The S&P/ASX 200 Index (ASX: XJO) is out of form again on Tuesday. In afternoon trade, the benchmark index is down 0.5% to 8,111.3 points.

Four ASX shares that are falling more than most today are listed below. Here's why they are dropping:

Atlas Arteria Group (ASX: ALX)

The Atlas Arteria share price is down 4.5% to $4.64. This has been driven by the toll road operator's shares going ex-dividend this morning. Last month, Atlas Arteria released its half year results and reported a 3.2% increase in toll revenue but a 2.9% decline in EBITDA. This led to the company declaring a 20 cents per share unfranked interim dividend. This will now be paid to eligible shareholders next month on 7 October. The good news is that management plans to pay another 20 cents per share dividend with its full year results in February, bringing its total dividends to 40 cents per share. This equates to an 8.2% dividend yield based on yesterday's close price.

Coles Group Ltd (ASX: COL)

The Coles share price is down almost 3% to $18.10. Investors have been selling Coles and Woolworths Group Ltd (ASX: WOW) shares this week after the ACCC took them both to court. The competition regulator is alleging that the two supermarket giants breached the Australian Consumer Law by misleading consumers through discount pricing claims on hundreds of common supermarket products.

Healius Ltd (ASX: HLS)

The Healius share price is down 4.5% to $1.65. This may have been caused by some profit taking after a strong gain on Monday following the announcement of an asset sale. In addition, the team at Citi has responded to the news by reaffirming its sell rating and $1.50 price target on the pathology company's shares. The broker has concerns over pathology margins in the near term. Though, it concedes that the sale of its Lumus imaging business to Affinity Equity Partners will leave it with a strong balance sheet.

Opthea Ltd (ASX: OPT)

The Opthea share price is down 2.5% to 71.2 cents. This may also have been driven by profit taking. This clinical-stage biopharmaceutical company, which is developing novel therapies to treat highly prevalent and progressive retinal diseases, has been a strong performer recently. So much so, its shares remain up over 30% since this time last month after today's pullback. Positive progress with its sozinibercept Phase 3 wet AMD program and its inclusion in the ASX 300 index have been boosting its shares.