http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15506491&query_hl=1&itool=pubmed_docsum

Nippon Ganka Gakkai Zasshi. 2004 Sep;108(9):566-71.

Bilateral retinal detachment after laser in situ keratomileusis

Kohzaki K, Sano Y, Toda K, Mitooka K, Nakamura Y, Kitahara K. Department of Ophthalmology, Jikei University School of Medicine, 3-25-8 Nishi-shinbashi, Minato-ku, Tokyo 105 8461, Japan.  

BACKGROUND: We report a case of bilateral retinal detachment after laser in situ keratomileusis(LASIK).  

CASE: A 49-year-old man received multiple laser photocoagulation for retinal lattice degeneration in both eyes and retinal tears in the left eye. He underwent bilateral LASIK in another country about 6 months after the laser photocoagulation. After the LASIK his eyes showed bilateral retinal detachment, 2 weeks later in the right eye and 5 months later in the left eye. We had to perform retinal detachment surgery four times, scleral buckling, vitrectomy, silicone oil tamponade, and removal of the silicone oil for the right eye, and one scleral buckling procedure for the left eye to achieve retinal attachment. Soon after each retinal surgery, we recognized diffuse flap edema and interface haze, three times in the right cornea and one time in the left, although this corneal flap edema subsided without any sequel.  

CONCLUSION: In this case, laser photocoagulation had been done several times to prevent retinal detachment in both eyes. However, retinal detachment occurred 2 weeks after LASIK in the right eye, and therefore, the LASIK procedure was considered to be the main factor influencing the development of the retinal detachment. The left eye showed retinal detachment 5 months after LASIK and we thought it possible that this retinal detachment occurred as a natural consequence of myopia. We believe it is important to hava a thorough funduscopic examination done before LASIK and it is necessary to pay attention to corneal edema and interface haze after retinal detachment surgery for post-LASIK patients.

J Huazhong Univ Sci Technolog Med Sci. 2006;26(3):372-3, 377.

Liu L, Lei C, Li X, Dong J.

Refract Surgery Center Tongji Hospital, Tongji Medical College, Huazhong university of Science and Technology, Wuhan 430030, China.

Changes of corneal properties induced by laser in situ keratomileusis (LASIK) results in low inaccurate intraocular pressure (IOP) readings by Goldmann applanation tonometry (GAT). Before and after LASIK, the applied value of IOP, measured by dynamic contour tonometry (DCT) in comparison to GAT, was evaluated. Before and 1, 4 weeks after LASIK, the IOP in 30 cases (60 eyes) was measured by GAT and DCT respectively. The obtained results were statistically processed by SPSS11.5 statistical software. The results showed that central corneal thickness (CCT) could affect GAT measurements but not DCT measurements. The comparison of IOP one and 4 weeks after LASIK revealed that the readings from GAT was separately decreased by 5.00 +/- 1.12 and 5.45 +/- 1.13 mmHg as compared with those before LASIK, while those from DCT had no significant difference. It was concluded that LASIK-induced changes of CCT could influence the accuracy of GAT measurements, but had no influence on those from DCT. DCT was more beneficial to the measurements of IOP in normal eyes and those subject to LASIK surgery.

J Cataract Refract Surg. 2006 Dec;32(12):2075-2079.

Munoz G, Albarran-Diego C, Sakla HF, Javaloy J, Alio JL.

From the Refractive Surgery Department Centro de Especialidades Marques de Sotelo and Hospital NISA Virgen del Consuelo (Munoz, Albarran-Diego), Valencia, and the Refractive Surgery Department (Munoz, Sakla, Javaloy, Alio), VISSUM Instituto Oftalmologico de Alicante, Alicante, Spain.

PURPOSE: To describe the incidence of transient light-sensitivity syndrome (TLSS) after laser in situ keratomileusis (LASIK) with the femtosecond laser and to identify preventive strategies.

SETTING: Hospital NISA Virgen del Consuelo, Valencia, Spain.

METHODS: The first 765 eyes operated on with the 15 KHz femtosecond laser were prospectively analyzed for subjective complaints and clinical findings compatible with TLSS. Intraoperative settings, postoperative treatment, and development of complications were analyzed.

RESULTS: Overall, TLSS developed in 10 eyes (incidence 1.3%). However, the incidence decreased from 2.8% to 0.4% when aggressive topical steroids were used during the first 3 postoperative days. Postoperative interface inflammation and postoperative use of a low-dose topical steroid regimen were associated with a higher incidence of TLSS.

This is from the Handbook of Ocular Disase Management

http://www.revoptom.com/handbook/sect5e.htm

And illustrates an important point that lattice degeneration is quite common, occuring in 8-11 percent of the population. Since this condition predisposes the retina to weakening tearing and detaching yet is simple to diagnose, it is straightforward that patients with this condition should not be exposed to the ocular trauma associated with the suction ring during LASIK.  

SIGNS AND SYMPTOMS - The patient is usually over age 20 and is nearly always asymptomatic, except for possible complaints of flashing lights (photopsia). There appears to be a higher incidence of myopia in patients with lattice degeneration. There is no racial or sexual predilection.  Lattice degeneration occurs in eight to 11 percent of the general population. It presents as a linear trail of fibrosed vessels within atrophied retina in a "lattice" pattern. It nearly always runs circumferentially between the equator and the ora serrata. The individual lesions are usually from one-half to six disc diameters and may run 360 degrees around the eye in a discontinuous pattern. There may be associated RPE hyperplasia, giving the lesion a pigmented appearance. Atrophic holes are often present in the lesion, occasionally large enough to encompass the entire lattice lesion. The incidence of atrophic holes in lattice degeneration ranges from 18 to 42 percent. A tractional linear tear will occur on the posterior edge of lattice lesions in 1.9 percent of lesions. Lattice degeneration is typically bilateral.  

PATHOPHYSIOLOGY - The etiology of lattice is questionable. It appears to be due to dropout of peripheral retinal capillaries with resulting ischemia, which induces thinning of all retinal layers. There is sclerosis of the larger vessels, with their lumen being filled with extracellular glial tissue, giving lattice degeneration its characteristic fibrotic appearance.  The retinal thinning has several effects:

(1) the overlying vitreous will be disturbed, resulting in a pocket of liquefaction overlying the lattice lesion known as a lacuna;

(2) the vitreous along the edges of the lattice lesion will undergo strong adhesion to the retina; and

(3) the ischemia and retinal thinning will disturb the retinal pigment epithelium, resulting in RPE hyperplasia and a pigmented appearance.  

Often the thinning becomes so profound that a full-thickness hole atrophies through the retina at the lattice lesion. The overlying liquefied vitreous has the ability to pass through the hole into the subretinal space and possibly lead to rhegmatogenous retinal detachment. This will occur in approximately two percent of cases of holes within lattice degeneration. Due to the liquefaction of the overlying vitreous, there is no vitreoretinal traction on the edges of a hole in lattice degeneration. If a posterior vitreous detachment occurs, the vitreoretinal traction along the posterior edge of a lattice lesion may result in a linear tear, with an ensuing progression to rhegmatogenous retinal detachment in 37 percent of cases.  

MANAGEMENT - The main concern with lattice degeneration is the chance of progression to rhegmatogenous retinal detachment. With many types of retinal breaks, the area is often prophylactically sealed with laser photocoagulation or cryoretinopexy to prevent this. In lattice degeneration alone, prophylactic treatment is not practical in that the risk of detachment is only 0.1 to 0.7 percent in the phakic eye. Atrophic holes in phakic eyes with lattice degeneration also do not require prophylactic treatment, as the risk of progression to detachment is two percent or less.  Furthermore, prophylactic treatment of lattice lesions in eyes with greater than 6.00D of myopia yields no benefit. These lesions need only routine, yearly monitoring with the patient educated about signs and symptoms of retinal detachment. However, a linear tractional tear forming at the posterior border of a lattice lesion has about a 37 percent risk of progression to retinal detachment and therefore should receive prophylactic therapy.  

CLINICAL PEARLS  - Lattice degeneration both with and without atrophic holes is generally benign and does not require prophylactic treatment, as the complications of treatment are more severe than the natural history of the untreated condition.  The ominous tractional tear at the posterior border of a lattice lesion is very difficult to see ophthalmoscopically. These tears will usually only become apparent upon scleral indentation. Perform scleral indentation, whenever possible, on every lattice lesion to look for an occult tractional tear.

Can J Ophthalmol. 2000; 35(4):192-203 (ISSN: 0008-4182)

Casson EJ; Racette L University of ottawa Eye Institute, Ont.  

We review the vision requirements for driving with the goal of revising current Canadian Ophthalmological Society (COS) recommendations for vision standards for driving. The report comprises two sections. In the first section we report the results of a survey of transportation authorities in Canada and the United States conducted on behalf of the COS to determine the current standards and medical review procedures. The results suggest that although the standards in Canada are more consistent than those in the United States, few of the standards in either country are evidence-based. In the second section we review the recent literature on visual function and driving. We conclude from this review that adequate contrast sensitivity is as important as, if not more important than, good visual acuity for driving and that there is little evidence to support a monocular standard for acuity, contrast sensitivity or visual field. Although there is evidence that the extent of a visual field defect is related to the ability to perform driving tasks, there is little evidence to suggest a relation between the location of the visual field defect and fitness to drive.

Acta Ophthalmol Scand. 2003 Oct;81(5):530-2.

LASIK complication: loss of electricity to the microkeratome during the forward pass.

Tuominen IS, Tervo TM. Department of Ophthalmology, Helsinki University Hospital, PO Box 220, HUS, SF-00029 Helsinki, Finland. ilpo.tuominen@hus.fi

CONTEXT: A 32-year-old woman was scheduled for myopic laser in situ keratomileusis (LASIK) because of myopia and anisometropia caused by retinal detachment surgery.

CASE REPORT: During surgery, a sudden malfunction of the microkeratome during the forward pass was experienced. It was not possible to reverse the blade manually along the suction ring. Moreover, disconnecting the suction from the control unit did not help at first, because the suction ring was firmly attached to the ocular surface. However, detaching the suction line from the control unit aborted the vacuum and allowed the surgeon to turn the whole microkeratome backwards, mimicking the normal blade movement. Finally, an almost normal flap was observed, and the operation was successfully completed. Afterwards, the wire to the electromotor of the microkeratome was found to be broken and subsequently replaced.

CONCLUSION: This type of unforeseen microkeratome malfunction may result in serious flap or other complications.

And non LASIK patients

J Cataract Refract Surg 2003; 29:275–278

Brian S. Boxer Wachler, MD 

Purpose: To compare binocular and monocular vision in patients treated with laser in situ keratomileusis (LASIK) and in non-LASIK patients.  

Setting: Jules Stein Eye Institute, Los Angeles, California, USA.  

Methods: This comparative cross-sectional study comprised 20 postoperative LASIK patients and 20 non-LASIK ametropic patients. LogMAR visual acuity, contrast sensitivity, and infrared pupillometry were tested. Outcome measures were better-eye monocular acuity, binocular acuity, better-eye contrast sensitivity, binocular contrast sensitivity, and pupil diameter under monocular and binocular conditions.  

Results: Binocular visual acuity and contrast sensitivity were statistically significantly better than the visual acuity in the better eye (P = .0047 to <.0001) in both patient groups. Pupil diameter was statistically significantly smaller under the binocular condition than the monocular condition (P <.0001) in both groups.  

Conclusions: Monocular testing induced larger pupil diameters, which was associated with reduced vision compared to binocular measurements in LASIK and non-LASIK patients.

http://www.journalofrefractivesurgery.com/showAbst.asp?thing=10147

Journal of Refractive Surgery Vol. 21 No. 2 March/April 2005

"In particular, a forward shift and an increase in power of the posterior surface was predicted for myopic LASIK, in agreement with previous experimental findings."          

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12701715&query_hl=21

Invest Ophthalmol Vis Sci. 2007 Jun;48(6):2570-5.

Rodriguez AE, Rodriguez-Prats JL, Hamdi IM, Galal A, Awadalla M, Alio JL.Vissum-Instituto Oftalmologico de Alicante, Alicante, Spain;

PURPOSE: To study the effect of the LASIK procedure performed with a femtosecond laser and a manual microkeratome on the conjunctival goblet cell and epithelial cell populations.

METHODS: In this prospective, nonrandomized, masked study, 64 eyes undergoing LASIK were included: 30 with the Moria M2 (M2) microkeratome and 34 with the IntraLase femtosecond laser (IL). The preoperative spherical equivalent was -2.0 +/- 3.8 D in the M2 group and -3.1+/- 3.1 D in the IL group. The time that the suction ring was applied on the eye was registered, and goblet cell density (GCD), epithelial cell morphology, and inflammatory cells were evaluated by conjunctival impression cytology, before and after the surgery.

RESULTS: All the patients in both groups showed a decrease in GCD after LASIK (P < 0.001) that recovered after 6 months. At 1 week, 1 month, and 3 months, GCD was lower with IL than with M2 (P < 0.019, P < 0.001, and P < 0.024, respectively). The mean period that the suction ring was applied was longer in the IL than in the M2 group (P < 0.001). There was a high correlation between the decrease in GCD and the suction time (R = 0., and the preoperative spherical equivalent (R congruent with 0.4).

CONCLUSIONS: Impression cytology showed a greater reduction in goblet cell populations after IL than after M2, probably because of the length of time that the suction ring exerted pressure on the conjunctiva. These changes in the goblet cells may contribute to the development of the ocular surface syndrome after LASIK procedures.

M.S. Sridhar, Christopher J. Rapuano, and Elisabeth J. Cohen;  Cornea Service, Wills Eye Hospital, Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pennsylvania, USA; *Inquiries to Christopher J. Rapuano, MD, Cornea Service, Wills Eye Hospital, 900 Walnut St, Philadelphia, PA 19107; fax: (215) 928-3854
Manuscript accepted 24 May 2001;

PURPOSE: To report a rare complication in which the patient accidentally removed the laser in situ keratomileusis corneal flap.

METHODS: Interventional case report. A 35-year-old woman underwent uncomplicated laser in situ keratomileusis surgery. Ten days after surgery, she inserted a soft contact lens into the right eye to improve her vision. She tried to remove the contact lens, but had pain and bleeding. She was referred 10 days later with a diagnosis of loss of flap.

RESULTS: On examination, she had a best-corrected visual acuity of 20/70 in the right eye. The right eye examination revealed no corneal flap, mild corneal edema, and significant haze. A central epithelial defect was found.

CONCLUSION: Accidental corneal flap removal can rarely follow laser in situ keratomileusis surgery. This complication provides insight into the weak adhesion of the flap onto the stromal bed after laser in situ keratomileusis surgery and, hence, the inherent risk of traumatic flap dislocation or amputation, which needs to be explained to the patient.

 BMC Ophthalmol. 2006 Apr 28;6(1):19 

Dada T, Pangtey MS, Sharma N, Vajpayee RB, Jhanji V, Sethi HS. 

ABSTRACT: 

BACKGROUND: Diffuse lamellar keratitis (DLK) is a relatively new syndrome that is increasingly being reported after LASIK. We have observed that a hyperopic shift may be associated with the occurrence of this diffuse lamellar keratitis. 

CASE PRESENTATION: A 26 year old man developed bilateral diffuse lamellar keratitis (DLK) following myopic LASIK. The residual refractive error was +0.5D OD and +0.25D OS at the end of the first week. The sterile infiltrates resolved over a period of 4-6 weeks on topical steroid therapy. A progressive hyperopic shift was noted in the right eye with an error +4.25Dsph/+0.25Dcyl 20 at the final follow up 6 months post surgery. 

CONCLUSION: Diffuse lamellar keratitis after LASIK may be associated with a significant hyperopic shift.

Cataract & Refractive Surgery Today April, 2006

Good—The Enemy of Great

Why refractive surgeons must adopt a philosophy of continuous improvement.

By Shareef Mahdavi

Excerpt: This past fiscal quarter, the refractive surgery industry in the US reached a milestone: 10 million eyes have now undergone laser vision correction since the first excimer lasers received FDA approval 1 decade ago. That's 5 million Americans who are ambassadors for LASIK as well as for the new generation of refractive procedures available to surgeons and their patients.

That's good, but it's not great.

I'm not sure whether the 10-million mark is a tremendous accomplishment or a mild disappointment. My columns over the past 5 years have explored why market adoption for LASIK and other refractive surgeries hasn't been higher, stronger, or faster. On the one hand, LASIK is now the single most commonly performed elective procedure in the country, far outpacing procedures performed by plastic surgeons. On the other hand, LASIK's adoption should be much higher given its high success rate (90% achieving a UCVA of 20/20), the immediacy of visual improvement (the "WOW" factor), and the emotional impact on peoples' lives ("It's a miracle!").

Read the entire article at http://www.crstoday.com/PDF%20Articles/0406/CRST0406_17.html 

Potential new post-laser refractive surgery complication identified

A new syndrome characterized by noninflammatory corneal opacification can occur in some patients within 9 days after undergoing LASIK or PRK, according to a study. The opacification gradually clears over several months and can also cause a possible hyperopic shift in refraction, the study authors said.

Baris Sonmez, MD, and Robert K. Maloney, MD, identified 23 eyes of 14 patients with the syndrome, which they termed central toxic keratopathy. Four eyes had undergone PRK and 19 eyes had undergone LASIK.

In all cases, eyes developed central corneal opacification in the laser-treated area 3 to 9 days after surgery, which persisted for 2 to 18 months, the authors reported. Eighteen of the 19 LASIK-treated eyes developed diffuse lamellar keratitis before the onset of the opacification, they noted.

Nine eyes also developed hyperopia over 2 D, one eye lost two lines of best corrected visual acuity, and two eyes lost one line, according to the study The hyperopia and residual striae can be treated with an enhancement procedure, but topical or oral corticosteroid treatment is not indicated, the authors noted.

The cause of the keratopathy is not known, they added.

The study is published in the March (2007) issue of the American Journal of Ophthalmology.

 found to cause 28- to 46-fold increase in aberrations!

Surv Ophthalmol. 2005 May-Jun;50(3):245-51.  

Comment in: Surv Ophthalmol. 2005 Nov-Dec;50(6):611-2; author reply 612.  

Bashford KP, Shafranov G, Tauber S, Shields MB.  Department of Ophthalmology and Visual Sciences, Yale University School of Medicine, New Haven, Connecticut; and Glaucoma Consultants of Colorado, P.C., Littleton, Colorado, USA.  

Glaucoma patients present a unique set of challenges to physicians performing corneal refractive surgery. Corneal thickness, which is modified during corneal refractive surgery, plays an important role in monitoring glaucoma patients because of its effect on the measured intraocular pressure. Patients undergo a transient but significant rise in intraocular pressure during the laser-assisted in situ keratomileusis (LASIK) procedure with risk of further optic nerve damage or retinal vein occlusion. Glaucoma patients with filtering blebs are also at risk of damage to the bleb by the suction ring. Steroids, typically used after refractive surgery, can increase intraocular pressure in steroid responders, which is more prevalent among glaucoma patients. Flap interface fluid after LASIK, causing an artificially low pressure reading and masking an elevated pressure has been reported. The refractive surgeon's awareness of these potential complications and challenges will better prepare them for proper management of glaucoma patients who request corneal refractive surgery.

J Cataract Refract Surg. 2002 Feb;28(2):356-9.  

Shaikh NM, Shaikh S, Singh K, Manche E.  Department of Ophthalmology, Stanford University School of Medicine, Stanford, California 94305, USA.  

We describe 2 patients, one a glaucoma suspect because of family history and the other with juvenile glaucoma. Both patients developed complications after laser in situ keratomileusis that required frequent topical steroids, leading to steroid-induced glaucoma. In both cases, corneal edema from the acute rise in intraocular pressure (IOP) caused inaccurate IOP measurement by standard methods. The inability to recognize glaucoma early may have resulted in significant irreversible vision loss.

After LASIK With Microkeratome and Femtosecond Laser Created Flaps

JOURNAL OF REFRACTIVE SURGERY 2007; 23(3):233

By Bryan C. Hainline, MD; Marianne O. Price, PhD; David M. Choi, MD; Francis W. Price, Jr., MD

PURPOSE: To report nine cases of severe central flap inflammation and necrosis after LASIK.

METHODS: A retrospective chart review was conducted on 17,100 LASIK cases performed at two laser centers in Indiana from January 1995 through May 2005. All patients with central lamellar flap necrosis were identified.

RESULTS: Severe central flap inflammation and necrosis occurred in nine eyes of eight patients. Six patients underwent flap creation with a mechanical microkeratome and two with a femtosecond laser. Of eight eyes with >2- month follow-up, one lost at least two lines of best spectacle- corrected visual acuity and two experienced a hyperopic shift in spherical equivalent refraction. Typically, inflammation was minimal the day after surgery, peaked 5 to 10 days later, and subsided by 60 days. Six of nine cases were treated by lifting the flap and irrigating the stromal bed. In each of these cases, few or no inflammatory cells were observed in the stromal bed, the posterior flap surface was intact, and the central portion of the anterior flap had a jelly-like consistency.

CONCLUSIONS: Central lamellar flap necrosis appears to differ from diffuse lamellar keratitis because the location of stromal inflammation is not in the flap interface but rather in the flap anterior stroma. Treatment with corticosteroids seemed to have little effect on outcomes. This is thought to be the first documentation of central lamellar flap necrosis following the use of a femtosecond laser. [J Refract Surg. 2007;23:233-242.]

   J Refract Surg. 2006 Apr;22(4):402-4. 

Cheung LM, Papalkar D, Versace P. 

Department of Ophthalmology, Prince of Wales Hospital, Randwick, Australia. 

PURPOSE: To report a case of traumatic flap dehiscence and Enterobacter keratitis 34 months after LASIK. 

METHODS: A 36-year-old man sustained a flap dehiscence following traumatic right eye gouging by a seagull claw. He presented the following day with uncorrected visual acuity (UCVA) in the affected eye of 3/200 and organic foreign body deposits underneath the flap. Systemic and topical antibiotics were administered and urgent surgical debridement and replacement of the LASIK flap was performed. An Enterobacter species was cultured from an intraoperative swab. 

RESULTS: After a prolonged postoperative course, including administration of topical ofloxacin, tobramycin, chloramphenicol, and dexamethasone, UCVA returned to 20/20. 

CONCLUSIONS: Good visual outcome after early debridement and appropriate antibiotics was achieved. Patients should be injury advised to seek prompt ophthalmic consultation after LASIK.

Cornea. 2005 Jul;24(5):509-22.  

Netto MV, Mohan RR, Ambrosio R Jr, Hutcheon AE, Zieske JD, Wilson SE.  The Cole Eye Institute, The Cleveland Clinic Foundation, OH 44195, USA.  

PURPOSE: The corneal wound healing response is of particular relevance for refractive surgical procedures since it is a major determinant of efficacy and safety. The purpose of this review is to provide an overview of the healing response in refractive surgery procedures.  

METHODS: Literature review.  

RESULTS: LASIK and PRK are the most common refractive procedures; however, alternative techniques, including LASEK, PRK with mitomycin C, and Epi-LASIK, have been developed in an attempt to overcome common complications. Clinical outcomes and a number of common complications are directly related to the healing process and the unpredictable nature of the associated corneal cellular response. These complications include overcorrection, undercorrection, regression, corneal stroma opacification, and many other side effects that have their roots in the biologic response to surgery. The corneal epithelium, stroma, nerves, inflammatory cells, and lacrimal glands are the main tissues and organs involved in the wound healing response to corneal surgical procedures. Complex cellular interactions mediated by cytokines and growth factors occur among the cells of the cornea, resulting in a highly variable biologic response. Among the best characterized processes are keratocyte apoptosis, keratocyte necrosis, keratocyte proliferation, migration of inflammatory cells, and myofibroblast generation. These cellular interactions are involved in extracellular matrix reorganization, stromal remodeling, wound contraction, and several other responses to surgical injury.  

CONCLUSIONS: A better understanding of the complete cascade of events involved in the corneal wound healing process and anomalies that lead to complications is critical to improve the efficacy and safety of refractive surgical procedures. Recent advances in understanding the biologic and molecular processes that contribute to the healing response bring hope that safe and effective pharmacologic modulators of the corneal wound healing response may soon be developed.  

From the conclusion:  

Wouldn't you think they'd want to figure this out before performing refractive surgeons on millions and millions of patients?

Graefes Arch Clin Exp Ophthalmol. 2001 Jul;239(6):416-23.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11561789&query_hl=11&itool=pubmed_docsum

Luna JD, Artal MN, Reviglio VE, Pelizzari M, Diaz H, Juarez CP. Fundacion Ver, Cordoba, Argentina  

BACKGROUND: The presence of vitreoretinal changes following laser in situ keratomileusis in myopia is evaluated.  

METHODS: Clinically, 50 patients (100 eyes) with marked anisometropic myopia, 50 low-myopic eyes (<4.00 D) and 50 high-myopic eyes (>7.00 D) were prospectively evaluated pre- and postoperatively for the presence of newly recognized entoptic phenomena (vitreous floaters, light flashes, or both), and for vitreoretinal changes using indirect depressed fundus examination, a +90 D preset lens, Goldman three-mirror contact lens, and kinetic ultrasound (KU) before and after bilateral LASIK. Patients with previous partial or total posterior vitreous cortex detachment (PVD) were excluded. Experimentally, groups of adult pigs underwent KU, retinal fluorescein angiography (FA), and electroretinography (ERG) before and after applying the microkeratome suction ring for 30 s.  

RESULTS: Clinically, 8% (4 eyes) had positive perception of postoperative vitreous floaters in the low myopia group, and 32% (16 eyes) in the high myopia group. Postoperative light flashes were noted only in the high myopia group, in 12% of cases. Partial or total posterior vitreous cortex detachment was detected by biomicroscopy in 2% (1 eye) of the low and in 10% (5 eyes) of the high myopia group and by KU in 4% (2 eyes) of the low and in 24% (12 eyes) of the high myopia group. Experimentally, 2 pig eyes out of 12 developed partial PVD by KU, immediately after microkeratome suction ring application. All pig eyes showed significantly diminished ERG amplitudes during and immediately after suction ring application. No FA changes or delays in retinal circulation time were noted during or immediately after removal of the suction ring.  

CONCLUSIONS: Vitreoretinal alterations after LASIK were demonstrated clinically mainly by KU in high myopes. Experimentally, PVD were also demonstrated. Diminished ERG recordings with normal retinal circulation following suction ring application may suggest some transient choroidal circulation abnormalities.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16386969&query_hl=7&itool=pubmed_docsum

American Journal of Ophthalmology
Volume 141, Issue 1 , January 2006, Page 1
Kuang-Mon Ashley Tuan OD, PhDa, Dimitri Chernyak PhDa and Sandy T. Feldman MD, MSb, ,

a) VISX Inc, Santa Clara, California
b) ClearView Eye and Laser Medical Center, San Diego, California.

Purpose: To evaluate the accuracy of the diagnostic capabilities of optical metrics generated from wavefront measurements in relationship to post–laser-assisted in situ keratomileusis (LASIK) visual complaints as expressed and drawn by patients.

Design: Retrospective analysis and observational case series.

Methods: Patient wavefront data from an investigational device exemption study for wavefront-guided ablations were used to derive normative modulation transfer function (MTF), encircled energy (EE), and Strehl ratio. These optical metrics and their point-spread functions (PSF) were compared with data from five postoperative patients with night vision complaints. Patients were asked to draw their symptoms, which were elicited by testing with a Fenthoff muscle light, while using their best-corrected distance vision. 

Results: The MTF, EE, and Strehl ratio of most patients were markedly different from those of the averages of 208 normal myopic eyes before and after LASIK surgery. The spatial extent of the PSF correlated positively with the severity of the visual complaints. Wavefront-derived PSFs were markedly similar to the patients’ drawings.

Conclusions: The results of this study demonstrate the diagnostic capability of the wavefront system in predicting visual symptoms and complaints of patients with high-order aberrations. Objective visual metrics from patients with night vision complaints were different from those of normal myopic eyes that had undergone LASIK procedures.

Excerpts: If the human eye were a perfect optical system, the appearance of a point source of light would be limited only by diffraction effects, and the source would appear as a single point to the observer. In addition to spherocylindrical components, the optical system of the human eye generates other complex optical aberrations, which contribute to the distortion of retinal images and determine the quality of the image formed on the retina. The optical imperfections of the eye cause rays of light traveling from a point source through the eye’s optics to intercept the retina at different locations, thereby blurring the appearance of the point. The distorted appearance of the point on the retina is called a point-spread function (PSF).

The recent development of wavefront aberrometers for use in ophthalmology has given clinicians an objective measurement method for optical aberrations other than sphere and cylinder. The wavefront maps generated by such devices represent deviations from the ideal diffraction-limited optical systems and enable the physician to precisely diagnose visual impairment. In addition to guiding customized refractive surgery, wavefront sensors can be used to evaluate the source of visual complaints. The appearance of the PSF can be computed directly from the wavefront measurement and corroborated by the patient with a simple drawing.

In recent years, much emphasis has been placed on the use of PSF and PSF-based metrics to objectively evaluate the quality of vision (Gross E, Wavefront Congress 2004, Abstract).3 and 4 Whereas the wavefront map (which is analytically defined by methods that include the Zernike coefficients) describes the aberrations in the pupillary plane, the PSF describes aberrations in the retinal plane. Retina-based descriptions of aberrations have been shown to correlate strongly with subjective visual metrics, such as visual acuity and contrast sensitivity.

In addition to correlating with subjective measures of visual performance, the PSFs are valuable tools for understanding visual symptoms, such as ghost images, which occur with multiple peaks of the PSF, or halos and starbursts, which may also be inferred from the appearance of the PSF. The purpose of this study is to determine whether quantitative analysis of PSFs is helpful to the clinician’s understanding of nighttime visual complaints.

Methods: This study was a retrospective analysis and observational case series. Two groups of patients were included in this study. The first group of eyes were nonsymptomatic and were used to establish normative values. Data from this group were gathered from 208 eyes from the six clinical sites in the United States that participated in the Institutional Review Board–approved investigative device exemption study for the CustomVue wavefront-guided laser vision correction procedure (VISX Inc, Santa Clara, California, USA). The second group of patients, all of whom had night complaints after laser-assisted in situ keratomileusis (LASIK), was recruited from the practice of ClearView Eye Center, San Diego, California, USA. 
 
The purpose of this part of the study was to see whether sketches of the point source of light made by patients with night vision complaints would be reasonably similar to the polychromatic PSF plot created by the WaveScan aberrometer, and to determine whether their optical metrics were different from the normal population. Inclusion criteria included a complaint of glare, halo, starburst at night, or a poorer quality of vision. Patients were also required to be willing to sketch their symptoms.

WaveScan version 3.5 software was used to convert the wavefront data into PSF. The PSF was computed by using multiple wavelengths to accurately simulate the appearance of white light and to account for chromatic aberrations of the eye. The Stiles-Crawford effect of the first kind, which depicts the probability of photon absorption by photoreceptors as a function of ray position from the pupil center, was also taken into account. Additionally, absorption spectra of the three retinal photoreceptor types were used to correctly weight different wavelengths in the PSF computations. Finally, spacing of the retinal receptor mosaic was used to determine the maximum spatial frequency that is used in the rendition of the PSF.

An important issue in assessing retinal image quality is a realistic computation of the PSF. The above method enables the instrument to create realistic renditions of the appearance of a white light point source on the image plane, which is the polychromatic PSF. An optical system with little aberration will generate a compact and high-intensity point source on the image plane. Therefore, the brain would be expected to perceive sharp images and resolve small details. A highly aberrated eye will form a PSF that spreads out and has lower contrast within the retinal plane. In this case, the brain would perceive a dim and blurry image resulting in low resolution and poor visual performance.

To effectively compare the visual impact of different PSFs, it is necessary to quantify PSF or PSF plots. To date, there is no consensus in the vision science community as to a standardized method for quantifying the visual impact of measured wavefront aberration. However, Strehl ratio, encircled energy (EE), and modulation transfer function (MTF) are the commonly used optical metrics believed to provide useful information on perceptual image quality and therefore predict visual performance.3, 4, 7 and 8 For this study, the PSF was broken down into two parts for visual evaluation: circle of blur; and the length of the vertical and horizontal strikes from the center. Optical metrics such as Strehl ratio, EE, and MTF were derived from the PSF8 with the intention of quantifying the visual impact of the PSF.

Strehl ratio is defined as the ratio of the peak intensities of the aberrated PSF and the diffraction-limited PSF. EE is the two-dimensional integral of the PSF. EE represents the proportion within a given radius of the image center and the total energy from a point source. EE was calculated at 1, 3, 5, 8, and 10 min of arc. MTF is the module of Fourier transform of the PSF. MTF represents contrast information, and it varies with spatial frequencies. MTF was calculated from 3 cycles per degree (cpd) to 30 cpd for this study. An MTF of 1 indicates that 100% contrast was maintained after the light passed through the optical system.
The normative value of the optical metrics described above was used for comparison with patients with postoperative visual symptoms. Lower-order wavefront information was deleted from the calculation to remove optical degradation arising from refractive error.

Results: All patients were healthy men ranging in age from 31 to 43. Patient demographic information is listed in Table 1. Their drawings and corresponding PSFs are presented in Figure 1. The postoperative follow-up period ranged from 6 months to 3 years. Postoperative uncorrected vision ranged from 20/30 to 20/20 and was correctable in each eye to 20/20 or better. However, patients reported visual symptoms at follow-up visits. Unfortunately, not all of the patients’ preoperative visual information was available.

Discussion: It is well known that patients with nighttime vision complaints may nevertheless have excellent uncorrected acuity. The clinician does not have many clinical tests outside of questionnaires to assess the extent of symptoms such as glare, halo, and starburst. Additionally, literature on clinical methods with which to demonstrate night complaints or quantify the visual disturbance is scarce. In this study, we have demonstrated that optical metrics derived from polychromatic PSF are a reliable quantitative method for the validation of night vision complaints.

The PSF diagram represents the appearance of one small spot of light after it passes through an optical system. The authors found the WaveScan-generated PSF to be consistently similar to the subjective visual experience of the study subjects despite differences in the artistic abilities of the patients. The polychromatic PSF plots derived from the wavefront measurements bear marked similarities to the drawings of the patients. The PSF plots show diffraction effects and some subthreshold light. Diffraction-based spatial frequencies are missing from drawings because they are not perceived. Additionally, the spacing of the photoreceptors limits visual acuity and spatial resolution of the retina. Occupation, personality, and level of detail orientation also appear to help determine the way patients perceive their visual quality. Therefore, patients with similar PSFs can have different reactions to their quality of vision. Nevertheless, the similarity between the PSF maps of subjects who have visual symptoms and their drawings are evident.

Optical metrics generated from the PSF were used to create a quantitative description of a PSF diagram. Optical metrics apply summations from different areas and orientations, and the result is a directionless quantitative number. The authors chose to use three metrics: Strehl ratio, EE, which signifies the intensity of the brightness of the image, and MTF, which represents contrast information. The study patients were compared with the normative values of EE and MTF generated from a cohort that had never undergone refractive surgery. Most optical metrics in the study patients were significantly worse than the normative values.

Lowered EE and MTF in the left eye of patient 4 are marginally significant, and there is a high amount of negative spherical aberration. The PSF maps are more vertically distributed. After averaging in all directions, the effect on overall optical metrics was reduced, which may explain why patient 4 had both positive visual symptoms but was within the normal limits of EE and MTF. However, patient 4’s PSF map shows an asymmetrical pattern in which the vertical dimension spreads outside the normal range. This extensive vertical spread of light accounts for the patient’s visual symptoms and correlates with his drawings.
 
After examining the visual functions of seven patients who underwent LASIK procedures, Holladay and coauthors hypothesized that corneas with an oblate shape or positive spherical aberration contributed to the decrease of visual functions. In our study patients, patients 1 and 4 had significant negative spherical aberration or prolate cornea (−0.41 μm and −0.25 μm, respectively) but also had visual symptoms. Spherical aberration was one of the few “abnormal” optical metrics for patient 4. This observation suggests that negative spherical aberration is not necessarily associated with visual satisfaction. On the contrary, when spherical aberration is present in sufficient magnitude, it could cause visual dissatisfaction.

In our study patients, some patients’ uncorrected visual acuity nevertheless experienced persistent visual symptoms, even with their best-corrected vision.

Polychromatic PSF plots generated from VISX’s polychromatic wavefront algorithms showed high correlation with the patients’ subjective visual experiences.

In conclusion, this study shows that wavefront systems are capable of predicting nighttime visual symptoms and complaints of patients whose visual acuities are otherwise good. Polychromatic PSF and the optical metrics derived from it are valuable diagnostic tools for predicting quality of vision and for evaluating the optical quality of an eye.

To understand the extent of the damage, you really should get the full-text of this article.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15808255&query_hl=16

1: Ophthalmology. 2005 Apr;112(4):634-44.

Dawson DG, Holley GP, Geroski DH, Waring GO 3rd, Grossniklaus HE, Edelhauser HF.

Department of Ophthalmology, Emory University School of Medicine, Atlanta, Georgia, USA.

OBJECTIVE: To perform confocal microscopy on postmortem human LASIK corneas and correlate these findings to histologic and ultrastructure evaluations.

DESIGN: Prospective, consecutive, observational case series.

PARTICIPANTS: Ninety postmortem LASIK corneas (47 patients) were evaluated for histopathology, of which 22 consecutive corneas (12 patients) were also evaluated by confocal microscopy. Six normal corneas (3 patients) served as controls.

METHODS: This observational case series involving 22 corneas from 12 patients with postoperative intervals from 1 month to 6.5 years after LASIK surgery were collected. The corneas were mounted in an artificial anterior chamber and perfused with balanced salt solution before confocal microscopy was performed on the center of the cornea. The corneas were then bisected and processed for light and transmission electron microscopy.

RESULTS: Confocal microscopy, along with histologic and ultrastructural correlations, demonstrated that the most prevalent alterations in the centers of LASIK corneas were a slightly thickened epithelium caused by focal basal epithelial cell hypertrophic modifications, random undulations in Bowman's layer over the flap surface, and a variably thick hypocellular primitive stromal interface scar. By using confocal microscopy, the interface wound was easily identified in 100% of the cases because numerous brightly reflective interface particles were always present in the hypocellular primitive stromal scar. These particles were found primarily to consist of organic cellular constituents, some of which were transient in nature.

CONCLUSION: After LASIK, active stromal wound healing in the central cornea results in the production of a hypocellular primitive stromal scar, whereas secondary tissue adjustments seem to cause the Bowman's layer undulations and the subsequent epithelial cell modifications. Most of the interface particles revealed by confocal microscopy in the region of the stromal scar are organic in nature and presumably innocuous to the cornea.

Clin Exp Optom. 2005 Mar;88(2):89-96.

comparison of outcomes for Asian and Caucasian eyes.

Albietz JM, Lenton LM, McLennan SG.

Queensland University of Technology, Brisbane, Australia.

BACKGROUND: Dry eye is a common complication of LASIK surgery. Our clinical impression was that post-LASIK dry eye was more problematic for our Asian patients. The aim of this study was to determine if dry eye after LASIK is more prevalent, more sustained and more severe in Asian eyes compared with Caucasian eyes.

METHODS: This