Hexagonal Keratotomy Research Articles

Cataract Surgery on an Octogenarian Patient with a History of Hexagonal Keratotomy

An 81-year-old female patient presents with poor vision and seeks options to improve her vision. The patient received a hexagonal keratotomy, an early refractive surgical technique used to improve hyperopia, more than 45 years prior. Due to the patient’s history, preemptive measures are taken to ensure corneal stability. Upon examination, dry eye disease, nuclear sclerosis, and cortical changes are present in both eyes. The patient has severe, irregular astigmatism. Preoperatively, aggressive treatment for dry eye disease was undertaken until stable biometry could be acquired. Femtosecond laser-assisted cataract surgery was performed sequentially at a one-week interval. The patient had bilateral small-aperture lenses (Apthera/IC8 Bausch Health). Aggressive dry eye treatment continued postoperatively, and the patient's UCVA at distance was 20/30; at intermediate was 20/30; and at near was 20/30.

Deep anterior lamellar keratoplasty for the management of iatrogenic keratectasia occurring after hexagonal keratotomy

Iatrogenic keratectasia has been reported subsequent to refractive surgery or trauma. Hexagonal keratotomy (HK) is a surgical incisional technique to correct hyperopia. A number of complications have been reported following this procedure, including irregular astigmatism, wound healing abnormalities and corneal ectasia. When visual acuity is poor because of ectasia or irregular astigmatism and contact lens fitting is not possible, penetrating or lamellar keratoplasty can be performed. Since incisions in refractive keratotomy are set at 90–95% depth of cornea, intraoperative microperforations are known to occur and lamellar keratoplasty may become difficult. We describe deep anterior lamellar keratoplasty (DALK) used to successfully manage keratectasia after HK. Pre DALK vision was 20/400 and post DALK vision was 20/30 two months after surgery. This report aims to show improved visual outcome in corneal ectasia secondary to HK. DALK can be a procedure of choice with proper case selection.

Intraocular lens power calculation after incisional and thermal keratorefractive surgery

To evaluate the efficacy of corneal topography in determining the central corneal refractive power in intraocular lens (IOL) power calculations after incisional and thermal keratorefractive surgery. Oregon Eye Institute, Eugene, Oregon, USA. This retrospective review comprised 20 eyes (14 patients) that had cataract extraction with IOL implantation or refractive lens exchange after radial keratotomy, hexagonal keratotomy, or laser thermal keratoplasty. The effective refractive power (EffRP) of the Holladay Diagnostic Summary on the EyeSys Corneal Analysis System was used to determine the central corneal refractive power, which was input into the Holladay 2 IOL calculation formula. Eighty percent of eyes achieved a postoperative spherical equivalent refraction within +/-0.50 diopter of emmetropia. The use of the EffRP increases the likelihood of an acceptable refractive outcome after cataract or refractive lens exchange surgery in eyes with a history of keratorefractive surgery.

Alterations of Corneal Extracellular Matrix After Multiple Refractive Procedures

To describe the clinical course and alterations of the corneal extracellular matrix (ECM) and basement membrane (BM) in a cornea after hexagonal keratotomy, transverse keratotomies, and keratomileusis. Frozen sections of this cornea and of 12 normal corneas were studied by immunofluorescence with specific antibodies. The patient history was analyzed to allow a clinical correlation. In the treated cornea, keratotomy scars and subepithelial fibrosis with neovascularization were seen. Around and beneath the epithelial plugs and along the keratotomy scars, deposits of types III, VI, VIII, and XIV collagen; fibrillin-1; fibronectin; and tenascin-C were found, together with short streaks of types IV (alpha 1-alpha 2) and VII collagen, laminin-1 and -5, entactin, and perlecan. alpha 3-alpha 4 Type IV collagen chains were abnormally absent from the BM around the epithelial plugs. At the edges of the keratomileusis flap, subepithelial fibrosis areas were found, with abnormal deposits of eight different collagen types, perlecan, fibronectin, fibrillin-1, and tenascin-C. The major part of the flap interface did not show ECM abnormalities. ECM alterations outside the scarred areas included the appearance of tenascin-C in the stroma and of alpha 1-alpha 2 type IV collagen in the epithelial BM, and the disappearance of fibronectin from Descemet's membrane. Five years after surgery, the treated cornea still presented BM abnormalities at sites of keratotomy scars and epithelial plugs. Several ECM components were abnormally expressed outside the scarred areas, consistent with an ongoing fibrosis in the treated cornea.

Thermokeratoplasty for the treatment of hyperopia: A clinical follow-up

SUMMARY Corneal curvature can be altered by shrinking stromal collagen with a retractable cautery probe tip that produces controlled thermal burns in a procedure termed hyperopic thermokeratoplasty (HTK). This procedure induces steepening of the central cornea. We performed HTK in 12 sighted eyes from eight patients placing a radial pattern of spots on the peripheral cornea, using the Fyodorov thermal unit. The number of spots and the shape ofthe optical zone (rounded or ovoid) was determined by a computer software provided by the manufacturer. Follow-up ranged from 24 to 54 weeks (mean of 31.50 weeks). Spherical equivalent changed from a preoperative mean of 4.10±1.12 diopters to -0.85±0.86 (P=0.001), 0.74±1.26 (P=0.001), 1.05±1.34 (P=0.001) and 3.84±1.13 diopters (P=0.16), respectively at 4, 12 and 24 weeks after the surgery and at the last Follow-up. The induced keratometric steepening at 4 weeks postoperatively (4.50±1.31, P=0.001), reduced to 1.04±0.43 diopters of corneal steepening at the last Follow-up (P=0.25). Uncorrected visual acuity improved at least two lines in nine eyes (75.0%), remained unchanged in one eye (8.3%) and decreased in two eyes (16.7%). Eight eyes (66.6%) had uncorrected visual acuity equal to or better than 20/40 at the last visit. None of the patients had recurrent erosions, stromal necrosis or vascularization. Endothelial cell counts performed six months after surgery in two patients that underwent unilateral surgery indicated no quantitative or qualitative effects from HTK. These data support previous studies indicating that central corneal topography can be modified by heating corneal stroma in a controlled fashion. Regression of effect and induction of astigmatism limited the success of our series. Surgical correction ofhyperopia includes hyperopic keratomileusis, hyperopic epikeratophakia, hexagonal keratotomy, thermokeratoplasty and more recently photorefractive keratectomy.1-5 Thermokeratoplasty, a surgical procedure that involves heating of the corneal tissues, was initially attempted in patients with keratoconus. 6 Initial reports of success 6 were followed by reports of profound initial flattening but with subsequent return to preoperative topography,7 and complications such as delayed epithelial healing, recurrent epithelial erosions, aseptic stromal necrosis and melting and vascularization8. The Los Alamos probe, an instrument designed to heat the stromal collagen using radiofrequency waves, was reported to procedure short-lived topographic changes. 9,10 Alternative methods of heating the corneal stroma to steepen the central cornea or using a hot copper wire, such as the one introduced by Fyodorov, or others using different types of thermalasers, have been reported. 4,11-16 Clinical experience reported in the literature with heating of the corneal tissues to produce topographic changes is limited. We report here our results in a prospective study using the Fyodorov thermal unit to treat hyperopia and hyperopia associated with astigmatism in sighted eyes.

Ruptured Globes Following Radial and Hexagonal Keratotomy Surgery-Reply

In reply We support the concept that long-term, prospective, inclusive collection of data on all traumatic ruptured globes is needed to answer the important question of whether refractive surgery that is not medically necessary predisposes the eye to traumatic rupture. Such a study was proposed to leaders of the refractive surgery community, but did not progress further. We believe that these cases indicate only a potential hazard that is underreported in the peer review literature and does not represent a complete case count, thus, cannot be used as a basis to determine the incidence of traumatic RK and hexagonal keratotomy wound rupture. Remember, many of our cases were of eyes ruptured following minor trauma that would not ordinarily cause a globe rupture, let alone loss of an eye. Because every eye ruptured through the RK or hexagonal keratotomy incision as much as 10 years postoperatively, these cases may be a

Mechanical methods in refractive corneal surgery.

The past year has seen considerable advances and debate with regard to several new and some established mechanical means of refractive surgery. Lamellar in situ keratomileusis is gaining increased interest, especially for the treatment of moderate and high myopia, although considerable questions still exist with regard to its safety, predictability, and the possibility of loss of lines of best corrected visual acuity. Mini-radial keratotomy may be of benefit in reducing the risk of traumatic rupture of radial keratotomy incisions, and a refinement of the nomograms for astigmatic keratotomy in the treatment of congenital astigmatism has been proposed. Another report on the use of hexagonal keratotomy for the treatment of hyperopia again raised concerns of its predictability. A blind eye study of intrastromal corneal rings has provided some reassurance with regard to its safety but has also raised doubts over its predictability. Meanwhile, several more reports of the use of both anterior and posterior chamber phakic intraocular lenses for the treatment of myopia have been presented.

Hexagonal keratotomy--should we still be trying?

I present my limited but positive experience with hexagonal keratotomy for hyperopia. Eighteen consecutive eyes of 12 patients underwent hexagonal keratotomy during 1993. In addition to the primary procedures, 14 enhancements were required in seven eyes for both astigmatism and undercorrection. Surgical planning was based on refractive data only. All surgeries were performed by one surgeon using the open hexagonal keratotomy pattern. The patients' average age was 56 years (range, 38 to 67 years). Fourteen eyes were corrected for emmetropia. They had an average preoperative refraction of +2.22 +/- 0.64 diopters (D) and an average postoperative refraction of +0.11 +/- 0.49 D. Four eyes were corrected for near vision (-2.00 D). They had an average preoperative refraction of -0.53 +/- 0.83 D, and postoperatively their average refraction was -1.78 +/- 0.50 D. All four could read J1 without correction postoperatively. No eye lost more than one line of spectacle-corrected visual acuity; none had a major sight-threatening complication. Hexagonal keratotomy can correct 3.50 D or less of hyperopia. Conservative surgery with one major reoperation procedure is suggested. Because of the highly variable results noted in the literature and several reports of significant complications, I no longer perform or recommend hexagonal keratotomy.

Ruptured globes following radial and hexagonal keratotomy surgery.

To ascertain if cases of radial keratotomy wound rupture were occurring and whether the globes ruptured through the corneal incisions. Cases of traumatic ruptured globe after incisional corneal refractive surgery were collected from ophthalmologists and from peer-reviewed and other ophthalmic literature. Twenty-eight human eyes (eight previously unreported) are known to have ruptured through refractive corneal incisions in activities of daily living (n = 12), assault (n = 7), motor vehicle accidents (n = 5), and sports (n = 4). Two patients died of their injuries. Of the remaining 26 ruptured eyes, eight (31%) recovered 20/40 or better visual acuity. Six eyes (23%) were totally blinded, six (23%) were legally blinded, and six (23%) had best corrected visual acuity of 20/40 to 20/100 despite multiple surgical procedures. As radial keratotomy becomes more popular the pool of patients who may experience traumatic ruptured globe will grow. Every patient who has had radial keratotomy should be aware that the surgery has weakened the eye(s).

Indications, results, and complications of refractive corneal surgery with mechanical methods.

Radial keratotomy (RK) incisions permanently weaken the cornea. This structural weakening can cause several complications and side effects, including diurnal fluctuation, progressive hyperopic shift, and the potential for traumatic rupture of the keratotomy scars. Minimally invasive-RK may be a useful alternative to reduce the invasiveness of RK while retaining its efficacy. Mild myopia can be treated by either RK or photorefractive keratectomy. Patients treated by RK in the first eye and photorefractive keratectomy in the second eye preferred the speed of recovery and the clarity of vision with RK. Combining the microkeratome and the excimer laser appears to be an ideal technique to correct high myopia. Laser ablation of the corneal lenticule while securely fixed by the suction ring in the Berlin microkeratome offers the advantage of perfect centration and fixation. Hexagonal keratotomy, used to treat hyperopia, appears to be an unpredictable, unsafe surgical procedure.

Clinical evaluation of hexagonal keratotomy for the treatment of primary hyperopia

We evaluated the effectiveness of spiral hexagonal keratotomy in correcting primary hyperopia in 199 eyes. One hundred eighty-four eyes (92.5%) had a minimum follow-up of three months. Mean follow-up was 11.9 months and maximum, 36.2 months. Secondary astigmatic keratotomy was performed on 54 eyes six to eight months after initial hexagonal surgery to correct induced astigmatism. The mean reduction in spherical equivalent was -1.6 +/- 0.9 diopters (D) (range -5.6 to +0.9 D). The mean increase in refractive cylinder was +0.5 +/- 0.9 D (range -2.3 to +3.0 D). Uncorrected acuity improved by +3.2 lines, while best corrected acuity decreased slightly by -0.26 lines. Loss of two or more lines of best corrected acuity that was attributable to surgery was between 0.5% and 4.0%.

Corneal Ectasia as a Complication of Repeated Keratotomy Surgery

Staged keratotomy surgery, or "enhancement surgery," may allow a more predictable outcome, but also subjects the patient to additional surgical risks. A 39-year-old man underwent astigmatic keratotomy for myopic astigmatism, followed by 12 enhancement procedures for residual astigmatism. These procedures effectively resulted in a double hexagonal keratotomy. The patient's best spectacle-corrected acuity deteriorated to counting fingers. Clinically, a conically-shaped protrusion of the central cornea, Munson's sign, diffuse subepithelial scarring, and central corneal thinning were noted. Penetrating keratoplasty was performed. Histopathologic examination showed central thinning, epithelial edema, disruption of Bowman's layer, marked stromal scarring, and focal areas of endothelial attenuation--findings consistent with keratoconus. This case illustrates that multiple keratotomy procedures may result in corneal ectasia in apparently normal eyes and suggests that hexagonal keratotomy may be more likely to cause iatrogenic keratoconus.

Complications of Hexagonal Keratotomy

We examined 15 eyes of ten patients with complications of hexagonal keratotomy, which included glare, photophobia, polyopia, fluctuation in vision, overcorrection, irregular astigmatism, corneal edema, corneal perforation, bacterial keratitis, cataract, and endophthalmitis. Wound healing abnormalities and anterior displacement of the central cornea adjacent to the incisions were common. Eight eyes lost best-corrected visual acuity of two or more Snellen lines. Three eyes required penetrating keratoplasty for visual rehabilitation. Histologic analysis of two of these corneas disclosed variations in wound depth and abnormalities of wound configuration, including considerable wound gaping. Hexagonal keratotomy appears to be an unpredictable, unsafe surgical procedure with a high complication rate, and it should be abandoned until well-controlled experimental trials establish its safety and efficacy.

Arcuate Keratotomy for the Correction of Spherical Hyperopia in Human Cadaver Eyes

A new experimental surgical technique to correct spherical hyperopia by steepening of the central corneal curvature was performed on human cadaver eyes. Ten eyes were used in the study. All were pretreated with glycerin to ensure a uniform corneal thickness between .55 and .65 mm on ultrasonic pachometry. A constant intraocular pressure of approximately 30 to 40 mm Hg was maintained in each eye by the injection of saline into the vitreous cavity. This was verified by pneumotonometry. A vertical blade diamond knife was set at 100% of the thinnest of four paracentral readings. Each eye underwent preoperative computed topography. One set of five eyes had 12 incisions made following a 5.75-millimeter diameter Mendez hexagonal marker that included unconnected T incisions at each junction (ie, "Hex T" pattern). The other set of five eyes had four arcuate incisions made following a 6-millimeter diameter zone marker; each incision was 60 degrees in arc. Immediately after surgery, computed topography was repeated. The hexagonal keratotomy set of eyes had an average steepening of the cornea of 0.80 D with a range of -1.05 to + 4.38 D. The arcuate keratotomy set had an average steepening of +2.12 D with a range of +1.27 to +3.27 D. This study suggests arcuate keratotomy may be a more effective procedure in the correction of spherical hyperopia when compared with hexagonal keratotomy. The amount of corneal steepening achieved in a cadaver eye model may not be the same as when performed in vivo.

Recent developments in refractive corneal surgery

The 4- and 5-year results of the Prospective Evaluation of Radial Keratotomy Study reveal a hyperopic shift of more than 1.0 D within the follow-up time in 22% and 24%, respectively, of the eyes that underwent radial keratotomy. The number of eyes with this complication increased progressively from 6 months to 4 years. Attempts to correct this progressive hyperopia are discussed. Results of clinical studies of myopic photorefractive keratectomy performed with the excimer laser are reviewed. Regarding safety and short-term efficacy, photorefractive keratectomy is a promising technique. In the past, corneal topography has been interpreted qualitatively. Ray-tracing analysis now allows quantitative estimation of the influence of aspheric corneas on the degradation of the retinal image. Three approaches to correct hyperopia, radial thermokeratoplasty, laser thermokeratoplasty, and hexagonal keratotomy are reviewed and discussed. Additional concave intraocular lenses for correction of high myopia are still undergoing clinical evaluation. Endothelial damage is the most dangerous short-term complication of implantation with these lenses.

AVOID BOTH RADIAL KERATOTOMY WITH SMALL OPTICAL ZONES AND HEXAGONAL KERATOTOMY

AVOID BOTH RADIAL KERATOTOMY WITH SMALL OPTICAL ZONES AND HEXAGONAL KERATOTOMY

Numerical Modeling of Radial, Astigmatic, and Hexagonal Keratotomy

A mechanical model of the human cornea is proposed and employed in a finite element formulation for simulating the effects of keratotomy on the cornea. The formulation assumes that the structural behavior of the cornea is governed by the properties of the stroma which is modeled as a thick membrane. The tensile forces in the cornea are resisted by the collagen fibrils embedded in the ground substance of the stromal lamellae. When the stromal lamellae are cut, as in keratotomy, it is assumed that they no longer carry any tensile forces, and the forces in the cornea are then resisted only by the remaining uncut lamellae. A constitutive model, which represents the anisotropy and inhomogeneity in the membrane rigidity induced by the incisions, has been employed in a geometrically nonlinear finite element membrane formulation for small strains with moderate rotations. This preliminary model is restricted to linear material behavior with no time dependency. A number of numerical examples are presented to illustrate the effectiveness of the proposed constitutive model and the finite element formulation for computing the immediate postoperative shift in corneal power resulting from radial, astigmatic, and hexagonal keratotomy. Surgical changes computed using the proposed model compare well with surgical corrections predicted by expert surgeons. The proposed computational model of the cornea and the effects of surgical procedures on it is based on a number of important simplifying assumptions regarding the mechanical properties and structure of the corneal tissue at the ultrastructure level. The encouraging results found with present model suggest that further development and refinement will be useful.

Complications of a Hexagonal Keratotomy Following Radial Keratotomy

Overcorrection is a frequent, significant complication of radial keratotomy (RK).1Treatment of patients with overcorrected RK requires spectacle or contact lens correction of the hyperopia. Lindquist and associates2described a technique of suturing the radial incisions to treat overcorrection following RK. In 1986, Mendez3presented hexagonal keratotomy as a surgical treatment of hyperopia and overcorrection after RK. We describe a patient who required a penetrating keratoplasty for corneal scarring and irregular astigmatism following hexagonal keratotomy for an overcorrected RK, with multiple intersecting incisions. See also p 1374. Report of a Case. —A 59-year-old man underwent RK of his left eye in July 1988. After surgery, his visual acuity was 20/20 with −6.25 sphere. Five months later, his visual acuity was 20/20 with +2.00 +2.50 × 175. 175. In December 1988, two additional radial cuts were performed in the horizontal meridian to correct the induced astigmatism. The astigmatism

Corneal Flattening by Shallow Circular Trephination in Human Eye Bank Eyes

Recent reports documenting central keratometric changes after removal of failed epikeratoplasty lenticules, compared to preoperative keratometry measurements, suggest that the annular corneal wound alters corneal curvature. Central corneal steepening has also been reported following circular and hexagonal keratotomy. We performed standard epikeratoplasty trephination with a Hessburg-Barron suction trephine followed by a peripheral lamellar spreading keratotomy on seven human eye bank eyes to determine the effect of these incisions on corneal topography. In seven human eye bank eyes, the mean acute central keratometric flattening from the shallow trephine incision was 2.81 D (SD 2.28, P = .017), with no significant change in keratometry due to peripheral lamellar spreading (P = .916). Computerized numeric and three-dimensional graphic analysis of the keratographs demonstrated this central topographic flattening. Further studies are needed to investigate the reversibility of host corneal changes induced by epikeratoplasty procedures.

Corneal Steepening in Human Eye Bank Eyes By Combined Hexagonal and Transverse Keratotomy

An interrupted 5 mm diameter hexagonal keratotomy was modified to include six paracentral transverse incisions to augment the central corneal steepening. This combined modified-hexagonal and transverse (or hexagonal-transverse) keratotomy was performed on human eye bank eyes to an estimated 85% corneal depth yielding a mean of 7.50 +/- 1.69 diopter increase in central keratometric power (P less than .001); this finding was confirmed by keratography. These results encourage further studies of this procedure and its potential to surgically correct mild amounts of hyperopia.