind of astigmatism is present in the cornea and a customized PRK/LASIK correction is done based on wavefront measurements an irregular astigmatism may be produced rather than treated. Corneal sensory nerve recovery should have an important role in the modulation of the corneal wound healing and post-operative anterior stromal scarring. PRK enhancement may be an option in eyes with previous LASIK after a sufficient time interval that in at least 2 years.

Algorithm for Correcting the Keratometric Error in the Estimation of the Corneal Power in Eyes With Previous Myopic Laser Refractive Surgery

Purpose: To calculate theoretically the errors in the estimation of corneal power when using the keratometric index (nk) in eyes that underwent laser refractive surgery for the correction of myopia and to define and validate clinically an algorithm for minimizing such errors. Methods: Differences between corneal power estimation by using the classical nk and by using the Gaussian equation in eyes that underwent laser myopic refractive surgery were simulated and evaluated theoretically. Additionally, an adjusted keratometric index (nkadj) model dependent on r1c was developed for minimizing these differences. The model was validated clinically by retrospectively using the data from 32 myopic eyes [range, −1.00 to −6.00 diopters (D)] that had undergone laser in situ keratomileusis using a solid-state laser platform. The agreement between Gaussian (PGaussc) and adjusted keratometric (Pkadj) corneal powers in such eyes was evaluated. Results: It was found that overestimations of corneal power up to 3.5 D were possible for nk = 1.3375 according to our simulations. The nk value to avoid the keratometric error ranged between 1.2984 and 1.3297. The following nkadj models were obtained: nkadj= −0.0064286r1c + 1.37688 (Gullstrand eye model) and nkadj = −0.0063804r1c + 1.37806 (Le Grand). The mean difference between Pkadj and PGaussc was 0.00 D, with limits of agreement of −0.45 and +0.46 D. This difference correlated significantly with the posterior corneal radius (r = −0.94, P < 0.01). Conclusions: The use of a single nk for estimating the corneal power in eyes that underwent a laser myopic refractive surgery can lead to significant errors. These errors can be minimized by using a variable nk dependent on r1c.

New-Generation Hybrid Contact Lens for the Management of Extreme Irregularity in a Thin Cornea After Unsuccessful Excimer Laser Refractive Surgery

Purpose: To report a very successful outcome obtained with the fitting of a new-generation hybrid contact lens of reverse geometry in a thin cornea with extreme irregularity due to the presence of a central island after unsuccessful myopic excimer laser refractive surgery. Methods: A 32-year-old man attended to our clinic complaining of very poor vision in his right eye after bilateral laser in situ keratomileusis (treatment or surgery) for myopia correction and some additional retreatments afterward. After a comprehensive ocular evaluation, contact lens fitting with a reverse geometry hybrid contact lens (SynergEyes PS, SynergEyes, Carlsbad, CA) was proposed as a solution for this case. Visual, refractive, and ocular aberrometric outcomes with the contact lens were evaluated. Results: Distance visual acuity improved from a prefitting uncorrected value of 20/200 to a postfitting corrected value of 20/16. Prefitting manifest refraction was +6.00 sphere and −3.00 cylinder at 70°, with a corrected distance visual acuity of 20/40. Higher order root mean square for a 5-mm pupil changed from a prefitting value of 1.45 to 0.34 µm with the contact lens. The contact lens wearing was reported as comfortable, and the patient was very satisfied with this solution. Conclusions: The SynergEyes PS contact lens seems to be an excellent option for the visual rehabilitation of corneas with extreme irregularity after myopic excimer laser surgery, minimizing the level of higher order aberrations and providing an excellent visual outcome.

Comparison of Intraocular Pressure before and after Laser In Situ Keratomileusis Refractive Surgery Measured with Perkins Tonometry, Noncontact Tonometry, and Transpalpebral Tonometry

Purpose. To compare the intraocular pressure (IOP) before and after Laser In Situ Keratomileusis (LASIK), measured by Diaton, Perkins, and noncontact air pulse tonometers. Methods. Fifty-seven patients with a mean age of 34.88 were scheduled for myopia LASIK treatment. Spherical equivalent refraction (SER), corneal curvature (K), and central corneal thickness (CCT) and superior corneal thickness (SCT) were obtained before and after LASIK surgery. IOP values before and after surgery were measured using Diaton, Perkins, and noncontact air pulse tonometers. Results. The IOP values before and after LASIK surgery using Perkins tonometer and air tonometers were statistically significant (). However, no significant differences were found () for IOP values measured with Diaton tonometer. CCT decreases significantly after surgery () but no statistical differences were found in SCT (). Correlations between pre- and postsurgery were found for all tonometers used, with and for the air pulse tonometer, and for Perkins, and and for Diaton. Conclusion. Transpalpebral tonometry may be useful for measuring postsurgery IOP after myopic LASIK ablation because this technique is not influenced by the treatment.

Distribution and visual impact of postoperative refractive error after cataract surgery in rural China: study of cataract outcomes and up-take of services report 4.

PURPOSE: To model the possible impact of using average-power intraocular lenses (IOLs) and evaluate the postoperative refractive error in patients having cataract surgery in rural China.SETTING: Rural Guangdong, China.METHODS: Patients having cataract surgery by local surgeons were examined and visual function was assessed 10 to 14 months after surgery. Subjective refraction at near and distance was performed bilaterally by an ophthalmologist. Patients had a target refraction of -0.50 diopter (D) based on ocular biometry.RESULTS: Of the 313 eligible patients, 242 (77%) could be contacted and 176 (74% of contacted patients, 56% overall) were examined. Examined patients had a mean age of 69.4 +/- 10.5 years. Of the 211 operated eyes, 73.2% were within +/-1.0 D of the target refraction after surgery. The best presenting distance vision was in patients within +/-1.0 D of plano and the best presenting near vision, in those with mild myopia (<-1.0 D to > or =2.0 D) (P= .005). However, patients with hyperopia (>+1.0 D) reported significantly better adjusted visual function than those with emmetropia or myopia (<-1.0 D). When the predicted use of an average-power IOL (median +21.5 D) was modeled, predicted visual acuity was significantly reduced (P= .001); however, predicted visual function was not significantly altered (P>.3).CONCLUSIONS: Accurate selection of postoperative refractive error was achieved by local surgeons in this rural area. Based on visual function results, aiming for mild postoperative myopia may not be suitable in this setting. Implanting average-power IOLs significantly reduced postoperative presenting vision, but not visual function.

Prevalence of refractive error in Europe: the European Eye Epidemiology (E3) Consortium

To estimate the prevalence of refractive error in adults across Europe. Refractive data (mean spherical equivalent) collected between 1990 and 2013 from fifteen population-based cohort and cross-sectional studies of the European Eye Epidemiology (E³) Consortium were combined in a random effects meta-analysis stratified by 5-year age intervals and gender. Participants were excluded if they were identified as having had cataract surgery, retinal detachment, refractive surgery or other factors that might influence refraction. Estimates of refractive error prevalence were obtained including the following classifications: myopia ≤−0.75 diopters (D), high myopia ≤−6D, hyperopia ≥1D and astigmatism ≥1D. Meta-analysis of refractive error was performed for 61,946 individuals from fifteen studies with median age ranging from 44 to 81 and minimal ethnic variation (98 % European ancestry). The age-standardised prevalences (using the 2010 European Standard Population, limited to those ≥25 and <90 years old) were: myopia 30.6 % [95 % confidence interval (CI) 30.4–30.9], high myopia 2.7 % (95 % CI 2.69–2.73), hyperopia 25.2 % (95 % CI 25.0–25.4) and astigmatism 23.9 % (95 % CI 23.7–24.1). Age-specific estimates revealed a high prevalence of myopia in younger participants [47.2 % (CI 41.8–52.5) in 25–29 years-olds]. Refractive error affects just over a half of European adults. The greatest burden of refractive error is due to myopia, with high prevalence rates in young adults. Using the 2010 European population estimates, we estimate there are 227.2 million people with myopia across Europe.

Effect of position of near addition in an asymmetric refractive multifocal intraocular lens on quality of vision

Purpose
To evaluate the impact of the position of an asymmetric multifocal near segment on visual quality.

Setting
Cathedral Eye Clinic, Belfast, United Kingdom.

Design
Retrospective comparative case series.

Methods
Data from consecutive patients who had bilateral implantation of the Lentis Mplus LS-312 multifocal intraocular lens were divided into 2 groups. One group received inferonasal near-segment placement and the other, superotemporal near-segment placement. A +3.00 diopter (D) reading addition (add) was used in all eyes. The main outcome measures included uncorrected distance visual acuity (UDVA), uncorrected near visual acuity (UNVA), contrast sensitivity, and quality of vision. Follow-up was 3 months.

Results
Patients ranged in age from 43 to 76 years. The inferonasal group comprised 80 eyes (40 patients) and the superotemporal group, 76 eyes (38 patients). The mean 3-month spherical equivalent was −0.11 D ± 0.49 (SD) in the inferonasal group and −0.18 ± 0.46 D in the superotemporal group. The mean postoperative UDVA was 0.14 ± 0.10 logMAR and 0.18 ± 0.15 logMAR, respectively. The mean monocular UNVA was 0.21 ± 0.14 logRAD and 0.24 ± 0.13 logRAD, respectively. No significant differences were observed in the higher-order aberrations, total Strehl ratio (point-spread function), or modulation transfer function between the groups. Dysphotopic symptoms measured with a validated quality-of-vision questionnaire were not significantly different between groups.

Conclusion
Positioning of the near add did not significantly affect objective or subjective visual function parameters.

Increase in microbial contamination risk with compression of the lid margin in eyes having cataract surgery

Purpose: To assess the bacterial contamination risk in cataract surgery associated with mechanical compression of the lid margin immediately after sterilization of the ocular surface.

Setting: Department of Cataract, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China.

Design: Prospective randomized controlled double-masked trial.

Methods: Patients with age-related cataract were randomly assigned to 1 of 2 groups. In Group A (153 eyes), the lid margin was compressed and scrubbed for 360 degrees 5 times with a dry sterile cotton-tipped applicator immediately after ocular sterilization and before povidone-iodine irrigation of the conjunctival sac. Group B (153 eyes) had identical sterilization but no lid scrubbing. Samples from the lid margin, liquid in the collecting bag, and aqueous humor were collected for bacterial culture. Primary outcome measures included the rate of positive bacterial culture for the above samples. The species of bacteria isolated were recorded.

Results: Group A and Group B each comprised 153 eyes. The positive rate of lid margin cultures was 54.24%. The positive rate of cultures for liquid in the collecting bag was significantly higher in Group A (23.53%) than in Group B (9.80%) (P=.001).The bacterial species cultured from the collecting bag in Group B were the same as those from the lid margin in Group A. The positive culture rate of aqueous humor in both groups was 0%.

Conclusion: Mechanical compression of the lid margin immediately before and during cataract surgery increased the risk for bacterial contamination of the surgical field, perhaps due to secretions from the lid margin glands.

Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Prevalence of corneal astigmatism before cataract surgery in Chinese patients

Purpose: To assess the demographics and distribution of corneal astigmatism before cataract surgery in Chinese patients. Setting: State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China. Design: Clinic-based cross-sectional study. Methods: From July 2009 to May 2011, preoperative bilateral partial coherence interferometry (IOLMaster) was performed in consecutive patients having cataract surgery. Patient demographics and keratometric data were recorded. Results: The mean age of the 2849 patients (4831 eyes) was 70.56 years ± 9.55 (SD); there was a predominance of women patients (64.0%). The mean axial length was 23.58 ± 1.13 mm. The mean corneal astigmatism in this cohort was 1.01 D (range 0.05 to 6.59 D). Corneal astigmatism was between 0.25 D and 1.25 D in 67.7% of eyes, 1.25 D or higher in 27.5% eyes, and less than 0.25 D in 4.8% of eyes. Astigmatism was with the rule in 25.1% of eyes, against the rule (ATR) in 58.2% of eyes, and oblique in 16.7% of eyes. The mean steep keratometry measurement was 44.76 ± 1.56 D. Against-the-rule astigmatism increased significantly with older age. Conclusions: Corneal astigmatism largely fell between 0.25 D and 1.25 D in these predominantly elderly female Chinese patients, and ATR astigmatism increased with age. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. © 2012 ASCRS and ESCRS.

Functional and anatomical outcomes of vitreoretinal surgery for posterior segment complications after elective cataract surgery

PURPOSE: To assess the outcomes in patients who required 1 or more vitreoretinal interventions for posterior segment complications arising from elective uneventful cataract surgery. SETTING: Tertiary referral center, single-center study. METHODS: A retrospective interventional case series included 56 consecutive patients who were referred for surgical correction of posterior segment complications within 6 months of cataract surgery. The study period was between 1996 and 2003, and the minimum follow-up was 5 months. RESULTS: Posterior segment complications were resolved with a single surgical intervention in 40 cases (71.4%). Within 5 months of primary surgical correction, persisting or newly arising posterior segment complications were noted in 16 cases (28.6%). After a mean of 2.1 +/- 1.4 (SD) additional surgeries, the number of eyes with posterior segment problems decreased to 7 (12.5%) (P = .035). Posterior segment complications requiring more than 1 vitreoretinal intervention included retinal detachment, endophthalmitis, and choroidal hemorrhages. After primary correction surgery, the mean best corrected visual acuity increased from 0.15 +/- 0.24 to 0.37 +/- 0.33 (P = .001) after a single intervention and to 0.39 +/- 0.32 (P>.05) after additional interventions. Although the intraocular pressure (IOP) decreased from 21.8 +/- 16.6 mm Hg to 14.9 +/- 3.4 mm Hg (P = .008), 4 (7.1%) consecutive vascular optic atrophies occurred. A reduction in corneal transparency was observed in 46.4% of patients before primary surgical correction and 12.5% after primary surgical correction (P<.001). CONCLUSIONS: In many cases, posterior segment complications arising from cataract surgery could be repaired with favorable functional and anatomical outcomes by a single vitreoretinal intervention. Additional surgery, if requested, provided stabilization of the anatomical and functional outcomes.

The posterior chamber phakic refractive lens (PRL): a review

Implantation of phakic intraocular lenses (pIOLs) is a reversible refractive procedure, preserving the patient’s accommodative function with minimal induction of higher order aberrations compared with corneal photoablative procedures. Despite this, as an intraocular procedure, it has potential risks such as cataracts, chronic uveitis, pupil ovalization, corneal endothelial cell loss, pigmentary dispersion syndrome, pupillary block glaucoma, astigmatism, or endophthalmitis. Currently, only two models of posterior chamber pIOLs are commercially available, the implantable collammer lens (STAAR Surgical Co.) and the phakic refractive lens (PRL; Zeiss Meditec). The number of published reports on the latter is very low, and some concerns still remain about its long-term safety. The present article reviews the published literature on the outcomes after PRL implantation in order to provide a general overview and evaluate its real potential as a surgical refractive option.