Graft-size selection and anisometropia reduction in penetrating keratoplasty (PKP).

PURPOSE: To compare the amount of myopia induced by same-size donor-to-host penetrating keratoplasty with that of the amount of myopia induced by over-sized donor-to-host penetrating keratoplasty. SETTING: Tertiary referral academic center. DESIGN: Retrospective cohort study. METHODS: Charts from patients who underwent penetrating keratoplasty by the same technique at Bascom Palmer Eye Institute between Nov 1, 2002, and January 1, 2006, were reviewed. The patients underwent optical penetrating keratoplasty using 12 interrupted 10-0 nylon sutures and a 12-bite continuous 10-0 nylon suture by a single surgeon (R.K.F.). The surgical technique used would be considered standard of care at most institutions. The Institutional Review Board, University of Miami Human Subjects Research Office, approved the study protocol. The donor graft was over-sized by 0.25mm in eyes when the intended final refractive target was greater than -1.00 diopters spherical equivalent (SE). The same-size donor graft was used when the intended final refractive target was less than -1.00 diopters SE. The selection of donor graft size was entirely based upon clinical parameters, meaning that the intended final refractive target was determined per each patient's fellow eye refraction, with the intention of reducing anisometropia. All patients received postoperative refraction and corneal topography. These measurements were performed at 6-8 weeks when the initial removal of sutures commenced, then at 6 months, then after completion of selective suture removal, then again at 12 months. RESULTS: At 12 months, the over-sized group resulted in -1.35 diopters (SD = 2.25) SE of refraction, and the same-size group resulted in -0.14 diopters (SD = 2.42) SE. This approached statistical significance (p = 0.052) in comparison to -1.00 diopters spherical equivalent. CONCLUSIONS: Using a donor graft that is over-sized by 0.25mm results in refraction of -1.00 diopters SE or more of myopia. Using a same-size donor-graft results in refraction of less than -1.00 diopters SE. Therefore, careful graft-size selection can result in a more favorable clinical outcome-namely, reduction in anisometropia-in patients undergoing penetrating keratoplasty.

Exposure to sunlight reduces the risk of myopia in rhesus monkeys.

Exposure to sunlight has recently been postulated as responsible for the effect that more time spent outdoors protects children from myopia, while early life exposure to natural light was reported to be possibly related to onset of myopia during childhood. In this study, we had two aims: to determine whether increasing natural light exposure has a protective effect on hyperopic defocus-induced myopia, and to observe whether early postnatal exposure to natural light causes increased risk of refractive error in adolescence. Eight rhesus monkeys (aged 20-30 days) were treated monocularly with hyperopic-defocus (-3.0D lens) and divided randomly into two groups: AL group (n=4), reared under Artificial (indoor) Lighting (08:00-20:00); and NL group (n=4), exposed to Natural (outdoor) Light for 3 hours per day (11:00-14:00), and to indoor lighting for the rest of the light phase. After being reared with lenses for ca. 190 days, all monkeys were returned to unrestricted vision until the age of 3 years. Another eight age-matched monkeys, reared with unrestricted vision under artificial lighting since birth, were employed as controls. The ocular refraction, corneal curvature and axial dimensions were measured before lens-wearing (at 23±3 days of age), monthly during the light phase, and at the age of puberty (at 1185+3 days of age). During the lens-wearing treatment, infant monkeys in the NL group were more hyperopic than those in the AL group (F=5.726, P=0.032). Furthermore, the two eyes of most NL monkeys remained isometropic, whereas 3 of 4 AL monkeys developed myopic anisometropia more than -2.0D. At adolescence, eyes of AL monkeys showed significant myopic anisometropia compared with eyes of NL monkeys (AL vs NL: -1.66±0.87D vs -0.22±0.44D; P=0.002) and controls (AL vs Control: -1.66±0.87D vs -0.05±0.85D; P<0.0001). All differences in refraction were associated with parallel changes in axial dimensions. Our results suggest that exposure to natural outdoor light might have an effect to reduced hyperopic defocus-induced myopia. Also, the data imply that early life exposure to sunlight may help to maintain normal development of emmetropization later in life, and thus lower the risk of myopic anisometropia in adolescent monkey.

[How can the shift of refraction due to vitreous substitutes be avoided? Posterior chamber intraocular lens for patients suffering from diabetic retinopathy]. / Wie ist die Refraktionsänderung bei Glaskörpertamponade zu vermeiden? Hinterkammerlinse für Patienten mit diabetischer Retinopathie.

Silicone filling of pseudophakic eyes usually results in strong unilateral hyperopia and binocularity is severely disturbed. This problem can be avoided by designing a concave posterior lens surface with the centre of curvature in the macula (Acri.Lyc 59RET®, haptics in capsular bag, body in vitreous cavity). The prospective study on 40 eyes with idiopathic macular foramen yields a mean refraction difference of 0.22 D with and without oil. The A-constant of the lens was found to be 115.7. Clinically relevant aniseikonia did not occur. The main indication is cataracts combined with diabetic retinopathy.

[Anisometropia and aniseikonia--unsolved problems of cataract surgery]. / Anisometropie und Aniseikonie--ungelöste Probleme der Kataraktchirurgie.

BACKGROUND AND PURPOSE: Aniseikonia is one of the relevant unsolved problems of modern cataract surgery and may cause severe functional problems such as deteriorated binocular vision, diplopia or headaches. The aim of the present study is to assist the clinician as to how to estimate lateral magnification in a pseudophakic eye and how to reduce or eliminate aniseikonia. METHODS: Based on the characterisation of a centred optical system in the paraxial space, the optical system eye is modelled with 2 x 2 matrices and the lateral magnification is extracted. This method is applied on the "thin lens model" as well as the "thick lens model" and illustrated in detail with 4 working examples. Additionally, we demonstrate how a predefined lateral magnification (e. g., from the contralateral eye) can be realised during cataract surgery by calculating an appropriate combination of an IOL and a spectacle correction. WORKING EXAMPLES: In example 1 the lateral magnification of the reference eye following cataract surgery is determined. In example 2 we estimate the lateral magnification behaviour that is expected after cataract surgery using the same IOL as in example 1. Example 3 gives an overview of how the magnification varies if the IOL position in the eye, the geometry of the lens or the central thickness is changed. Example 4 shows how to calculate an appropriate combination of an IOL and spectacle correction to realise an eikonic imaging of both eyes. CONCLUSION: The present study should sensitise ophthalmic surgeons for the still unsolved problem of aniseikonia after cataract surgery and should give them a simple mathematical tool to help determine object-image magnification and show how to reduce or eliminate aniseikonia during cataract surgery.

Surgical technique for control of postkeratoplasty myopia, astigmatism, and anisometropia.

PURPOSE: We previously demonstrated that selective suture removal reduces keratoplasty astigmatism; however, a myopic shift was induced with the increasing number of interrupted sutures removed. This study is an attempt to determine the effects of a modified surgical technique on postkeratoplasty myopia, astigmatism, and anisometropia. DESIGN: A cohort study compared with historical controls. METHOD: Optical penetrating keratoplasties were performed on 92 eyes of 84 patients. The study group consisted of 92 consecutive penetrating keratoplasties performed using 12 interrupted 10-0 nylon sutures and a tight 12-bite continuous suture and an average K reading of 46.00 diopters for eyes undergoing combined and intraocular lens exchange procedures. All patients had refraction, keratometry, and videokeratoscopy postoperatively starting at 6 weeks and at the completion of selective suture removal. RESULTS: Before suture removal, the average spherical equivalent was -0.160 +/- 3.59 diopters; it was -1.58 +/- 3.66 diopters at the completion of suture removal at 1 year and -1.44 +/- 3.72 at the last follow-up visit, averaging 20.7 months. Final refractive, keratometric, and videokeratoscopy astigmatism was 2.81 +/- 1.82, 4.19 +/- 2.94, and 3.58 +/- 2.03 diopters, respectively. Anisometropia, using the spherical equivalent of the operated and fellow eyes, was 2.49 +/- 2.25 diopters at completion of the study. A best-corrected visual acuity of 20/50 or better was achieved in 59% of patients. CONCLUSIONS: Low myopic spherical equivalent and anisometropia were achieved using a K reading of 46 diopters for calculation of intraocular lens power. The use of tighter continuous sutures and selective removal of fewer interrupted sutures only served to increase final astigmatism, with no significant effect on the final spherical equivalent.

Suturing technique for control of postkeratoplasty astigmatism and myopia.

PURPOSE: We previously demonstrated that selective suture removal reduces keratoplasty astigmatism; however, a myopic shift was induced with increasing number of interrupted sutures removed. This study is an attempt to determine the effects of a modified surgical technique on postkeratoplasty myopia, astigmatism, and anisometropia. METHODS: Optical penetrating keratoplasties were performed on 92 eyes of 84 patients. The study group consisted of 92 consecutive penetrating keratoplasties performed using 12 interrupted 10-0 nylon sutures and a tight 12-bite continuous suture, and use of an average keratometry (K) reading of 46.00 diopters for eyes undergoing combined and intraocular lens (IOL) exchange procedures. All patients had refraction, keratometry, and videokeratoscopy postoperatively, starting at 6 weeks and at the completion of selective suture removal. RESULTS: Prior to suture removal, the average spherical equivalent was -0.160 +/- 3.59 diopters. It was -1.58 +/- 3.66 diopters at the completion of suture removal at 1 year and -1.44 +/- 3.72 at the last follow-up visit, averaging 20.7 months. Final residual refractive, keratometric, and videokeratoscopic astigmatism was 2.81 +/- 1.82, 4.19 +/- 2.94, and 3.58 +/- 2.03 diopters, respectively. Anisometropia, using the spherical equivalent of the operated and fellow eyes, was 2.49 +/- 2.25 diopters at completion of the study. A best corrected visual acuity of 20/50 or better was achieved in 50 patients (59%). CONCLUSIONS: Low myopic spherical equivalent refraction and anisometropia with moderate residual astigmatism were achieved by using tighter continuous sutures, an average K reading of 46 diopters for calculation of IOL power, and selective removal of fewer sutures.

[A research of infant refraction in Kunming Municipality].

OBJECTIVE: To study the infant refraction, detect ametropia in mass screening refraction and correct the ametropia properly for the treatment and prevention of amblyopia and strabismus as early as possible. METHODS: The refraction status of 1 146 children (2 291 eyes, aged 1 month -3 years) were determined with retinoscopy after tropicamide cycloplegia. RESULTS: The results of statistics showed that 89 eyes (3.88%) had emmetropia, 2 139 eyes (93.37%) hypermetropia, 38 eyes (1.66%) myopia, 560 eyes (24.44%) astigmatism and 25 eyes (1.09%) mixed astigmatism. In cases with ametropia, most of them were mild, and 97 eyes (4.23%) were moderate and severe. Anisometropia occurred in 34 infants (2.97%), and 7 infants (11 eyes, 0.48%) had strabismus. The degree of hypermetropia decreased with the increase of age. The percentage of astigmatism decreased with the age increase (chi(2) = 7.46, P<0.01), and the degree of astigmatism also decreased with the age increase (chi(2) = 26.1l, P < 0.01). Myopia increased with the age increase (chi(2) = 4.06, P < 0.05). CONCLUSIONS: The prevention of amblyopia and strabismus in children should begin at the infant period, and the cases with moderate and severe ametropia should wear eye glasses as early as possible.

Screening for anisometropia in preschool children.

PURPOSE: A preschool vision screening program was reviewed to evaluate eccentric photoscreening (EP), visual acuity, and stereopsis in identifying anisometropia. METHODS: Patients referred by the screening were examined to assess efficacy of the three screening techniques in a population of preschool children. Testability and comparison of screening results to the classification of anisometropia (> or = 1 D) by retinoscopy obtained during a complete examination were evaluated. RESULTS: Although EP identified 94.5% of the anisometropic children as abnormal, only 27.8% were classified as anisometropic by EP. Of the anisometropic children, 36.1% failed acuity, but only 19.4% failed based on a 2 line or greater interocular acuity difference. Stereopsis correctly identified only 7.3% of anisometropes as abnormal. CONCLUSIONS: The sensitivity of EP in identifying anisometropic children as abnormal was superior to acuity and stereopsis, yet its ability to identify anisometropia specifically was poor. Anisometropia of low magnitude or that masked by the dead zone of the EP system was frequently classified as isometropic. Altering the EP referral criterion and/or taking photographs through adequate power plus lenses may improve the sensitivity for specifically identifying anisometropia. However, caution must be exercised when using EP to examine the prevalence of anisometropia in a population or if used to screen for only amblyogenic refractive errors (i.e., anisometropia), because many anisometropes will be missed, resulting in inaccurate prevalence data and significant underreferrals.

Minimizing anisometropia in bilateral pseudophakia.

One hundred twenty patients who had bilateral posterior chamber intraocular lens implantation were analyzed for postoperative anisometropia. All pairs of lenses had the same A constant and similar designs. Several parameters were analyzed to identify patients at higher risk for clinically significant anisometropia upon implantation of the second eye and determine whether the results of the first eye could be used to modify the implant power selected for the second eye to reduce the risk of anisometropia. In most cases, simply using the value of the linear regression prediction for emmetropia in the second eye without modifications minimized anisometropia.

The Montgomery Lecture. Some factors which affect the visual outcome of corneal transplantation.

Corneal transplantation, which began in Dublin early in the nineteenth century, is now widely practised. Most grafts are done for visual reasons, some to manage corneal destructive disease. The factors associated with allograft rejection are well known, but a clear graft does not mean that the transplantation procedure has been successful. Successful corneal grafts enable patients to improve their life-style. To achieve this, the graft must be transparent and free of optical aberrations, the eye must be capable of achieving good vision, and the patient must have a life-style which would benefit from a successful functioning graft. A study of patients who have had corneal grafts identified the presence of a functioning graft, the lack of need for a contact lens, and the achievement of visual acuity in the operated eye which exceeds that of the contralateral eye, as requirements for patient satisfaction.

Intraocular lens implantation after penetrating keratoplasty. Improved unaided visual acuity, astigmatism, and safety in patients with combined corneal disease and cataract.

Twenty-two eyes with combined corneal disease and cataract were followed prospectively after nonsimultaneous intraocular lens (IOL) placement after penetrating keratoplasty; the majority had a penetrating keratoplasty and planned extracapsular cataract extraction (ECCE) followed later by the placement of an IOL. The mean follow-up after IOL placement was 25 months (range, 3-55 months). No graft failures occurred after secondary surgery. All graft sutures were removed in 86% (19/22) of eyes before IOL surgery. Ninety-five percent (21/22) of the eyes achieved refractive errors within 2 diopters (D) of the desired result. Corneal astigmatism decreased from 4.88 to 2.92 D after secondary surgery and wound revision. Unaided visual acuity was 20/40 or better in 68% (15/22) and 20/100 or better in 91% (20/22) of the eyes. The advantages of excellent unaided visual acuity, reduced astigmatism, and lack of anisometropia and graft failure outweigh the disadvantage of some delay in final visual rehabilitation (11 months) and increased secondary capsulotomy rate (85%) in this series with two separate surgeries compared with previously reported triple procedure results.