keratoconus3

To Wolfgang Haigis and to all ophthalmologists throughout the world.

One of the final frontiers in ophthalmology is the consistently accurate calculation of intraocular lens power for all eyes. For eyes where the anterior segment may be abnormal in some way ( influencing the effective lens position), consistently accurate IOL power calculations have remained elusive. This statement is never more true than in the case of a person suffering from keratoconus. What is required is a formula or method by which any eye surgeon any where in the world can rapidly and easily work out what lenses to use when confronted with such a person requiring cataract surgery.

One ophthalmologist has recently been reported as saying that performing cataract surgery on a patient suffering from keratoconus is not uncommon. If it is so common, then why is it that so few research papers have been published on the subject?

Before enquiring further into this problem we need to examine various cases involving cataract surgery for people suffering from keratoconus.

Case No 1:

Cataract and refractive surgery today, 1 February 2010, complex case management.

Double vision after toric IOL implantation

By Uday Devgan, Michael Ehrenhaus, and Warren E. Hill.

Case presentation

A 67 year old male presents with a chief complaint of poor vision in both eyes, worse in his left eye. He has glasses for driving, but they do not work. He has osteoarthritis but is otherwise healthy and takes no medication.

On examination, the patient's UCVA is 20/40 OD and 20/80 OS. Near vision with his reading correction is J 5 OD and J10 OS. His manifest refractions are - 7.5 + 5.75 X 110= 20/30 OD and- 7.50 + 6.00 X 60 = 20/60 OS. The external examination, his pupils and his ocular motility are normal. A slit lamp examination reveals clear corneas and anterior chambers. There is a 1+ nuclear and posterior subcapsular cataract in his left eye. The IOP measures 17 mm Hg OD and 19 mm Hg OS and the fundus examination is normal.

Keratometry values are 50.7 @ 110/43.5 @20 OD and 50.1 @68/43.1@158 OS.

An ophthalmologist advises the patient that his primary problem is cataract and his secondary problem is forme fruste keratoconus. The patient is given the option of a toric IOL with the understanding that in the best case scenario the refractive cylinder will be reduced by approximately 50%.

Based on the AcrySof Toric Calculator, the ophthalmologist decides to implant a 13.5 D AcrySof Toric IOL with 3.00 D of cylinder in the patient's left eye. The surgeon creates a scleral tunnel incision at the 70° meridian to avoid inducing progression of the FFKC. The procedure is uncomplicated.

On the first postoperative day, the patient's UCVA is 20/100 and his chief complaint is double vision which is determined to be monocular diplopia in the operated eye. By 1 week postoperatively, his UCVA has improved to 20/40 and surgery on his right eye is scheduled. The implantation of a 12.00 D AcrySof Toric IOL with 3.00 of cylinder in the patient's right eye is scheduled. The implantation of a 12.00 D AcrySof Toric IOL with 3.00 D of cylinder in the patient's right eye is without complication. The surgeon creates a scleral tunnel incision at the 114° meridian.

One day after surgery, the patient's UCVA is 20/50 OD and he again complains of monocular horizontal diplopia 3 months after surgery, the manifest refraction is- 1.75 +4.00 X 105 = 20/25 OD and - 0.50 + 2.25 X 47 = 20/25 OS . The patient continues to complain of diplopia even with spectacle correction. Corneal topography as expected has not changed.

Preoperatively , the patient had more than 7.00 D of keratometric astigmatism, yet he had no subjective diplopia even without correction. After surgery, although his refractive cylinder has decreased by 3.00 to 5.00 D the patient has new complaints of diplopia. How would you explain the worsening monocular diplopia after the implantation of toric IOLs in this case? How would you manage this patient's complaints? What is your policy regarding toric IOLs in patients with keratoconus?

My comments case no 1

This patient does not seem to have anisometropia which is most unusual in a case of Keratoconus.

In his right eye, the Ks ranged from 50.7 D@ 110° and 43.5 D @ 20°.

In his left eye, the Ks ranged from 50.1 D@ 68 ° and 43.1 D @ 158°.h

This patient has only mild keratoconus in both eyes.

I note that the eye surgeon used the AcrySof Toric Calculator (Alcon Laboratories Inc. Fort Worth Tx. ) in order to work out what lenses to use.

Case No 2

Sheri L. Rowen

CASE PRESENTATION

A 71-year-old black male had been experiencing decreased vision over the past few years and requested consultation for management. He inquired whether he was a candidate for laser vision correction. In 1997, he had 20/30 BSCVA. By January 2000, he had BSCVA of 20/40 OD and 20/25 OS with correction of -7.50 + 6.00 X 145 OD and -1.50 + 2.00 X 048 OS. Early cataracts were detected, and keratoconus was discovered upon topography.

The patient grew increasingly unhappy with his inability to see and tried a gas permeable contact lens fitting in an attempt to improve his vision, which unfortunately was unsuccessful.

By 2001, the patient reported nighttime glare, which limited his ability to drive; his eyesight was deteriorating, and he could not see well enough to recognize familiar faces. The patient now had 2+ nuclear sclerosis, dense cortical changes, and a posterior subcapsular cataract in the right eye. His BSCVA was 20/70 OD and 20/60 OS.

HOW WOULD YOU PROCEED?

1. What is the proper management of this case?

2. How much visual loss was attributable to cataracts versus keratoconus?

3. How reliable do you expect the A-scan to be?

4. What type of IOL should be inserted?

SURGICAL COURSE

I performed cataract surgery and implanted two STAAR toric lenses in this patient to alleviate the excessive astigmatism caused by the keratoconus. In the OD eye, four Sonomed A-scan measurements revealed four completely different outcomes due to irregular K readings. Toric IOLs required to approach emmetropia ranged from 13.5 + 3.5 up to 16.0 + 3.5. It was impossible to rely on any of the measurements, due to the extreme variations.

I decided to insert a 16.0 + 3.5 X 130 (based on reasonably consistent axis readings, the spherical component was the hypothesis). The Ks ranged from 43.37 @ 37 and 50.50 @ 131 OD; the axial length measurements ranged between 23.75 and 24.75. OS axial length was 23.81 with Ks of 43.62/178 and 46.12/88. An 18.5 + 3.5 D X 88 STARR toric IOL was inserted.

The patient's surgery was performed, and his vision on postoperative day 1 was 20/40 OD and 20/40 OS uncorrected. He is now able to read 20/30 without correction, and his postoperative refraction is -2.00 + 2.00 X 125 OD, correctable to 20/30-2 and -2.75 + 1.50 X 48, correctable to 20/25.

OUTCOME

The patient was ecstatic with the results, and sees very well both near and far without correction. I believe this toric lens technology will allow us to treat complex keratoconus patients without any ill effects on their corneas.

The patient's axis of astigmatism remained the same over the past 10 years, and even if the diopters of cylinder increase, he will still benefit greatly by having at least 2.5 D corrected by the IOL. In this case, the patient improved by more than 5.0 D, reducing his cylinder from >7.0 D to 2.0 D, an unexpected, but positive result.

Toric IOL technology is slowly gaining popularity, and if used correctly will be a great adjunct to all cataract and intraocular refractive technology. The lens is always oriented along the steep axis of astigmatism, that is, the highest number using the plus cylinder. It is never based on the refraction of the patient as the lens can contribute to that number, skewing the effect of correcting corneal astigmatism only. It is difficult to ascertain exactly how we eliminated 5.0 D of astigmatism in this patient's right eye; however, the crystalline lens must have contributed to his extreme astigmatism. I have found this to be true in cataract and refractive patients using this technology, but I am truly overwhelmed by these results in a keratoconus patient.

Sheri L. Rowen, MD, is an Assistant Clinical Professor at the University of Maryland, Baltimore, Maryland, Director of the Eye & Cosmetic Surgery Center at Mercy Medical Center, Baltimore, Maryland, and Director of Rowen Laser Vision & Cosmetic Center, Towson, Maryland. Dr. Rowen has no financial interest in any companies mentioned within this case study. (410) 332-9500; srowdance@aol.com

My comments case no 2

This patient suffers from extreme astigmatism.

In his right eye, the Ks ranged from 43.37 D @ 37° and 50.50 D @ 131°.

In his left eye, the Ks ranged from 43.62 D @ 178° and 46.12 D @ 88°.

Despite his extreme astigmatism, this patient only exhibits mild keratoconus in both eyes.

Mild keratoconus: mean K < 48 D,

Moderate keratoconus: mean K 48 D - 55 D,

Severe keratoconus : mean K > 55 D.

Case No 3

Use of the Toric Intraocular Lens for Keratoconus Treatment

Jasmin Zvornicanin,1 Emir Cabric,2 Vahid Jusufovic,1 Zlatko Musanovic,1 and Edita Zvornicanin3

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This article has been cited by other articles in PMC.

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Abstract

A 50 year old man presented to Eye clinic University clinical centre Tuzla with bilateral visual impairment. Clinical examination revealed low visual acuity and keratoconus in both eyes, white cataract in right eye and diabetic retinopathy in left eye. Ultrasonography examination was normal. The patient underwent Trypan blue capsule staining, phacoemulsification and implantation of intraocular lens Alcon AcrySof SN60T9 16 D spherical and 6.0 D cylinder power. Phacoemulsification went uneventful and early postoperative recovery was successful. Visual acuity improved to 0,8 and fundus examination revealed background diabetic retinopathy. Postoperative follow up two years after surgery showed no signs of keratoconus progression and visual acuity maintained the same.

Keywords: phacoemulsification, cataract, corneal ectasia

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1. INTRODUCTION

Keratoconus is characterized by progressive corneal protrusion and thinning, leading to irregular astigmatism and impairment of visual function (1). It is essentially a bilateral condition, though presentation can be markedly asymmetric (1,2). Keratoconus is multifactorial progressive disease that usually starts in puberty, generally slowly progresses in early years and usually stabilizes in fourth and fifth decade of life (2). The reported incidence of keratoconus ranges from 1.3 to 25 per 100 000 per year and prevalence ranges from 8.8 to 229 per 100 000 (1).

Several options for management of keratoconus are available such as: spectacles and soft contact lenses in early cases, rigid gas permeable lenses, deep anterior lamellar keratoplasty, photo refractive keratectomy, intrastromal corneal ring segments and corneal crosslinking for moderate and corneal transplantation surgery for severe cases (1, 2). Toric intraocular lenses (IOL) can be a viable solution for patients with irregular astigmatism due to keratoconus (3) and cataract patients with keratoconus (4–10).

The purpose of this report is to present results of two year follow up in a case of stabile keratoconus and white cataract successfully treated with phacoemulsification and toric intraocular lens implantation.

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2. CASE REPORT

A 50-year-old man with history of low vision for more than 10 years presented to Eye clinic University clinical centre Tuzla. Ocular history revealed bilateral gradual vision decrease 20 years ago. The patient never used contact lenses and has one pair of spectacles with -5 D, which he uses for the last 6 years. Systemic assessment revealed history of diabetes mellitus for 6, arterial hypertension for 12 and posttraumatic stress syndrome for 15 years. The patient allegedly regularly takes his medication and smokes at least 20 cigarettes a day. He is war veteran, unemployed and has negative family history of ocular or systemic diseases. The patient submitted documentation of ophthalmic examinations in the last 6 years, with unchanged refraction, stabile corneal finding and noted cataract progression.

Complete ophthalmologic examination on presentation revealed the following findings: the corrected distance visual acuity (CDVA) was light perception in the right eye and 0.4 with–3.0 Dsph ~–5.0 Dcyl axis 82° in the left eye. Tonometry was 15.6 mm Hg in both eyes. Slitlamp examination revealed a central corneal protrusion and mature white cataract in the right eye and central corneal protrusion with Vogt striae and incipient posterior subcapsular cataract in the left eye. Fundus in the right eye was not visible due to cataract and the fundus in the left eye showed signs of background diabetic retinopathy with regular optical coherence topography (OCT) finding. Ultrasonography examination, motility examination and pupil responses were normal in both eyes.

Different treatment options were discussed and patient insisted on cataract surgery and preoperative preparations were made. Corneal topography (Auto Ref-Topographer RT-7000; Tomey, USA) in the both eyes showed oblique axis of corneal astigmatism and pattern consistent with keratoconus with the thinnest portion of the cornea decentred inferotemporally (Figure 1). Keratometry indices in the right eye were as following: K = (K–47.2) = 2.4 D; I-S = 2.0 D; AST = (SimK1–SimK2) = 7.53 D; SRAX = 25° and KISA% = (K) x (I-S) X (AST) x (SRAX) x 100 / 300 = 301.2% (11). Keratometry measurements by simulated K, automated (Auto Ref-Topographer RT-7000 Tomey, USA) and manual keratometry (Javal-Schiote; Rodenstock, Dusseldorf, Germany) determined the K = 49.6 D (K1 = 45.79 D, K2 = 53.32 D) with the agreement on the steepest meridian location at 99°. Axial length (LAX) measured with B scan biometry and both contact and immersion A scan (Ultra Scan; Alcon, Fort Worth, USA) biometry was 22.3 mm in right and 23.06 mm in left eye. Anterior chamber depth (ACD) was 3.19 mm in right and 3.66 mm in the left eye. Dioptric intraocular lens (IOL) power of 18 D was calculated using SRK II formula (IOL power = A–0.9K–2.5LAX) and manufacturer web based program–toric IOL calculator was used to determine IOL cylinder power and axis alignment (http://www.acrysoftoriccalculator.com).

Figure 1

Preoperative corneal topography

Estimated corneal astigmatism was 7.53 D and highest toric IOL available at the market in January 2012 was Acrysof SN60T9 (Alcon, Ltd., Fort Worth, USA) with 6.0 cylinder power at the IOL plane (4.1D at the corneal plane). Clear cornea cut 2.8 mm at the steepest meridian 99° with surgically induced astigmatism (SIA) 1 D (12) was planned. Remaining 2.5 D of corneal cylinder were calculated in the spherical equivalent. Calculated spherical IOL power is 18D, but 16D IOL was used in order to leave a small myopic refraction (13).

Preoperative cornea marking at the 0° and 180° positions was done, at slit lamp in vertical position with the patient sitting upright and looking forward. Marking of the corneal steepest meridian and incision site at 99° was performed at the operating table with a degree gauge. Trypan blue anterior capsule staining and capsulorhexis were performed followed by phacoemulsification (Infinity Vision System; Alcon, Fort Worth, USA). Surgery proceeded uneventfully and measured phaco-time was 23 seconds. Implantation of toric intraocular lens Acrysof SN60T9 (16.0 D spherical and 6.0 D cylinder power) was performed using Monarch III IOL delivery system cartridge B (Alcon, Fort Worth, USA).

Postoperative small amounts of keratitis and corneal oedema were noted. The patient was treated with topical 0.1% dexamethasone (Maxidex; Alcon, Couvreur, Belgium) and 0.3% tobramycin (Tobrex, Alcon, Couvreur, Belgium) both 4 times daily for three weeks. Seven days after cataract extraction uncorrected distance visual acuity (UDVA) in right eye improved to 0.8 and postoperative fundus examination showed signs background diabetic retinopathy. At the last follow-up (24 months postoperatively) UDVA in right eye maintained 0.8, with a manifest refraction of –0.5 Dsph and -1.25 Dcyl axis 100° and CDVA in left eye 0,2 with –3.5 Dsph ~–5.0 Dcyl axis 82°. Topography finding in both eyes was stabile with SIA in right eye 1.42 (remaining topography astigmatism 6.1 Dcyl axis 101°). Slitlamp examination revealed stabile cornea, no signs of IOL rotation and alignment axis placed at 100° and no signs posterior capsule opacification in right eye and corneal protrusion with Vogt striae and posterior subcapsular cataract in the left eye (Figure 2). Posterior segment of both eyes was stabile with background diabetic retinopathy and regular OCT findings. No postoperative complications occurred during follow up period and the patient is satisfied.

Figure 2

Corneal topography 2 years after surgery

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3. DISCUSSION

Cataract extraction is the only treatment option for a patient with developed cataract. Any surgical intervention in keratoconic eye can increase the risk of progressive and irreversible corneal ectasia (14). Stability and stage of keratoconus must be considered if any surgical intervention is to be performed. Young age, a positive family history, changes in refractive error and possibility of eye rubbing are known risk factors associated with keratoconus progression (1, 2). Because of the patient’s age of 50 at the presentation, negative family history and documented stabile corneal finding for the last 6 years, the risk of keratoconus progression was considered as minimal.

Cataract extraction in patient with keratoconus is challenging task, due to numerous difficulties related to intraoperative and postoperative complications, IOL power estimation, namely interpretation of keratometry readings, determining the astigmatism axis and accurate axial length measurement. Minimally invasive one step surgical procedure is ideal solution for solving the problem of both, cataract and keratoconus. Careful intraoperative manipulation, with reduced parameters should minimise the risk of postoperative corneal decompensation. Although IOL power calculation in these patients is complex and sometimes unpredictable, SRKT- II formula is suggested as most accurate for patients with cataract and keratoconus (15).

In order to achieve accurate IOL calculation regardless of which formula is used, it is essential to precisely and exactly determine keratometry and axial length readings. When compared with IOL master, Pentacam and an auto keratometer, manual keratometry gives most accurate results in evaluation of preexisting corneal astigmatism in cataract surgery with toric IOL implantation. (16). In this case, topography and manual keratometry gave similar results in determination of keratometry and astigmatism axis alignment, while automatic keratometry revealed a slightly different result, similar to previous reports (6, 10, 16). Using the actual K values with a target of low myopia is a suitable option for spherical IOL selection for eyes with a mean K of ≤55 (10), but in patients with posterior keratoconus, IOL power calculation from conventional keratometry may be inaccurate (17). When determining the axial length, manifest visual axis should be perfectly aligned and special attention should be given to ACD measurement, because of its direct influence on the reduction of the cylinder IOL power in the corneal plane (13). First IOL-s used for correction of astigmatism in keratoconus were phakic IOL-s, but only for refractive purposes (3). Only few reports in literature concern the use of toric posterior chamber IOL-s in keratoconus patients (4–10). Development IOL-s with higher cylinder power has made possible correction of full amount of corneal astigmatism (6–9). Cataract surgery in eyes with keratoconus can result with good postoperative visual acuity and low levels of postoperative astigmatism (6–8). To our knowing this is the first case of white cataract and keratoconus treated with toric IOL, without refractometry data, based only on topographic and biometry data. Careful patient selection and detailed preoperative assessment with special emphasis on corneal stability is crucial part of operative strategy in patients with cataract and keratoconus (4–10).

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4. CONCLUSION

Cataract extraction with toric IOL implantation can be used to correct irregular astigmatism and significantly improve visual acuity in patients with stable keratoconus and cataract.

My comments case no 3

This patient would have moderate keratoconus in his right eye.

In his right eye, the Ks ranged from 45.79 D and 53.32 D, the mean being 49.6 D.

I note that the eye surgeon used the SRK ll formula and a manufacturer web based program toric IOL calculator in order to determine what lens was used. Calculated spherical IOL power was 18 D, but 16 D IOL was used in order to leave a small myopic refraction.

Cataract surgery was only performed on one eye, namely the right eye.

Case No 4

International Journal of Keratoconus and Ectatic Corneal Diseases May August 2012.

Treatment of stable keratoconus by cataract surgery with toric IOL implantation.

Levy J. , Pitchkhadze A. , Lifshitz T.

Abstract

We present the case of a 73 year old patient who underwent successful phacoemulsification and toric intraocular (IOL) implantation to correct high stable astigmatism due to keratoconus and cataract. Preoperative refraction was - 3.25 -4.0 X 98°. A toric IOL (AcrySof SN60T6) with a spherical power of 16.5 D and a cylinder power of 3.75 D at the IOL plane and 2.75 D at the corneal plane was implanted and aligned at an axis of 0°. Uncorrected visual acuity improved from 6/60 to 6/10. Postoperative best corrected visual acuity was 6/6, 6 months after the operation. In conclusion, phacoemulsification with toric IOL implantation can be performed in eyes with keratoconus and cataract.

Introduction

Surgical correction of refractive errors in patients with keratoconus is still challenging. As the disease progresses, it is usually associated with significant astigmatism and often accompanied by myopia.

Case report

A 73 year old man sought consultation due to decreased visual acuity in his left eye. 4 years before he underwent phacoemulsification and non toric IOL implantation in the right eye. On presentation, uncorrected visual acuity (UCVA) was 6/60 OU. Refraction was – 0.75 – 5.0 X 65° OD and- 3.25 – 4.0 X 98° OS. Nuclear sclerosis and posterior subcapsular cataract + 2 was observed in the left eye. The posterior segments were unremarkable.

Corneal topography performed with Orbscan showed central thinning of 457 microns and positive islands of elevation typical for keratoconus in the right eye. In the left eye a less pronounced inferior cone was observed, without any area of significant thinning near the limbus typical for pellucid marginal degeneration. Keratometry (K) values for the steep and flat axis were 57.49 D at 138° and 52.57 D at 48° OD and were 47.73 D at 0° and 45.48 D at 90° OS. Corneal topography was stable for several years.

Due to the postoperative high residual astigmatism in the right eye we decided to perform phacoemulsification and implant a toric IOL in the left eye. A web based toric IOL calculator program was used to determine the optimal cylinder power and alignment axis of the IOL.

A standard phacoemulsification was performed with a 3.2 mm limbal incision at 90°. A hydrophobic acrylic toric IOL with a spherical power of 16.5 D and a cylinder power of 3.75 D at the IOL plane and 2.57 D at the corneal plane was implanted and aligned at an axis of 0°. 3 weeks after surgery, the UCVA was 6/12 and the BSCVA was 6/7.5 and 3 months after surgery UCVA was 6/10 and the BSCVA was 6/6 with a refraction of 0.75 – 1.5 X 125°. 6 months after the procedure the patient's satisfaction is high and refraction remains stable.

1 year postoperatively, the UCVA was 20/25 In both cases with a refraction of - 0.25 -0.50 X 140° and 0.25 - 0.50 X 60° respectively. No progression and no IOL rotation were observed.

My comments case no 4

This patient would have definitely exhibited signs of anisometropia.

In his right eye, the Ks ranged from 57.49 D @138° and 52.57 D @ 48°.

In his left eye, the Ks ranged from 48.73 D @ 0° and 45.48 D @ 90°.

This patient would have had moderate keratoconus in his right eye and mild keratoconus in his left eye.

I note that the eye surgeon used a web based toric IOL calculator program in order to determine what lens was to be implanted into the left eye. A lens with spherical power of 16.5 D was chosen. Unfortunately, details of the lens implanted into the right eye were not available.

Details of how well this patient coped with his anisometropia after the cataract operation were not available as well.

Case No 5

Ophthalmology times 15 May 2013

Dr Srikumaran MD

Cataract surgery in patients with keratoconus requires special considerations with respect to wound construction, IOL calculations, and the choice of implant.

Baltimore—Good outcomes are possible with cataract surgery in patients with keratoconus—even without corneal transplantation.

Keratoconus is a bilateral non-inflammatory ectasia characterized by progressive thinning and steepening of the cornea and development of high irregular corneal astigmatism. Treatment depends on disease severity and ranges from glasses and contact lenses to corneal transplantation, according to Divya Srikumaran, MD.

Patients with keratoconus typically have the disease stabilize later in life. Yet, many of these patients subsequently develop visual disability from age-related cataracts.

“Cataract surgery in these patients requires special considerations with respect to wound construction, IOL calculations, and the choice of the implant you will place in these eyes,” said Dr. Srikumaran, assistant professor of ophthalmology in the division of cornea, cataract, and external diseases, Wilmer Eye Institute, Johns Hopkins School of Medicine, Baltimore, and medical director, Wilmer at Odenton.

Wound construction

Wound construction is another variable that should be carefully considered and chosen in patients with keratoconus, Dr. Srikumaran said.

“These corneas are very steep and thin,” Dr. Srikumaran said. “Wound healing may not be the same, and the ability to make a self-sealing, clear corneal incision may not be the same as in a patient without keratoconus so it is safer to suture these wounds.”

Alternatively, some surgeons advocate using a modified scleral tunnel incision in these patients, where entry is made through the sclera with a small limited conjunctival peritomy, to ensure a more stable and water-tight incision than may be created in a thin corneal incision, she explained.

Lens power calculations

Lens power calculations are more challenging in patients with keratoconus, Dr. Srikumaran continued.

“Most of the formulas we have are based on ideal eyes,” she said. “The steep corneas and the high astigmatism make it difficult to obtain accurate and consistent keratometry readings on these patients.”

In addition, eyes with keratoconus tend to have higher axial lengths and deeper anterior chambers, making the effective lens position (ELP) different compared with a normal eye, she added.

The first-generation IOL power calculation formula, the SRK, is reasonably accurate for average axial lengths and normal corneal curvature.

“The second-generation formulas were developed to try to modify the formula with a fudge factor for longer and shorter eyes,” Dr. Srikumaran said.

Third-generation formulas use axial length and keratometry to try to predict ELP and improve refractive outcomes. The fourth-generation formulas use the measured anterior chamber depth and additional variables to predict even more accurately the ELP postoperatively and thus improve refractive outcomes.

In 2007, researchers from Wills Eye Institute compared SRK, SRK II, and SRKT with first-, second- and third-generation formulas. They found that the SRK II was the most accurate in achieving the desired postoperative refraction.

“We were surprised to see that SRKT, a more advanced formula and one that has been shown to be better in eyes with myopia, would not perform better than the SRK II,” Dr. Srikumaran said. This may be affected by a small sample size and variability in the stages of keratoconus.

Lens selection

Monofocal lenses should be used in all these patients, Dr. Srikumaran continued.

“These patients will already have high astigmatism resulting in higher-order aberrations,” she said. “If you place a multifocal lens you may worsen the quality of vision by inducing even more aberrations or reducing contract sensitivity.”

The new toric lenses have not been FDA approved in these patients, but there has been a lot of interest in this patient population. Some recent limited case studies that suggest that improved uncorrected visual acuity may result from these lenses in these patients. Additional studies would need to determine the ideal candidates for this.

“But in a patient in whom contact lenses will be required postoperatively, or in whom there is any consideration of needing contact lenses, a toric lens should not be placed,” Dr. Srikumaran concluded.

Divya Srikumaran, MD

P: 410/874-1425

F: 410/874-1429

E: Dsrikum1@jhmi.edu

Dr. Srikumaran did not indicate any financial interest in the subject matter. This article was adapted from Dr. Srikumaran’s presentation at the 25th annual Current Concepts in Ophthalmology meeting, held in association with Wilmer Eye Institute and Ophthalmology Times.

My comments case no 5

The SRK ll formula did not work in my case and I obtained the following results :

Date of test : 8 September 2017

Eye Suite IOL V 4.2.1 HAAG STREET DIAGNOSTICS SRK ll formula

Tecnis 1 ZCBOO AMO, RE + 9.5 D , LE N/A.

The Eye Suite IOL V 4.2.1 was unable to provide any results for my left eye.

I suspect that most people suffering from keratoconus will obtain similar results.

My Keratoconus formula is partly based on Divya Srikumaran's speech, mentioned here. That is the only reason why I included the article mentioned in the Ophthalmology Times on 15 May 2013, on this website.

My overall comments

Most of the cases described here, involve cases where the patient has only mild keratoconus , which means that ALMOST ALL CASES of keratoconus requiring cataract surgery are currently being left untreated everywhere. The only other significant point to note is that in most of the cases referred to here, the eye surgeons chose what lenses to use by referring to the IOL Calculator program and most experienced what could be described as extreme difficulty in choosing the lenses.

There are other cases claiming to have carried out successful cataract surgery on keratoconus patients. They were not included in this study because they were lacking in sufficient details. The cases described here were the only ones where the eye surgeons were willing to disclose sufficient details in order to justify their inclusion.

It would be fair to say that in the history of cataract surgery, there have only ever been 4 cataract operations that have ever been performed on a person suffering from keratoconus.

SOURCES

https://sites.google.com/view/keratoconus

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