**9. Pseudophakic dysphotopsia**

One of the most common causes of patient dissatisfaction after uneventful cataract surgery is a pseudophakic dysphotopsia [123, 124]. It represents a set of subjective optical complaints following intraocular lens implantation and is categorized as positive and negative dyspho‐ topsia. Positive dysphotopsia are bright artifacts on the retina that represent undesired optical images described by the patients as halos, arcs, light rings, flashes, and streaks. The phenom‐ enon called negative dysphotopsia manifests as a temporal dark crescent-shaped shadow, similar to scotoma, and represents the absence of light reaching certain portions of the retina after in the-bag posterior chamber IOL implantation [125]. It has been first described almost 15 years ago, by Davison [126] and since then it is a matter of discussion in many scientific papers. The cause of this phenomena has been widely discussed in the literature and many explanations have been proposed such as optics with a sharp or truncated edge [124, 126, 127], IOL materials with high index of refraction [126-130], anatomical predispositions of the eye such as prominent globe [131], shallow orbit [131], anterior surface of the IOL more then 0.46 mm from the plane of posterior iris [131], brown iris [132], temporally located clear cornea incisions [132], a negative afterimage [133], neuroadaptation [133], and reflection of the anterior capsulotomy edge projected onto the nasal peripheral retina [134]. Negative dyspho‐ topsia is more poorly tolerated than positive and could lead to IOL explantation [131, 135, 136]. Certain clinical manifestations have been recognized and nicely summarized by Masket and Fram [134].

Still, there has not been much theoretical exploration in the past to explain in detail and to validate all possible explanations of the negative dysphotopsia phenomenon. In the recent study, designed to evaluate negative dysphotopsia, Holladay et al. [125] used ray tracing simulation, using the Zemax optical design program and described "type 3 shadow-penum‐ bra" as the optical mechanism that has been referred to as negative dysphotopsia and believe that it explains all 10 clinical manifestations enumerated by Masket and Fram [134].They concluded that primary optical factors for negative dyshotopsia are small pupil, a distance behind the pupil of ≥0.06 mm and ≤ 1.23 mm for acrylic (≥ 0.06 mm and ≤ 0.62 mm for silicone), a sharp-edged design (corner edge radii ≤ 0.05 mm) and functional nasal retina that extends anterior to the location of the shadow. The final parameter that determines whether the shadow is visible is the location of the anterior extent of the functional nasal retina. Secondary factors include the high index of refraction optic material, the patient′s angle α, nasal location of the pupil relative to the optical axis, and transparent versus translucent status of the peripheral nasal capsule [125].

Animal [119] and clinical [108] studies show that IOL design, rather than IOL material, is the critical factor in minimizing LEC migration across the posterior capsule after IOL implantation. The continuous-edge IOL has two design characteristics that may have led to the significant decrease in PCO, and that is a 360-degree continuous square optic edge, and greater space between the optic and haptic at the optic–haptic junction to encourage apposition of the anterior capsule and posterior capsule. A continuous square edge around the optic and angled haptics allows close apposition of the IOL optic to the posterior capsule, which Nishi et al. [120] found inhibits LEC migration. A rabbit model study [121] found that the addition of a square edge across the optic–haptic junction decreased LEC migration behind the IOL optic over migration with an IOL of the same type but without a square edge at the optic–haptic

In the treatment of PCO, neodymium: yttrium-aluminum-garnet (ND:YAG) laser is used to cut the clouded posterior capsule allowing light to transmit normally [122]. It can produce complications such as ocular inflammation, an increase in intraocular pressure, IOL damage,

One of the most common causes of patient dissatisfaction after uneventful cataract surgery is a pseudophakic dysphotopsia [123, 124]. It represents a set of subjective optical complaints following intraocular lens implantation and is categorized as positive and negative dyspho‐ topsia. Positive dysphotopsia are bright artifacts on the retina that represent undesired optical images described by the patients as halos, arcs, light rings, flashes, and streaks. The phenom‐ enon called negative dysphotopsia manifests as a temporal dark crescent-shaped shadow, similar to scotoma, and represents the absence of light reaching certain portions of the retina after in the-bag posterior chamber IOL implantation [125]. It has been first described almost 15 years ago, by Davison [126] and since then it is a matter of discussion in many scientific papers. The cause of this phenomena has been widely discussed in the literature and many explanations have been proposed such as optics with a sharp or truncated edge [124, 126, 127], IOL materials with high index of refraction [126-130], anatomical predispositions of the eye such as prominent globe [131], shallow orbit [131], anterior surface of the IOL more then 0.46 mm from the plane of posterior iris [131], brown iris [132], temporally located clear cornea incisions [132], a negative afterimage [133], neuroadaptation [133], and reflection of the anterior capsulotomy edge projected onto the nasal peripheral retina [134]. Negative dyspho‐ topsia is more poorly tolerated than positive and could lead to IOL explantation [131, 135, 136]. Certain clinical manifestations have been recognized and nicely summarized by Masket

Still, there has not been much theoretical exploration in the past to explain in detail and to validate all possible explanations of the negative dysphotopsia phenomenon. In the recent study, designed to evaluate negative dysphotopsia, Holladay et al. [125] used ray tracing simulation, using the Zemax optical design program and described "type 3 shadow-penum‐

junction.

196 Advances in Eye Surgery

and Fram [134].

cystoid macular edema, and retinal detachment.

**9. Pseudophakic dysphotopsia**

Holladay et al. showed that a sharp or truncated optic edge was the most significant factor in positive dysphotopsia[124].Advances in lens edge design have minimized such problems, but still a significant number of patients report of different photic phenomena [123, 124, 127, 137]. Square-edge IOL design appears to be the primary cause of reflected nighttime glare [124]. Radford et al. reported on overall incidence of 20.7% in the Akreos group and 21.3% in the SN60-AT group [127]. Also, a study of patient-reported glare symptoms found fewer symp‐ toms with Akreos IOLs than with other acrylic lenses [138]. Osher reported the incidence of negative dysphotopsia 15.2% on the first postoperative day, decreasing to 3.2% after 1 year, then 2.4% after 2 and 3 years. Kinard et al. reported on 40% of study patients complaining about central flashes 1 year postoperatively, and 3% rating it with the highest score. They found that some of the patients originally thought to be a complete success had dissatisfaction from dysphotopsia but silently put up with it [139]. The mechanism of neuroadaptation is still the least understood of all factors involved in the process of pseudophakic dysphotopsia. As Jin et al. disscussed, there are patients who have 2-mm IOL dislocation who should have debili‐ tating dysphotopsia and yet adapt very nicely. On the other hand, some have perfectly centred IOL with excellent vision, good coverage of the IOL edge by the anterior capsule, and still report severe symptoms of dysphotopsia long after surgery [137]. Holladay said that neural adaptation can mitigate and reduce symptoms but not eliminate them, just as halos with multifocal IOLs diminish with time but never disappear [140]. The positive symptoms seem to diminish with time, or the patients get more used to them. Regarding the IOL features that could contribute to dysphotopsia, hydrophobic acrylic lenses with higher refractive index have a greater risk of dysphotopsia [126-130]. On the other hand, hydrophilic acrylic intraocular lenses with lower refractive index could be superior in that matter due to less affinity toward dysphotopsia [126-130]. Bournas et al. showed that the lens optic diameter is negatively associated with the risk of dysphotopsia [141]. It is believed that with 6.0 mm, 6.5 mm, and 7.0 mm intraocular lenses are less likely to experience the photic phenomena because the edge line of the IOL is out of view [142, 143]. On the other hand, Arnold concluded that the optic size of the IOL does not correlate with any forms of dysphotopsia [144]. Four surgical methods were used to treat negative dysphotopsia: secondary piggyback IOL implantation, reverse optic capture, in-the-bag exchange, and iris suture fixation [131, 134, 136, 145]. Holladay explained that exchanging the posterior chamber IOL for an anterior chamber IOL or using a fully (not partially) rounded-edge IOL are the only two treatments that are sure to eliminate negative dysphotopsia. Exchanges for a silicone material, secondary piggyback IOLs, and reverse optic capture usually will improve the symptoms but cannot guarantee elimination of negative dysphotopsia [140]. Folden recently presented a Neodymium:Yag laser anterior capsulectomy as a surgical option in the management of negative dysphotopsia [146]. Osher believed that short term, transient symptoms of negative dysphotopsia were incision related, mostly at patients with clear temporal incision, were the cornea is not covered by the eyelid. He hypothesized that corneal edema-associated beveled temporal incision was related to the transient symptoms of dysphotopsia [132]. On the other hand, Cooke described a case where negative dysphotopsia resolved after IOL exchange with clear temporal incision, after prior surgery with scleral tunnel incision at 10.30 o′clock position, entirely covered by the upper lid [147]. Radford et al. stated that although 22% of patients who had a clear temporal incision and 66% of patients who had a superior scleral incision reported symptoms of dysphotopsia at 1 week, the difference between groups was not statistically significant. At 8 weeks 16% of patients with a clear temporal incision and 42% of patients with superior scleral incision reported symptoms of dysphotopsia, however the difference was not statistically significant again [127]. Also, additional studies comparing temporal clear corneal incisions with nasal [128] and superior [131] found no difference in the incidence of negative dysphotopsia. Although a significant number of patients report photic phenomena, it seems to resolve over time in the majority of cases [141, 144, 148]. They resolve by capsule opacification due to fibrosis, cortical adaptation, or a patients final compromise with the problem [149]. It is important to consider the amount of time between the surgery and telephone contact date because as time goes by, anterior capsule opacification (ACO) may shield the optic edge from light, protecting the patient from edge effects [150]. Holladay et al. agree with Hong et al.[151] that the spontaneous resolution or transient nature of negative dysphotopsia is a result of opacification (translucency/diffusivity) of the peripheral capsule. They stated that the opaci‐ fication of the nasal capsule is the explanation for 12.8% of negative dysphotopsia that spontaneously resolved by 2 or 3 years of the original 15.2% in Osher′s study [125], mentioned earlier.

#### **10. Femtosecond Laser Assisted Cataract Surgery (FLACS)**

Since premium intraocular lenses (IOLs) are getting more used for the achievement of the best refractive outcome, methods to increase accuracy and precision in cataract surgery are being investigated [152-154]. Femtosecond Laser assisted cataract surgery is one of the solutions with its ability to perform anterior capsulotomy, lens fragmentation, and to create self-sealing corneal incisions [155, 156]. The femtosecond laser (FSL) emits coherent optical pulses with a wavelength of 800 nm and duration on the order of 10 -15 seconds. Due to its ability to alter delicate tissue in a precise and predictable way, it is used extensively in ophthalmology. Also, one of the major advantages is that it can cut tissue with almost no heat development. Today, there are many ongoing clinical studies utilizing the femtosecond lasers to perform several steps in cataract surgery such as incisions, capsulorhexis, and disassembly of the lens.

The femtosecond laser allows precision crafting of the lengths, angles, lanes, and shapes of clear corneal incisions to levels of consistency exceeding any manual technique [32]. Although FLACS can be a promising surgical modality, there are questions of its widespread utility and accessibility [157]. The laser system such as LenSx (Alcon, Fort Worth, TX) produces a kHz pulse train of femtosecond pulses. In order to view the patients eye and to localize specific targets, an optical coherence tomography (OCT) imaging device and a video camera micro‐ scope are used. It is generally used for the creation of single plane and multi-plane incisions in the cornea, anterior capsulotomy and phacofragmentation. A beam of low energy pulses of infrared light is focused by the laser into the eye, leading to a micro-volume photodisruption of a tissue. After scanning the beam, numerous micro-disruptions are created in order to form an anterior capsulotomy incision as well as lens fragmentation incision, which are program‐ med depending on the location, shape, and size. [157-159]. Femtosecond laser assisted cataract surgery showed a lot of advantages in comparison to conventional cataract surgery. Some of them are less induced coma and astigmatism, manipulation, and phacoemulsification time [160]. A lot of arguments can be found in the literature regarding the increased risk of postoperative endophthalmitis following manually created clear corneal incision [161, 162]. In that matter, femtosecond laser assisted cataract surgery could be superior for it may allow for more square architecture, which has proven more resistant to leakage, added stability, and reproducibility at various intraocular pressures (IOPs) [163-165]. Femtosecond lasers also provide more accurate, safe, and adjustable cuts for limbal relaxing incisions, as well as predictable capsulorhexis [166]. Capsulorhexis performed with femtosecond laser has a higher degree of circularity, less risk for incomplete capsulorhexis-IOL overlap, better IOL centration [167, 168], and greater strength [168, 169]. It has been shown that the unpredictable diameter observed in manual capsulorhexis can have effects on IOL centration, with subsequent poor refractive outcomes, unpredictable anterior chamber depths, and increased rates of posterior capsular opacification [170-172].Some studies provided evidence of easier phacoemulsification performed with femtosecond laser [165, 173], reduced ultrasound energy for all grades of cataract [173, 174], and even more predictable IOL power calculations with laser assisted cataract surgery [175]. Taking into account that ultrasound phacoemulsification could damage the corneal tissue [176, 177], femtosecond laser assisted cataract surgery promises improved safety and lesser complications in that way also. On the other hand, patients with dementia, tremor, or with deep set orbits might not be good candidates for FLACS, as well as patients with poor dilated pupil, posterior synechiae, iris floppy syndrome, small eyelid fissure, and ocular motor paralysis [157].

Long-term clinical studies of the outcomes of the femtosecond laser assisted cataract surgery will provide evidence for the confirmation of its superiority over phacoemulsification.

### **11. Conclusion**

reverse optic capture usually will improve the symptoms but cannot guarantee elimination of negative dysphotopsia [140]. Folden recently presented a Neodymium:Yag laser anterior capsulectomy as a surgical option in the management of negative dysphotopsia [146]. Osher believed that short term, transient symptoms of negative dysphotopsia were incision related, mostly at patients with clear temporal incision, were the cornea is not covered by the eyelid. He hypothesized that corneal edema-associated beveled temporal incision was related to the transient symptoms of dysphotopsia [132]. On the other hand, Cooke described a case where negative dysphotopsia resolved after IOL exchange with clear temporal incision, after prior surgery with scleral tunnel incision at 10.30 o′clock position, entirely covered by the upper lid [147]. Radford et al. stated that although 22% of patients who had a clear temporal incision and 66% of patients who had a superior scleral incision reported symptoms of dysphotopsia at 1 week, the difference between groups was not statistically significant. At 8 weeks 16% of patients with a clear temporal incision and 42% of patients with superior scleral incision reported symptoms of dysphotopsia, however the difference was not statistically significant again [127]. Also, additional studies comparing temporal clear corneal incisions with nasal [128] and superior [131] found no difference in the incidence of negative dysphotopsia. Although a significant number of patients report photic phenomena, it seems to resolve over time in the majority of cases [141, 144, 148]. They resolve by capsule opacification due to fibrosis, cortical adaptation, or a patients final compromise with the problem [149]. It is important to consider the amount of time between the surgery and telephone contact date because as time goes by, anterior capsule opacification (ACO) may shield the optic edge from light, protecting the patient from edge effects [150]. Holladay et al. agree with Hong et al.[151] that the spontaneous resolution or transient nature of negative dysphotopsia is a result of opacification (translucency/diffusivity) of the peripheral capsule. They stated that the opaci‐ fication of the nasal capsule is the explanation for 12.8% of negative dysphotopsia that spontaneously resolved by 2 or 3 years of the original 15.2% in Osher′s study [125], mentioned

**10. Femtosecond Laser Assisted Cataract Surgery (FLACS)**

Since premium intraocular lenses (IOLs) are getting more used for the achievement of the best refractive outcome, methods to increase accuracy and precision in cataract surgery are being investigated [152-154]. Femtosecond Laser assisted cataract surgery is one of the solutions with its ability to perform anterior capsulotomy, lens fragmentation, and to create self-sealing corneal incisions [155, 156]. The femtosecond laser (FSL) emits coherent optical pulses with a wavelength of 800 nm and duration on the order of 10 -15 seconds. Due to its ability to alter delicate tissue in a precise and predictable way, it is used extensively in ophthalmology. Also, one of the major advantages is that it can cut tissue with almost no heat development. Today, there are many ongoing clinical studies utilizing the femtosecond lasers to perform several steps in cataract surgery such as incisions, capsulorhexis, and disassembly of the lens.

The femtosecond laser allows precision crafting of the lengths, angles, lanes, and shapes of clear corneal incisions to levels of consistency exceeding any manual technique [32]. Although

earlier.

198 Advances in Eye Surgery

The procedure of phacoemulsification revolutionized cataract surgery, especially since the introduction of sutureless clear corneal cataract incisions, which has led to reduced surgical time, lower induced astigmatism, faster postoperative and visual recovery, and less compli‐ cations. Advances in technology and knowledge from the fields of optics and biomaterials have led to the development of minimally invasive procedures, as well as numerous various premium intraocular lenses that are designed to enable the best refractive outcomes with one goal: restoration of vision for distance and near and spectacles independence. The develop‐ ment of acrylic materials with a higher index of refraction and square edge designed intraoc‐ ular lenses in order to prevent posterior capsular opacification led to patients having portions of their retina exposed to reflected light from the optic edge ending with dysphotopsia on the other hand. To achieve the best possible postoperative result, careful selection of patients, individual approach, and patient's education is mandatory.

In order to increase accuracy and precision in cataract surgery, together with patient demands for additional safety, femtosecond laser assisted cataract surgery is offered and being investi‐ gated as one of the possible solutions. As it appears safe and with many benefits in providing the best possible outcomes for cataract surgery, it stays on long-term clinical studies to provide evidence for the confirmation of its superiority over phacoemulsification.
