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Indian Journal for the Practising Doctor

Optical Management of Keratoconus

Author(s): Verma, A

Vol. 5, No. 5 (2008-11 - 2008-12)

ISSN: 0973-516X

Verma, A

Dr Arun Verma, M.S. (Ophth), Senior Consultant, Dr. Daljit Singh Eye Hospital, Amritsar. Contact address: 20, Sandhya Enclave, Majitha Road, Amritsar. [Phones: 0183-2572567, (M) 98141-25204] Email: drarunverma (at) glide.net.in, vermaarun00 (at) gmail.com; Website: www.cureureyes.com.

Keratoconus is a bilateral, progressive, non-inflammatory conic deformity of the central or more commonly the paracentral cornea caused by abnormal thinning of the stroma. The apex of the cone is located downward and nasally from the visual axis and may protrude 10 to 15D or an additional 2mm in relation to the normal height of the cornea, which is 2.5mm. The area of ectasia is generally limited to 3 to 6mm in diameter and this is the zone of greatest thinning.

Onset of keratoconus: The condition begins in adolescence – mean age of onset is 15 years – but the authors have seen it in a 7-year-old male child. It rarely develops after 30-year age. Frequently starts in one eye, the other eye can lag behind by 5 years. The disease process may remain active for 10 years during which time changes can be very rapid, and then may undergo remissions and relapses until the ages of 40 to 45 years, when it seems to stop. The condition shows no gender predilection and is bilateral in over 90% of the cases.

Prevalence: Keratoconus is said to affect approximately 1 in 2000 but our findings suggest that the prevalence may be much higher (perhaps 1 in 1000). In about 10% of cases, there is a familial history with an autosomal dominant inheritance pattern. The condition may also be associated with systemic conditions like Marfan’s syndrome, Osteogenesis Imperfecta, Down Syndrome, and Atopic Dermatitis. Familial association between keratoconus and keratoglobus has been reported. Keratoconus may worsen during pregnancy.

Vision in Keratoconus: Many people do not even know that they have keratoconus and many times it is missed an eye surgeon. The visual defect begins as myopia and irregular astigmatism, which may progress rapidly or sometimes take years to develop. It can severely affect the way we see the world and adversely affect simple tasks such as driving, watching TV, or just reading a book. Some keratoconus patients have described their vision as being “blind with light.” This distortion has been compared to viewing a street sign through the car windshield during a rainstorm.

Signs and Symptoms

The first signs and symptoms of keratoconus often appear between the ages of 15 and 30 years and include

  • Distorted vision, principally irregular astigmatic myopia,
  • Subepithelial scarring,
  • Fleischer’s ring,
  • Abnormal corneal and retinoscopic reflexes,
  • Decreasing corneal sensation,
  • Rarely, a rupture occurs in Descemet’s membrane, resulting in acute hydrops (profound local corneal edema), pain and a sudden decrease in vision.

Diagnosis Diagnosis of keratoconus in the early stages can be elusive. It depends upon the following;

  1. K reading indicating high cylinder axes or irregular mires
  2. Changing astigmatic refractive errors
  3. Vision that is not correctable by spectacles to 6/6
  4. Scissor movement on retinoscopy
  5. Placido-disc reflection
  6. Slit lamp findings including Fleischer’s ring and evidence of corneal ruptures with scarring
  7. Phacometric findings to indicate a thinning of the cornea

Placido-disc – Placidodisc is a flat disc on which has been painted alternating black and white rings that encircle a small, central, round aperture. The cornea is used as a front-surface convex mirror that reflects from the normal cornea a series of perfectly uniform, concentric circles. In keratoconus, the reflected target is distorted and the concentric circles are uneven, frequently broken and without symmetry.


Normal

Early

Moderate
 

Keratometer: The initial keratometric sign of keratoconus is jumping and inclination of the mires. These can easily be missed in mild or early cases. As the cornea advances, the mires appear smaller. To extend the range of the keratometer, an ancillary lens is placed on the front of the keratometer. If a +1.25 D lens is used, this extends the range to 60 D. To record a reading, 8 D is added to the drum reading (for example, if the drum reads 45 D, adding 8 D yields an actual reading of 53 D). A +2.25 D lens extends the range to 68 D by adding 16 D to the reading.

Slit lamp detection: Slit lamp diagnosis is difficult in the early stages, whereas it becomes very obvious in the late stages with apical thinning, Fleischer’s ring, increased endothelial reflex, increased visibility of the nerve fibers, scarring of the Bowman’s membrane and so on.

Fleischer’s Ring: Yellow-brown to olive-green ring of hemosiderin pigment deposited deep in the epithelium, which may or may not completely surround the base of the cone in about 50% cases. Locating this ring initially may be made easier by using a cobalt filter and carefully focusing on the superior half of the cornea’s epithelium. Once located, the ring should be viewed in white light to assess its extent.

Lines of Vogt: Small brush like lines, vertical or oblique, found in the deep layers of the stroma along the meridian of greatest curvature; the lines disappear when gentle pressure is exerted on the globe through the lid, but are easily viewed when they reappear after this pressure is removed. In advanced cases posterior corneal folds are present.

the advanced stages of the disease. The steepest part of the cornea (apex) is generally the thinnest and represents an actual reduction in the number of stromal lamellae rather than an overall thinning process.

Corneal Scarring: Sub-epithelial corneal scarring, occurs because of ruptures in Bowman’s membrane. Deep opacity of the cornea can also occur. Flat-fitting contact lenses may produce or accelerate corneal scarring. A raised “callous” is possible but is easily treated by simple debridement or laser ablation. ↓

Swirl Staining: Swirl staining occurs because basal epithelial cells drop out and the epithelium slides from the periphery as the cornea regenerates. Thus, a hurricane, vortex, or swirl stain may occur. Swirl staining may be due to rubbing of the eye or can also result from flat- fitting contact lenses. ↓

Direct ophthalmoscopy: Direct ophthalmoscopy may show a shadow. If the pupil is dilated and a +6.00 D lens is in the ophthalmoscopic system, the cone may appear as oil or honey droplet when the red reflex is observed.

Munson’s Sign: This sign, occurring in advanced keratoconus, is said to be positive when the cornea protrudes enough to angulate the lower lid during inferior gaze.

Diagnostic Topography

One of the most useful applications of computer-assisted topography is the detection of keratoconus before the onset of slit lamp findings or retro-illumination techniques. Even in the presence of regular keratoscopy mires, there may be subtle signs of keratoconus.

Because topography provides important information about corneal curvature in the periphery of the cornea, it is showing promise as an aid to contact lens fitting in complex corneal topographies of keratoconus.

Classification

Keratoconus can be classified by cone shape, central K reading, or progression. The simplest classification systems are based on K reading or shape:

  1. Classification (based on severity of curvature)
    • Mild <45 D in both meridians
    • Moderate 45-52 D in both meridians
    • Advanced >52 D in both meridians
    • Severe >62 D in both meridians
  2. Classification (based on shape of cone) · Nipple small diameter (5mm.); round shape; easiest to fit with contact lenses
    • Oval large diameter (>5mm.); often displaced inferiorly; difficult to fit with lenses
    • Globus largest diameter (>6mm.); 75% of cornea affected; most difficult to fit with lenses

Treatment Options

Three treatment options are available:

  1. Spectacle Correction
  2. Contact Lenses
  3. Surgery

Treatment with spectacles

Spectacles may work in mild cases (forme fruste type) of keratoconus, which does not progress. With spectacles, compensation cannot be made for the irregular astigmatism and distortion that accompanies keratoconus.

Although most patients can continue to read and drive, some feel quality of life is adversely affected by spectacles. In short, they are never satisfied with their spectacles and go in for rapid changes of their glasses and most of them never ever getting 6/6 vision.

Treatment with contact lenses

Contact lenses and that too rigid gas permeable lenses are the only treatment option left for almost all cases of keratoconus and these should be the first and preferred remedy. The lens covers the irregular astigmatism and the distorted optic properties of the anterior surface of the ectatic cornea by providing a regular, spheric optic surface before the eye and thereby dramatically improving vision.

The patients should be informed upon diagnosis that they should go in for contact lenses immediately.

Types of RGP lenses

Various types of RGP lenses are available, which can be bicurved or multicurved.

The bicurve lenses are usually of diameter of 9.2, 9.5, 9.8 or even 11.0mm. The peripheral curve is 2-3mm flatter than the base curve and can be used in advanced cases of KC.

The multicurve lenses are of various series

  1. Apical: 7.5, 8.0, 8.5mm diameter
  2. small thin: 8.00 to 9.0mm diameter
  3. Contour: 8.5 –9.5mm diameter

The intermediate and peripheral curves are usually 2 and 3mm flatter than the base curve.

Perfect fit

A good fit should have a central feathery touch of 2 to 3mm with a thin band of touch at the periphery. The three-point touch adds to the stability of the lens on the cornea and distributes the weight of the lens not only on the apex but over other bearing areas as well.

A light apical touch is desirable so that the lens can function as a pressure bandage on the thin, central corneal apex. There should be adequate centering and adequate movement

RGP lens fitting in keratoconus

Dedication, gentleness and patience is more important than expertise. Many times the doctor may lose hope but the assistant’s perseverance comes up with a perfect fit the next day. It may take days of hit and trial to come up with a perfect fit.

Post fitting care

Wearing time should be increased very slowly (1/2 to 1 hour daily) for at least 20 days.

Total wearing time should be divided in 2 shifts with 2 hours of rest without lenses.

Follow up should be frequent and regular

Most common reason for contact lens failure

The most common reason for contact lens failure in keratoconus is poor fitting and poor vision. The eye surgeon should keep in mind that the success or failure is depends on a balance of what the patient perceives as adequate functional vision and the comfortable wear time. Recent advances in design and materials have greatly increased the proportion of patients who can be successfully fitted with contact lenses.

Outcome

Although it is reported that 10 % of patients with keratoconus require surgery. In one of our series, only 7 patients (0.58%) were subjected to surgery.

The most common cause of decreased vision after PKP is high post-op astigmatism. In fact, post-op astigmatism in keratoconus patients is higher than in other keratoplasty patients. Approximately 75% of patients who undergo PKP will require contact lenses to correct their myopia and astigmatism after surgery.

The author’s observations………………..

The author has been fitting contact lenses in keratoconus patients for the past 24 years. In the first 12 years of my practice, I had been using rigid single curved lenses with quite satisfactory results.

In the last 12 years I have fitted over 1200 patients of keratoconus, and from that I have deduced the following statistics:

Incidence- My practice has made me to infer that Keratoconus occurs in about 1 per 1000 patients. The recorded literature says that the incidence is 1 in 2000. That implies, kerotonus is twice as common as recorded in literature which is primarily of Western deductions.

Relation with allergic conjunctivitis- More than 25% of my patients come from the J&K State. I have not been able to find a plausible reason for this unexpected prevalence there. Keratoconus patients invariably suffer from allergic conjunctivitis, more so our Jammu& Kashmir patients when compared to patients from other states. I is possible that a higher prevalence is somehow linked.

Sex ratio-Contrary to the available reports, we have fitted in more males 708(59%) as compared to females 492(41%). Unilateral cases were only 108 (9%) as compared to bilateral in 1092 (91%).

Age of the patients- 36 (3%) patients were less than 10 years old. The youngest child receiving a contact lens from us was a 7 yr-old male child.

672(56%) patients were between the ages from 11 to 20 years, 468(39%) between 21 to 30 years and 24(2%)patients were above the age of 30 years.

One female patient was fitted with a contact lens for the first time at the age of 54 years. She had all along been groping with the vision of 6/24 and after fitting with contacts, she could see 6/9.

Spectacle astigmatism

Spectacle astigmatism varied between 3.0 D to 15.0 D. As regards the type of astigmatism, it was with the rule in 372 (31.1%) patients, against in 444 (37.6%) and oblique in 252(21.3%) patients.

Specification of the lenses

Regarding the specification of the lenses, the base curves varied between 45D to 69 D. In 300(25%) cases, the base curves were between 45D to 52D.

Powers of the fitted lenses varied from +3.0D to –25D. Overall diameter of the lenses varied from 7mm to 9.8mm

Shape of the cone

In 756 (63%) of our patients, the cones were oval in nature. In 432 (36%) patients, it was nipple in shape and only. 12(1%) patients had keratoglobus like picture.

Piggy back system

A rigid lens fitted over a soft lens increases comfort in some patient intolerant to rigid lenses. Problems include handling and care of two different types of lenses and difficulty in obtaining centration of the rigid lens. Since the combination of lenses results in a relatively thick total “lens” on the cornea, oedema due to lack of oxygen is a common problem. We have used this system successfully in 46 of my early cases.

Hydrogel (Soft) Lenses and Toric Lenses

Since these lenses take the shape of the cornea, the corneal shape is transferred through the lens. Because of the corneal distortion, soft and toric soft lenses do not adequately correct vision. Only in the beginning or in mild cases of keratoconus can they be used.

Traditional PMMA Rigid Lenses

PMMA is rarely used anymore because it allows no oxygen to pass through it. The cornea has high oxygen requirements because it has no blood supply to bring oxygen to it.

Prognosis and Outcome: (Visual results)

Our KC patients have been fortunate to get extremely good visual results with contact lenses:

6/6 in 768 (64.4%) patients
6/9 in 336 (28.4%) patients and
6/12 in 84 (7.1%) cases.

In only one patient we had a vision of 6/18.

Active Vision Therapy

We subjected 228(19%) of our patients with vision less than 6/6 to active vision therapy, because, in our experience, these patients suffer additionally from Amblyopia. We have been able to help almost all these patients with our series of pleoptic exercises.

Comments

There is some controversy as to whether rigid or gas permeable lenses cause, aggravate or contribute to keratoconus. Most of the eye surgeons do not support this hypothesis, because if it were true, the incidence of keratoconus should have been much higher in lens users than it is in the general population. The starting age of a contact lens patient and that of the keratoconus patient are similar. Also in the early phase of keratoconus, the person may be merely myopic, and so it is quite natural to assume that one caused the other.

We have been using rigid and GP lenses for the past so many years and have not found any progression of the disease. On the contrary, in 1020 (85%) of the cases, there has been stabilisation of the cone and in 180(15%) there has been regression.

Surgical correction (PKP)

The decision to go in for PKP is not straightforward. Corneal scarring in visual axis causing visual reduction or intolerance to contact lenses are indications for PKP.

PKP is still not as accurate or as predictable (graft rejection occurs in 11% to 18%) as correcting keratoconus with contact lenses, which have more than 99 % chance of achieving 6/6 vision. Every effort should be made to fit the patient with contact lenses and most of the patients will benefit from contact lens refitting by changing the lens design or material.

PRK

Keratoconus is considered a contraindication to PRK because the removal of additional tissue from an already ectatic cornea may lead to further ectasia and unpredictable results.

Conclusion

Fitting lenses requires patience, perseverance and expertise

These patients have strong fears of losing their sight every time they come to the doctor for follow up.

Success in fitting these persons requires the surgeon to be optimistic, reassuring and calm, because the patient will be tense, agitated and worried.

Compliance is the key to the longterm success for all contact lens wearers. It is even more so for keratoconus patients, since they are totally dependent upon contact lenses for all their visual needs.

We tell all patients that keratoconus should not stop them from accomplishing their goals, but should rather serve as a motivational spur. People from all walks of life have experienced this disorder, including people famous in politics, entertainment industry, medicine and business.

Final word

Those who handle their KC successfully develop their own coping mechanisms. These include wearing sunglasses for driving, and carrying extra contact lenses.

While it is important that the patient should accept keratoconus as an undeniable fact in his life and realize that he has to adapt to it, it is essential for him to understand that adapting is not surrendering. He controls his life, keratoconus does not!

Keratoconus: Keratoconus can result in extremely complex and variable topographical maps, most typically showing areas of inferior steepening. The cone can assume various shapes and sizes, and the apex can be at various locations in relation to the central cornea.

Keratoconus: (Colour Doppler) The apex of the corneal cone is coloured red, indicating a steep area, while the blue areas indicate relatively flat areas.

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